Senescence and costs of reproduction in the life history of a small precocial species

Species following a fast life history are expected to express fitness costs mainly as increased mortality while slow-lived species should suffer fertility costs. Because observational studies have limited power to disentangle intrinsic and extrinsic factors influencing senescence, we manipulated reproductive effort experimentally in the cavy (Cavia aperea) which produces extremely precocial young. We created two experimental groups: One was allowed to reproduce continuously (CR), the other intermittently (IR) by removing males at regular intervals. We predicted that the CR-females should senesce (and die) earlier and produce either fewer and/or smaller, slower growing offspring per litter than those of the IR group. CR-females had 16% more litters during three years than IR-females. CR-females increased mass and body condition more steeply and both remained higher until the experiment ended. Female survival showed no group difference. Reproductive senescence in litter size, litter mass ...遵循快速生活史策略的物种，其适合度代价主要表现为死亡率升高；而慢速生活史物种则应承受生育力相关代价。由于观测研究难以厘清影响衰老的内在与外在因素，我们针对产下极端早熟幼崽的豚鼠（Cavia aperea）开展了繁殖投入操控实验。我们设置了两组实验：一组可连续繁殖（CR组），另一组通过定期移除雄性个体实现间歇繁殖（IR组）。我们预测，CR组雌性的衰老（及死亡）进程会更早，且每胎产仔数量更少、幼崽体型更小、生长速度更慢，相较于IR组雌性的后代。三年内，CR组雌性的产仔胎数比IR组多16%。CR组雌性的体重和身体状况增长更为迅速，且直至实验结束时这两项指标均保持更高水平。两组雌性个体的存活率无显著差异。胎仔数、胎仔质量方面的生殖衰老……