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Conservation Genetics of Freshwater Mussels

Freshwater mussels are recognized as one of the most endangered group of organisms in the world. Scaleshell musselI am currently working on improving our understanding of phylogeography, population structure and genetic variation in freshwater mussels using a variety of molecular tools. I am also interested in understanding the role of processes such as gene flow and natural selection in maintaining genetic variation. 

Ongoing projects in my lab include questions related to species delineation in the genus Cyprogenia; understanding the impacts of gender mediated gene flow; comparing the genetic diversity and population structure of closely related common and endangered species.

Phylogenetics Systematics and Evolution of Fishes and Mussels

My research in the area of phylogenetic systematics has involved using DNA sequence data to improve our understanding of the evolutionary relationships of organisms.  Phylogenetic hypotheses provide a framework to address questions as diverse as species delineation, biogeography, and character evolution.

Past research projects on the Centrarchidae and the Petromyzontiformes have been sponsored by the National Science Foundation. Topics of more recent research includes freshwater shrimps in the family Atyidae and freshwater mussels in the genus phylogeny of freshwater mussel genus Ptychobranchus.

Iowa Pleistocene Snail

The Iowa Pleistocene Snail (Discus macclintocki) is a small terrestrial snail (5–8 mm in diameter) that is included on the US list of endangered species. Discus macclintocki is endangered mainly due to its dependence on rare algific (cold-air) talus slopes adjacent to stream-beds in northeastern Iowa and northwestern Illinois. Algific talus slopes were formed during the Wisconsin period of the Pleistocene Epoch along major river drainages where glacial runoff and large amounts of ice accumulated. D. macclintocki appears to have a limited temperature tolerance that prevents its expansion into the areas between slopes, which have harsher climates. Because of these temperature requirements, D. macclintocki is believed to be a relict species, surviving only on these isolated algific talus slopes since the last glacier receded and the temperatures increased approximately 16,500 years ago. Several surveys documenting the location of colonies of D. macclintocki have been conducted as well as demographic studies. These surveys indicate that variation in recruitment appears to be driving fluctuations in population growth and that snails are highly subdivided within sites.

My lab is conducting a genetic survey of D. macclintocki populations using hypervariable microsatellite markers and single nucleotide polymorphisms (SNPs).  Because they are co-dominant markers and evolve quickly, microsatellites and SNPs have advantages over mitochondrial DNA in resolving population structure, even at fine geographic scales.  Improving our understanding the population structure of D. macclintocki will provide information to conservation managers on gene flow within and between populations, effective population size, sustainability and other genetic attributes of extant populations.  The information obtained from this study will provide managers with the necessary population genetic data to make appropriate decisions on the listing status and future management of D. macclintocki.

North American Atyid Shrimps

The family Atyidae is large and cosmopolitan in distribution, including both surface (epigean) and cave dwelling (stygobytic) forms.  The majority of atyid species are epigean and are tropical and sub-tropical in distribution.  North America is home to four recognized species of Atyidae:Syncaris pacificaS. pasadenae, Palaemonias alabamae, and P. ganteri. Historically, only two named species, the Kentucky Cave Shrimp (Palaemonias ganteri) and the Alabama cave shrimp (P. alabamae) were known from the southeastern United States.  Recently however, an undescribed third species (Palaemonias sp.) of cave shrimp was discovered from two localities in Alabama.  Genetic comparison of this new population to known populations of P. alabamae revealed significant genetic differences and indicate an absence of gene flow between these populations. Similarly, genetic comparisons of specimens of Syncaris pacifica from various drainages revealed the presence of multiple mitochondrial haplotypes. 

A recent collaboration with an international group of colleagues resulted in a 2012 publication in Molecular Phylogenetics and Evolution [63:  82–96].  This multi-gene based global phylogenetic hypothesis of the Atyidae revealed some interesting patterns including multiple subterranean invasions and indicated some trans-oceanic dispersal of the ancestors of these freshwater shrimps.