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Coffee with the squirrels today: They don’t give their kids mating advice

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Staff writer Lesley Ciarula Taylor explains for Toronto Star readers “Why female red squirrels aren’t choosy about their mates”:

Guelph scientists have solved the puzzling question of why female squirrels are rampantly promiscuous, sleeping with an average of 10 males in one day.

It almost entirely depends on how many guys show up.

That’s the finding reported by University of Guelph researchers from their study of 85 female North American red squirrels. Female squirrels do not pass any specific mating tendencies (one, some, or many guys) on to their daughters.

“A lot of folks who have looked at this before looked at whether it’s good or bad for a squirrel to be promiscuous,” [lead investigator Eryn] McFarlane told the Star on Wednesday. “I wanted to look at whether it was genetic, regardless of whether it was good or bad.”

What she found is that risks and benefits don’t have much to do with how females behave.

[ … ]

This is the first study that says genetics or heredity have little to do with a female squirrel’s sex life.

Goodbye, selfish gene. Or, to put it in the vernacular, none of the ladies are chaste, but some are more chased than others. It depends on how many guy squirrels are around to chase them.

For the tale of how the Washington Post thought it had discovered natural selection among squirrels, go here.

Look, squirrels are, well, squirrelly, but anyway here’s the Abstract:

The tendency of females to mate with multiple males is often explained by direct and indirect benefits that could outweigh the many potential costs of multiple mating. However, behaviour can only evolve in response to costs and benefits if there is sufficient genetic variation on which selection can act. We followed 108 mating chases of 85 North American red squirrels (Tamiasciurus hudsonicus) during 4 years, to measure each female’s degree of multiple male mating (MMM), and used an animal model analysis of our multi-generational pedigree to provide what we believe is the first estimate of the heritability of MMM in the wild. Female red squirrels were highly polyandrous, mating with an average of 7.0 ± 0.2 males on their day of oestrus. Although we found evidence for moderate levels of additive genetic variation (CVA = 5.1), environmental variation was very high (CVE = 32.3), which resulted in a very low heritability estimate (h2 < 0.01). So, while there is genetic variation in this trait, the large environmental variation suggests that any costs or benefits associated with differences among females in MMM are primarily owing to environmental and not genetic differences, which could constrain the evolutionary response to natural selection on this trait.

Female squirrels do not pass any specific mating tendencies (one, some, or many guys) on to their daughters.
Yes they do: they found a "moderate" level of additive genetic variance, so females are passing on some mating tendencies. I haven't read the paper, but I'm guessing (from how I read the abstract) that here they're looking at number of matings per mating chase, rather than over the lifetime of the individual. The latter would average out some of the environmental variation, and give a higher heritability. But I've no idea if that would be enough to make the heritability non-trivial. Heinrich

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