The expensive beetle horn hypothesis

Carl Zimmer has a great post discussing a paper by Douglas Emlen and colleagues (2005) on beetle evolution. I don't normally do a lot of beetle blogging, but this paper is a great study in evolutionary trade-offs related to sexual selection and the evolution of novel body structures.

From Zimmer's post:

The researchers proposed that growing horns would force a trade-off with other important parts of the body, such as eyes and antennae. And the beetle tree supports their proposal. It is harder for beetles to detect the odor of dung with their antennae in a pasture than in a forest, because the odor plumes last longer in the woods. Four out of the five gains of new horns took place in forestsperhaps because beetles could afford to grow smaller antennae in a place where smelling wasnt so hard. On the flip side, in seven of the nine cases in which horns were lost, the beetles became nocturnal. Beetles that fly at night need larger eyes, and so they cant afford to shunt resources to big horns any more. The pressure to evolve bigger horns still exists in these lineages, but its been offset by other demands.

References:

Emlen DJ, Marangelo J, Ball B, and Cunningham CW. 2005. Diversity in the weapons of sexual selection: horn evolution in the beetle genus Onthophagus (Coleoptera: Scarabaeidae). Evolution 59:1060-1084. Abstract