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The interplay between agonistic character displacement and reproductive interference in rubyspot damselflies (Hetaerina spp.)

  • Author(s): Drury, Jonathan
  • Advisor(s): Grether, Gregory F
  • et al.

Aggressive interactions between species are common despite being relatively understudied. Agonistic character displacement (ACD) theory makes predictions about how selection should act on traits that mediate the occurrence of interspecific aggressive interactions. Previous research on rubyspot damseflies (Hetaerina spp.) documented several cases of divergent agonistic character displacement acting on wing coloration and competitor recognition to diminish wasteful interspecific aggression. However, these and other studies of the evolutionary consequences of interspecific aggression have largely ignored how interactions between males and females of different species affect interspecific interactions between males. In chapter 1, we present a theoretical model that demonstrates that when individuals engage in local mate competition, selection may actually favor interspecific aggression. We then test this model in rubyspot damselflies (Hetaerina spp.) and show that in a comparison of several species pairs, levels of reproductive interference correlate positively with levels of interspecific aggression. In chapter 2, we document a previously undescribed seasonal polyphenism in the wing coloration of male and female smoky rubyspot damselflies (Hetaerina titia). We show that this polyphenism--an increasing amount of dark pigmentation on the wings of both sexes over the breeding season--impacts species recognition between H. titia and a sympatric congener (H. occisa). Additionally, we find that, in accord with comparisons across populations, seasonally decreasing levels of reproductive interference within a population correspond to a decreasing degree of interspecific aggression. In chapter 3, we present a phenotype manipulation experiment carried out on H. americana, whose results support the hypothesis that sympatric shifts in male traits resulted from ACD and lead us to reject the alternative hypothesis that reproductive character displacement in female mate recognition is responsible for these shifts. Finally, in chapter 4, we present a new statistical method to correct for phylogenetic non-independence in pairwise species comparisons, and we use this method in conjunction with a new phylogeny we constructed of nine Hetaerina species to show that interspecific differences in female wing coloration are correlated with the degree of reproductive interference. We also apply this phylogenetic correction to an analysis of predictors of interspecific territoriality in New World wood warblers (Parulidae).

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