"It is possible, however, that breeding for long spines introduced a secondary trait that affects fertility," Polak said. Unintended consequences, he said, are well known to animal breeders.
To prove that it was the spines and not some other trait, some beetles had their genital spines surgically modified using micro-scale laser surgery. Polak's laboratory has gained an international reputation for using a precision laser system to make microscopic changes to insect bodies.
Insects modified through both methods were then observed throughout the competitive mating process. The international team found that the longer genital spines directly contributed to successful fertilization. Seminal fluid from the males was also tracked through high-resolution radioisotope labels, and shown to enter the female body more quickly after mating with long-spined males than short-spined males.
"This provides experimental evidence that male genital morphology influences success in postcopulatory reproductive competition," Polak said.
There is more work to be done, Polak said, to understand the mechanism at work here. It is possible that these longer spines help introduce bio-active molecules from seminal fluid into the female circulatory system. These added proteins and peptides, which have yet to be characterized, may create effects within the female that contribute to male reproductive success. It is also possible that genital spines exert mechanical effects within the female by stimulating her reproductive tract during copulation, thereby inducing the female to uptake and use more of her current mate's sperm.
| Contact: Greg Hand greg.hand@uc.edu 513-556-1822 University of Cincinnati Source:Eurekalert |