Meeting Abstract

P1.166  Saturday, Jan. 4 15:30  Migration-selection balance: The added complexity of symbiosis in reef-building corals DAVIES, S/W*; TREML, E; KENKEL, C; MATZ, M/V; Univ. of Texas, Austin; Univ. of Queensland; Univ. of Texas, Austin; Univ. of Texas, Austin daviessw@gmail.com

The ability of a species to adapt to local environments while maintaining high migration rates provides an interesting evolutionary conundrum. If local selection is sufficiently strong, unfit immigrants will be effectively removed from the population by natural selection. However, if migration is stronger than selection, potentially adaptive alleles could be swamped out by the arrival of less fit immigrants. How then might highly dispersive species, such as the majority of broadcast spawning corals, adapt to their local environments? Genetic analyses of population structure in two species of acroporid coral hosts across the Micronesian Pacific have demonstrated broad genetic connectivity spanning hundreds to thousands of kilometers. These data are also well supported by our spatially explicit biophysical model of larval dispersal and our coalescent modeling using MIGRATE-n. Algal genetic data (Symbiodinium sp. genotypic clade C2) extracted from the same coral hosts reveal much more differentiation, according to eight microsatellite loci. Symbiont populations are consistently differentiated between islands and even between reefs on the same island. It is therefore possible that local adaptation in the coral holobiont might be achieved through an association of broadly dispersing coral hosts with less dispersive, locally adapted symboints. This framework may be one explanation for the overwhelming prevalence of horizontal symbiont transmission in broadcast-spawning corals.