"The mating system of these flies is best described as 'scramble competition,'" Grieshop said. "They swarm on rotting fruit. Some females are receptive. Others are not. The premium goes to males that can mate efficiently with many females before they are usurped by sexual rivals"
In such a chaotic environment females are known to exercise choice prior to mating according to the scent of pheromones, sounds of mating calls, or the visual cues of courtship dances, Grieshop said. But with regard to the surgical treatments of these genital spines, females apparently do not discriminate between competing male treatments.
"It appears that these spines promote male copulation success in this sort of environment," Grieshop said. "Identifying the precise function of a trait that varies across species, such as these spines, provides insight into the evolutionary pressures that caused them to evolve and also how new species may arise. Most adaptive functions of genitalia so far discovered only make a difference after mating has begun. For genitalia to make a difference before copulation is unusual. This puts genital traits on the same playing field as so-called 'secondary sexual traits,' like coloration or other adornments."
The research, he said, encourages the scientific community to consider male genital trait evolution as being similar to that of secondary sexual traits, which may facilitate the understanding of one of the greatest unknowns in evolutionary biology: why male genitalia are so incredibly variable across species.
|Contact: Greg Hand|
University of Cincinnati