Genetic Variability in Developing Periodical Cicadas

Journal of the Arkansas Academy of Science Volume 48 Article 19 1994 Genetic Variability in Developing Periodical Cicadas Alvan A. Karlin University of Arkansas at Little Rock Eric C. Stout University of Arkansas at Little Rock Lance T. Adams University of Arkansas at Little Rock Lisa R. Duke University of Arkansas at Little Rock James J. English University of Arkansas at Little Rock Follow this and additional works at: http://scholarworks.uark.edu/jaas Part of the Entomology Commons Recommended Citation Karlin, Alvan A.; Stout, Eric C.; Adams, Lance T.; Duke, Lisa R.; and English, James J. (1994) "Genetic Variability in Developing Periodical Cicadas," Journal of the Arkansas Academy of Science: Vol. 48 , Article 19. Available at: http://scholarworks.uark.edu/jaas/vol48/iss1/19 This article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able to read, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking prior permission from the publisher or the author. This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact , . Journal of the Arkansas Academy of Science, Vol. 48 [1994], Art. 19 Genetic Variability in Developing Periodical Cicadas Alvan A. Karlin,Eric C. Stout, Lance T. Adams, Lisa R. Duke and James J. English Department of Biology University of Arkansas at Little Rock Little Rock, AR 72204 Abstract There are few events in nature that are more predictable than the emergence of periodical cicadas. The insects emerge from the ground after 13 or 17 years (depending on brood and species) of development. Karlin et al., (1991) biochemically examined over 750 Magicicada tredecassini belonging to Brood XIX which emerged during the spring of 1985. In this study they found evidence for rapid deterioration of heterozygosity for two esterase loci, Gi-3-pdh and Gpi, and suggested that this deterioration may be related to differential mating classes. To test this hypothesis, we re-sampled from this same brood at the same location during fall (1993) and winter (1994), nine years into the 13 year development of this brood. The current biochemical data suggest no significant deviations from Hardy-Weinberg expectations for either Est-3, Gl-3pdh or Pgm-1, but inseveral cases Est-1 or Est-2 displayed significant departures. Our failure to find excess heterozygosity in the nymphal sample is interpreted to support weakly the size-mediated mating system hypothesis. Introduction There are three morphologically identifiable species of periodical cicadas (genus Magicicada) each of which las 13- and 17-year life cycle forms. These are considered as six separate species (Alexander and Moore, 1962), although the recent findings for the Decim pair calls this reatment into question (Martin and Simon, 1988, 1990; Simon et al., 1993). Periodical cicada year classes termed "broods", have been analogized with incipient species because adults of each year class are temporally reproductively isolated all other year classes (Simon, 1988). Members of a ear-class are synchronized. They emerge from the round within a two week period with most of the indiiduals emerging during days two and three (Karban, 1982). The emergence occurs regularly, every 13 or 17 years depending on particular location (Marlatt, 1907; Alexander and Moore, 1962; Lloyd and Dybas, 1966; Lloyd and White, 1976). Thus, for the 17-year cicadas potentially 17 different year classes could exist (broods IXVII),and for 13-year cicadas there could be 13 different reproductively isolated broods (XVIII-XXX)(Marlatt, 1898). Currently, only 12 17-year broods and three 13year broods are known to exist (Simon, 1988). In this study we focused our attention on one species, Magicicada tredecassini, from Brood XIXin northwestern Arkansas. In a previous study, Karlin et al. (1991) examined almost 500 individuals captured as they emerged from the ground and another 500 individuals captured three weeks later in chorus centers for several biochemical Eom traits. They interpreted the data to suggest that heterozygosity for two esterase loci (Est-1 and Est-3), glyceraldehyde-3-phosphate dehydrogenase (Gi-3pdh), and glucose phosphate isomerase (Gpi) decreased markedly between sample periods. They proposed that the observed decline in heterozygosity could be a result of a phenotypic mating system linked to individual size as proposed by Karban (1982). If the larger (or smaller) males are more (or less) heterozygous, one class may mate earlier and hence be removed preferentially from the chorus population sample. Observations in support for this hypodiesis include finding the larval population in Hardy-Weinberg equilibrium for the genes in question. Although finding Hardy-Weinberg equilibrium is a weak demonstration of support, if the genes are not in equilibrium frequencies, we can strongly reject the hypothesis. One alternative hypothesis would implicate a constant decline in heterozygosity over the life cycle of the periodical cicadas. This hypothesis leads us to predict a heterozygote excess for these genes in the larval population allowing for the decline we observed in the adult population. Thus, we can use heterozygote excess as detected by deviations from Hardy-Weinberg expectations to support this hypothesis. Materials and Methods Nine-year-old nymphs of 13-year periodical cicadas {Magicicada tredecassini) were collected at a single locality, near Durham, Washington Co., Arkansas, in October, 1993 and February, 1994. The main study site used by Karlin et al. (1991) was revisited for this study. Proceedings Arkansas Academy of Science, Vol.48, 1994 89 Published by Arkansas Academy of Science, 1994 89 Journal of the Arkansas Academy of Science, Vol. 48 [1994], Art. 19 Oak trees (Quercus sp.), hickory trees (Carya sp.) and black locust trees (Robinia pseudoacacia) showing obvious evidence of cicada galleries (scaring on the outer branches) were selected. We carefully dug 10-20 cm. into the ground approximately 1 2 m from the tree base and searched from nymphs. Once an individual was located, - - careful excavation followed to locate additional individuals. To insure genetic diversity, we sampled 5 15 individuals from each of 10 trees. Individuals collected from a tree were placed together into a plastic bag filled with dirt. The bag was refrigerated on ice until returned to the laboratory at University of Arkansas Little Rock. Once in the lab, the bags were frozen at -70°C until used. On the morning of electrophoresis, individual cicadas were partially thawed and their total length measured with vernier calipers. Measurements were recorded to the nearest 0.1 mm. To prepare proteins (...truncated)