Fingering Infidelity
by Walter Piperwn
DNA fingerprinting, the same technique that has achieved renoun in criminal investigations, has had a great impact on the study of animal mating systems. Ten years ago, techniques for determining parentage were onerous, inefficient, and seldom used. As a consequence, scientists were forced to infer parentage of young animals based solely on behavioral observations. Determining maternity was often straightforward, particularly in mammals, in which females give birth to and then care for young over an extended period. On the other hand, paternity assignment was riddled with problems.
The development of molecular techniques to generate "DNA fingerprints," individual-specific patterns of DNA fragments that are passed from parents to offspring, has made the assignment of paternity and maternity a simple matter in cases where DNA samples are available from a young animal and two putative parents. One of the most striking findings from early DNA fingerprinting studies is the frequent discovery of extrapair young, that is, young that are the genetic offspring of a female and a male other than her mate, in songbirds. In cardinals, seven percent of all young result from extrapair matings, while the figure is 28 percent in red-winged blackbirds, 35 percent in indigo buntings, and 50 percent in tree swallows.
Scientists now recognize that while most birds are socially monogamous, pairing with a single member of the opposite sex, far fewer produce offspring with only one mate. It is also clear that the tendency of male songbirds to "shadow" their mates before and during the egg-laying period is an attempt to prevent extrapair matings.
(ZooGoer 25(3) 1996. Copyright 1996 Walter Piper. All rights reserved.)
