February 05, 2008

Freezing Away the Males

Frost conesAmbient temperature predicts sex ratios and male longevity -- Catalano et al., 10.1073/pnas.0710711104 -- Proceedings of the National Academy of Sciences

Temperature affects the sex ratio of many species. There are also evolutionary arguments that stressed mothers would have a higher risk of spontaneous abortion (or non-conception) of male offspring, since they represent a smaller fitness gain than a daughter. Catalano, Bruckner and Smith looked at average temperature data from Scandinavia in the 1800's and compared it to gender ratios from the same and next year. They found an increase of one extra male per 1000 females born per degree of temperature.

Looking at the maps on the Wikipedia page about sex ratio per country suggests that high and low latitude countries more often have female-skewed gender ratios. But one should take that with a grain of salt, since clearly there are many other factors such as smoking, malnutrition, endocrine disruptors and deliberate selection at work here.

However, the serious Swedish famine in the 1860's doesn't seem to have made much of a mark in the data. The droughts of 1888 seem to have made a much clearer mark in the secondary sex ratio. There seems to be a very neat correlation between the temperatures, gender ratio and emigration from Sweden. I wonder if the emigration would act as a confounder?

Posted by Anders3 at February 5, 2008 08:12 PM