Promiscuous Females Continue to Mystify

New research on seed beetles challenges one of the leading explanations for why many female animals mate with multiple males despite the time and energy costs.

Researchrs tested the hypothesis that promiscuous behavior could help a female produce genetically fit offspring, because the sperm that ultimately fertilizes the female’s egg would tend to come from a male who also possesses "good" genes. This effect might arise because the sperm itself outcompetes the others or because the female somehow gives that sperm preferential access to the egg.

Surprisingly, the researchers found that when female seed beetles were mated with two male seed beetles, the "low-quality" male sired more offspring than males of "high" quality (as measured by the number of offspring sired when mated just once).

That suggests the paternal genetic contribution to offspring does not drive female promiscuity. Instead, the explanation may involve conflict between "sexually antagonistic" alleles — coding sequences on genes — that are beneficial to one sex but harmful to the other.

The results, from Trine Bilde of the University of Aarhus in Denmark and colleagues, are detailed this week in the journal Science.