Genetic elements of courtship inDrosophila: Mosaics and learning mutants

Behavior Genetics, Sep 1984

Richard W. Siegel, Jeffrey C. Hall, Donald A. Gailey, Charalambos P. Kyriacou

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Genetic elements of courtship inDrosophila: Mosaics and learning mutants

Behavior Genetics Genetic Elements of Courtship in Drosophila: Mosaics and Learning Mutants Richard W . Siegel 0 1 Jeffrey C. Hall 0 1 Donald A. Gailey 0 1 C h a r a l a m b o s P. Kyriacou 0 1 0 This research has been supported m part by grants from the Lewis Fund to R.W.S., from the NIH to J.C.H. (GM-21473), and from the SERC (in the U.K.) to C.P.K. aDepartment of Biology, University of California at Los Angeles , Los Angeles , California 90024. 2Department of Biology Brandeis University , Waltham , Massachusetts 02254. 3Department of Psychology, Umverslty of Edinburgh , Edinburgh EH8 9TJ, Scotland , USA 1 INTRODUCTION COURTSHIP: CONTROLLING STIMULI AND NEURAL SUB- STRATES Courting Mosaics Courtship Stimuli and Their Neural Processing EXPERIENCE-DEPENDENT COURTSHIP Aftereffects Following Courtship of Young Males Aftereffects on Receptivity of Females Exposed to Courtship Song Aftereffects Following Courtship of Mated Females Courtship by "Males" That Are Mosaic for Learning Mutations Clocks, Mutants, and Conditioned Courtship SPECULATIVE QUESTIONS AND CONCLUSIONS Do Courtship Signals Inform or Manipulate? Is There a Selective Advantage for Drosophila; courtship; learning; circadian - 385 385 387 388 389 INTRODUCTION In recent years workers in several laboratories have initiated fresh approaches to the study of courtship behavior in Drosophila melanogaster. These investigations have focused particularly on genetic, physiological, and neurological aspects of these complex behavioral interactions. Such studies have revealed subtle changes in sexual behavior, caused by either genetic mutations or the fly's previous experience. In this paper we review this work and speculate as to the biological significance of these findings. At times our discussions take on a distinctive sociobiological flavor. There is a voluminous literature on courtship behavior in D. melanogaster. The classical accounts have been reviewed several times (e.g., Ehrman, 1978; Spieth and Ringo, 1983; Ewing, 1983) . It is sufficient for our purposes to mention here only the highlights of the earlier descriptions and experiments. When a sexually mature male and a mature (virgin) female fly are brought together, the male orients toward the female, taps her with his forelegs, and follows her closely if she moves. During orientation or following, the male extends one wing or the other at different moments and vibrates it to produce a courtship song (see Ewing, 1977) . Later in the sequence, the male extends his proboscis and contacts the female's genitalia. The next step is one or more attempted copulations in which the male curls his abdomen anteriorly from a position close to and behind the female. These actions on his part seem to be facilitated by one of the female's responses to the male's courtship, in that her general movement becomes slower; therefore, she ostensibly becomes a better target for copulation attempts (e.g., Cook, 1977; Markow and Hanson, 1981; Tompkins et al., 1982) . If such attempts are to be successful, the female will part her wings and separate her genital plates, allowing intromission. The female's response to courtship differs when a mature male is paired with a fertilized female. He follows, extends and vibrates his wings, and may even attempt copulation; but the female responses now include what are called repelling behaviors (see discussion by Ewing, 1983) . The most conspicuous of these is extrusion of her ovipositor. Also, the positions of a mated ~ wings and genital plates do not change to facilitate copulation, and, under laboratory conditions at least, courtship is very rarely consummated. The foregoing behavioral sequences are, seemingly, exhibited by flies without sexual or social experience, although such an assertion relies primarily on ancedotal evidence. A corollary is that courtship appears, at least superficially, to be rather invariant between pairs of wild-type flies. One infers that these reproductive interactions are narrowly constrained behavioral traits reflecting the genetically determined anatomy and physiology of the fly's nervous system. A classical view states that courtship serves the dual functions of synchronizing sexual arousal, especially in terms of overcoming female inhibitions and male aggressions (Bastock, 1967) , and permitting the careful mutual assessment of mates before pairing. Hence, courtship behaviors are thought, in part, to indicate to each member of a courting pair something about the " v i g o r " of the other as a potential breeder of "quality" alleles into the next generation. Visual, auditory, tactile, and chemical signals are exchanged and are integrated so as to provide information on both the readiness and the suitability of each mate for procreation. The utility of an elaborate courtship display for the species would be to allow for the recognition of conspecific partners of optimal genotypes. The two key features of this formulation are the informational content of the courtship behavior and the capacities of the flies to make choices among different partners in accord with selective advantages. The avoidance of wasted physiological and material resources is also an important factor. Recent results reviewed here suggest a somewhat different view of the function of courtship in Drosophila. Courtship may serve to manipulate, rather than to inform, a given member of a courting pair. In this view, the fly providing courtship s i g n a l s l s o m e of the most important of which are chemosensory cues (also see articles by Tompkins and by Jallon, this issue)--manipulates the behavior of the potential mating partner and gains an advantage over other flies of the same sex. The integration of signals, such as reproductive pheromones, by higher functions of the central nervous system is thus likely to serve selfish interests. The behavioral results of this sensory reception and information processing may have little to do with mate selection. We discuss the ideas revolving around manipulative components of courtship partly in the context of the putative adaptive value of learning and memory in courtship. That there are experience-dependent elements in the reproductive behavior of these flies is introduced by our review of the discovery that general learning and memory mutations perturb certain components of courtship in Drosophila melanogaster. COURTSHIP: CONTROLLING STIMULI AND NEURAL SUBSTRATES Courting Mosaics Several investigators have studied the courtship of mosaic flies with the aim of locating the sex-specific foci for each reproductive behavioral component (see reviews by Hall, 1982; Quinn and Greenspan, 1984) . The experimental goal has been to identify tissues which must be genetically male or female in order that a mosaic fly express a characteristic sexspecific behavior. Sex mosaics can be readily produced and recognized in D. m e l a n o g a s t e r (reviewed by Hall et al., 1976) . These start out as normal XX female embryos but lose an X chromosome early in development so that the mosaic has both male and female tissues. Employing a wide array of such gynandromorphs, with many different male-female tissue distributions, it has been found from tests of their courtship performance with females that the male-typical behaviors--tapping, following, and wing extension--depend solely on male brain tissue (with the genotype of sense organs being irrelevant). A basically normal song (which in a mosaic may or may not accompany wing extension), plus attempted copulation, occurs only in mosaics whose thoracic ganglionic tissues are all or part male. In order to elicit courtship from normal males, mosaics must have a female abdomen or one that is partly of this genotype. In tests of the same type of mosaics with males it has been found that female brain tissue is necessary for receptivity to the male's copulation attempts. The influence of tissues on or in the female's abdomen, with respect to the elicitation of courtship, seems consistent with the role that a variety of chemical cues plays in the initial stimulation and later modulation of male-female courtship interactions (again, see accompanying reviews). It is likely that the female controls the manufacture or release of pheromone-like cues from her abdominal tissues. Whereas olfactory cues, whether from the female's abdomen or elsewhere, facilitate courtship and mating, they are apparently not essential, in that mutants which cannot respond to certain odors can mate (see Tompkins, this issue, for details). Similarly, vision is useful but not essential since blind flies or those in the dark can mate (e.g., Kyriacou, 1981; Tompkins et al., 1982) . The results from these mosaic studies are significant in several respects. First, they indicate the anatomical regions which must be genetically of one sex or the other for courtship sequences to occur. Second, they suggest that there is an interplay between sex-specific foci both within a fly and between members of a pair of flies during courtship (Hotta and Benzer, 1976) . Thus, the posterior parts of the female (the abdomen) provoke the male to perform the earlier steps in courtship display, and this in turn leads to receptive behaviors from the female. As noted above, a fly must have male brain tissue if it is to express the male-specific behaviors relatively early in the courtship sequence. Therefore, it can be suggested that signals from the male head somehow trigger the thoracic ganglia (when they are at least in part haplo-X) to mediate the later step, attempted copulation. We elaborate further on these points in the discussion that follows. Courtship Stimuli and Their Neural Processing Courtship behavior seems to begin as a male response to chemical cues released constitutively by another fly. That is, it appears that chemicals which stimulate male courtship (see Tompkins and Jallon, this issue) do not depend on the presence of another fly for release. Thus, isolated immature males and females that have been maintained separately from males after eclosion liberate courtship stimulants (Tompkins et al., 1980; Gailey et al., 1982). Females from a variety of other insect species depend only on environmental changes in, for example, light and temperature to release chemicals which attract males (see Leonard el al., 1974). Similarly, there are no results in Drosophila which suggest that mature males bring about or induce the release of substances which stimulate the onset of courtship. With respect to the behavior of the male toward females, it should be stressed at once that all the major courtship elements occur in most normal male flies which express any courtship at all (see, for example, Tompkins and Hall, 1983) . Since that sequence of behavioral components is independent of the total amount of courtship behavior performed, and also of the so-called "attractiveness" of the female, it can be inferred that the mechanism for its control is restricted to the male. Results given next support this inference and have been chosen for review because they have begun to suggest questions concerning the neural mechanisms underlying these actions. A priori, one can imagine that there is a head-tothoracic ganglionic flow of information which controls courtship motor outputs (again, as inferred from the aforementioned mosaic analyses of male-specific behavior). It is useful to consider this pathway in the context of evidence from several neurogenetic studies in Drosophila (reviewed by Hall, 1982) which suggest that much chemosensory and visual input is processed in the brain and in regions of the head ganglia which are becoming increasingly well defined. Less work has been directed toward analysis of female-specific courtship behaviors in D. melanogaster. However, the data which are available reveal that the brain is again the primary site for input and processing of male-generated '~ at least for reception of the auditory component by the female's antennae (reviewed by Ewing, 1977) . The neural substrates for this processing would again be "built into" the female brain by the action of the genome. One of the female courtship responses is a change in locomotor activity. Mature virgin females become quiescent (e.g., Markow and Hanson, 1981) for periods whose durations are inversely related to the mating efficiency of the male (Tompkins et al., 1982). Young males, 1 day old or less, include individuals which court but cannot mate [see Jallon and Hotta (1979) and Tompkins et al. (1980), who note that many such immature males do not court at all]. Mature virgin females that are courted by such males do not reduce their locomotor activity, nor do immature virgin females (1 day old or less) when they are courted by mature males (D. A. Galley and R. W. Siegel, unpublished). The female stopping behavior is evidently a response to airborne chemicals released by the courting male, for this behavior is defective in mature virgin females which are genetically s m e l l b l i n d (Tompkins et al., 1982) . Song-like auditory input, by itself, can also elicit a slowdown in female movements (Schilcher, 1976a) . It is not surprising that these female-specific behaviors, or at least overt receptivity to mating attempts, depend on a diplo-X brain (Tompkins and Hall, 1983) . One imagines that such receptivity is in part controlled by the brain's processing of olfactory (Tompkins et al., 1982) and auditory (Schilcher, 1976a) input, in the same general manner that these categories of stimuli are important to initiate processing events in a courting male. In the case of mosaics analyzed for female receptivity, the hypothetical processing centers for the inputs just noted could be the two dorsal, anterior sites which are the minimal internal tissues that must be diploX in order that a gynandromorph be receptive to male courtship (Tompkins and Hall, 1983) . In contrast, the requirement for male courtship, in its early stages, is that cells in the dorsal posterior brain be haplo-X (Hall, 1979; Schilcher and Hall, 1979) . Certain gynandromorphs are able to express both male and female courtship functions (Cook, 1978; Szabad and Fajszi, 1982) . These mosaics probably had mixed haplo-X//diplo-X brains, but no internal marking was included in these studies. Other matters concerning the "genotypic control" of male and female reproductive behaviors are discussed in the following section, which describes some of the genes that are involved in certain elements of courtship. E X P E R I E N C E - D E P E N D E N T C O U R T S H I P It is reasonable to suppose that the energy cost of courtship behavior is offset by the benefits of sexual reproduction. Thus it is surprising that wild-type males will avidly court conspecifics with whom they cannot copulate. Courtship of sexually immature males and of fertilized females would appear to be biologically inappropriate as well as wasted effort. One response of these courted males and females is that they are apparently compelled to exert themselves by performing repelling behavior. Such fruitless courtship occurs almost every time a mature male is placed with an immature male or with a fertilized female (e.g., Gailey et al., 1982; 1984) . Aftereffects Following Courtship of Young Males For several hours after males emerge from pupal cases they neither court nor copulate, and yet they have the surprising capacity to stimulate mature males to courtship responses (see above). The mature male follows, extends and vibrates his wings, then protrudes his probiscis at, and attempts to copulate with, the young male. Whether wing vibration produces a courtship song identical to that produced with mature virgin females (cf. Ewing, 1977) is not known. The response of the young male is to flick the wings and to decamp (e.g., Cook and Cook, 1975; Jallon and Hotta, 1979) . Subsequent results showed that the courtship response of the mature male decays and is soon absent (Gailey et al., 1982). When 20 mature males were individually paired with 20 immature males, all of the mature males courted at the outset, but 30 min later only 10 expressed any courtship. Moreover, the courtship index (CI; the percentage of an observation period during which courtship is expressed) declined from 67 for the initial 10-min interval to 17 for the third 10-min period.. Further evidence for modification of coursthip behavior following pairing with an immature male has come from observations of mature males either kept in isolation for 30 min or paired with another m a t u r e male for this amount of time. Males having undergone either of these two types of experience courted immobilized young males with the high intensity which is characteristic of the response to virgin females (CI, at least 30). In contrast, males which first courted i m m a t u r e males subsequently expressed almost no response to the immobile males (CI -~ 1). The depressed response of mature males, having undergone this prior experience, is retained for 4-5 h (Gailey et al., 1982). These experiments lead to some thoughts about the mechanism for this behavioral modification. First, it should be noted that this particular example of experience-dependent courtship is "specific," in the sense that males "trained" to no longer court immature males still court females at normal levels (Gailey et al., 1982; 1984). Second, the phenomenon cannot be explained as a general reaction to the overt rejection experienced by the male, to "discouragement," or to behavioral fatigue. For example, consider the following situation. Males will court immature unreceptive virgin females, who perform their usual repelling responses (Connolly and Cook, 1973) and fail to copulate (Manning, 1967) . Males courting these kinds of females show no diminution of courtship activity for at least 30 min (Gailey et al., 1984). Immature males, as courtship objects, exert altogether different effects on the subsequent behavior of the courter. These depressive aftereffects are elicited even when the immature males are unable actively to reject courtship because they have been entirely immobilized. Such a courtee is still courted by a mature male, and this is followed by the typical courtship modification (Gailey et al., 1982). Even apparent odor traces from young males are sufficient to cause a depressive aftereffect when males exposed to such substances are subsequently placed with immature males. Pairs of mature males will also court each other when placed in small chambers previously occupied by immature males, implying that there are at least traces of courtship stimuli left behind in the chambers. In the context of this implication, it is significant that a mature male who was isolated in a chamber which previously contained immature males thereafter expresses a depressed level of courtship when he subsequently is tested with an actual young male (Gailey et al., 1982). These results indicate that the decrease in responsiveness of mature males to young males is caused by chemosensory factors released by young males (see Jallon, this issue, for more details); these chemicals induce both the initial courtship response and the subsequent courtship modification. Perhaps, then, modified courtship is caused by the mature male learning to avoid the chemical odorants released by young males. This suggestion was examined further by testing males from six mutant strains, previously shown by Quinn and colleagues (see reviews by Quinn and Greenspan, 1984; Tully, this issue) to be defective in associating chemical cues with electric shocks. Males from five of these six mutant lines failed to modify their response to immature males as a consequence of a prior courtship experience (Gailey et al., 1982). The sixth mutant, cabbage (cab), is especially instructive, in that males do exhibit courtship modification, but the refractory p e r i o d - - w h i c h normally lasts 4-5 h - - i s reduced to an hour or less (Gailey et al., 1982). These results indicate that the mechanism for the modified courtship, which could be a case of habituation (given the results on odor traces discussed above), may involve several genetically specified steps which are also common to associative conditioning. Other aspects of nonassociative learning (outside the realm of courtship behavior) are impaired by this same array of mutations (Duerr and Quinn, 1982) . Yet, the affects of these genes on "higher" and "simpler" learning are not always the same, implying that the mechanisms share some but not all of their genetically determined features. For example, turnip (tur) flies [defective in associative learning by definition, because of the tests used to isolate this mutant (Quinn et al., 1979)] are normal in sensitization to sugar stimuli but are defective in habituation (Duerr and Quinn, 1982) . The mutation amnesiac (amn) disrupts the later retrieval of associatively learned information (Quinn et al., 1979); yet with regard to courtship modification, amn blocks the initial capacity of males to become conditioned by immature males (Gailey et al., 1982). A simple mechanism which can account for all of the results of testing mutant and normal males in these courtship situations is that immature males constitutively release a chemical which stimulates mature males to court them. The mature males soon become habituated to that substance, decreasing their responsiveness in the presence of the first immature male (Gailey et aI., 1982) and then being markedly unresponsive to a second such male. Aftereffects on Receptivity of Females Exposed to Courtship Song Responsiveness of females to male courtship can in certain instances be increased experimentally. The relevant phenomena seem to be in the realm of behavioral sensitization. Here again the associative/nonassociative conditioning mutants are pertinent. Females that had been previously subjected to electronically generated courtship sounds (cf. Schilcher, 1976a,b; Kyriacou and Hall, 1982) begin to mate more rapidly when they are mixed with males (Schilcher, 1976b; Kyriacou and Hall, 1984) . These enhancing aftereffects last about 1-3 min, in that the males need to be introduced to the females within that time period (i.e., poststimulation) in order for the reduced copulation latencies to reveal themselves (Kyriacou and Hall, 1984) . Superficially, at least, this phenomenon would seem to be a case of sensitization, and it is interesting that several learning mutations impair sensitization of the proboscis extension reflex, in tests using sugar stimuli (Duerr and Quinn, 1982) , just as they impinge on habituation (Duerr and Quinn, 1982) . Three of these mutations, dunce, rutabaga, and amnesiac, have now been shown to block or attenuate acoustic sensitization (Kyriacou and Hall, 1984) . Females homozygous for either of the first two mutations show no aftereffects of song prestimulation. Those heterozygous for either variant, or homozygous for amnesiac, have shortened copulation latencies when mixed with males just after prestimulation; but if one waits 1 min after the end of the song stimulus and then introduces males to the prestimulated dnc/+, rut/+, or amn/amn females, the enhancing aftereffects on copulation latency have disappeared (Kyriacou and Hall, 1984) . Therefore the mating behavior of these prestimulated females depends on their prior experience, and the parallels between the effects of these mutations on associative conditioning and those on acoustic priming are striking. Such similarities extend to the fact that mutant/wild-type heterozygotes for dnc and rut forget more quickly in both associative conditioning and in acoustic prestimulation tests (Dudai, 1983; Kyriacou and Hall, 1984) . Aftereffects Following Courtship of Mated Females There is a demonstrable energy cost connected with the courtship of a fertilized female. Males court such females with a reasonable degree of intensity (though see below), and the mated females persistently generate repelling behaviors (e.g., Connolly and Cook, 1973) . The frequency of copulation is about 1% under laboratory conditions when the females are tested 1 day after they initially mated (e.g., Siegel and Hall, 1979) . Intuitively, courtship directed at mated females would be expected to be relatively limited, and this is the case: males paired with fertilized females (which had copulated one day previously) showed an approximately twofold decrease in their amount of courtship behavior during a 60-rain observation period; there was no decrease in courtship activity for males paired with virgin females (Siegel and Hall, 1979) . Although the sex behaviors of both the male and the fertilized female waned during these observation periods, three further experiments served to focus attention on the male. First, it was noticed that males which had courted fertilized females thereafter expressed diminished levels of courtship activity with virgin females. The male courtship responses to virgins were inversely related to the length of time that these males were paired with fertilized females. Second, when males which had experienced courtship with fertilized females were tested with virgins, it was found that the duration, or quantity, of each of the courtship components was reduced, but the quality of each activity and their sequence was not disturbed. Third, such modified (i.e., depressed) courtship behavior persisted for 2 to 3 h in wildtype males (Siegel and Hall, 1979) . Fertilized females, however, express no behavioral modification following their limited experience with a male; these females repel subsequent males with the same intensity and persistence as before (R. W. Siegel, unpublished). This aftereffect on male behavior has been termed an example of conditioned courtship, in that it seems to involve a specific experiencedependent behavioral change. The alternative possibility, that fertilized females have a generally depressing effect on male behavior, is excluded by the following observations. After being paired with mated females, males do not appear to be generally debilitated. Most interestingly, males from the a m n e s i a c strain recover the normal response to females after only 30 min (Siegel and Hall, 1979) . If some sort of debilitation is to explain the aftereffect, then one would imagine that a m n should show as lengthy an aftereffect as do normal males. Finally, males which have been " t r a i n e d " by mated females (i.e., males which exhibit relatively weak courtship at subsequent females) remain responsive to immature males (Gailey et al., 1984). Decrements in male courtship following pairing with fertilized females are limited to interactions with females. Reduced courtship toward females occurs only in those males which have previously courted fertilized females, not for those which, for example, had been courting young males (Galley et al., 1984) . Furthermore, D. A. Galley and R. W. Siegel (unpublished) have shown that male courtship behavior can be conditioned by fertilized females which were immobilized either by disruption of their central nervous system (decapitation or crushing of the head) or by the effects of a temperature-sensitive paralytic mutation (as long as such immobile females had been courted first; see below). Hence, elaborate rejection behaviors are not a requirement for the aftereffect. Nor is it likely that female repelling behaviors are sufficient to bring about conditioning. This was concluded from observations of immature virgin females, who might reject a male for an hour without causing him to court poorly during or after such an experience. It is chemicals which are uniquely associated with fertilized females that play a decisive role in this case of courtship behavioral modification. Tompkins et al. (1983) showed that olfactorily defective males cannot be conditioned as are wild-type males. It had been previously demonstrated that extracts of volatile compounds from fertilized females can induce two mature males to court each other (Tompkins and Hall, 1981) . Extracts from fertilized females also reduce the courtship that a male performs in response to a live virgin female (Tompkins and Hall, 1981) , suggesting that fertilized females are associated with an "inhibitory" chemical cue. These observations also suggest that males simultaneously perceive both courtship-stimulating and aversive chemical signals which are provided by fertilized females (again, see Tompkins' accompanying review for details). The male might associate these two stimuli with an object of courtship, and he thus learns to avoid female courtship stimulating signals later o n - - e v e n when they are unconnected with aversive cues, that is, when he subsequently encounters a virgin female. The male would in a sense be anticipating that this courtship object will emanate a hypothetically ~'noxious" substance. Evidence on the manner in which this apparent aversive material is involved in conditioning the male's later courtship behavior comes from experiments designed to reconstruct, somewhat artificially, the combined cues necessary to effect training. A male isolated in a small chamber, containing an extract of fertilized females along with another fly, subsequently expresses courtship modification; extracts from virgin females and from mature males have no such effect (Tompkins et al., 1983) . The " o t h e r fly" in this situation may be a virgin female or even a paralyzed mature male (Tompkins et al., 1983) . This courtship object must be paired with the fertilized female extract simultaneously, not sequentially, in order for an aftereffect on the male trainee to occur (Tompkins et al., 1983) . Conventional theories of learning would suggest that if males do associate courtship-stimulating signals with the putative aversive signal, then the aversive signal must be perceived after and not before the stimulus provoking courtship. Evidence for such a temporal sequence would offer additional support for the existence of an aversive cue in these behavioral phenomena. When a fertilized female is immobilized after her first mating but before she is courted again, and then is paired with a test male, that male courts the female but does not express later courtship modification. However, if the fertilized female is courted for a brief period, then immobilized, a test male with which she is paired is conditioned. This result (Jackson et al., 1983; Gailey et al., 1984) demonstrates that fertilized females must be courted and must have normally functioning central nervous systems at the time they are courted if they are to condition male behavior. The idea that fertilized females release an aversive conditioning signal in response to a courting male has been examined further. Males from the mutant strain Don Giovanni (dg) court fertilized females as if they were persistently courting virgins. Afterward, these males express vigorous courtship with test virgins (i.e., the males were not trained). These dg males are conditioned in a normal manner by courtship with immature males, and the general behavior of flies from this strain seems normal (cf. Gailey et al., 1984). Mutant dg males can be conditioned by courtship with fertilized females but only in special circumstances. If fertilized females are courted by wild-type males, immobilized, and then courted by dg males, the dg males show a normal decrease in their courtship with virgins (i.e., as occurs with regard to wild-type males). In addition, fertilized females which are courted by dg males prior to immobilization do not condition the behavior of wild-type males (D. A. Gailey and R. W. Siegel, submitted for publication). Hence, we infer that these mutant males are defective in the capacity to induce fertilized females to release the aversive signal; this would explain why dg males do not normally express conditioning effects. If these ideas are correct, dg males should be as capable as normal flies in other associative learning tasks. This was found to be so. When artificial odors were presented together with electric shocks (cf. Quinn and Greenspan, 1984) , males learned to avoid those odors (R. W. Siegel and D. Byers, unpublished). Therefore the mutant can express conditioned behavior in circumstances which bypass its particular defect. When coupled with an object of courtship, an extract prepared from fertilized females will condition male behavior, whereas an extract from virgin females will not. A male is thus initially required to fertilize the female, who then becomes capable of eliciting a male's experience-dependent behavior. Our observations indicate that copulation but not fertilization is required. That is, females which have mated with sterile males can condition other males (R. W. Siegel and J. C. Hall, unpublished), whereas females successfully fertilized by mutant Don Giovanni males do not condition (see Gailey et al., 1984). Male-specific e l e m e n t s - - s u c h as the antiaphrodisiacs transmitted during copulation or the inhibitor made in the female's reproductive tract from that antiaphrodisiac (see Tompkins, this issue)--together with the courtship-stimulating cues which still emenate from mated females are requisites for the male's behavioral modification. A series of observations on males derived from mutant strains which are known to be defective in their general learning abilities lends additional support to the notion that aftereffects caused by exposure of males to fertilized females are in the realm of conditioned behavior. Gailey et al. (1984) found that males of all the relevant strains are markedly defective with respect to courtship conditioning, following pairing with fertilized females. These were males expressing any of three different dnc mutations or males from the cab, rut, or tur strain. Such mutants were shown to be normal with respect to eliciting conditioning cues from fertilized females (see above). That they are unable to respond normally to this courtship training regime seems, again, to be due to faulty information storage or retrieval. In one mutant, rut, the problem may be in storage or even perception of mated females (i.e., the training fly). All the other mutant males can tell the difference between mated and virgin females (there is generally twice the amount of courtship with virgins as with fertilized females); but rut males courted fertilized or virgin females with equal and relatively high vigor (Gailey et al, 1984). Perhaps their olfaction in this behavioral situation is mediocre. The rut gene is known to disrupt adenylate cyclase (see review by Aceves-Pifia et al., 1983) , an enzyme defect which might impair behaviors other than learning. Earlier observations by Maynard Smith (1956 ) showed that this phenomenon is not limited to D. melanogaster. As part of a larger investigation of mating behavior in D. subobscura, he reported that whereas 47 of 52 males without prior courtship experience promptly copulated with virgin females, only 5 of 13 males which had courted fertilized females 3 h earlier copulated with virgin females. Seven of the remaining eight males copulated with virgins after a day of isolation. In addition, Maynard Smith (1956 ) reported that males kept in groups, rather than in isolation, court inefficiently; this effect disappeared after males were isolated for a day. A similar grouping effect was reported by Bastock and Manning (1955) for D. melanogaster and has been since confirmed (e.g., Schilcher, 1976a) . Nothing is known of the mechanism involved. Courtship by "Males" that Are Mosaic for Learning Mutations Mosaic analyses of genotypic differences related to courtship have recently moved beyond the matter of gynandromorphs per se. We have begun to assess the conditioned courtship of flies that are phenotypically male and are mosaic for normal and mutant alleles of various learning mutations. Since the pattern of mosaicism within these males' nervous systems can be revealed histochemically (cf. Hall, 1979; Schilcher and Hall, 1979) , we hope to identify "learning foci" for these mutations, which could be interpreted as neural substrates for particular components of experience-dependent courtship. We have no predisposition as to what these neural substrates might be. For instance, might the mosaics reveal that a given mutation must be expressed in only a very limited portion of the brain in order that defective learning occur, or will this analysis show that most or all of the CNS must be mutant if the fly's behavior is to be abnormal? Tests of conditioned courtship seem as if they will be an ideal way to study learning and memory in a series of mosaics, because the flies can (and must) be tested individually. A second requirement is that the normal vs. mutant behavioral differences be essentially all-or-none. This is fulfilled in the case of dnc-induced defects in conditioning of mature males by exposure to young males (Gailey et al., 1982). That is, almost every dnc + male learns (courts poorly after training), whereas nearly every dnc male does not (continues to court vigorously). We have, therefore, constructed a preliminary series of dne+//dnc mosaics. Each one was part diplo-X (i.e., heterozygous for a dnc mutation) and part haploX (i.e., hemizygous for this mutation). The basic courtship behavior of such a sex-chromosomal mosaic is often nonexistent or extremely aberrant (as was implicit in the earlier discussion of the mosaic mapping of male-specific and female-specific neural foci). Thus, we turned each of our dnc+//dnc mosaics into a pseudomale, by introducing homozygosity for the transformer mutation (one of the several sex determination mutations in D. melanogaster; see Baker and Belote, 1983, for review) . Diplo-X flies which are tra/tra look like males (though not entirely) and behave in a normal male fashion (Hall, 1979; Schilcher and Hall, 1979; Kyriacou and Hall, 1980) . Behavioral testing followed by histochemical analysis of our internally marked dnc mosaics has led us to the tentative conclusion that the focus for the primary action of this gene is in the male's brain (D. A. Gailey and J. C. Hall, unpublished). It remains to be seen, from the necessary study of several more mosaics of this type, whether this brain focus will hold up and whether the focus in these tissues is narrowly local or diffuse. There are already some implications of our preliminary results. For example, the d n c - e n c o d e d gene product, which is almost certainly a particular form .of cyclic AMP phosphodiesterase (reviewed by Davis and Kauvar, 1984) , is present in essentially all body segments of the fly, although it is rather concentrated in the head (Shotwell, 1983) . Yet, our results suggest that the presence of this enzyme with respect to learning seems to be important only in the brain. Otherwise, our mosaics with large amounts of mutant tissue in posterior regions would have learned abnormally. There is one more related neurochemical matter which can now be addressed. Tempel et al. (1984) have recently shown that temperaturesensitive dopa-decarboxylase mutants ( D d # s) are defective in associative conditioning, as measured in the aforementioned mass fly tests (also see Tully, this issue). The authors also report that, in single-fly tests, D d c ts males (raised at a low temperature, then heat treated as adults) are aberrant in the aftereffects they exhibit subsequent to courtship of mated females. Similar defects have recently been revealed in analogous tests using immature males to train the D d c ts males (D. A. Gailey and J. C. Hall, unpublished). The enzyme being manipulated here is, like the phosphodiesterase, distributed fairly ubiquitously in the fly (e.g., Wright, 1977; Livingstone and Tempel, 1983) ; but a depletion of dopa-decarboxylase, and the consequent lowering of dopamine and/or serotonin levels (cf. Livingstone and Tempel, 1983) , may affect conditioning by exerting quite local effects on the relevant brain functioning. This possibility needs to be addressed in tests of D d c + / / D d # s mosaics. Another potential implication of experiments on mosaics expressing a given behavioral/biochemical mutation is that they can lead to a comparison of neural substrates underlying associative vs. nonassociative learning. Our tests of d n c mosaics thus far have involved "young-male learning," an experience-dependent effect which appears to be nonassociative habituation. With regard to "mated-female learning," which seems to be more in the realm of associative conditioning, there is now a test which essentially creates the necessary all-or-none behavioral results of training normal and mutant flies. In the initial report of dncinduced effects on mated-female learning, Gailey et al. (1984) showed that three mutant alleles of the dunce gene cause defects in courtship conditioning. These tests were done with virgin females as the "tester" flies, with whom the males were placed after previous exposure to mated females (cf. Siegel and Hall, 1979) . The effects of training are not extremely severe in terms of courtship decrements expresged in the presence of such virgin females (cf. Siegel and Hall, 1979) . But when mated females are used as testers (as well as trainers), then the aftereffects last at least 12 h (D. A. Galley, unpublished). Furthermore, every dnc ยง male expresses a high level of training, and every dnc male shows poor training that does not overlap with the performance of the normal males (S. Kulkarni, unpublished). This background of behavioral results will make it possible for us meaningfully to analyze a series of dnc+//dnc mosaics for their ability to be associatively conditioned. In fact, it should be possible to test a given mosaic for association-type conditioning with fertilized females and then to reuse this mosaic in a test for nonassociative habituation with young males. Some mosaics may be able to learn by one mode but not the other, unlike normal males, who can store and retrieve both kinds of information (D. A. Gailey, unpublished). If such results were found in tests of the mosaics, they would imply that there might be separable neural foci underlying these two apparently different types of learning which, nonetheless, are connected formally by virtue of the fact that several of the conditioning mutations affect each of these categories of behavior. What structures in the Drosophila brain might be important for learning? When we proceed with the mosaic studies discussed above, we should keep the mushroom bodies in mind. These dorsally located calyces, peduncles, and lobes have been considered "association centers" in many arthropods and are involved in learning in social insects such as bees (see review by Menzel and Erber, 1978) . Drosophila has mushroom bodies, albeit rather meager ones (compared to bees), and there is now a series of mushroom-body mutants available (Heisenberg, 1980). These were isolated on anatomical criteria and are now being studied behaviorally, especially with regard to a variety of olfactory and conditioning tests. Two of the mutants have been shown to be defective in mass-fly associative learning. One mutant which is abnormal in these tests is mushroom-bodies deranged (mbd) (M. Heisenberg and D. Byers, unpublished; cf. Heisenberg, 1980) . Another is mushroom-bodies-miniature (mbm) (A. Borst and M. Heisenberg, unpublished; see brief description of this mutant by Technau, 1984; Quinn and Greenspan, 1984) . This is a particularly interesting case, because mbm females have very small mushroom bodies and exhibit weak shock-odor learning; but mbm males are normal, both anatomically and in this component of conditioned behavior. With respect to courtship, M. Heisenberg (unpublished) has collected preliminary data showing that rnbd males (which are structurally quite abnormal) are somewhat defective in the habituation tests involving immature males. It was perhaps disappointing, however, to find that the same mutant males exhibit normal aftereffects subsequent to their courtship of mated females (Heisenberg, 1980) . Yet the other brain mutants have not been tested in this way, nor have any of them been examined in memory tests related to courtship modification. Whatever these experiments eventually reveal, the mosaic studies of the learning and memory mutants should determine whether the mushroom bodies or other brain regions--or all of t h e m - - a r e involved in conditioned courtship. Given the new and expanding information on the behavioral significance of these brain regions, it is worth recalling our earlier conclusions from mosaic studies of basic male behavior. The dorsal, posterior brain focus, which must be haplo-X if a D. melanogaster gynandromorph is to exhibit any male-like courtship actions, seems to be rather near the cortical " K e n y o n cells" which innervate the peduncles of the mushroom bodies [see Hall (1979) and Hefsenberg (1980) for relevant facts and discussion]. It could be that the morphology and the function of these bodies are sex specific and are components of the neural substrate Which controls reproductive behavior. This general proposal is made by analogy to the well-known sexual dimorphisms in the brains of various vertebrates and their presumed role in sexually dimorphic behavior (e.g., Arnold, 1980; MacLusky and Naftolin, 1981) . It is therefore of interest that the mushroom-body peduncles in D. melanogaster are in fact sexually dimorphic in structure (Technau, 1984) . This anatomical difference may be behaviorally significant. Clocks, Mutants, and Conditioned Courtship The response of an organism to environmental cues can be largely dependent upon the temporal pattern in which the cues occur. There are narrow limits within which the temporal properties of that pattern can vary if associative or nonassociative conditioning is to occur. Given these generalities, one might imagine that disruption of the internal timing devices of an organism could also upset conditioning. Mutations which disturb both daily (circadian) rhythms and the rapid cycling rhythm of the courtship song are available (reviewed by Konopka, 1984) . Jackson et al. (1983) discovered that males carrying any one of five independently isolated mutations previously shown to lengthen the period of the fly's rhythms respond inefficiently to conditioning cues. Controls on these experiments excluded artifacts, such as changes in sensory perceptions, alterations in cues, time of day, and abnormal courtship behaviors per se. Therefore, conditioned responses to immature males and fertilized females were disturbed, suggesting that these mutants with their "slowly ticking" internal timers are perturbed in mechanisms common to both types of learning. Consistent with this metaphor, it seems, is the fact that short-period per ~ males are normal in conditioned courtship (Jackson et al., 1983) ; but it is perhaps odd that arrhythmic p e r ~ flies are also normal in these tests (Jackson et al., 1983) , as they are in their general learning and memory (Aceves-Pifia et al., 1983) . Can these results reveal anything about the mechanism basic to conditioning? Even if they do not, they may be of some heuristic value. Autonomous or endogenous rhythmic neuronal firing has been noted among both invertebrates and vertebrates (reviewed by Delcomyn, 1980) . So-called "bursting neurons" almost certainly exist in Drosophila. It would not be surprising if their firing patterns were linked with internal timers which are in part controlled by the action of clock genes. Could it be that the number of neuronal bursts per time increment is involved in information storage and retrieval? If so, one could imagine that, in long-period mutants, the number of bursts in a time interval may be low enough to upset conditioning. Or perhaps conditioning requires that autonomous firing patterns need to be "in register" with the transmission of signals from the environment. It will potentially be very informative to study mosaics for the per-long and andante mutations (cf. Konopka, 1984; Jackson et al., 1983) , using courtship conditioning, as the behavioral tests. Brain regions affected by these mutations, with respect to these traits, could conceivably be the same as those affected by conditioning mutations such as dnc. Could it also be that the foci influenced by these clock genes, with regard to the various rhythm phenotypes (Konopka, 1984; Kyriacou and Hall, 1980) , are neural tissues strongly related to those which are affected by the learning and memory variants? An analysis of mutant vs. normal rhythms in mosaics expressing a per mutation has proven feasible (Konopka et al., 1983). This implies that a comparison of the "clock foci" to the "learning foci" will eventually be possible as well. SPECULATIVE QUESTIONS AND CONCLUSIONS Do Courtship Signals Inform or Manipulate? Courtship signals are sensory cues which are produced by one organism, perceived by a conspecific, and are effective in evoking in the latter the characteristic actions which normally (but not inevitably) culminate in copulation. It is convenient to refer to the signal producer as the " a c t o r " and the signal recipient as the " r e a c t o r . " It is implicit here that courtship signals can be distinguished from other signals, such as alarms, and that the former are in some way "specified by the genome," at least in the sense that they are to some degree species specific. As for the function of courtship signals, it is a commonplace idea that they typically serve to coordinate the behaviors and, in some cases, to bring together prospective mates. None of the recent work on reproductive behavior in Drosophila melanogaster appears to be in serious disagreement with these statements. Courtship signals in this species, however, can bring together and stimulate interactions between flies which cannot copulate with one another. This deserves further comment. If courtship signals are to be effective, they must modify the behavior and physiology of the reactor, bringing it into functional accord with the behavior of the actor. At this point, we pause to note that behavioral biologists can perhaps be divided into two camps. One holds the seemingly traditional view that courtship signals serve only to convey information from the actor to the reactor. This is followed, presumably, by the reactor's integration of the signals, producing behavioral changes which ultimately result in copulation. Another view, which seems to be less widely held or at least more recently invoked, is that there is little or no informational content in the signals per se; instead, these signals are means b y which the actor manipulates the reactor to his own advantage. Reducing these contrasting views to their simplest terms, we ask whether courtship signals in Drosophila inform, or do they instead persuade the recipient? It should be mentioned, as well, that a classical ethological view embodying information exchange stresses the mutual benefit to both actor and reactor; such would enhance, perhaps, the evolution of the communication system. Others, in contrast, argue that communication benefits the actor only and that if there is any benefit to the reactor it is at best incidental and probably irrelevant. The two viewpoints are stated most forcefully by Dawkins and Krebs (1978) , Hinde (1981) , and Caryl (1979, 1982). The suggestion that courtship signals function to convey information from the actor to the reactor presents several difficulties in considering reproductive behavior in D. meIanogaster. For example, a particular signal from one individual can convey what is true at one moment; at the next, the signal lies. Thus, a sexually immature female, who repels a male's copulation attempts and is unreceptive to them, nevertheless produces courtship stimulating chemicals. If the cue is informational, its information is false. A few hours later, this female is a mature virgin and will copulate in response to male courtship. The same (or at least the same general type of) courtship-stimulating cues are released as before, but their informational content has in a sense changed from false to true. Finally, fertilized or aged females continue to produce courtship-stimulating materials; yet they do not normally copulate (e.g., Connolly and Cook, 1973) , so the stimulating signal once more contains false information. Consider, too, that immature males induce mature males to court them; this is difficult to reconcile with an hypothesis which holds that signals have informational content of benefit to both actor and reactor. Our knowledge of the detailed aspects of courtship signals in D. meIanogaster favors the idea that some signals are manipulative, especially in light of the ostensibly false stimulating cues that have just been discussed. It would seem, for example, less energetically expensive to both males and females if a fertilized (or an old female) were to shut off production of courtship-stimulating substances. The fertilized female possesses aversive substances as well as aphrodisiacs; the former do cause relatively depressed responses on the part of the male. By provoking the male to court, the mated female can manipulate him in order to benefit herself as the actor. This is because a male which courts a fertilized female is distracted from courtship of and copulation with a virgin female. By eliciting a male to court, the mated female gains an advantage over virgin females, because the probability that such virgins will be fertilized and contribute to the next generation is diminished. Therefore, the capacity of fertilized females to elicit courtship, in part through their continued production or release of aphrodisiacs, provides a means of manipulating male behavior to their advantage. It could also be argued that immature and aged females distract the attention of males from other females, to the benefit of any future progeny or those that are developing. In summary, the behavioral interactions we have discussed can be viewed in the context of courtship signals serving to manipulate rather than inform. The female manipulates the male, causing him to fertilize her eggs. Following fertilization she manipulates secondary males through her signals in order to gain advantage over other females. The mating male manipulates the female, causing her to help him in gaining an advantage over secondary males. The manipulated male here may even gain some benefit himself within this system. We now turn to a discussion of this putative benefit and to others which are related to conditioned behavior in these flies. Is There a Selective Advantage for Drosophila's Ability to Learn and Remember? The attractiveness of a fertilized female could provide the male who mated with her a means of gaining an advantage over other males. The male here provides as his legacy a female that can occupy the attentions of his male competitors. Hence, his own chances of finding another virgin female to inseminate could be improved. In addition, the aversive stimuli associated with mated females may cause males subsequently to avoid not only other mated females (which it is a good idea for them to avoid) but also virgin females. A male trained with a fertilized female for an hour takes 2-3 h to rebound back to normal, whereas this aftereffect lasts between 12 and 24 h if the male is again paired with a mated female. Perhaps the initial experience with the fertilized female subsequently biases the male's responsiveness more toward virgins than mated females than would otherwise have occurred (even though responsiveness in general is depressed). In a situation where most females are fertilized, one imagines that learning to avoid these females more strongly than virgins could in effect sharpen up the male's discrimination between the two. There might even be a selective advantage to males who modify their courtship in this way. Such interpretations are rather counterintuitive. It of course appears to be maladaptive that males can be conditioned with fertilized females to show depressed responsiveness to virgins. However, Hewitt et al. (1983) have examined the genetic architecture for olfactory conditioning in shock-avoidance tests, and their results have revealed a close relationship between this type of learning and biological fitness. Since this conditioning phenotype has common genetic elements with courtship modification tests using both young males and fertilized females, we assume that the aftereffects on male behavior of these courtship experiences are not artifactual--in the general sense, and especially with regard to depressed courtship of subsequent mated females. Turning to the sex appeal of immature males, this attractiveness could be viewed as a mechanism whereby newly emerged males decrease the mating opportunities of older males and therefore increase their own potential for mating when they have matured. An additional speculation would be that the young male " w a n t s " to be courted in order to "sharpen u p " his own courtship behavior for later on. Perhaps there is a critical period during the development of the adult male when his eventual singing behavior is susceptible to influence from a mature song. Such a phenomenon would be analogous to the development of song in some birds (Arnold, 1980; Konishi and Gurney, 1982) . Such a situation could cut both ways in terms of who is the manipulator and who is being manipulated. The young male may require hearing a robust, species-specific song to fully mature his own, whereas the older male may " c h e a t " and sing a quite untypical song in order to disrupt this development. This (absurd?) idea can be easily tested by comparing the songs of mature males directed to virgin females with those sung to young males. G e n o t y p e W i l d t y p e d u n c e d n c / + r u t a b a g a r u t / + c a b b a g e t u r n i p t u r / + a m n e s i a c D d d s p e r i o d - l o n g p e g p e r ~ a n d a n t e p s i - 2 p s i - 3 m b d + N T N T N T + D e f e c t i v e E x p e r i e n c e - D e p e n d e n t C o u r t s h i p in B e h a v i o r a l a n d N e u r o l o g i c a l I t s m e r e o r y S h o c k - o d o r a s s o c i a t i v e l e a r n i n g i t s m e r e o r y S u g a r - o d o r a s s o c i a t i v e l e a r n i n g I t s m e m o r y H a b i t u a t i o n S e n s i t i z a t i o n ( t o s u g a r s t i m u l i ) . . + . . . . + + + + + N T N T + N T N T N T + ( - ) ( - ) + d N T N T + N T N T N T ( - ) Conditioning mutants, clock mutants, biochemical mutants (some of which overlap the first two categories), and an anatomical brain mutant have been tested m various features of the apparent learning and memory which accompany male or female reproductive behavior. The clock mutants (per's, psi's, and andante) are described by Konopka (1984) and Jackson et al. (1983) ; all have long-period phenotypes except the short-period pet ~ and the arrhythmic p e r ~ mutant. The symbol for the brain mut~tnt listed here (mbd) stands for m u s h r o o m - b o d i e s d e r a n g e d (Heisenberg, 1980) . The results on the courtship tests are summarized here (by the symbolic entries in the matrix) and are compared to the effects of these genetic yariants on some of the more general aspects of conditioning in D. m e l a n o g a s t e r (for more details see Tully, this issue). A + entry means that the learning or memory tested was normal or nearly so. A means that the same test revealed demonstrably worse than normal (wild-type) performance though not necessarily a totally absent response. ( - ) means that aberrant memory is inferred (but has not been directly tested), because learning per se is abnormal. In the tests of general associative conditioning using electric shocks and odors (again, refer to Tully's accompanying article), an absence of or defect in "learning" (i.e., a - entry) often seems to mean that the effects of training tend to decay so rapidly that no learning is revealed; that is, several of these mutants are unable to learn but are extremely fast forgetters (for discussion see Tempel et al., 1983; Dudai, 1983) . The same genetic variants may cause a given component of courtship "learning" (as formally distinct from " m e m o r y " in terms of the column headings in this table) to be subnormal for the same reason. NT, not tested. b rut males apparently cannot discriminate between mated females and virgin females in the first place, in that they court both kinds of females with approximately the same vigor, unlike what is found for wild-type males or those expressing the other conditioning mutations listed here (Gailey et al., 1984). Therefore the defective aftereffect exhibited by rut males may not be a learning abnormality. a m n flies do show subnormal "habituation indices," but they are also lower than normal in their " n a t i v e " responsiveness to sugar stimuli. Thus, their learning defect in this particular case is difficult to assess unambiguously (Duerr and Quinn, 1982) . d Ddet~ mutants are defective in associative learning per se. The absence of an influence of this gene on memory is inferred from testing the effects of D d c variants in heterozygous condition on associative conditioning (Tempel et al., submitted for publication). " Since D d c t~ mutants have been shown to have much higher than normal thresholds for their basic responsiveness to sugar stimuli, it would be difficult to test for aberrant habituation or sensitization using such stimuli (Tempel et al., 1984). = Something that should be borne in mind concerning these outlandish ideas is that the brain of D. melanogaster is not quite so completed in its development as one might think. The mushroom bodies in the dorsal brain of young adults initiate a new round of development beginning at eclosion. The fiber number in the peduncles of these bodies increases by at least 15% during the first week of adult life (Technau, 1984) . This increase depends on environmental inputs, including stimuli received by a fly from other individuals. Technau (1984) has also demonstrated that, whereas the absence of visual inputs does not block this increase in fiber number, disturbing antennal input (the entry point for song stimulation) does. Therefore we must for the moment, at least, entertain the unlikely possibility that a young male's aphrodisiacs elicit auditory stimuli which may modulate postpupal brain development and which, in turn, may influence his later production of courtship song. We already know (C. P. Kyriacou and J. C. Hall, unpublished) that males kept in isolation from egg to adult produce superficially normal pulse and hum song. We have not yet tested whether this song is normal in all its various components. Our final phenomenon which involves memory in courtship behavior is the priming effect of artificial songs on females (Schilcher, 1976b; Kyriacou and Hall, 1984) . Here there is an increased reproductive success associated with the previous experience of females. In the laboratory, 2 rain of intensive prestimulation of females with courtship songs leads to a priming effect where female receptivity is enhanced for approximately 1-3 min. In the real world, courtship interactions may be brief, and it is not difficult to imagine that the female's receptivity to such stimuli may linger a little after initial reception. The benefits of this are obvious for the courting male, as this will increase the probability that he will mate. For the female, the adaptiveness of such priming and "summation" of stimuli (Manning, 1967) may be related to her " c o y n e s s . " The female's only clue as to the fitness of the male is his courtship behavior, and thus her initial reluctance to mate allows her to screen the male. Consequently any kind of simple, even transient memory may help her to integrate the relevant information from an elaborate display. Here, we are back to the perhaps more conventional view of the informational content of courtship signals as opposed to their manipulative potentials. It is worth pointing out that an early study by Schilcher (1976b) suggested that only the hum component of the song, not an invariant pulse song, was an effective primer for the female. Thus hums appeared to " a r o u s e " the female, whereas the pulse could be considered as the species-specific "trigger" for mating. Kyriacou and Hall (1984) fully confirmed Schilcher's findings but noted that when a more natural speciesspecific pulse song, including the rhythmic component, was applied to females, this p r o v e d to be an e v e n m o r e effective priming stimulus than h u m song in enhancing subsequent mating success. T h e r e f o r e both pulses and h u m s can be r e m e m b e r e d by the female. Finally. in passing, it should be reiterated that a species-specific, cycling pulse song also gives faster mating speeds c o m p a r e d to an invariant pulse song, or one with an inappropriate r h y t h m , w h e n these sounds are used to stimulate males and females simultaneously ( K y r i a c o u and Hall, 1982) . One m o r e implication o f the m a n y speculative ideas discussed h e r e is that these kinds o f e x p e r i m e n t s n e e d to be e x t e n d e d b e y o n d the labo r a t o r y into field studies or at least m o r e natural settings. This will permit a t r u e r a s s e s s m e n t o f any functional significance or adaptive value which can be inferred f r o m the laboratory. Of course, it could be that some of these observations are rather d r e a r y l a b o r a t o r y artifacts. N e v e r t h e l e s s , r e p r o d u c t i o n - - w h e t h e r or not it is a n a l y z e d in an artificial s e t t i n g - - i s implicitly tied to fitness. T h e mutationally induced abnormalities which disturb the effects o f previous e x p e r i e n c e on courtship b e h a v i o r bring these genes into focus as having e v o l v e d to do m o r e than m e r e l y aid flies to avoid electric shocks. Table I presents a s u m m a r y o f these genetically c a u s e d abnormalities in artificial elements of conditioned b e h a v i o r and in t h o s e which we d e e m to be quasirealistic. L e a r n i n g in D r o s o p h i l a would a p p e a r to h a v e b e e n f a v o r e d by natural selection (Hewitt et aI., 1983) , and t h e r e f o r e it is important to identify those p r o c e s s e s in the life history of the fly which are particularly sensitive to behavioral plasticity. We would suggest that r e p r o d u c t i v e b e h a v i o r is one o f those p r o c e s s e s ; " r e w a r d learning" involving nutritive unconditioned stimuli (Tempel et al., 1983) is likely to be another one. F u r t h e r studies which intensify the analyses o f these behaviors, their neural underpinnings, and the genes themselves should continue to p r o d u c t valuable information as t h e y are carried out in parallel. Aceves-Pifia , E. O. , Booker , R. , Duerr , J. S. , Livingstone , M. S. , Quinn , W. G. , Smith , R. F. , Sziber , P. P. , Tempel , B. L. , and Tully , T. P. ( 1983 ). Learning and memory in Drosophila studied with mutants . Cold Spring Harbor Syrup . 48 : 831 - 840 . Arnold , A. P. ( 1980 ). Sexual differences in the brain . Am. Sci . 68 : 165 - 173 . Baker , B. S. , and Belote , J. M. ( 1983 ). Sex determination and dosage compensation in Drosophila melanogaster . Annu. Rev. Genet . 17 : 345 - 393 . Bastock , M. ( 1967 ). Courtship, A Zoological Study , Heinemann, London. Bastock , M. , and Manning , A. ( 1955 ). The courtship of Drosophila melanogaster . Behaviour 8 : 85 - 111 . Booker , R. , and Quinn . W. G. ( 1981 ). Conditioning of leg position in normal and mutant Drosophila . Proc. Natl. Acad. Sci. USA 76 : 3940 - 3944 , Caryl , P. G. ( 1979 ). Communicationby agonistic displays: What can game theory contribute to ethology? Behaviour 68 : 136 - 139 . Caryl , P. G. ( 1982 ). Animal signms: A reply to Hinde . Atom. 3ehav . 30 : 240 - 244 . Connolly , K. , and Cook , R. ( 1973 ). R~ectio~n behaviours by female Drosophila melanogaster: Their ontogeny, causality and effects upon the behaviour of the courting male . Behaviour 52 : 155 - 171 . Cook , R. ( 1977 ). Behavioral role of the sex combs in Drosophila melanogaster and Drosophila simulans . Behav. Genet . 7 ; 349 - 358 . Cook , R. , and Cook , A. ( 1975 ). The attractiveness to males of female Drosophila melanogaster: Effects of mating, age, and diet . Anim. Behav . 23 : 521 - 526 . Davis , R. L. , and Kauvar , L. M. ( 1984 ). Drosophila cyclic nucleotide phosphodiesterases . Adv. Cyclic Nucleotide Res . 16 : 393 - 402 . Dawkins , R. , and Krebs , J. R. ( 1978 ). Animal signals: Informataon or manipulation? In Krebs , J. R. , and Davies , N. B. (eds.), Behavioral Ecology , Sinauer Associates, Sunderland, Mass., pp. 282 - 309 . Delcomyn , F. ( 1980 ). Neural basis of rhythmic behavior in animals . Science 210 " 492 - 498 . Dudai , Y. ( 1983 ). Mutations affect the storage and usage of memory differentially in Drosophila . Proc. Natl. Acad. Sci. USA 80 : 5445 - 5448 . Duerr , J. S. , and Quinn , W. G. ( 1982 ). Three Drosophila mutations that block associative learning also affect habituation and sensitization . Proc. Natl. Acad. Sci. USA 79 " 3646 - 3650 . Ewing , A. W. ( 1977 ). Communication in Diptera . In Sebeok, T. A. (ed.), How Animals Communicate , Indiana University Press, Bloomington and London, pp. 403 - 417 . Ewing , A. W. ( 1983 ). Functional aspects of Drosophila courtship . Biol. Rev . 58 : 275 - 292 . Galley , D. A. , Jackson , F. R. , and Siegel , R. W. ( 1982 ). Male courtship in Drosophila: The conditioned response to immature males and its genetic control . Genetics 102 : 771 - 782 . Galley , D. A. , Jackson , F. R. , and Siegel , R. W. ( 1984 ). Conditioning mutations in Drosophila melanogaster affect an experience-dependent behavioral modification in courting males . Genetics 106 : 613 - 623 . Hall , J. C. ( 1979 ). Control of male reproductive behavior by the central nervous system of Drosophila: Dissection of a courtship pathway by genetic mosaics . Genetics 92 : 437 - 457 . Hall , J. C. ( 1982 ). Genetics of the nervous system in Drosophila . Q. Rev. Biophys . 15 : 223 - 479 . Hall , J. C. , Gelbart , W. M. , and Kankel , D. R. ( 1976 ). Mosaic systems . In Ashburner, M., and Novitski , E. (eds.), The Genetics and Biology of Drosophila , Vol. la, Academic Press, London, pp. 265 - 314 . Hall , J. C. , Siegel , R. W. , Tompkins , L. , and Kyriacou , C. P. ( 1980 ). Neurogenetics of courtship in Drosophila . Stadler Genet. Symp . 12 : 43 - 82 . Heisenberg , M. ( 1980 ). Mutants of brain structure and function: What is the significance of the mushroom bodies for behavior? In Siddiqi , O. , Babu , P. , Hall , L. M. , and Hall , J. C. (eds.), Development and Neurobiology of Drosophila , Plenum Press, New York, pp. 373 - 390 . Hewitt , J. K. , Fulker , D. W. , and Hewitt , C. A. ( 1983 ). Genetic architecture of olfactory discriminative avoidance conditioning in Drosophila melanogaster . J. Comp. Psychol . 97 : 52 - 58 . Hinde , R. ( 1981 ). Animal signals: Ethological and game-theory approaches are not incompatible . Anim. Behav . 29 : 535 - 542 . Hotta , Y. , and Benzer , S. ( 1976 ). Courtship in Drosophila mosaics: Sex-specific foci for sequential action patterns . Proc. Natl. Acad. Sci. USA 73 : 4154 - 4158 . Jackson , F. R. , Gailey , D. A. , and Siegel , R. W. ( 1983 ). Biological rhythm mutations effect an experience-dependent modification of male courtship in Drosophila melanogaster . J. Comp. Physiol . 151 : 545 - 552 . Jallon , J. -M. , and Hotta , Y. ( 1979 ). Genetic and behavioral studies of female sex appeal in Drosophila . Behav. Genet . 9 : 257 - 275 . Konishi , M. , and Gurney , M. E. ( 1982 ). Sexual differentiation of brain and behavior . Trends Neurosci. 5-20-23. Konopka , R. J. ( 1984 ). Neurogenetics of Drosophila circadian rhythms . In Huettel, M, D. (ed,), Evolutionary Genetics of lnvertebrate Behavior , Plenum Press, New York (in press). Konopka , R. J. , and Benzer , S. ( 1971 ). Clock mutants of Drosophila melanogaster . Proc. Natl. Acad. Sci. USA 68 : 2112 - 2116 . Konopka , R.. Wells , S. , and Lee , T. ( 1983 ). Mosaic analysis of a Drosophila clock mutant . Mol. Gen. Genet . 190 : 284 - 288 . Kyriacou , C. P. ( 1981 ). The relationship between locomotor activity and sexual behaviour in ebony strains of Drosophila melanogaster . Anim. Behav . 29 : 462 - 471 . Kyriacou , C. P. , and Hall , J. C. ( 1980 ). Circadian rhythm mutations in Drosophila melanogaster affect short-term fluctuations in the male's courtship song . Proc. Natl. Acad. Sci. USA 77 : 6729 - 6733 . Kyriacou , C. P. . and Hall , J. C. ( 1982 ). The function of courtship song rhythms in Drosophila . Anim. Behav . 3 : 794 - 801 . Kyriacou , C. P. , and Hall , J. C. ( 1984 ). Learning and memory mutations impair acoustic priming of mating behaviour in Drosophila . Nature 308 : 62 - 65 . Livingstone , M. S , and Tempel , B. L. ( 1983 ). Genetic dissection of monoamine synthesis in Drosophila . Nature 303 : 67 - 70 . Manning , A. ( 1967 ). The control of sexual receptivity in female Drosophila . Anim. Behav . 15 : 239 - 250 . Markow , T. A. , and Hanson , S. J. ( 1981 ). Multivariate analysis of Drosophila courtship . Proc. Natl. Acad. Sci. USA 78 : 430 - 434 . MacLusky , N. J. , and Naftolin , F. ( 1981 ). Sexual differentiation of the central nervous system . Science 211 : 1294 - 1303 . Maynard Smith , J. ( 1956 ). Fertility, mating behaviour and sexual selection in Drosophila subobscura . J. Genet . 54 : 261 - 279 . Menzel , R.. and Erber , J. ( 1978 ). Learning and memory in bees . Sci. Am . 239 :(1): 102 - 110 . Quinn , W. G. , and Greenspan , R. J. ( 1984 ). Learning and courtship in Drosophila: Two stories with mutants . Annu. Rev. Neurosci . 7 : 67 - 93 . Quinn , W. G. , Sziber , P. P. , and Booker , R. ( 1979 ). The Drosophila memory mutant amnesiac . Nature 277 : 212 - 214 . Schilcher , F. von (1976a). The role of auditory stimuli in the courtship of Drosophila melanogaster . Anim. Behav . 24 : 18 - 26 . Schilcher , F. yon (1976b). The function of pulse song and sine song in the courtship of Drosophila melanogaster . Anim. Behav . 24 : 622 - 625 . Schilcher , F. von, and Hall, J. C. ( 1979 ). Neural topography of courtship song in sex mosaics of Drosophila melanogaster . J. Comp. Physiol. A 129 : 85 - 95 . Shotwell , S. L. ( 1983 ). Cyclic adenosine 3' :5'-monophosphate phosphodiesterase and its role in learning in Drosophila . J. Neurosci , 3 : 739 - 747 . Siegel , R. W. , and Hall , J. C. ( 1979 ). Conditioned responses in courtship of normal and mutant Drosophila . Proc. Natl. Acad. Sci. USA 76 : 3430 - 3434 , Spieth , J. T. , and Ringo , J. M. ( 1983 ), Mating behavior and sexual isolation in Drosophila . In Ashburner, M. Carlson, J. L. , and Thompson , J. N , (eds.), The Genetics andBiology of Drosophila , Vol. 3c , Academic Press, London, pp. 223 - 284 . Szabad , J. , and Fajszi , C. ( 1982 ). Control of female reproduction in Drosophila: Genetic dissection using gynandromorphs . Genetics 100 : 61 - 78 . Technau , G. ( 1984 ). Fiber number in the mushroom bodies of adult Drosophila melanogaster depends on age, sex, and experience . J. Neurogenet . 1 : 113 - 126 . Tempel , B. L. , Bonini , N. , Dawson , D. R. , and Quinn , W. G. ( 1983 ). Reward learning in normal and mutant Drosophila . Proc. Natl. Acad. Sci. USA 80 : 1482 - 1486 . Tempel , B. L. , Livingstone , M. S. , and Quinn , W. G. ( 1984 ). Mutations in the dopadecarboxylase gene affect learning in Drosophila . Proc. Natl. Acad. Sci. USA 81 : 3577 - 3581 . Tompkins , L. , and Hall , J. C. ( 1981 ). The different effects on courtship of volatile compounds from mated and virgin Drosophila females . J. Insect Physiol . 27 : 17 - 21 . Tompkins , L. , and Hall , J. C. ( 1983 ). Identification of brain sites controlling female receptivity in mosaics of Drosophila melanogaster . Genetics 103 : 179 - 195 . Tompkins , L. , Gross , A. C. , Hall , J. C. , Gailey , D. A. , and Siegel , R. W. ( 1982 ). The role of female movement in the sexual behavior of Drosophila melanogaster . Behav. Genet . 12 : 295 - 307 . Tompkins , L. , Siegel , R. W. , Gailey , D. A. , and Hall , J. C. ( 1983 ). Conditioned courtship in Drosophila and its mediation by chemical cues . Behav. Genet . 13 : 565 - 578 . Wright , T. R. F. ( 1977 ). The genetics of dopa decarboxylase and c~-methyl dopa sensitivity in Drosophila melanogaster . Am. Zool . 17 : 707 - 721 .

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Richard W. Siegel, Jeffrey C. Hall, Donald A. Gailey, Charalambos P. Kyriacou. Genetic elements of courtship inDrosophila: Mosaics and learning mutants, Behavior Genetics, 1984, 383-410, DOI: 10.1007/BF01065442