Evolution of Adaptive Variation at the Molecular Level: Snake Venom Proteins
Snake venom proteins represent a fascinating system for studies of molecular variation at the molecular level because proteomic and genomic analysis have shown high levels of variation in diverse species yet the evolutionary and functional basis of this variation remains unclear. Using venom proteins from rattlesnakes (Sistrurus and Crotalus) and lance-headed vipers (Bothrops) as a model system, we are addressing a series of questions about the evolutionary basis for inter- and intraspecific variation in venom proteins in relation to snake diets. These include: 1) How do venom proteins vary within and between species? 2) What is the functional significance of this variation in terms of toxicity to specific prey? 3) How do the genes encoding these proteins vary within and between species and what role has natural selection at the molecular level played in molding this variation? 4) What is relative importance of gene regulation vs. structural variation in proteins as a cause of variation in venom composition within and between species? We are addressing these questions through a combination of field work on wild snake populations, lab work on the genetic basis of venom variation, functional analysis of venom toxicity and proteomic analyses of venom composition. Recently, we have also become interested in the molecular bases for coevolutionary interactions between Pacific rattlesnakes and California ground squirrels as part of Matt Holding’s PhD project. Finally, our recently awarded NSF-FAPESP grant will use a broad sampling of venomous snakes from the New World to address two major questions about venom evolution: First, is there a relationship between venom function and species level diversification rates? Two, are the molecular mechanisms by which differences in venom are generated are the same or different across species? Current collaborators on this research include Juan Calvete (Instituto Biomedicina de Valencia), Terry Farrell (Stetson University), Darin Rokyta (Florida State University), Chris Parkinson (University of Central Florida), Ana Moura, Inacio Azevedo and Erika Hingst-Zaher (Instituto Butantan), Hussan Zaher (USP) and Jim Biardi (Fairfield University).
Conservation Genetics of Endangered Species
Genetic analyses can guide the conservation and management of wildlife species by providing information on how demographically ‘connected’ and genetically variable populations are in space and time, by identifying genetically distinct populations and/or taxa of special conservation concern, and through the use of genes as biological “tags” for sourcing harvested individuals. One taxon of particular interest is the Eastern Massasauga Rattlesnake (Sistrurus c. catenatus); with support from the Ohio Division of Wildlife, we have conducted state- and range-wide assessments of genetic diversity within this taxon. We are also currently assessing levels of adaptive genetic variation in venom genes to assess the impact of declining population size on functional genetic varaition. We are also using genetic and elemental markers to source bats that are killed by wind farms. Collaborators in this work include Greg Lipps (OBCP) and Bryan Carstens (OSU).
Evolution and Ecology of Unisexual Vertebrates
Animals in which asexual lineages coexist with sexual species over millions of years challenge explanations for the maintenance of sex, because such lineages should rapidly go extinct due to the ecological and genetic costs of parthenogenesis. In vertebrates, one such group is unisexual (all female) Ambystoma salamanders, which coexist with related sexual species throughout eastern North America. These unisexual lineages, which are frequently polyploid, are among the oldest (up to 5 million years) “asexual” lineages documented in any vertebrate. A recent hypothesis for why unisexual Ambystoma persist is that, in fact, they combine both asexual and sexual reproduction into a unique mode of reproduction termed kleptogenesis. Kleptogenetic females breed asexually but may also occasionally add or replace a genome from a congeneric sexual male to their zygotes, and hence may gain the long-term ecological and genetic benefits of both asexual and sexual reproduction. We are interested in a series of questions about these extraordinary animals such as: 1) what is the frequency and evolutionary significance of kleptogenetic sexual behavior? 2) How does gene expression in polyploid unisexuals with their highly variable genomes? 3) Why are unisexual female salamanders so ecologically successful? This work is being done in collaboration with Katy Greenwald (Eastern Michigan University).