Hybridization in reef fishes

Hybridization was thought to be rare in the sea however, recent studies across the Indo-Pacific have begun to challenge this idea. Hybridization has been shown to occur naturally in many parts of the world with several regions known as hybrid hotspots. Examples of these are Cocos-Keeling and Christmas Island located and the boundary between the Indian and Pacific Oceans and the Socotra Archipelago located at the mouth of the Gulf of Aden where it intersects the Red Sean Province and Indian Ocean. There are, however, many examples of non-natural hybridization events that are typically facilitated by human influence. The consequences of hybridization (and the preceding introduction of non-native species) in a naive environments can result in drastic impacts to the ecosystem as well as lead to uncertainty regarding the evolutionary trajectory of the native species. 

Research that I recently published confirmed hybridization between a Hawaiian endemic damselfish and a non-native congener that is thought to have arrived in Hawaii from rafting alongside trash that originated elsewhere in the Pacific. The Indo-Pacific Sergeant is not native to Hawaii and was first observed in Hawaiian waters in 1992. In that time span it has colonized the entered 2600km of the Hawaiian Archipelago and has begun breeding with the endemic Sergeant. I found that a quarter of the population of both species on some island are made of hybrids and this number is likely to continue to grow. Their continued immigration and the frequency of hybridization leaves the long-term persistence of the evolutionary distinct endemic Hawaiian Sergeant uncertain

The endemic Hawaiian Sergeant Major, Abudefduf abdominalis (right), the hybrid offspring of A. abdominalis and A. vaigiensis (center), the non-native Indo-Pacific Sergeant Major, A. vaigiensis. Photos: Keoki Stender

Photo: Interspecific school of Sergeant Majors, Abudefduf abdominalis (Hawaiian endemic), A. vaigiensis (Indo-Pacific), and their hybrid. Photo credit: Keoki Stender