Wednesday, January 20, 2010

Sexual Dimorphism Redux

Photo Copyright 2010 by Barry Fackler

Another example of how vastly different the sexes can appear in the same species of reef fish in Hawai'i. The plain little fish above are initial phase Bird Wrasse which can be either male or female. They are small (~3 in.) and, except for a little streak of red on their snouts, fairly drab. Below is the supermale of the species which is substantially bigger (6 to 7 in.) and endowed with vivid blue and green colors including a patch of nearly-neon green above the pectoral fin.

Photo Copyright 2010 by Barry Fackler

All Bird Wrasse have curved snouts that allow them to pull their prey from among the arms of branching coral. This feature resembles the beak of an endemic bird, the Scarlet Hawaiian Honeycreeper or i'iwi. These fishes swim swiftly and erratically making them very difficult to photograph.

Wrasse sexuality can be a somewhat complicated matter. For purposes of today's post I'll just point out that Bird Wrasse supermales begin life as females and then, for reasons unknown, some morph into the colorful and socially dominant form. Gender-changing is common in wrasse as well as parrotfish.

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