In this study we review the morphological variation within the Rhinella crucifer species group using geometric morphometrics. We sampled 270 specimens from 78 localities comprising all genetic units delimited for the group. We placed 12 landmarks and 89 semi-landmarks defining morphological structures of the anterior region of the body (head and parotoid glands) on standardized photographs of dorsal aspects of specimens. We checked for the existence of size-free morphological variation using exploratory multivariate analyses and tested for differences among categories (genetic units) using canonical variate analyses. We investigated the effects of relatedness by conducting canonical analyses hierarchically, and tested for phylogenetic signal using reconstruction of morphologies on a tree derived from mitochondrial data. We then corrected for relatedness using phylogenetic principal component analysis, and tested for the influence of the physical environment (temperature, humidity and altitude) with a partial Mantel test of matrix correlation. Our results revealed that there is size-free shape variation in the group. Shape changes are related to specific structures in the head, with landmarks and semilandmarks highlighting changes in a complementary way. We were able to statistically detect the effect of phylogenetic distance with landmarks when considering the closest genetic units as a single category. A significant proportion of the variation in head shape can be explained by environmental variables, suggesting that conditions of the physical environment should also be considered as a source of morphological variation.
Understanding how species' ecological niches evolve can shed light on observed large-scale biogeographic patterns, temporal range shifts, and the potential ability for species to cope with climate changes. Here, we investigated climatic niche evolution in the Neotropical treefrog genus Pithecopus by testing for phylogenetic niche conservatism (PNC). We first evaluated niche overlap patterns based on pairwise niche comparisons of sister species pairs inferred from two alternative topologies for the genus, where higher niche overlap for those pairs compared to random species pairs would represent evidence of PNC. Second, we evaluated phylogenetic conservatism of climatic niches by fitting evolutionary models for niche position and niche breadth across the two alternative phylogenetic trees for the genus. Sister species pairs did not show higher mean niche overlap when compared to random pairs. Comparisons considering species' elevational habitats, on the other hand, showed that lowland sister species had greater niche overlap and montane species lower overlap than expected given the prevailing environmental conditions in each habitat, suggesting different evolutionary histories of niche differentiation for species with different elevational ranges. The best fit of niche position and breadth to both stasis and drift models supported the existence of PNC. We conclude that evolution of climatic niches in Pithecopus suggests overall PNC and that the contrasting patterns found for lowland and mountainous species reinforce the importance of considering the effects of habitat type in understanding climatic niches dynamics.
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