THE DEGREE OF EXTRA-PAIR PATERNITY INCREASES WITH GENETIC-VARIABILITY

The amount of extra-pair paternity in socially monogamous bird species varies from 0% to 76% extra-pair offspring, The causes of this remark able interspecific variation are largely unknown, although intraspecif ic analyses suggest that females seek extra-pair matings to improve th e genetic quality of their offspring. If this is a general explanation for the occurrence of extra-pair matings, then proportionally more fe males should seek to modify the paternity of their clutch when there i s more variation among males in their genetic quality. Here we test th is prediction in birds and show that interspecific variation in the pr oportion of extra-pair offspring is positively related to the proporti on of polymorphic loci as measured by protein electrophoresis, even wh en controlling for potentially confounding variables. Genetic variabil ity was also assessed, for sister pairs of species and populations dif fering significantly ire extra-pair paternity, by using random priming , which provides an estimate of genome-wide diversity. We found that g enetic diversity was higher in the populations with a higher level of extra-pair paternity, These results suggest that the amount of genetic variability in a population may be an important factor influencing ma ting patterns.