BREEDING SYSTEM AND GENETIC VARIANCE IN THE MONOGAMOUS, SEMI-SOCIAL SHREW, CROCIDURA-RUSSULA

The population-genetic consequences of monogamy and male philopatry (a rare breeding system in mammals) were investigated using microsatelli te markers in the semisocial and anthropophilic shrew Crocidura russul a. A hierarchical sampling design over a 16-km geographical transect r evealed a large genetic diversity (h = 0.813) with significant differe ntiation among subpopulations (F-ST = 5-6%), which suggests an exchang e of 4.4 migrants per generation. Demic effective-size estimates were very high, due both to this limited gene inflow and to the inner struc ture of subpopulations. These were made of 13-20 smaller units (breedi ng groups), comprising an estimate of four breeding pairs each. Member s of the same breeding groups displayed significant coancestries (F-LS = 9-10%), which was essentially due to strong male kinship: syntopic males were on average related at the half-sib level. Female dispersal among breeding groups was not complete (similar to 39%), and insuffici ent to prevent inbreeding. From our results, the breeding strategy of C. russula seems less efficient than classical mammalian systems (poly gyny and male dispersal) in disentangling coancestry from inbreeding, but more so in retaining genetic variance.