Research Projects
Glacial recolonization of North America by the acorn barncle, Semibalanus balanoides
In the Northwest Atlantic fluctuating glaciation throughout the Pleistocene left its signature in the genomes of many organisms. Classical effects of glacial re-expansion include serial bottlenecking of genetic diversity along latitudinal clines. Populations of S. balanoides were sampled along an 800 kilometer North American Atlantic transect to assess population genetic structure in this ecologically critical species. The haplotype network to the right shows the signature of a deep evolutionary split, suggesting extended periods of evolution in isolated subpopulations for this species.
Ecological genetics of the Mpi polymorphism in barnacles
The mannose-6-phosphate enzyme is polymorphic in Semibalanus, and balancing selection has been hypothesized as the mechanism for the maintenance of diversity. Until recently investigations of this protein have relied on the old, but extremely useful, technique of allozyme electrophoresis. I have taken the next step in this system by cloning and sequencing this gene to find patterns of indicative of selection at the DNA level. I am also hoping to incorporate 454 pyrosequencing data to frame the question of how evolution has proceeded at this locus in the context of whole genome evolution in Semibalanus.
Population genetics of Fundulus heteroclitus along a North American glacial cline
The estuarine teleost Fundulus heteroclitus undergoes a sharp genetic and phenotypic break along the Atlantic coast in New Jersey. This change is the result of glacial legacy and has resulted in a hybrid zone of the two subspecies to the North and South. I am interested generally in clines because, quoting Darwin, "Those forms which possess in some considerable degree the character of a species, but which are so closely similar to some other forms, or are so closely linked to them by intermediate gradations, that naturalists do not like to rank them as distinct species, are in several respects the most important to us." I am planning to use molecular markers with dense genome coverage to survey variation along the cline and use introgression analyses to attempt to discover selected loci.
I do additional work on F. heteroclitus in collaboration with the U.S. Environmental Protection Agency offices in Narragansett, RI and the Whitehead Lab at Louisiana State University.
Phylogenetic comparative methods strengthen the evidence for reduced genetic diversity among endangered tetrapods
This has been a side project for me that stems out of a general interest in what dictates effective population sizes (Ne) in species. Barnacle work has convinced me that the Hedgecock effect (Hedgecock, 1994) is very real and the variance in reproductive success is tightly linked with maximum fecundity. As a result, Ne, and by extension genetic diveristy, should vary non-randomly with phylogeny. The tree on the right is a hand built tetrapod tree with 894 tips. I have arrayed diversity data on the tree and am using it find the correlation between genetic diversity and extinction risk. I hope this project will demonstrate the importance of using the comparative method in conservation.