Climate change and the future of ectotherms and plants biodiversity

 

My research is focused on the physiological consequences of climate change on both plants and (primarily) lizards. This project is an extension of the models for risks extinctions predicted by Sinervo et al. 2010. Current evidence suggests that climate change has caused extinctions of Mexican lizards and an expected increase on the risk for those species closer to the tropics. For plants, we predict that the altered global patterns of temperature and rainfall are transforming communities and causing local extinctions of plant species and their associated fauna. For this project, we are modeling ectotherms demographic collapse scenarios as a result of restrictions in activity time, which reduces energy gains (e.g., feeding and water stress) below levels needed for reproduction. My direct contribution is the core bioinformatics analyses that include modeling and development of R-based tools to analyze field and experimental data from our collaborators doing fieldwork in the US, Africa, Australia, Europe, North and South America. I am also in charge of the assessment of species distributions databases, quality control of field experiments, and modeling distributions under thermal gradients and future climate models. My objective is to generate data repositories that integrate changes in temperature, precipitation, and associated plant die-offs. Using phylogenies of lizards and frogs, we will assess whether some clades are phylogenetically predisposed to extinction as a consequence of climate change and evolved life-history strategies. The following labs are directly participating in this effort: Sites, Sinervo, Miles, Pittermann.

Biogeography of the Neotropics

 

I am interested in the ecological and biogeographical factors that influence the rates and patterns of diversity distribution in the Tropics. During my doctoral research, I studied the patterns of historical biography in the Neotropics using a combination of ancestral area reconstructions and maximum likelihood estimation of ancestral distributions. Our research has shown the importance of highlands, such the Andes, as sources of ancestral diversity in Amazonia. Furthermore, our work has contributed to appreciate biodiversity as an outcome of networks of source-sink relationships among ecoregions of the Amazonia. However, the development of GIS-based methods has increased the accuracy for reconstructing patterns of diversity. The expected results of this project include (i) reconstruction of past, present, and future biodiversity in the Neotropics; (ii) estimation of relevant climatic, phylogenetic, and anthropogenic effects into a network using my research on SEM (Structural Equation Models) methodology; and (iii) application of multivariate comparative methods to determine patterns of species radiations and conservation priorities in the Neotropics. These methodology will centered on the re-evaluation of ancestral distributions of ectotherms and plants in the Neotropics using paleoclimate and paleogeographic projections, taxon area distributions inferred from current species distribution models (SDM), and paleomodeling of SDMs using general least squares (GLS), general additive models (GAM) and other higher-level multivariate estimators.

 

Comparative transcriptomics of New World reptiles and amphibians

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Genomic techniques allow the acquisition of vast quantities of genetic data that are useful to explain biological diversity. Our collaborators and I are looking for exemplar adaptation in casquehead lizards (Corytophanidae) and desert iguanas (Iguanidae), Liolaemus lizards, and poison frogs (Dendrobatidae). Our work iguaninan lizards is centered on patterns of gene expression between species present in Patagonian Andes, SW deserts of US and Central Americanvlowlands that have contrasting physiological adaptations. This is a new collaboration between Sites Lab, Dr. Catherine Stephen, Drs. Luciano Avila and Mariana Morando (Centro Nacional Patagónico, Argentina). Our work in poison frogs is centered on the adaptations for aposematism (i.e., co-occurrence of conspicuous coloration and defense). Some of the topics on this research include the evolution of ion channels that are known targets of poison frog alkaloids. We are also interested in the hidden diversity of parasites associated with aposematically - defended frogs revelaed by frog transcriptomes. This combined effort is carried out together with Dr. Lauren O’Connell (Harvard), Rebecca Tarvin (UT-Austin), Dr. David Cannatella (UT-Austin), Dr. Harold Zakon (UT-Austin), Dr. Marcio Pie (UFPR - Universidade Federal do Paraná, Brazil) and Dr. Luis A. Coloma (Centro Jambatu de Investigación y Conservación de Anfibios, Ecuador).

Biocomplexity: Integration among physiological, environmental, behavioral, genetic, and phylogenetic variables

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My interest in the evolution of complex traits is focused on highly integrated traits. First, I am interested in the emergence of aposematism as a network of predator-deterrence adaptations. Specifically, I found a highly correlated set of traits that gives rise to aposematic complex phenotypes, namely, (i) alkaloid accumulation; (ii) diet specialization on alkaloid-rich prey; and (iii) high metabolic rate in the form of athletic prowess. Second, I am interested in the emergence of mate attraction from acoustic signals as a network of physiological, behavioral, and morphological adaptations. Specifically, I am investigating phenotypic networks that compartmentalize acoustic signals into sub-networks of spectral, temporal, and structural components. Third, I am interested in the relationship between biotic and abiotic environmental variables that gave rise to the current diversity of complex traits and species. Finally, I am interested in identifying the overall genomic-phenotypic-biogeographic network structure exemplified by the poison frogs.

Complex phenotypes assemblage and persistence in large clades

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Organismal traits are organized in modular units assembled in increasing levels of organization and hierarchy. Levels of complexity are determined by a set of direct and indirect connections that give rise to emergent properties. Complex phenotypes are not different from networks, and they can be easily mapped as hierarchical arrangement of nodes (individual component traits) connected by edges (interactions). My current research addresses how to estimate network structure from matrices of correlations or covariances among component traits after correcting for phylogenetic signal. I have modified and adapted network construction methodologies commonly used in Econometrics and Social Statistics. As a result, I have implemented a methodology that addresses complex traits as phenotypic networks using maximum likelihood approaches that maximize structure simplicity but preserve inter-trait correlational identity. Moreover, an ongoing aspect of my research is dedicated to estimate the persistence of phenotypic networks over extended phylogenetic history.

 

Experimental physiology and patterns of phenotypic integration

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Metabolic rates are fundamental to understand the rise, permanence, and diversification of complex phenotypes. I am interested in the emergence and maintenance of aposematic phenotypes in poison frogs in relationship with their physiology. To address this question, I experimentally measured metabolic rates during activity (i.e., AMR) and rest (i.e., RMR) of 54 species of poison frogs. My results support an association between being an aposematic frog (i.e., conspicuously colored and toxic) and having a high AMR. As an extension of my research, I am interested in the generality of this association among aposematic ectotherms.

Life history predictors of the rates of molecular evolution in ectotherms

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I am interested in how life history traits also affect the rates of molecular evolution. For instance, body size, generation time, production of reactive oxygen species (ROS), and high resting metabolic rate (RMR) predict variations in the pace of molecular evolution. However, phylogenetic correlation analyses failed to support a relationship between RMR and molecular evolution in ectotherms. An alternative is to test other metabolic rates, such as active metabolic rate (AMR), and their association with molecular evolution. Based on a multivariate and phylogenetic comparative approach, I provided a mechanistic hypothesis of the link between AMRs and the rate of molecular evolution in a large ectotherm clade, the poison frogs. I proposed that faster rates of molecular evolution are associated with increases in ROS within germ line cells during periodic bouts of hypoxia/hyperoxia related to aerobic exercise. As further research, I am interested in testing if my hypothesis also applies broadly across to complete genomes and transcriptomes in ectotherms and endotherms.

Multivariate methods in phenotypic network structures

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Modeling phenotypic networks is crucial for understanding the emergence of biological complexity across the Tree of Life. To model such networks, I adapted several multivariate methods (e.g., Structural Equation Modeling or SEM) to estimate network structure from large phenotypic databases. Through my research, I found that SEM is a suitable method to test the structure of networks by estimating multiple models of causal/correlational relationships among variables. In addition, SEM allows comparisons of multiple alternative network structures with different levels of trait integration. Four ongoing topics of my research on SEM include the reliability of multilevel network models; inclusion of mix models of discrete/continuous variables; autocorrelation and longitudinal analysis across phylogenetic structure; network structure estimation under different models of trait evolution; and multi-gene phylogenies addressing multi-trait networks.

 

Describing herp biodiversity and natural history

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The tropics of the New World harbors more than half of all living terrestrial organisms, and it is one of the most threatened regions by human development. However, most groups of amphibians and reptiles require more studies on their natural history. For example, one of my focal group of reptiles (Corytophanidae) are well-known by their dimorphic headcrest and bipedalism, but these have not been studied using geometricmorphometric approaches. Likewise, poison frogs are among the most specious and charismatic clades of this region. Not surprisingly, the pace of description of new species of poison frogs has followed the availability of large phylogenies of the group. To this date, more than 300 species have been described as summarized by AmphibiaWeb. However, the description of phenotypic diversity and natural history is highly concentrated on few aposematic dendrobatids. I am participating in the description and characterization of several new taxa and their phylogenetic relationships. To date, we have described more than 10 new species of poison frogs.