Biology subjects

Dean M Castillo

Publications and source records attributed to Dean M Castillo.

3 recordsLinked to original sources

bioRxiv2016

Factors contributing to the accumulation of reproductive isolation: a mixed model approach

The analysis of large data sets describing reproductive isolation between species that vary in their degrees of relatedness has been extremely influential in the study of speciation. However, several limitations make it difficult to test specific hypotheses about which factors predict the evolution of reproductive isolation. In particular, the statistical methods typically used are limited in their ability to test complex hypotheses involving multiple predictor variables or interactions between variables; at least one method, the Mantel Test, has also been found to be unreliable. In this paper, I describe a framework to determine which factors contribute to the evolution of reproductive isolation using phylogenetic linear mixed models. Phylogenetic linear mixed models do not suffer from the same statistical limitations as other methods and I demonstrate the flexibility of this framework to analyze data collected at different evolutionary scales, to test both categorical and continuous predictor variables, and to test the effect of multiple predictors simultaneously, all of which cannot be achieved using any other single statistical method. I do so by re-analyzing several classic data sets and explicitly testing hypotheses that had previously been untested directly, including differences in accumulation of reproductive isolation between sympatric and allopatric species pairs.

Evolutionary Biology↗

bioRxiv2016

Remating responses are shaped by male post-copulatory manipulation but not reinforcement in D. pseudoobscura

Reinforcement occurs when hybridization between closely related lineages produces low fitness offspring, prompting selection for elevated reproductive isolation specifically in areas of sympatry. Both pre-mating and post-mating prezygotic behaviors have been shown to be the target of reinforcing selection, but it remains unclear whether remating behaviors experience reinforcement, although they can also influence offspring identity and limit formation of hybrids. Here we evaluated evidence for reinforcing selection on remating behaviors in D. pseudoobscura, by comparing remating traits in females from populations historically allopatric and sympatric with D. persimilis. We found that the propensity to remate was not higher in sympatric females, compared to allopatric females, regardless of whether the first mated male was heterospecific or conspecific. Moreover, remating behavior did not contribute to interspecific reproductive isolation among any population; that is, females showed no higher propensity to remate following a heterospecific first mating than they were following a conspecific first mating. Instead, we found that females are less likely to remate after initial matings with unfamiliar males, regardless of species identity. This is consistent with one scenario of postmating sexual conflict in which females are poorly defended against post-copulatory manipulation by males with whom they have not co-evolved. Our results are generally inconsistent with reinforcement on remating traits, and suggest that this behavior might be more strongly shaped by the consequences of local antagonistic male-female interactions than interactions with heterospecifics.

Evolutionary Biology↗

bioRxiv2016

Reinforcement of conspecific sperm precedence weakens sexual selection in sympatric populations of Drosophila

Sexual selection is well recognized as a driver of reproductive isolation between lineages. However, selection for increased reproductive isolation could reciprocally change the outcomes of sexual selection, when these processes share a genetic basis. Direct selection for reproductive isolation occurs in the context of reinforcement, where selection acts to increase prezygotic barriers to reduce the cost of heterospecific matings. Many studies of reinforcement focus on premating reproductive barriers, however postmating traits-such as conspecific sperm precedence (CSP)-can also respond to reinforcing selection. We tested whether i) CSP responded to reinforcing selection, and ii) this response in sympatric populations altered intraspecific sperm competition (ISC) and the strength of sexual selection, with the sister species Drosophila pseudoobscura and D. persimilis. We used sperm competition experiments to evaluate differences in CSP and ISC between two sympatric and two allopatric populations of D. pseudoobscura. Using multiple genotypes for each population allowed us to estimate not only patterns of phenotype divergence, but also the opportunity for sexual selection within each population. Consistent with a pattern of reinforcement, the sympatric populations had higher mean CSP. Moreover, ISC was altered in sympatric populations, where we observed decreased average offensive sperm competitive ability against conspecific males, allowing less opportunity for sexual selection to operate within these populations. These data demonstrate that strong reinforcing selection for reproductive isolation can have consequences for sexual selection and sexual interactions within species, in these important postmating sperm competition traits.

Evolutionary Biology↗