Biologists are uncovering increasing evidence that females are much more than passive players in the game of reproduction. Examples include ducks with labyrinth-like vaginas that open or close to dead ends depending on the suitor and female flies that store sperm from different suitors, seemingly for selectively sorting for later use.
Now, new research indicates that some species' females might have yet another reproductive trick at their disposal: sensing whether sperm cells carry X or Y chromosomes and, potentially, being able to influence the gender of their offspring.
Researchers at the University of Sheffield exposed five different female pigs to either mostly X-chromosome sperm or mostly Y-chromosome sperm, The Scientist reports. The pigs, they found, seemed to respond to the chromosomal differences in those two sperm types, by either increasing or decreasing the level of activity in about two percent of their genes prior to fertilization. Some of these genes, the researchers told The Scientist, could help or hurt either X- or Y-carrying sperm.
As The Scientist points out, however, these results are certainly preliminary. Only a handful of pigs were used in the study, and in nature or on the farm they would receive sperm with a more or less equal mix of X and Y chromosomes rather than hand-picked biased samples. Many questions remain, The Scientist continues, including whether pigs actually can sense sperm gender in mixed samples, and, if so, both how they do it and what they do with that information.