Larger Hermit Crab Penises May Prevent Shell Theft

ABOVE: A hermit crab from the highly social terrestrial species Coenobita compressus in a normal walking posture.
MARK LAIDRE

Over the course of evolution, penis size has been subject to female choice and competition with male rivals. In a study published today (January 16) in Royal Society Open Science, Mark Laidre, a biologist at Dartmouth College, introduces a new idea: that larger penises help animals keep hold of precious resources. He compared hundreds of specimens of nine related species of hermit crab and showed that crustaceans that have more valuable shells have longer sexual tubes, helping them keep a grip on their homes while they extend their reproductive organs toward a mate.

“It is a relatively novel way of thinking about the evolution of penis size,” says Morgan Kelly, a biologist at Louisiana State University who was not involved in the work.

For the past decade or so, Laidre has been ...