Meeting Abstract
The impact of climate change on populations of reef-building corals will depend on the rate at which they can adapt to increasing temperature, which will in turn depend on the extent of heritable variation in heat tolerance in coral metapopulations. Here we identify regions in the genome of the coral Acropora millepora harboring alleles responsible for variation in thermotolerance across latitudes. Reciprocal crosses were made between two A. millepora colonies from locations separated by five degrees of latitude and differing in average annual temperatures by 1.5 degrees Celsius. The resulting larval cultures were either subjected to strong selection by heat resulting in >95% mortality, or to benign conditions resulting in no mortality over the experimental period. The selection experiment was replicated twice for each of the reciprocal crosses. The larvae and the parental colonies were then genotyped individually using 2bRAD methodology. The genotyping results were used to construct a high density genetic linkage map of the A.millepora genome. Regions responsible for variation in larval heat tolerance were identified as those displaying reproducible shifts in allele frequency between heat-selected and unselected larval cohorts. Two genomic regions displayed extremely strong selection signals, and four additional regions were significantly enriched by less pronounced selection signals. Notably, selection varied between reciprocal crosses and was predominantly directed against paternal haplotypes, suggesting the importance of compatibility of paternal alleles with a particular maternal background. This most likely reflects the importance of mitochondrial type in determining heat tolerance. Our results demonstrate the presence of selectable genetic variation for heat tolerance within natural populations of A. millepora.
