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We quantified the climatic niche using mechanistic physiological and correlative niche models and then estimated niche differences among species using ordination techniques and tests of niche overlap and equivalency. Previous work on this group shows that a mechanical sexual barrier has evolved between species that differ mainly in body size and that the barrier may be a by-product of selection for increased body size in lineages that have invaded xeric environments however, baseline information on niche divergence among members of the group is lacking. Here, we examine whether climate-based niche divergence in lizards of the Plestiodon skiltonianus species complex is consistent with the outcomes of such a process. skiltonianus group is based largely on mtDNA data, and preliminary analysis of whole genome, restriction-associated digest sequences shows conflicting signals with respect to the number of times that the different morphotype pairs have evolved.Īdaptation to different thermal environments has the potential to cause evolutionary changes that are sufficient to drive ecological speciation. At least some molecular phylogenetic evidence also indicates that the mechanical barrier has evolved in parallel between multiple sister species pairs (Richmond and Jockusch 2007), a common signature of divergent natural selection (Schluter 2000) however, the evidence for parallelism within the P. No-choice mating experiments have shown that copulation success is dependent on the size difference between paired individuals and that a mechanical incapa-bility arising from the geometry of the mating posture is the main reproductive barrier causing nonrandom mating between morphospecies (Richmond and Jockusch 2007 Richmond et al. Most work on this group to date has focused on understanding the role of body size divergence in reproductive isolation, rather than the causes of the size divergence itself. Given that correlated divergence in size and ecology is common in animals, similar constraints imposed by the geometry of the mating posture may apply to a variety of major animal lineages and merit further attention in speciation research. This model shows that the mechanical barrier is more important than behavioral barriers at small and intermediate degrees of size divergence, suggesting that it acts earlier during speciation when body morphology is more similar between diverging lineages.
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We used a predictive model to estimate the contributions of behavioral and mechanical barriers to reproductive isolation between populations with differing degrees of size divergence. In this study, we used hierarchical Bayesian modeling of mate compatibility experiments to show that body size divergence in lizards of the Plestiodon skiltonianus complex contributes to reproductive isolation in at least three ways: males preferably court females that are more similar in size, females reject males that are highly divergent in size, and the size difference of a male and female in copula constrains the ability to align the genitalia for intromission.
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Geodist cartoon driver#
Mechanical reproductive barriers have been dismissed as a major driver of animal speciation, yet the extent to which such barriers cause reproductive isolation in most animal groups is largely unknown and rarely tested.