Anticipating Sex Increases Breeding Potential

Does the anticipation of sex make animals better breeders? It appears to for quails. When researchers placed male quails in environments they learned to associate with mating, the birds sired more offspring than their untrained counterparts. The findings may provide clues to the evolution of conditioned learning in a variety of animals, including humans.

Conditioned learning--or conditioning--was most famously demonstrated by Ivan Pavlov more than 100 years ago. Pavlov would ring a bell and then feed a dog. After a while, the dog began salivating every time he heard the bell, suggesting he had learned to associate the sound with food. Since then, researchers have studied how conditioning develops, but few have looked at how it might have evolved.

Psychologist Michael Domjan and colleagues at the University of Texas, Austin, set out to explore the question. If conditioning improves the odds of reproducing, they reasoned, the trait would be adaptive and spread through the population.

The researchers placed male quails, which readily breed in captivity, in boxes with green walls or tilted floors for 5 minutes and then introduced them to a female for a romantic liaison. After 5 days of conditioning, one male was placed in a green or tilted box for 5 minutes, and another male was placed in an unfamiliar box. Then both were introduced to a single female within minutes of each other.

Normally, two males breeding with the same female in succession each have a 50% chance of fathering the chicks. However, a paternity test showed that conditioned males had a 72% chance of being the father, the team reports in this month's issue of Psychological Science.

Domjan suspects that when the quails knew sex was coming, they were somehow psychologically transformed and their sperm became more competitive. He suggests that the conditioning increases sperm concentrations or the amount of semen released. "We tend to think of sexual behavior as instinct-driven," Domjan says, "yet our results show that learning plays as big a role in reproduction." The results, he says, provide an evolutionary explanation for why the behaviors Pavlov observed would have been selected for.

"This is as novel as it is exciting," says psychologist Karen Hollis of Mount Holyoke College in South Hadley, Massachusetts. "Now that we know this, what I'm really interested in is whether conditioning provides the same advantages for females, and I have no doubt that this is where Domjan and his colleagues are going."

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