Hybridisation and the evolution of coral reef biodiversity

Hybridisation has traditionally been considered rare and unimportant in generating biodiversity in the marine environment, particularly in coral reefs ecosystems. Here we review the literature for evidence of hybridisation in coral reef organisms and find that hybridisation is prevalent in well-studied groups, namely fish and hermatypic corals. At least 183 fish and 81 scleractinian coral species are reported to hybridise, with the highest prevalence in angelfishes and psammocorid corals (hybridisation in 46–50% of species in each family). Mapping the geographic location of hybrids revealed that hybridisation was positively associated with proximity to biogeographic borders for fish but not corals, and not linked with areas of low species richness in either group. Molecular studies detected admixture, indicative of past hybridisation, in 30 of 53 cases for fish, and in 22 (possibly 39) out of 47 studies for corals. Patterns of introgression described in the fish studies supported a decrease in lineage diversity in nine cases and the formation of hybrid lineages in seven cases. In the other 14 cases, the two parent species remained genetically distinct despite evidence of introgression. For corals, the evidence of hybrid lineages was rare (5 species), rather there was more support indicating that hybridisation leads to a decrease (36 species), or no change (27 species), in lineage diversity. Collectively, these results show that hybridisation can influence the evolution of fishes and corals in multiple ways and suggests the prevalence of hybridisation is likely to be significantly underestimated for coral reef taxa. The application of new genomic tools will advance our knowledge of the prevalence and evolutionary importance of hybridisation in coral reef organisms. Furthermore, these tools will aid in identifying how natural and assisted hybridisation may help coral reef species adapt to increasing environmental changes.