Biology of Rattlesnakes
With approximately 40 species, rattlesnakes are among the most fascinating, conspicuous, and ecologically diverse groups of squamate reptiles in the Western Hemisphere. They make excellent subjects for many questions in evolution and ecology. For example, the rattle system is an unequivocal evolutionary novelty, and much of my current research interests involve development and evolutionary history of this complex anatomical structure. My graduate research involved body size evolution and systematics of speckled rattlesnakes, and my collaborators and I are currently studying population genomics and mito-nuclear discordance in island populations of these snakes from the western Sea of Cortés, Mexico. We’ve documented extraordinary mitochondrial evolutionary dynamics associated with oversea dispersal and introgression between populations of insular giants and insular dwarfs, and plan to publish this research soon.
Some previous research on rattlesnakes involved sexual dimorphism and diet in populations of lance-headed rattlesnakes and dusky rattlesnakes from high-elevation grasslands in central Mexico, phylogeny of rattlesnakes with an emphasis on the Mexican long-tailed species, and rattle segment retention in juvenile ridge-nosed rattlesnakes from Chihuahua, Mexico. |
Evolution of Morphology, Body Size, and Sexual Size Dimorphism
My major interest in biology has long been phenotypic evolution, and in particular body size, as it a fundamental factor in physiology, ecology, morphological evolution, demography, and genomic evolutionary dynamics. Related to body size, I’m interested in the evolution and maintenance of sexual size dimorphisms, developmental mechanisms of growth, allometry of morphology, and phenotypic integration. Current projects include variability of sexual size dimorphism over time, craniodental integration in domestic dogs, body elongation and limb reduction in squamates, and distinguishing between sex-specific and sex-“agnostic” factors of body size evolution across Amniota. In addition to these projects, I am working with Nate Bendik on growth and body size distributions among disjunct "island" populations of plethodontid salamanders in isolated karst spring systems in central Texas.
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Macroecology and Community Assembly
Macroecology is the study of biological diversity and phenomena at large spatial, temporal, and phylogenetic scales. Some of our current research has been to extend our species and clade-specific studies to the macro-scale; however, in the process we have become more interested in macroecological and macro-evolutionary methods and inference. In particular, at large scales data quality seems to be sacrificed and many assumptions are involved that have little empirical support. For example, what are the effects of surrogate variables, extrapolation of imprecise data, etc., on our ability to detect real patterns and infer processes from these patterns? As a first pass in this research arena, Koy Regis and I are examining the influence of separate mass and carapace length datasets as surrogates of body size in evaluating allometry of sexual size dimorphism across turtles. Turtles are ideal for this comparison because they have been the topic of several previous studies of sexual size dimorphism at the macro scale, which have resulted in conflicting results.
I have also long been interested in community assembly. My earliest research involved a comparison of lizard assemblages between natural savanna habitats and bush-encroached savanna in Namibia. With Jill DeVito and others, I examined physiological tolerances and community assembly of riparian spiders at a site in New York state, and with Michelle Lawing, I evaluated lizard assemblage structure along elevation gradients in the Bonneville Basin of western Utah and adjacent Nevada. Currently, I am working on island occupancy patterns and minimum area thresholds for snakes in an island archipelago in the western Sea of Cortés. Also, with Ed Barnes, I am studying herpetofaunal assemblages of the Texas Cross Timbers ecoregion.
I have also long been interested in community assembly. My earliest research involved a comparison of lizard assemblages between natural savanna habitats and bush-encroached savanna in Namibia. With Jill DeVito and others, I examined physiological tolerances and community assembly of riparian spiders at a site in New York state, and with Michelle Lawing, I evaluated lizard assemblage structure along elevation gradients in the Bonneville Basin of western Utah and adjacent Nevada. Currently, I am working on island occupancy patterns and minimum area thresholds for snakes in an island archipelago in the western Sea of Cortés. Also, with Ed Barnes, I am studying herpetofaunal assemblages of the Texas Cross Timbers ecoregion.
Systematics and Phylogeography of Amphibians and Reptiles
A major and continuing area of research has been systematics and phylogeography of amphibians and reptiles. With collaborators from University of Texas at Arlington, I have been involved in the taxonomic assessment of hylid frogs of the genus Plectrohyla from southern Mexico, and assisted in the description of a new species of gymnophthalmid lizard from Venezuela. Recently, our long-term research on speckled rattlesnakes culminated in a taxonomic revision of the group, including the recognition of three species from within the former C. mitchellii complex. Currently, I am working with collaborators from UTA on a major systematic and taxonomic revision of a clade of blunt-headed vinesnakes from western Mexico. This group of bizarre arboreal snakes is fascinating for their deep cryptic diversity and evolutionary history that corresponds with the complex evolution of the tropical thornscrub formation of the Pacific versant of Mexico.
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