COS 306-3 - Out to sea: Ocean currents and patterns of asymmetric gene flow in an intertidal fish species

Abstract: The mangrove rivulus fish (Kryptolebias marmoratus) is an intertidal fish species restricted to the highly fragmented New World mangrove forests of Central America, the Caribbean, and Florida. Mangrove patches are biological islands with dramatic changes in both abiotic and biotic conditions in-between patches. Therefore, migrants moving between patches are subject to novel abiotic conditions that may modulate the probability of successful dispersal. Using over a thousand genetic samples from 17 populations across the range that were genotyped at 32 highly polymorphic microsatellites, range-wide population genetic structure was evaluated with five complementary approaches that found eight distinct population clusters. Comparing assignments between clustering approaches facilitated a more robust interpretation. However, an analysis of molecular variance indicates significant population structure within the seventeen populations suggesting rivulus has sub-population level genetic differentiation. Integrating the range-wide genetic data with biophysical modeling based on ten years of ocean current data suggests that ocean currents and the distance between populations over water drive gene flow patterns on broad scales. Rather than asses oceanographic connectivity as simply the number of particles exchanged between populations via ocean currents, we quantify the time particles spend near the receiving population to simultaneously evaluate if populations are connected by ocean currents and how local surface currents impact successful retention of migrants. Furthermore, directional migration estimates suggest asymmetric gene flow that is also significantly related to ocean currents and distance. Specifically, populations in the center of the range received migrants and gene flow from auxiliary populations but fail to export individuals suggesting that the populations are sinks harboring genetic variation that may not be introduced to other populations across the range. Hence, the inherent asymmetry of ocean currents may be responsible for the chaotic distribution of genetic variation across the range and observed patterns of metapopulation structure.