In a new approach to conservation genetics, researchers used a high-quality genome of the coral Acropora millepora, along with environmental data, to study this coral's variable responses to climate change, a trait of key conservation importance. Their results, which suggest a unique genetic signature in corals likely to bleach, could be used to forecast potential bleaching events before they occur and to identify the coral populations most vulnerable or tolerant to future climate warming. When sea temperatures get too hot, corals will expel the vital photosynthetic algae that live within their tissues, causing the coral to turn white, or "bleach," and ultimately to die. However, the thermal limits of corals and their responses to bleaching events vary within species. While it's thought that these tolerances are partly heritable, due to the lack of high-quality genomic resources for coral species, the genes responsible remain elusive. To identify any potential genetic variants associated with bleaching, Zachary Fuller and colleagues first produced a chromosome-level genome assembly of A. millepora - a shallow-water coral susceptible to bleaching - and compared it to genome-wide association (GWAS) data generated for 213 other A. millepora coral colonies collected during a bleaching event in the Great Barrier Reef. While Fuller et al. found no specific genetic variants directly associated with bleaching, they were able to show that a polygenic risk score comprising signals throughout the coral genome could be used to predict bleaching potential in the wild. The analysis also revealed a considerable amount of genetic diversity in the gene sacsin, which is involved in heat stress response. The diversity suggests local environmental adaptation. "The genome Fuller et al. created using long-read technology to cope with repetitive regions will be an enormous resource for future studies of coral ecology, evolution, cell biology and development, facilitating preciously untenable investigations in this ecologically important system," write Rachael Bar and Leslie Guerrero in a related Perspective.
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Journal
Science