Cryptic colouration and melanism in the sand-burrowing beetleChaerodes trachyscelides(Coleoptera: Tenebrionidae)

Abstract

Abstract The flightless, sand-burrowing beetle Chaerodes trachyscelides White is confined to the intertidal zone of sandy marine beaches in New Zealand. The dorsal surface varies from black to pale whitish-yellow, and most specimens closely match the colour of the sand they live on. On a beach with pale sand, about 98% of specimens are whitish on the dorsal surface, and about 1% areblack. Conversely, on a beach with black sand, about 96% are black and about 1% are whitish. The beetles live under cast-up marine algae on which they feed, and burrow beneath it in the sand. When predatory sea birds pick up such algae, invertebrates, including C. trachyscelides, fall out, run a short distance, ana burrow into the sand. I suggest that a higher proportion of beetles coloured less like the sand are eaten by seabirds, and that these predators exert differential selection (genetic or phenetic) against non-cryptically-coloured individuals. However, there is as yet no way of telling whether the genetic mechanism is t...