Meeting Abstract
Increasingly frequent thermal stress events are causing strong selection for higher thermal tolerance in corals. While most studies have focused on thermal tolerance associated with the coral’s symbiotic algae, a recent study shows the larval thermal tolerance of Acropora millepora depends on maternal background, suggesting mitochondrial (mt) variation might also play an important role in coral thermal tolerance. To assess mt variation, 225 individuals were sampled throughout the mid-range of the Great Barrier Reef (GBR). DNA was extracted and individuals were genotyped using whole-genome resequencing. There are two mt haplotypes, and mt genome alignments of 12 acroporid species suggests one of the haplotypes is introgressed from another species. Both mt haplotypes are found at high frequencies in populations across the mid-GBR. However, it is unclear whether mt haplotype frequencies correspond with local thermal regimes, as samples do not span the entire 3°C thermal range of the GBR. To assess whether there are mitonuclear interactions associated with the haplotypes, larvae were obtained by crossing A. millepora adults with different mt haplotypes, thus crosses share the same nuclear background, but differ in their mitochondria. For each cross, ~2,000 larvae were reared at 28°C, as a control, and at 36°C, as a heat selection treatment. DNA samples were taken when only 25% of the larvae remained in the 36°C heat selection treatment. The survivors of the heat selection treatment and the unselected larval pools were sequenced, and bulk genotyped using 2b-RAD. If the two mt haplotypes result in different genomic loci responding to heat selection, this suggests mitonuclear interactions play a role in coral thermal tolerance.
