Department of Biology
University of Pennsylvania
433 South University Avenue
Philadelphia, PA
19104-6018
(215) 898-7356
schmidtp@sas.upenn.edu
Megan Phifer-Rixey
My dissertation research is focused on understanding how environmental variation can act as a selective agent in natural populations. Organisms residing in the rocky intertidal regions of the northern Atlantic Ocean experience significant and, to some extent, predictable variation in abiotic conditions including temperature, humidity, wind and wave exposure. The intertidal has been a "model system" for ecologists for decades and my research utilizes known information about abiotic gradients and ecological relationships to better understand the evolutionary consequences of environmental heterogeneity.
The herbivorous snail Littorina obtusata (the "flat periwinkle") is found throughout the Gulf of Maine. It is a common member of the rocky intertidal community and has an important role as an herbivore, a competitor, and as prey. Unlike many marine invertebrates, it does not release larvae into the water column, but rather deposits egg masses on algae. This form of dispersal may limit gene flow, but the potential for rafting of egg masses is non-trivial. Focusing on Littorina obtusata allows us to investigate the opposing forces of local selection and gene flow.
Variation in thermal regime can be an important selective force. Previous work in this lab documented clinal variation in MPI over thermal gradients in the Gulf of Maine. MPI is an enzyme that breaks down sugars found in algae and is an important part of the glycolytic pathway. Subsequent experimental work suggested that MPI genotype contributes to variation in survivorship under thermal stress.
There is also extensive morphological variation in this species, including variation in shell color. Using an inferential and an experimental approach, we are investigating the forces contributing to the maintenance of shell color polymorphism in this species. We have documented consistent clines in shell color morph frequencies in the Gulf of Maine that contrast with neutral structure. In addition, experimental manipulations directly link shell color to fitness under stressful thermal regimes. My current work is focused on a fine-scale characterization of neutral structure in this species and additional field based tests of the fitness effects of shell color.
Education:
Duke University, Durham, North Carolina
B.S. in Biology, 2001
University of Pennsylvania, Philadelphia, Pennsylvania
Candidate for a Ph.D. in Biology, click here (.doc) for CV
Publications:
Phifer-Rixey, M., Heckman, M., Trussell, G., and P.S. Schmidt. 2008. Maintenance of clinal variation for shell colour phenotype in the flat periwinkle Littorina obtusata. Journal of Evolutionary Biology 21(4): 966-978.
Schmidt, P.S., M. Phifer-Rixey, G.M. Taylor and J. Christner. 2007. Genetic heterogeneity among intertidal habitats in the flat periwinkle, Littorina obtusata. Molecular Ecology 16(11): 2393-2404. PDF
Email: Megan Phifer-Rixey
Phone: (215) 898-7356 (lab)
Mailing address:
Department of Biology
University of Pennsylvania
433 South University Avenue
Philadelphia, PA 19104-6018