When it comes to a dung beetle's junk, size doesn't matter. At least, not to the process of rapid evolution that creates new species. Researchers say that what matters there, as males and females evolve together and distinguish themselves from related species, is shape.
Intercourse between Onthophagus beetles--the genus used in the current study, which includes the dung beetle O. taurus as well as other scarab beetles--is far from simple. It begins with the male climbing onto the female's back and inserting his penis's grabbing appendages (called parameres) into special pits on her underside. "For simplicity," the authors refer to the female's collection of equipment here as the "pygidial flap." Once the male has gripped the female tightly, he inflates his endophallus and--well, you know the rest.
Beetles and other arthropods are known to have quickly evolving genitals; often, the genitals are the key to telling similar species apart. So ...
