Individual reproductive success and effective population size in the greater white-toothed shrew Crocidura russula

In order to investigate the determinants of effective population size in th e socially monogamous Crocidura russula, the reproductive output of 44 indi viduals was estimated through genetic assignment methods. The individual va riance in breeding success turned out to be surprisingly high, mostly becau se the males were markedly less monogamous than expected from previous beha vioural data, Males paired simultaneously with up to four females and polyg ynous males had significantly more offspring than monogamous ones. The vari ance in female reproductive success also exceeded that of a Poisson distrib ution (though to a lesser extent), partly because females paired with multi ply mated males weaned significantly more offspring. Polyandry also occurre d occasionally, but only sequentially (i.e. without multiple paternity of l itters). Estimates of the effective to census size ratio were ca. 0.60, whi ch excluded the mating system as a potential explanation for the high genet ic variance found in this shrew's populations. Our data suggest that gene f low from the neighbourhood (up to one-third of the total recruitment) is th e most likely cause of the high levels of genetic diversity observed in thi s shrew's subpopulations.