NO EVIDENCE OF SPERM SELECTION BY FEMALE COMMON SHREWS

There is currently much interest in the suggestion that females are ca pable of post-copulatory (or cryptic) choice for male genetic compatib ility. Here, I investigate this idea using data from mixed-paternity l itters of the common shrew (Sorer araneus). Females of this species ar e highly promiscuous and, in natural populations, regularly incur cost s of inbreeding by mating with close relatives. Selection should there fore favour female ability for sperm selection on the basis of male re latedness. No evidence was found in support of this idea. Relative num ber of offspring sired within mixed paternity litters was not signific antly correlated with genetic similarity of males to the female mated. Relative fertilization success was, however, significantly related to male epididymal sperm counts. I conclude that most variation in relat ive fertilization success of male common shrews can be explained in te rms of sperm competition, and that females of this species may not be capable of sperm selection.