HENRY

One of Darwin’s pet examples of sexual selection were the Diving Beetles, where he argued that the male and female members of the same species co-evolved their mating techniques (i.e. males with large suction cups to hold the females).

However, it appears that this is more of an inter-sex arms race, where the females develop modifications of their dorsal surface to hinder the male suction cups:

To trace the evolutionary history of sex-specific characters in diving beetles, we used the recently revised genus Acilius which contains 13 extant species distributed over the Northern Hemisphere. The genus is characterized by having dense macropunctures on the dorsal surfaces, females with prominent, setose furrows on the elytra, and males with broadly expanded protarsi equipped ventrally with three large and many minute suction cups. These structures even attracted the attention of Charles Darwin, who regarded the setose female furrows in Acilius as an example of an aid for males to better grip females during mating. However, it is clear from basic physical laws and simple experiments, that the mechanically working male suction cups function best on smooth surfaces where complete contact around their circumference enables attachment.

Continued at Phylogeny of Diving Beetles Reveals a Coevolutionary Arms Race between the Sexes.

Posted on June 13th, 2007 by Simon Greenhill