Recently we have published two studies based on the isopod system of Asellus aquatics. This species occurs in two ecotypes, which resides in different habitats. As the ecotypes are present in several Swedish lakes, this system has been studied in depth with regard to parallel evolution. Our new articles address differences in mating behavior between the ecotypes. As other crustaceans, A. aquaticus exhibits precopulatory mate guarding where the male captures a female before she is receptive and carries her beneath him until she is ready to mate. This behavior is target for sexual conflict in several isopods as the optimal initiation of pairbonding may differ between the sexes.
One of our articles, published in the latest number of Journal of Evolutionary Biology, deals with differences between the ecotypes in mate guarding duration, but also in differences in female survival and offspring production. Among other things, we found a pattern of parallel evolution in these traits. The other article, published in open access journal PLoS ONE, deals with differences in mating propensity between the ecotypes and how this is affected by demographic factors. Here, we found that the novel ecotype seem to have evolved a plastic behavior as response to sex ratio, in contrast to the ancestral ecotype.
You could find both abstracts below, and both articles are included in Kristina Karlsson Green’s thesis that will be defended on next Friday.
Phenotypic Plasticity in Response to the Social Environment: Effects of Density and Sex Ratio on Mating Behaviour Following Ecotype Divergence
The ability to express phenotypically plastic responses to environmental cues might be adaptive in changing environments. We studied phenotypic plasticity in mating behaviour as a response to population density and adult sex ratio in a freshwater isopod (Asellus aquaticus). A. aquaticus has recently diverged into two distinct ecotypes, inhabiting different lake habitats (reed Phragmites australis and stonewort Chara tomentosa, respectively). In field surveys, we found that these habitats differ markedly in isopod population densities and adult sex ratios. These spatially and temporally demographic differences are likely to affect mating behaviour. We performed behavioural experiments using animals from both the ancestral ecotype (‘‘reed’’ isopods) and from the novel ecotype (‘‘stonewort’’ isopods) population. We found that neither ecotype adjusted their behaviour in response to population density. However, the reed ecotype had a higher intrinsic mating propensity across densities. In contrast to the effects of density, we found ecotype differences in plasticity in response to sex ratio. The stonewort ecotype show pronounced phenotypic plasticity in mating propensity to adult sex ratio, whereas the reed ecotype showed a more canalised behaviour with respect to this demographic factor. We suggest that the lower overall mating propensity and the phenotypic plasticity in response to sex ratio have evolved in the novel stonewort ecotype following invasion of the novel habitat. Plasticity in mating behaviour may in turn have effects on the direction and intensity of sexual selection in the stonewort habitat, which may fuel further ecotype divergence.