RSS Socotra is a convergence of hybrid reef fish

MASA Admin

8 May 2007
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Socotra is a far flung island of the Western Indian Ocean which is incredibly hard to reach, and even harder to study underwater. A couple years back however, a team of researchers including California Academy of Sciences ichthyology curator and MACNA 2014 Keynote speaker Luiz Rocha, traveled to this outer territory of Yemen and discovered an incredible diversity of never before seen hybrid reef fish.

Socotra lies at the convergence of three very distinct biogeographic regions; the Indo-Polynesian province, the Western Indian Ocean Province, the western Arabian Sea Province, and last but not least, the one and only Red Sea. While Socotra itself may be only 82 miles long, it is the crossroads for different types of reef fish species who’s distribution ranges for thousands and thousands of miles.

The veritable melting pot of so many different species, some of them closely related, has resulted in a nearly unrivaled degree of hybridization, and many hybrids which are documented nowhere else in the world. The location of Socotra and its archipelago of islands is a hot spot of hybridization because there are many fish that are regional endemics from the Red Sea and the Gulf of Aden, but with limited representation at Socotra.

Meanwhile Other reef fish from the Western Indian Ocean or the Indo-Polynesian province might be at the edge of their distribution at Socotra. The short version of why there are so many hybrids at Socotra is that there are often cases of one species being particularly rare, while a closely related species might be locally abundant.

No fewer than fourteen species of reef fish were documented as hybridizing at Socotra, spanning four different families including damselfish & clownfish, butterflyfish, surgeonfish, and hawkfishes. The butterflyfish hybrids are particularly diverse at Socotra, with Chaetodon collare X C. lunula crossings, C. gardineri X C. leucopleura hybridizing, and the gorgeous C. melapterus and C. trifasciatus pictured above also blending their genes.

At Socotra there are also hybrids of Amphiprion bicinctus x A. omanensis and the hawkfishes Cirritichthys calliurus x C. oxycephalus. But for us, the real main event of this discovery and this paper is the observations of incredible hybrids of the clown tang and the sohal tang, Acanthurus lineatus x A. sohal.

The Sohal-Clown surgeonfish crosses were particularly abundant and their colors really ranged from full on lineatus surgeonfish, to full on sohal tang, and everything in between. In Socotra at least, it appears that there is a stable, inter-breeding population of these two surgeonfish species which results in one of the most striking crosses of Acanthurus found anywhere in the world.

The seven cases of reef fish hybrids found at Socotra is remarkable because they sampled such a tiny part of the marine environment of this little island, and they never even dove beyond 85 feet. Future expedition could easily, and most certainly, uncover more cases of reef fish hybridization but in the meantime we’ll just keep ogling that crazy sohal clown tang hybrid.

The full results of this hybridization hotspot can be found in the paper by Dibattista et. al can be found in the Journal of Biogeography, 2015.
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