Project: Patterns of Larval Dispersal and Postsettlement Selection Shaping Connectivity of Oyster Populations Along an Ecotone

From NSF Award Abstract:
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.