Reproductive strategies and life-history traits of the Savi's pine vole, Microtus savii

Reproductive strategies, growth rates, survival, and their correlates with life-history traits are studied in the Savi's pine vole (Microtus savii) un der both natural and laboratory conditions. 119 reproductive events were mo nitored, 50 out of which came from wild-born females and 69 came from capti ve-born females. Fertility rates were nearly identical in both males and fe males. Mean age at first parturition of females averaged 72.6+/-12.1 days, and the mean time elapsed between the constitution of a given pair and the first partum was 31.5+/-11.5 days. The litter size of captive-bred females (2.49+/-0.7; range: 1 to 4) was nearly identical to that of the free-rangin g females (2.5+/-1.1). The newborn sex ratio did not significantly deviate from equality. Litter size was independent on season and on number of times that a given pair reproduced. Nevertheless, litter size tended to be inver sely correlated with the length of the interpartum time, and was positively correlated with parental age. The size of the litter from which the mother and the father of a given litter were generated tended to be positively co rrelated with the litter size produced by them, but only the relationship r elative to males attained statistical significance. Females first gave birt h to young at an age between 65 and 99 days. Female puberty was attained at 50.2+/-13.1 days, almost the same as male puberty (x = 47.2 +/- 11.1 days) . Females gave birth to young on average once every 29.4 days. The interpar tum time was not influenced by either female age or male age, but was short er in spring and winter (wet seasons in the Mediterranean bioclimate) than in summer and autumn (dry seasons). Mean weight of the juveniles was negati vely correlated with the litter size. The facts that litter size was consti tuted by a small number of young and that the mean gestation time was relat ively prolonged suggest that Microtus savii is a K strategist within the Mi crotinae, whereas these rodents are well known to be usually extreme r-stra tegists. In general terms, our data are consistent with those coming from o ther fossorial voles, and suggest that fossorial voles (i) give birth to a lesser number of young per litter than above-ground active voles, and (ii) have an age at puberty delayed in comparison with that of above-ground acti ve voles.