First-generation fitness consequences of interpopulational hybridisation in a Great Barrier Reef coral and its implications for assisted migration management

The translocation of populations within their natural distribution ranges to instigate crossings between genetic stocks may enhance adaptive potential and resilience. Colonies of the reef-building coral, Acropora millepora, collected in the warmer central Great Barrier Reef (GBR) were experimentally crossed with conspecific colonies from the cooler southern GBR. Fertilisation success was high in all purebred and regional hybrid crosses (>83 %). After 4 months in the field at the southern location, survival rates differed as follows: native purebreds > regional hybrids > central GBR purebreds. The southern GBR purebreds were smaller at settlement compared with the other groups, but this difference disappeared towards the end of the grow-out period. While no benefit of genetic mixing in the F1 generation of this species was evident from our work, it is possible that hybrid vigour exists for other traits, such as thermal tolerance, and over different spatial scales, for different species, or in later generations.