July 24, 2003 ITHACA, N.Y. -- Billing and cooing in an old and familiar love nest doubles and even triples some birds' chances of producing progeny, researchers at Cornell University have discovered. Their study, which focused on Japanese quail, is the first to document what farmers and researchers have long suspected: that breeding is often more successful when animals mate where they have mated before. In this study, the inseminations were more likely to fertilize eggs when they occurred in cages where the birds had previously encountered birds of the opposite sex.
"We now know that fertilization isn't just a matter of plumbing; there's a lot of strategic decision-making going on that is regulated by the brain in response to the social and physical environment," says Elizabeth Adkins-Regan, a professor in the departments of psychology and of neurobiology and behavior at Cornell.
"Pavlovian conditioning has long been assumed to be adaptive. This study is the strongest evidence yet that Pavlovian sexual conditioning increases the reproductive success of animals, both male and female," she says.
In Pavlovian sexual conditioning, external cues allow anticipation of mating and lead to improvements in mating behavior. This study shows that the conditioning contributes to successful fertilization and not simply successful mating.
The study, conducted with Emiko A. MacKillop, Cornell '02, a former Cornell research assistant now in graduate school at the State University of New York in Binghamton, is published online at The Royal Society Web site and will be published in print, in the society's Proceedings: Biological Sciences on Aug. 22. The Royal Society is an independent United Kingdom academy promoting the natural and applied sciences.
The Cornell researchers put 26 male Japanese quail, a species already well established in neuroendocrine research, with females in two sets of cages. In one set, the males had mated with females before, but they had not previously encountered a female in the second set of cages. The researchers were able to document how often the females were fertilized in both situations.
"We found that inseminations fertilized at least one egg twice as often in cages where the males had been placed with females previously, compared with matings in cages where the males had not previously hosted a female," says Adkins-Regan.
To test the females, the same experiment was conducted with the sexes reversed. The rate of eggs fertilized was three times greater in cages where the females had previously been exposed to males, compared with those in cages where they had not previously encountered males.
The findings could be relevant for breeding endangered species as well as farm animals. "Pavlovian conditioning is a universal property of nervous systems," says Adkins-Regan. "It is likely, therefore, also to be relevant to fertilization success for wild animals in natural mating systems."
The research was supported, in part, by the National Science Foundation.
o Elizabeth Adkins-Regan: http://www2.psych.cornell.edu/regan/
o The Royal Society: http://www.pubs.royalsoc.ac.uk/biol_lett/biol_lett_main.htm
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