Research Overview

   Figure 1—Schematic of the mechanisms driving responses to environmental change. Responses are mediated by the phenotypic tolerances of individuals (e.g., physiology, morphology, and behavior). Phenotypes are unlikely to remain static as environments change but will instead shift through evolution and plasticity. I use an integrative approach, combining experiment and modeling, to explore each arrow. 

Figure 1—Schematic of the mechanisms driving responses to environmental change. Responses are mediated by the phenotypic tolerances of individuals (e.g., physiology, morphology, and behavior). Phenotypes are unlikely to remain static as environments change but will instead shift through evolution and plasticity. I use an integrative approach, combining experiment and modeling, to explore each arrow. 

We integrate across biological organization to explore the mechanisms that drive species’ responses to global change. Responses to changing environments are complex, encompassing most biological processes (outlined in Figure 1). Most directly, the phenotype of individuals drive population response, but phenotypes vary as a result of phenotypic plasticity and evolution. We iterate between experiment and mathematical modeling to directly address how phenotype, genotype and environment interact to shape species' responses to global change.

Major goals of the TREE Lab are to 1 ) identify the organismal traits and environmental parameters that most limit species' persistence, 2 ) examine the ability of organisms to respond to environmental variation through adaptive evolution or phenotypic plasticity, and 3 ) develop models that examine the effects of environmental variation on populations while accounting for evolutionary processes and phenotypic plasticity.  To do this, we integrate field and laboratory experiments with ecological modeling.  We also integrate multiple "toolkits" including those associated with functional genomics, cellular physiology, behavioral ecology, thermal physiology, endocrinology, geometric morphometrics, and theoretical ecology.  Currently we primarily work with three model systems: the fence lizards of the genus Sceloporus (mostly S. occidentalis and S. undulatus), alligator lizards (genus Elgaria), and crested geckos (Correlophus ciliatus).

 

Research Foci:

phenotypic plasticity and microevolution In Response to climate change

 Male plateau fence lizard ( Sceloporus tristichus ).  photo credit: A. Camacho

Male plateau fence lizard (Sceloporus tristichus).  photo credit: A. Camacho

Most analyses of species responses to climate change assume that species are uniform groups of individuals with stationary phenotypic characteristics that perfectly disperse to suitable habitats.  These assumptions are clearly violated in nature but the impact of these violations on our understanding of species responses to climate change is uncertain.   We recently collaborated with Lauren Buckley and Michael Angilletta to estimate phenotypic variation and phenotypic plasticity in the Sceloporus undulatus species complex.  Currently, we are collaborating with Tonia Schwartz at Auburn University to leverage transciptomics to identify networks that plastically respond to environmental variation. 

 

Comparative THERMAL PHYSIOLOGY

 Right: Northern alligator lizard ( Elgaria coerulea ), Left: Southern alligator lizard ( E. multicarinata )

Right: Northern alligator lizard (Elgaria coerulea), Left: Southern alligator lizard (E. multicarinata)

The thermal environment defines a major axis of the fundamental niche for reptiles and many other organisms. While we know many reptiles are at risk of decline resulting from increased temperatures associated with climate change, little is known about which physiological traits are most affected by the thermal environment, or the capacity of these traits to change through phenotypic plasticity or adaptive evolution.  We use an integrative approach to discover the mechanisms that limit thermal tolerance, including transcriptomics via RNAseq, respirometry (cellular and whole-organism), metabolomics (GC-MS), and hormone analyses).  We are currently examining the importance of the oxygen environment for mediating thermal tolerance. We also aim to look at how thermal performance can interact with competitive ability to limit geographic distributions.

 

Effects of temperature on developing reptiles

Embryonic development is a time when reptiles, and many other organisms, are highly sensitive to their environment.  In reptiles, thermal and hydric variation can have profound effects on offspring phenotype and survivorship.  Perhaps most notably, many reptile species display temperature-dependent sex determination, where temperature directly determines the sex of the offspring.  A large focus of TREE Lab research is examining how the incubation environment affects offspring development, and how this sensitivity affects the overall ecology and evolution of species.  Current work is examining the effects of natural incubation environments on development of the New Caledonian Crested Gecko (Correlophus ciliatus).

 

Effects of environmental variation on maternal behavior

One way that natural populations of oviparous reptiles might cope with climate change is if females alter nesting behavior adaptively.  Females might compensate for warming temperatures by digging deeper nests, nesting at shadier sites, or nesting earlier in the year.  We are very interested in addressing the question "Will this work?" for each of these possibilities.  Telemeco's recent research with Sceloporus tristichus lizards suggests that nesting plasticity rarely buffers populations whenever climate change is expected to result in novel environments.  (Figure. Left: Bassiana duperreyi with eggs, Middle: Experimental arenas for assessing nesting behavior, Right: Chrysemys picta digging her nest)

 

Morphological evolution in alligator lizards

The southern alligator lizard (Elgaria multicarinata) is currently recognized as a single species.  However, recent molecular analyses by Feldman and Spicer (2006) suggest that this species represents 2–4 cryptic species.  We are collaborating with Chris Feldman at the University of Nevada, Reno and Brian Lavin to combine and morphological data to test various phylogenetic hypotheses for this complex.   

Top left: southern alligator lizard (Elgaria multicarinata) head photograph for morphometric analysis.  Top right: representative photographs of hemipenes from (A, B) E. multicarinata and (C, D) E. panamintina.  Bottom left: deformation grids displaying head shape variation in 5 E. multicarinata/panamintina complex clades.  Bottom right: PCA plot of hemipene shape variation in 5 E. multicarinata/panamintina complex clades