Basic Research Program

My basic research program focuses on the origin and maintenance of sexual and parthenogenetic reproduction in a genus of freshwater snails (Campeloma) found throughout the southeastern United States. The main focus of our laboratory is testing competing hypotheses for the maintenance of sexual reproduction versus parthenogenetic reproduction. One of the main theoretical models (The RED QUEEN Hypothesis) for why sexual reproduction is so common, despite its severe costs, is that sex and recombination produce greater genetic diversity in offspring and may thus provide an elusive moving target for parasites. Parthenogenetic snails may be able to avoid high levels of parasitism by dispersing away from habitats with high parasite loads or alternatively, they may reduce competition with sexuals. I have been focusing my field research in the Florida panhandle and the Atlantic coastal plain in Georgia and South Carolina where sexual and parthenogenetic (all female) populations often coexist in the same river drainage. Another aspect of my basic research program is to reconstruct the phylogeny of sexual and parthenogenetic reproduction in Campeloma using mtDNA sequence variation. There are two kinds of parthenogens: hybrid and non- hybrid parthenogens. In the Florida panhandle, hybrid parthenogens appear to have arisen from a hybridization event between sexual species from the Florida Gulf Coast and the coastal Atlantic river drainages. In the Atlantic coast, parthenogens appear to have arises spontaneously from a sexual ancestral species.

 

Click on this thumbnail, which shows the geographic distribution of sexual and parthenogenetic groups in Florida and the Atlantic coastal plain.

 

 

We have successfully amplified 2 mtDNA genes (cytochrome b and 16S ribosomal mtDNA) using PCR. We have determined the maternal ancestry of these hybrid parthenogens, the age of hybrid and non-hybrid parthenogens (all short-lived evolutionarily speaking), and have strong indirect evidence that both parthenogens have dispersed great distances during the recent Pleistocene. We have begun attempts to amplify nuclear introns from the calmodulin, tubulin, and elongation factor-1 genes.

Click on the thumbnail, which shows the wide spatial distribution of parthenogenetic haplotypes (white circles) and the limited sequence divergence between haplotypes, relative to sexual populations (red circles). These patterns suggest that these parthenogens arose recently and underwent a rapid range expansion during the Pleistocene.

 

At present, we are determining direct and indirect estimates of dispersal by sexual and parthenogenetic females. We also are beginning efforts to describe the stability and metapopulation dynamics of parthenogenetic and sexual populations. The focus of a pending NSF proposal is to experimentally test predictions from the two leading contenders for the maintenance of sex: the Red Queen and mutation accumulation models.

I am looking to attract 2-3 Ph.D. students to my laboratory in the next few years and, depending upon NSF support, I may be able to support students during the summer on research assistantships. Please e-mail if you’re interested in my basic or conservation biology research.

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Conservation Biology Research Interests

With the implementation of the new Ph.D. program in Conservation Biology, I plan to expand my research interests into certain aspects of Conservation Genetics and Conservation Ecology. Given my basic research interests, I would like Ph.D. students to develop independent dissertation projects in perhaps some of the following broad areas: the role of extinction and recolonization (metapopulation dynamics) in the maintenance of genetic variation and population sustainability; effects of parasites on endangered or threatened groups; ecology and genetics of invasive, non-native organisms. There are some good organisms and habitats to study these questions. Given their threatened status, freshwater unionid mussels from the southeastern United States would be excellent candidates to study population sustainability, metapopulation dynamics, and population structure using various molecular markers (nuclear and mtDNA).

Recently, I have become intrigued with studying freshwater snails from Cuatro Cienegas in northern Mexico. In this protected region, there is a diverse array of aquatic habitats ranging from lakes, rivers, temporary streams, and sinks. There are unusually high levels of endemism in snails and fishes in this region. In some freshwater snails, some species show shell armature that rivals those of marine snails, and is probably a response to an endemic cichlid fish. Some phenotypes of this cichlid specialize on snails. Recently, an exotic snail, Melanoides tuberculata, has invaded this ecosystem. There are some real concerns about its effect on the native snail fauna. I am interested in studying various topics related to conservation issues in this basin: population structure and speciation of Mexipyrgus; population viability analysis of various snail species in different habitats; and coevolutionary interactions between cichlids and snails. An excellent introduction to this fascinating area is available on the Web site maintained by Dean Hendrickson at UT-Austin.

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Research Interests

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Grants

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Recent Publications


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