Local maladaptation and maternal effects in the soft scale insect Saissetia coffeae (Hemiptera: Coccidae)

When selection pressures favor different genotypes in different parts of a species' range, local adaptation may result. This phenomenon is of evolutionary interest because divergence within a species can be the first step in the process of speciation. When it comes to local adaptation, asexual taxa are unusual. Migration among contrasting selection regimes does not compromise the adaptation of individuals to local conditions, as can occur in sexual species. However, asexuals are likely to be relatively low in genetic diversity, possibly inhibiting their ability to become evolutionarily fine-tuned to local selection regimes.; In Chapter 1, "Local maladaptation in the soft scale insect Saissetia coffeae (Hemiptera: Coccidae)", I report the results of a field experiment in which I tested whether or not the phloem-feeding generalist S. coffeae was locally adapted to two of its primary host species near the La Selva Biological Station in Costa Rica. In fact, S. coffeae displays a pattern of maladaptation to these hosts. Such a pattern is very unusual. It may be a result of fluctuations in selection regimes, or perhaps a response on the part of the plant populations, but no obvious, fully satisfying explanation for this pattern exists. In Chapter 2, "Maternal effects in the soft scale insect Saissetia coffeae (Hemiptera: Coccidae)", I investigate the possibility that maternal effects may tailor the phenotype of S. coffeae to a particular host in the absence of genetic changes. While I found no evidence of "conditioning" to particular host species, there are intriguing hints that maternal effects do prepare the next generation of S. coffeae for some aspects of their environment, especially the risk of attack by fungi.; In Chapter 3, "Migration load and the coexistence of ecologically similar sexuals and asexuals", I use numerical simulations to explore how gene flow among contrasting selection regimes might allow asexuals to invade part of the range occupied by an inherently superior sexual taxon. I show that, while migration load allows the invasion of part of the sexuals' range, these effects diminish as invasion continues, making stable coexistence possible between sexuals and asexuals.