National Geographic reports the discovery a lovely new freshwater crab, Insulamon palawanense, which sports a purple carapace and red claws. It was found on the Philippine island of Palawan, and is small (1-2 inches across).
(All photos by Hendrik Freitag.)
The crab’s brilliant hues may simply help the species recognize its brethren, said study author Hendrik Freitag, of the Senckenberg Museum of Zoology in Dresden, Germany.
“The particular violet coloration might just have evolved by chance, and must not necessarily have a very specific function or reason aside from being a general visual signal for recognition,” said Freitag, whose study was published in February in the Raffles Bulletin of Zoology.
I’m a bit dubious about bright colors as “species recognition” signals. That might be the correct explanation, but doesn’t explain why other species are more drab. Perhaps individuals of this species need brighter colors because there are fewer individuals and need more obvious signals to find each other. But there could be other explanations as well, including mutual sexual selection or aposematism (color warning of toxicity, though that seems unlikely). But Freitag saying that “it could have evolved by chance” (implying genetic drift) doesn’t comport with the selective explanation—individual recognition of conspecifics—that he offers immediately thereafter.
Large Insulamon males—such as this I. johannchristiani, another of the newfound species—sport a reddish color, possibly to signal their power, Freitag said.
Smaller, less dominant Insulamon males and females are purple, he noted.