Population persistence and the scale of local adaptation are determined by both larval connectivity and post-settlement selection when habitats are spatially heterogeneous for growth and/or reproduction. Unfortunately, the relative importance of factors acting before and after settlement that limit recruitment and gene flow is still unknown for most species and most marine ecosystems. This is partly because the interactions between larval behavior and hydrography are difficult to study, so dispersal constraints are only inferred indirectly. In addition, many marine species are not amenable to strong spatial tests of post-settlement selection and these experiments are difficult to accomplish at the large spatial scales relevant to high dispersal species. Consequently, only a handful of natural systems have yielded results that distinguish pre- and post-settlement constraints on gene flow such that our understanding of mechanisms generating genetic and phenotypic population structure is piece meal.
The intellectual merit of the study is that it achieves this dual goal in an estuarine species inhabiting semi-connected lagoons along eastern Florida where there is a latitudinal gradient in environmental variables, community composition, and potential larval dispersal vectors. Much of the western North Atlantic coastline includes shallow lagoons enclosed by barrier islands, but only a handful of studies have measured connectivity among estuaries, and none among lagoons. This project builds on significant previous research on the eastern oyster, Crassostrea Virginica to integrate pre- and post-settlement measurements. High resolution genetic identification of migrants will be used to construct a connectivity matrix among 30 populations in each of three years. Statistical associations will be tested between dispersal patterns and hypothesized dispersal vectors and constraints. Cohort analysis will be used to test for spatial variation in genotype-specific survivorship along the entire coast. Also, in each of two years, relative postsettlement survivorship and performance will be measured in field common gardens in which local individuals, migrants and hybrids are compared. Finally, fertilization efficiency of within- and between-population crosses will be compared to test the hypothesis that gamete incompatibilities limit gene flow. The results will be integrated in models that describe the spatially and/or temporally dynamic balance between dispersal and selection, define the spatial scale of local adaptation along the ecotone, and identify abiotic gene flow constraints that may affect codistributed species.
The broader impacts of this study derive from its focus on important habitats for diversity and fisheries management, and on the involvement of underrepresented groups. The oyster populations under study inhabit eastern Florida lagoons that possess the highest diversity of any estuary in the United States, yet this coastline is undergoing rapid development. In addition, the Cape Canaveral lagoons contain the oldest marine protected area in North America. Understanding the impact of this reserve on surrounding fished populations hinges on dispersal across its boundaries and on habitat quality, both of which are studied here. This study will also support one PhD student who will focus on the measurements of selection for her dissertation. The graduate student is a female African-American who endeavors to study marine evolutionary ecology, a goal spanning two fields with extremely low minority representation. The P.I. has a continuing interest in attracting the next generation of scholars. Currently four undergraduates work in the Hare lab on projects related to the Florida ecotone. Three of the undergraduates are women and the fourth an African-American. Funding from NSF will allow undergraduate participation to be expanded to include summer field work in Florida. Previous undergraduates working in the Hare lab have obtained Howard Hughes fellowships and contributed to publications (Gaines et al. 2005). The University of Maryland graduates more African-Americans than any of the top 20 universities in this country. This provides a large pool of minority candidates for possible recruitment to the Hare lab. The P.I. has a history of integrating primary research results into lectures in introductory genetics. Research results are also disseminated via lab web page postings.
