Meeting Abstract
Reef-building corals are currently threatened by rapid changes in local and global stressors and hybridization offers a potential shortcut for rapid adaptation and evolutionary rescue in these species. The sympatric corals Acropora palmata and A. cervicornis form the hybrid, A. prolifera, whose abundance has continued to increase, either through fragmentation or sexual reproduction, while the parental species decline. Previous work indicates that weakened prezygotic isolation mechanisms in A. cervicornis but not A. palmata could allow for continuous unidirectional gene flow between the two species. Furthermore, asymmetric introgression from A. palmata to A. cervicornis has been recorded in three nuclear loci. In contrast, we found evidence for backcrossing with A. palmata across three hybrid zones although the frequency of hybrids and backcrosses differs across the range. Here we used genomic sequence data from the two parental species and their hybrids to further characterize the patterns of genomic synteny, divergence and introgression across three hybrid zones. We identified over 1 million genetic variants between the parental species. Using pairwise SNP fixation index estimates between parental populations we identified genomic regions with exceptionally low and high differentiation among parental species. We further estimated the distribution of introgression across the genome by examining absolute pairwise divergence between the reference A. palmata genome and 20 additional A. palamta genomes across 50kb windows. Combined, these approaches elucidategeographic variation in genomic hotspots of introgression as well as barriers to hybridization with implications for how hybridization may shape adaptation in these important foundation species across the Caribbean and North-West Atlantic.
