Meeting Abstract
Reef-building corals are under strong selection for higher thermal tolerance as increasingly frequent thermal stress events are causing worldwide die-offs. Until recently, the mitochondrial (mt) genome has been overlooked as a source of adaptive genetic variation. Current studies suggest mt genomes can maintain non-neutral polymorphisms under strong selection, and these polymorphisms can be linked to variation in host fitness. Most of the previous literature has focused on thermal tolerance associated with the coral’s symbiotic algae. However, a recent study revealed Acropora millepora larval thermal tolerance depends on maternal background, suggesting mt variation might play an important role in coral thermal tolerance. Four adult colonies from two locations in the Great Barrier Reef (GBR) were cross-fertilized, and their larvae were scored for thermal tolerance. Maternal effects accounted for 66% of the total variation (87%) in thermal tolerance. In addition, larvae of parents from the warmer location had significantly higher thermal tolerance than larvae of parents from the cooler location. Analysis of gene expression revealed heat-tolerant larvae up-regulate nuclear-encoded mt membrane components, along with oxidoreductase activity, which was suggested to contribute to the high maternal effect. Beyond that experiment, this potentially key aspect of coral thermal tolerance remains unexplored. Currently, there are two known mitochondrial haplotypes in A. millepora, which are both found at high frequencies in populations spanning the GBR. Experiments are being conducted to determine whether haplotype frequencies correspond to local thermal regimes and how mt variation impacts adult thermal tolerance.
