Early Spring Means More Bat Girls

ScienceDaily (May 4, 2012) — There must be something in the warm breeze. A study on bats suggests that bats produce twice as many female babies as male ones in years when spring comes early. The earlier in the spring the births occur, the more likely the females are to survive and then reproduce a year later, as one-year olds, compared to later-born pups, according to Robert Barclay's research published in PLoS ONE.

"The early-born females are able to reproduce as one year olds, whereas male pups can't," explains Barclay, professor in the Department of Biological Sciences.

"Thus, natural selection has favoured internal mechanisms that result in a skewed sex ratio because mothers that produce a daughter leave more offspring in the next generation than mothers who produce a son."

The length of the growing season has an impact on the ratio of female to male offspring and the time available for female pups to reach sexual maturity, the study found. This suggests that not only does sex-ratio vary seasonally and among years, but it also likely varies geographically due to differences in season length.

Continued:  http://www.sciencedaily.com/releases/2012/05/120504172055.htm