Data from: Does genetic distance between parental species influence outcomes of hybridisation among coral reef butterflyfishes?

Christmas Island is located at the overlap of the Indian and Pacific Ocean marine provinces, and is a hotspot for marine hybridisation. Here we evaluate the ecological framework and genetic consequences of hybridisation between butterflyfishes Chaetodon guttatissimus and Chaetodon punctatofasciatus. Further, we compare our current findings to those from a previous study of hybridisation between Chaetodon trifasciatus and Chaetodon lunulatus. For both species groups, habitat and dietary overlap between parental species facilitate frequent heterospecific encounters. Low abundance of potential mates promotes heterospecific pair formation and the breakdown of assortative mating. Despite similarities in ecological frameworks, the population genetic signatures of hybridisation differ between the species groups. Mitochondrial and nuclear data from C. guttatissimus × C. punctatofasciatus (1% divergence at cyt b) show bidirectional maternal contributions and relatively high levels of introgression, both inside and outside the Christmas Island hybrid zone. In contrast, Chaetodon trifasciatus × C. lunulatus (5% cyt b divergence) exhibit unidirectional mitochondrial inheritance and almost no introgression. Back-crossing of hybrid C. guttatissimus × C. punctatofasciatus and parental genotypes may eventually confound species-specific signals within the hybrid zone. In contrast, hybrids of C. trifasciatus and C. lunulatus may coexist with and remain genetically distinct from the parents. Our results, and comparisons with hybridisation studies in other reef fish families, indicate that genetic distance between hybridising species may be a factor influencing outcomes of hybridisation in reef fish, which is consistent with predictions from terrestrially-derived hybridisation theory.