UC Berkeley

In face of environmental changes, species, either move, changing their distributions, or maintain their ranges. Staying in place and facing the new conditions demand adjustments by changes in phenology, acclimation, via behavioral or phenotypic plasticity, or adaptation. Failure to adjust or move consequently leads to population decline and eventual extinction.

The overarching goal of this work is to investigate the mechanisms by lizard species of two tropical genera, Leposom (Gymnophthalmidae) and Enyalius (Leiosauridae), respond to environmental changes at multiple spatial and temporal scales, in the Brazilian Atlantic Forest. I apply a highly integrative approach that combines species distribution modeling, climate data, phylogeography, morphology and thermal physiology and show (1) how geographic isolation, shifts in habitat use, and historical climatic stability explain the patterns of concordance/discordance between genetic divergence and phenotypic disparity in Leposoma scincoides, (2) how climatic variation and current environmental gradients, both at the macro- and microclimatic scales, affect thermal sensitivity across the two species' ranges and (3) how habitat suitability shape species' distribution ranges and spatial patterns of genetic structure in Enyalius catenatus and E. pictus .

Despite deep phylogeographic structure in L. scincoides, and therefore ample opportunity for intra-specific lineages to diverge phenotypically, there is an overall pattern of phenotypic stasis in morphology and physiology. This is most likely due to similar environmental conditions acting on morphology at the climatically stable core of the distribution, and to constraints on thermal tolerances. However, geographically isolated lineages inhabiting more seasonal areas, that were unstable climatically during the Pleistocene, are morphologically distinct. Among those, similarity in morphology was observed between lineages that further broadened their habitat use, occupying more open areas as well as forested habitats. Moreover, morphological variation correlates with climate. These results highlight how distinct phenotypic traits likely to respond to environmental change show very different patterns of variation, conditional on evolutionary lability, plasticity and (possibly) interaction among traits.

Macroclimatic data are not a good proxy for the environmental conditions experienced by the two lizard species in their microhabitats; there is great overlap in temperature availability in similar microhabitats along a macroclimatic gradient in the Central Brazilian Atlantic Forest and climate variables correlated with thermal physiological traits only at the microclimate scale. Both species show narrow thermal tolerances and differences in thermal physiology between the two species can explain some of their ecological differences. Thermal sensitivity is conserved among lineages within L. scincoides, whereas plasticity and acclimation are prominent in E. catenatus' thermal physiology, but the capacity to acclimate to extreme temperatures in the later is limited. These results are alarming if confronted with the rapid anthropogenic changes in habitat cover and climate change predicted to afflict this region.

There is strong phylogeographic structure and high levels of genetic diversity in Enyalius catenatus and E. pictus. These results are consistent with the notion that in this region, Quaternary forest refuges provided stable climatic conditions that promoted persistence of phylogeographic diversity and stable populations. Nevertheless, divergence times, between E. catenatus and E. pictus and among intraspecific lineages, earlier than the late Pleistocene point to a long and complex history of diversification in Enyalius, that requires a variety of factors to explain spatial patterns of genetic structure. Instances of discordance between the species distribution models and genetic structure were pondered carefully in the context of ecological and natural history and the limitations of the models.

My findings show that patterns and mechanisms of divergence and disparity are complex and multifaceted in this region, with geographic as well as ecological components playing important. This study presents an integrated approach to test evolutionary hypotheses that combine phylogeographic and phenotypic data and put it in the context of the landscape, taking into account geographic, environmental, and historical aspects of the habitat. It adds to the growing body of literature that explores phylogeographic patterns of prevalent elements of the Brazilian Atlantic Forest fauna and if/how they responded to climatic oscillations in the Pleistocene. More broadly, it contributes to the growing literature on South America's biogeography and the origin and maintenance of Neotropical diversity.