Hopkins Marine Station Student Paper

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Title: The effects of limited larval dispersal on population genetics in Botryllus schlosseri
Student Author(s): Williams, Megan
Faculty Advisor(s): Powers, Dennis
Pages: 20
Location: Final Papers Biology 175h
Date: June 1991
Abstract: Many sessile marine invertebrates exhibit a common suite of adaptations, including life histories with both a sexual and an asexual phase, clonality and/or coloniality, and the ability to distinguish between clonemates and non-clonemates. These characteristics, together with limited, or philopatric, dispersal patterns in free-swimming larvae, are all present in the common tunicate Botryllus schlosseri. This organism presents an ideal model for the study of the problems in population genetics posed by complex life cycles, because the genetics of its fusion-rejection reaction are well-understood, and it is relatively easy to collect and maintain in the laboratory. I present here the results of experiments using both histocompatibility tests on live Botryllus oozids in the laboratory, and arbitrarily-primed PCR, as tools for population genetics research. My work with Botryllus oozoids involved testing the rates of fusion and non-fusion between pairs of offspring obtained from wild colonies containing fertilized eggs. I compared fusibility rates for the offspring of near-neighbor colonies to those for offspring of non-neighboring colonies, and found that there was a significantly higher rate of fusion between offspring of neighbors than between offspring of non-neighbors. My work with arbitrarily-primed PCR was aimed at developing the technique for further work in Botryllus; I was able to detect genetic diversity based on differences in the patterns of amplification products obtained with different DNA samples. I also describe some preliminary conclusions as to the most effective conditions for arbitrarily-primed PCR reactions using Botyrllus DNAs.