Meeting Abstract
Global warming is expected to result in preferential survival of coral migrants from warmer to cooler locations as well as in overall decline in genetic diversity due to bleaching-related mortality. We sought to quantify these trends using population genomics and biophysical modeling. We have genotyped five populations of the common reef-building coral Acropora millepora spanning the latitudinal extent of the Great Barrier Reef (GBR) using 2bRAD (~25,000 SNPs genotyped at >98% accuracy). These data were analyzed using non-equilibrium coalescent-based methods to estimate pairwise immigration rates and historical effective population sizes. Our biophysical model predicted coral immigration rates in the absence of spatially varying selection, with 1km resolution across the GBR. Genomic data revealed strong bias towards preferential spread of immigrants from lower to higher latitudes; however, so did the biophysical model, indicating that this bias was attributable to local currents rather than the differential migrants’ survival. We did not see evidence of recent decline in genetic diversity: the most recent expansion and contraction trends of A. millepora populations date back several thousand years, prior to the anthropogenic global warming. Our results give hope for coral persistence under future climate: their genetic variation has not yet been affected and the observed southward migration trend will facilitate the spread of heat-tolerant genotypes from low-latitude locations throughout the GBR.
