Scientists from Australia have discovered a hotspot in the eastern Indian Ocean where unusually high numbers of natural hybrid fishes occur.
The team from the ARC Centre of Excellence for Coral Reef Studies, at James Cook University's School of Tropical and Marine Biology in Queensland, found the hybridisation hotspot between the Christmas and Cocos Islands.
Marine hybrid fishes are generally considered quite rare, but the area between the islands is home to a massive 11 reef fish hybrids spanning six different fish families - the highest number of hybrids ever recorded at a single location.
In most cases, at least one of the parent species that form the hybrids is a rarity at the site, with less than three individuals found over an area spanning 3000 square metres.
The scientists believe that the scarcity of potential mates mean that the fish are breeding with closely related species, rather than with their own kind.
The authors said: "These islands also represent a marine suture zone where many of the hybrids have arisen through interbreeding between Indian and Pacific Ocean species.
"For these species, it appears that past climate changes allowed species to diverge in allopatry, while recent conditions have facilitated contact and subsequent hybridization at this Indo-Pacific biogeographic border.
"The discovery of the Christmas-Cocos hybrid zone refutes the notion that hybridization is lacking on coral reefs and provides a natural laboratory for testing the generality of terrestrially derived hybridization theory in the marine environment."
The hybrids found at the site include:
Acanthurus leucosternon x Acanthurus nigricans
Naso elegans x Naso lituratus
Melichthys indicus x Melichthys vidua
Chaetodon guttatissimus x Chaetodon punctatofasciatus Chaetodon ornatissimus x Chaetodon punctatofasciatus Chaetodon ornatissimus x Chaetodon meyeri
Chaetodon lunulatus x Chaetodon trifasciatus
Thalassoma jansenii x Thalassoma quinquevittatum
Centropyge flavissima x Centropyge eibli
Centropyge eibli x Centropyge vrolikii
Centropyge flavissima x Centropyge vrolikii
For more information see the paper: Hobbs JP, Frisch AJ, Allen GR, Van Herwerden L (2008) - Marine hybrid hotspot at Indo-Pacific biogeographic border. Biol Lett. 2008 Dec 23.