Differences in Mating Propensity Between Immature Female Color Morphs in the Damselfly Ischnura elegans (Insecta: Odonata)
Martijn Hammers
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1
Rosa Ana Snchez-Guilln
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1
Hans Van Gossum
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R. A. Snchez-Guilln Departamento de Ecoloxa e Bioloxa Animal, Universidade de Vigo
, EUET Forestal,
Campus Universitario
, 36005 Pontevedra,
Spain
1
M. Hammers Animal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen
, P.O. Box 14, 9750 AA Haren,
The Netherlands
2
) Evolutionary Ecology Group, University of Antwerp
, Groenenborgerlaan 171, 2020 Antwerp,
Belgium
Female-limited color polymorphisms occur in a variety of animal taxa where excessive male sexual harassment may explain the coexistence of multiple female color morphs. In the color polymorphic damselfly Ischnura elegans, mature and immature female color morphs coexist at the mating site where males are in search for suitable mating partners. Here, we study male preference and female mating propensity for the two immature female morphs. As would be expected, compared to mature morphs, both immature female morphs mate much less. Within immature females, one morph consistently mates more frequently compared to the other morph, a pattern that is similar for the ontogenetically corresponding mature female morphs. Preference experiments with the two differently colored immature female morphs, however, did not indicate male mate preference for either morph. Low mating frequencies of immature females at natural sites in combination with relatively high attractiveness of immature models in terms of male preference indicate that female behavior influences female mating success.
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For species that show sexual conflict over fertilizations, reproductive success in
males typically is optimized through maximization of the mating rate. Females, in
contrast, only tend to require mating a few times to produce their optimal number of
viable eggs (e.g. Arnqvist and Nilsson 2000). Consequently, females are expected to
receive more male sexual attention than desired, which may interfere with female time
and energy budgets and may even lead to injuries (e.g. Crudgington and Siva-Jothy
2000). To avoid costs associated with excessive male sexual harassment, females
will be selected to develop counter-adaptations. These may include avoiding
encounters with males (e.g. Krupa et al. 1990) or forming associations with single
males (e.g. Clutton-Brock et al. 1992; Rowe et al. 1994). Another adaptation in
response to costly superfluous male mating attempts may be female-limited
polymorphism, where one female morph may avoid recognition by males through
resembling the males phenotype (Robertson 1985; Cook et al. 1994).
Femalelimited color polymorphism is observed in a variety of vertebrate and invertebrate
taxa, including birds (Galeotti et al. 2003), fish (Turner et al. 2001), lizards (Vercken
et al. 2007) and insects (Nielsen and Watt 2000). Where it occurs sexual selection
has often been indicated as a driving force for coexistence of multiple female morphs
in natural populations (Gross 1996; Gray and Mckinnon 2007).
In the case of odonates, female-limited polymorphism is common (Fincke et al.
2005) and female morphs differ in body coloration and sometimes in behavior (e.g.
Sirot et al. 2003; Fincke et al. 2005). Odonates have extraordinarily developed color
vision (Armett-Kibel and Meinertzhagen 1983; Corbet 1999; Briscoe and Chittka
2001), which makes coloration one of the most important visual cues for males in
mate recognition (Corbet 1999). Males may face little challenge in recognizing
females based on body coloration when only one female type is present, but could
become distracted when faced with multiple female color morphs (Fincke 2004).
Interestingly, one of the female morphs in damselflies is similar in body color to the
conspecific male (androchrome), while the other(s) is (are) not (gynochrome).
Similar to predators forming a search image for the most common prey type (e.g.
Murdoch 1969), frequency-dependent mate selection may act on female morphs,
with female color morphs receiving different amounts of male sexual harassment
(e.g. Miller and Fincke 1999; Van Gossum et al. 1999; Van Gossum et al. 2001a, b).
Alternatively, or in addition, mate-searching males may be challenged when part of
their potential female partners resemble the conspecific males phenotype and
behavior. Such a female morph is considered a functional male-mimic that gains an
advantage over the other female morphs as it receives less male attention (e.g.
Robertson 1985; Sherratt 2001). Most studies to date mainly focused on male mate
preference, while male and female mating success not only depends on male mate
preference, but also on female willingness to mate.
Indeed, due to the mating morphology of damselflies, males can only achieve
copulation if females cooperate (see Fincke et al. 1997 for review; but see Cordero
and Andrs 2002). Males will attempt to clasp a female at her pronotum using their
anal appendages to reach tandem formation (e.g. Miller 1987). After this, females
have (...truncated)