Reef fish hybridization: Lessons learnt from butterflyfishes (genus Chaetodon)

Natural hybridizationis widespread among coral reef fishes. However, the ecological promoters and evolutionary consequences of reeffish hybridizationhave not been thoroughly evaluated. Butterflyfishesform a high number of hybridsand represent an appropriate group to investigate hybridizationin reeffishes. This study provides a rare test of terrestrially derived hybridizationtheory in the marine environment by examining hybridizationbetween Chaetodon trifasciatusand C. lunulatus at Christmas Island. Overlapping spatial and dietary ecologies enable heterospecific encounters. Nonassortative mating and local rarity of both parent species appear to permit heterospecific breeding pairformation. Microsatellite loci and mtDNA confirmed the status of hybrids, which displayed the lowest genetic diversity in the sample and used a reduced suite of resources, suggesting decreased adaptability. Maternal contribution to hybridizationwas unidirectional, and no introgressionwas detected, suggesting limited, localized evolutionary consequences of hybridization. Comparisons to other reeffish hybridizationstudies revealed that different evolutionary consequences emerge, despite being promoted by similar factors, possibly due to the magnitude of genetic distance between hybridizingspecies. This study highlights the need for further enquiry aimed at evaluating the importance and long-term consequences of reeffish hybridization.