Anne-Marie writes, in Hot Mommas Make Boys:
A study published in the latest edition of the Journal of Mammalogy reports the results of a 30 year study on a population of northern elephant seals (Mirounga angustirostris), which shows that the male:female pup ratio is significantly higher in years with warmer sea surface temperature and weaker atmospheric pressure differentials.
What is the mechanism behind this? Unlike reptiles, which actually have their biological sex determined by temperature, the sex of mammalian embryos is entirely dependent on their chromosomes. This is where the phenomenon differs between the two taxa: reptiles depend on environmental factors to determine sex, whereas in mammals it is the sex ratio of offspring that complete development that is affected. Sex ratios are adjusted by selectively resorbing or aborting embryos of a specific sex. But which sex gets the boot when times are hard?
Global warming? More and more male elephant seals fighting to death over fewer and fewer females? Yikes!