Date of Award

5-2007

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Marine Biology

Advisor

Susan Brawley

Second Committee Member

Carolyn Engel

Third Committee Member

Keith Hutchison

Abstract

Reproduction in the brown alga Fucus vesiculosus L. is confined to calm, sunny conditions. Levels of water motion on opposite sides of a coastal point often vary during the reproductive season, and this environmental asynchrony might cause reproductive isolation. I tested whether populations of F. vesiculosus on opposite sides of Schoodic Point, Maine, exhibited reproductive asynchrony due to asynchronous environmental conditions. I characterized environmental conditions (i.e., wind speed, wind direction, levels of irradiance) to obtain threshold values for gamete release. These data were used to construct a regional, predictive model for fucoid reproduction in the Gulf of Maine and as a basis for evaluation of the population genetics research. I examined the population genetic structure of F. vesiculosus at Schoodic Point and Pemaquid Point, Maine to test whether genetic structure correlated with coastal topography. Using surface drifters, I characterized near-shore circulation patterns around the study sites to investigate whether gene flow correlated with directionality of currents. Laboratory studies examined the longevity of F. vesiculosus gametes and the viability of zygotes produced from crosses with aged gametes; these data helped to evaluate how these life history stages contribute to gene flow. Although genetic structure was not found to correlate with coastal topography, the genetic, oceanographic, and laboratory studies highlight the dynamic connection between near-shore coastal oceanography and population genetics. The results suggest the importance of storm-detached, rafting, reproductive individuals in structuring populations at both local and regional scales. Finally, I conducted a genetic analysis of F. vesiculosus populations throughout the northwestern Atlantic to place the coastal points study into a larger spatial context (ca. 2000 km). I investigated how present day populations are connected with respect to recent glacial history (ca. 18,000 yr). Results reveal distinctive northern and southern groups with unexpected patterns of genetic diversity, and support hypotheses that southern and northern glacial refugia existed during the last glacial maximum. Examination of herbarium specimens reveal contemporaneous low genetic diversity in F. vesiculosus at its southernmost boundary (Beaufort, North Carolina) has existed at least 40 years.

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