Postdoctoral Fellow
Hubbard Center for Genome Studies
Department
of Zoology & Program
in Genetics
University of New Hampshire
B.S., Biology, Bucknell University, 1993
Ph.D., Biology, University of South Florida, 1998
2003 - Present: Postdoctoral Fellow, HCGS
2001 - 2002: USDA Postdoctoral Fellow, Genomics and Genetic Mechanisms, HCGS
2000 - Present: Instructor, Tropical Field Biology, UMass, Amherst and St. John, USVI
1999 - 2000: Alfred P. Sloan Postdoctoral Fellow, Molecular Evolution, UNH
I work on cichlid fishes and their relatives, a celebrated assemblage whose richness and diversity are unparalleled among vertebrates. This group is central to discussions of core evolutionary phenomena (adaptive radiation, modes of speciation, ecological convergence, trophic partitioning, sexual selection). I am primarily interested in the evolution of cichlid jaws, teeth and color patterns.
In the past few years, we have built the cichlid system into a model for evolutionary genetics. First, we can map the genetic basis of phenotypic differences by crossing species with different morphologies, color patterns or behaviors. Second, we can zero in on causative genes using recently developed genomic resources. Third, we can study the evolutionary history of genotype/phenotype associations in natural populations.
Each of the three African rift lakes Tanganyika, Malawi and Victoria houses a monophyletic group of cichlids that has evolved convergent feeding morphologies in a short period of evolutionary time. For instance, each lake has piscivorous species with long snouts and gracile jaws used to engulf prey; as well as species, characterized by short and firmly reinforced jaws, that scrape algae from the surface of rocks. Tooth shape ranges from widely spaced and pointy unicuspids in zooplanktivorous and insectivorous species to closely packed and flexible tricuspids in algal scrapers. In collaboration with Craig Albertson and Tom Kocher, I have mapped differences in the shape of cichlid jaws and teeth to common chromosomal regions and shown that these phenotypes experienced a history of strong directional selection. This work suggests that the rapid and replicative nature of cichlid trophic evolution is the result of divergent selection on chromosomal packages encoding functionally linked elements of the craniofacial skeleton.
Variation in cichlid tooth shape has a simple genetic basis and can be explained by substitution at a small number of loci. Moreover, the trajectory of tooth development differs among species. All cichlids develop a set of unicuspid first-generation teeth. The timing of replacement by adult multi-cusped dentitions varies among taxa and correlates with feeding ecology. Field observations from Lake Malawi indicate that tooth shape changes rapidly in space and time. The future of this project includes (1) continued study of tooth shape evolution in natural populations, (2) determining the genetic and environmental components of variation in tooth shape and (3) using in situ hybridization to trace the expression patterns of candidate genes in developing teeth.
I have identified a single region of the cichlid genome responsible for OB, an orange blotch color mutation found (almost) exclusively in females. In addition, I have used molecular markers, linked to OB in our mapping cross, to distinguish between blotched and normal individuals from nature. Notably, OB maps in close proximity to a gene for tooth shape, and a tandem array of cone opsin genes. In total, we have found four different genetic correlations between genes controlling jaw/tooth shape and those influencing color in Lake Malawi cichlids. These data provide some of the first empirical evidence for theoretical models which predict linkage of ecological and marker phenotypes in rapidly evolving systems.
My research has been funded by grants from the National Science Foundation, the Alfred P. Sloan Foundation, the National Institutes of Health, the United States Department of Agriculture and the National Geographic Society.