The White-bonnet Anemonefish. Is it a true species?
© Gerry Allen
Teluk Buli (Buli Bay)
N 00º47.457' E 128º19.279'
One of the most interesting fishes encountered so far on our expedition is a rare "odd-ball" anemonefish that has been seen twice over the past week while diving on outer reefs of northeastern Halmahera. This fish, the White-bonnet anemone fish has a very interesting story.
In 1973, Gerry Allen discovered what appeared to be a new species of anemonefish, which he named Amphiprion leucokranos, commonly known as the White-bonnet anemonefish. The original discovery was made at Madang on the northern coast of Papua New Guinea.
"So much for what we learned in school – that different species cannot interbreed and produce viable reproductive offspring. It seems it is not that simple!"
A very strange pattern emerged as Dr. Allen studied this fish in its natural habitat over the next few decades. Like all members of genus Amphiprion it is invariably associated with large sea anemones, which offer its fish host a safe haven among its tentacles that sting all other fishes. Anemonefishes are protected by a special chemical compound in its body slime that suppresses the normal stinging reaction. But unlike other anemonefishes, the White-bonnet seldom associates with fish of its own kind. Rather it is usually paired up with either the Orange Anemonefish (Amphiprion sandaracinos) or the Orange-finned Anemonefish (A. chrysoperus).
Gerry got a shock several years ago at Kimbe Bay, Papua New Guinea when he found a pair of the other two species (Orange Anemonefish and Orange-finned Anemonefish) tending a nest of eggs! It suddenly became clear to him that the White-bonnet anemonefish was in fact a hybrid cross of these two species.
The intriguing aspect of this phenomenon is that an apparently large number of the hybrids survive and then mate with each other, producing viable offspring. This state of affairs has apparently persisted over thousands of years to the extent that the hybrid can be predictably found throughout the co-occurring range of the parental species, which includes the Solomon Islands, New Guinea, and parts of eastern Indonesia. Likewise, the hybrid White-bonnet never occurs when only one of the parent species is present as is the case for the Orange-finned throughout Micronesia and Polynesia or for the Orange Anemonefish over much of the Indo-Malayan Archipelago.
Even though we now have good evidence that the White-bonnet is a hybrid a strong argument can be made that it is actually a valid species resulting from the hybridization phenomenon. Similar evolution of species via hybridization is known to occur in other groups of organisms, notably plants and reef corals. Dr. Allen is currently conducting genetic studies of this problem with a team from Boston University and the Atlanta Aquarium.
So much for what we learned in school – that different species cannot interbreed and produce viable reproductive offspring. It seems it is not that simple!
– Ali & Gerry
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Photo: (top) The White-bonnet Anemonefish. Is a true species? © Gerry Allen
(bottom) The White-bonnet Anemone Fish with an Orange-finned Anemonefish: two species or one and a half? © Gerry Allen