title: Niche divergence builds the case for ecological speciation in skinks of the Plestiodon skiltonianus species complex.
abstract: Adaptation to different thermal environments has the potential to cause evolutionary changes that are sufficient to drive ecological speciation. 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. 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. 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. Our results show that the thermal niches of size-divergent, reproductively isolated morphospecies are significantly differentiated and that precipitation may have been as important as temperature in causing increased shifts in body size in xeric habitats. While these findings alone do not demonstrate thermal adaptation or identify the cause of speciation, their integration with earlier genetic and behavioral studies provides a useful test of phenotype-environment associations that further support the case for ecological speciation in these lizards.
authors.affiliation: Museum of Vertebrate Zoology Integrative Biology University of California, Berkeley 3101 Valley Life Sciences Building Berkeley CA 94720.
authors.forename: Guinevere O U
authors.identifier: 0000-0003-1877-0591
authors.initials: GO
authors.lastname: Wogan
authors.affiliation: U.S. Geological Survey Western Ecological Research Center 4165 Spruance Rd. Suite 200 San Diego CA 92101-0812.
authors.forename: Jonathan Q
authors.initials: JQ
authors.lastname: Richmond
keywords: Adaptation; environmental niche models; niche overlap; phenotype–environment association; thermal adaptation