A new form of lionfish has been evolving in the Red Sea during the past four decades, says new research.
According to a study undertaken by Lev Fishelson of Tel Aviv University which was published today in the journal Environmental Biology of Fishes, the lionfish, Pterois volitans, found in the Red Sea has changed in appearance over the past 40 years and a new form has evolved.
Rather than the normal ray-like supraocular tentacles which appear just above the eyes of the lionfish , the new form has evolved feather-like tentacles in which one or both have a sharply defined black eye spot with a white ring around it.
In adults, these tentacles are much broader at the tips than the ray-like tentacles of most volitans, and look rather like a peacock's feather. They can measure up to 5cm in length and over 1cm in width at the tip.
The normal form of Pterois volitans is a quite different looking fish.
The additional ornamentation of the supraocular tentacles of Pterois volitans has been known about for some time, and Fishelson has been monitoring the structure and its spread through the volitans populations of the Red Sea for the past 25 years.
It is believed to have been first recorded in the Red Sea at the southern tip of Sinai, but fish bearing the same characteristics have steadily progressed up the Gulf of Aqaba.
Over the past decade, both lionfish morphs have been found living together at the northern end of the Gulf.
Incipient evolutionIn a study undertaken by Fishelson in Eilat in 1975, which looked at the morphology of 80 Pterois volitans, none of the specimens with a spotted, feather-like tentacle were found, although five specimens did have wider tentacles than normal.
However, a follow-up study on the same reefs in Eilat a few years ago found two of the new form of lionfish among 35 specimens examined, but these fish had the eye-spot on just a single tentacle. The feather-like tentacled form has subsequently been found outside the Red Sea in the Pacific Ocean.
The precise reason why P. volitans in the Red Sea have been undergoing this evolution to produce a new form isn't known.
One possibility is that the eye-spots have been selected to artificially enlarge the head of the fish, which might be important in communicating with members of the same species, or defending itself against other species.
The other hypothesis is that the elliptical tentacles were selected to imitate tiny fish which act as a bait to attract piscivores that the lionfish can then swallow with its capacious mouth.
It might also be due to sexual selection. Many fishes select phenotypic traits, including ornamentation, and there is a possibility that the evolution of these markings might be sexually selected.
Fishelson believes that the new morph is a rare fish, as few ichthyologists he consulted were aware of it, and there are few specimens in museum spirit collections.
Like many widespread Indo Pacific fish species, P. volitans can differ slightly in its meristics and colouration across its natural range. This has led some scientists to suggest that such widespread species may in fact be made up of several closely related but distinct species.
For more information see the paper: Fishelson, L (2006) - Evolution in action-peacock-feather like supraocular tentacles of the lionfish, Pterois volitans - the distribution of a new signal. Environmental Biology of Fishes (2006) 75:343-348.