THE BREEDING SYSTEM OF THE COMMON SHREW (SOREX-ARANEUS), FROM A GENETIC PERSPECTIVE

Common shrews (Sorex araneus) breed in their second calendar year, mat uring rapidly in the spring. The first oestrus is remarkably synchrono us within a site. Early-maturing males may be able to develop a more a dvantageous pattern of dispersion at the time of this oestrus than lat e-maturers. The mating system is promiscuous; cytogenetic and DNA fing erprinting studies have revealed that a particular litter may be sired by up to 6 males. Females appear to mate multiply in order to avoid i nbreeding. Indeed, there is no genetical or behavioural evidence of so cial structuring or inbreeding within sites of the type observed in th e house mouse (Mus musculus domesticus). Throughout this article we em phasise that an appreciation of the breeding system of the common shre w is important for those wishing to understand the remarkable pattern of chromosomal variation in this species.