Mating systems are studied due to their interest in ecology and evolution. In rodents, mating strategies have been inferred from the spatio-temporal arrangement of males and females, and breeding success has usually been estimated through the number of embryos counted by palpation of pregnant females. However, these might not be trustable proxies to describe the mating systems and to estimate survival rate of pups. In this study, we surveyed breeding and reproduction of the southern water vole (SWV) (Arvicola sapidus) in six ponds over a three-year period. We combined capture-mark-recapture data with parentage analyses based on 444 individual genotypes with seven microsatellites: i) to estimate reproductive rate, ii) to compare field-based and molecular estimates of the mortality rate of juveniles and the effective breeding success of adults, iii) to find individual traits or environmental conditions related to breeding success, and iv) to describe the mating system of SWV. Our results suggest that mortality rate during the pre- and post-weaning period is around 63% and 27%, respectively, and reinforce our hypothesis that the high reproductive rates in SWV compensate for the high mortality of juveniles. Parentage analyses assigned one or two parents to 80% of the target juveniles and suggest promiscuity as the mating system of SWV, probably as a strategy to minimize infanticide by males, although deviations from promiscuity might arise depending on variations of ecological factors. Weight is positively correlated with reproduction rate, as heavier (dominant) females allocate nests in better habitat patches (minimizing nest predation) and heavier (dominant) males expand their home ranges so they can have access to more mates.

由于对交配系统具有生态和进化的兴趣，因此对其进行了研究。在啮齿动物中，已从雄性和雌性的时空排列中推断出交配策略，通常通过对怀孕雌性进行触诊计数的胚胎数来估计育种成功。但是，这些可能不是描述交配系统和估计幼仔成活率的可靠代表。在这项研究中，我们调查了南方水田鼠（SWV）（Arvicola sapidus），在三年的时间里在六个池塘中。我们结合了基于444个个体基因型和七个微卫星的捕获标记捕获数据与亲子关系分析：i）估计生殖率，ii）比较实地和分子对少年死亡率和成年有效繁殖成功率的分子估计，iii）寻找与育种成功相关的个体特征或环境条件，以及iv）描述SWV的交配系统。我们的研究结果表明，断奶前和断奶后的死亡率分别约为63％和27％，这进一步证实了我们的假设，即SWV的高生殖率弥补了未成年人的高死亡率。亲子关系分析将80％的目标少年指定为一两个父母，并建议将滥交作为SWV的交配系统，尽管可能会因生态因素的不同而出现滥交情况，但这可能是尽量减少雄性杀婴的一种策略。体重与繁殖率呈正相关，因为重的（优势）雌性将巢分配在更好的栖息地中（最大程度地减少了巢的捕食），而重的（优势）雄性则扩大了家的范围，因此他们可以与更多的配偶接触。