Sex! Identity theft! Burying beetles!
The â€śCoolidge effectâ€? â€“ I would have named it for a different American president â€“ is a tendency of some males to be more interested in a new sex partner than one they have mated with in the past. Males that donâ€™t help care for young may have more descendants this way than if they put all their eggs (so to speak) in one basket. But to avoid remating with the same partner, one first needs to remember them all.
Most chimps and humans can probably remember all previous partners, but what about other species? One burying beetle looks much like another, or so it seems to us. In this weekâ€™s paper, Sandra Steiger and coauthors asked whether males of this species prefer novel mates and, if so, how they tell them apart.
Male beetles had a female introduced into their chamber every ten minutes, but the first four were actually the same individual. (So the police chief, whose assistant was bringing him the same newspaper every day to save money, says, â€śI know people think policemen are stupid, but look at this paper; a doctor has run over his own mailbox four days in a row!â€? Joke credit: Milan Copic.) The fifth female was different. The males took longer to mate with the first female each time she was introduced, but mated as quickly with the new female as when the first female was first introduced.
But how do they tell them apart? Female crickets avoid mating again with the same male by scent-marking them. Reasoning that two inbred brothers probably smell somewhat similar, the authors tested whether males readily mate with a female who had previously mated with their brother. They do, so scent-marking doesnâ€™t seem likely.
On the other hand, males seemed somewhat reluctant (a slight delay, not statistically significant) to mate with the sister of a previous mate. Sisters could resemble each other in various ways, but biometric identification in insects is usually based on odors, rather than face recognition, for example. So the authors doused novel females with essence-of- previous-mate (extracted in solvent from four of her inbred sisters). These females were avoided, relative to control females doused only in the solvent.
Male burying beetles are less likely to mate with the same females repeatedly, apparently because remembered smells -- how long can they remember a smell? -- make them less interested. Before switching perfumes, remember that humans are not burying beetles.