Size Matters

The disproportionately endowed carabid beetle reveals that the size of female—and not just male—genitalia influences insemination success.

Tracy Vence
Jul 1, 2014

LOCK AND KEY: Size-matching between male (left) and female (right) genitalia aids mating success in a beetle species. (Scale bar, 2 mm)TEIJI SOTA AND YUTAKA OKUZAKI


The paper
Y. Okuzaki, T. Sota, “How the length of genital parts affects copulation performance in a carabid beetle: Implications for correlated genital evolution between the sexes,” J Evol Biol, 27:565-74, 2014.

The subject
Studies of various species have shown that the size of male genitalia can affect reproductive success. The male carabid beetle Carabus subg. Ohomopterus maiyasanus has a notoriously long copulatory piece—a hook on the root end of its penis. The female, too, can boast an elongated vaginal appendix into which this hook is inserted, and Teiji Sota of Kyoto University in Japan wanted to determine why such size matching may have evolved.

The experiment
Sota and a colleague evaluated the copulation performance of size-matched and...