Département de Biologie, Université de Sherbrooke, Québec, Canada.
Am Nat. 2010 Oct;176(4):414-23. doi: 10.1086/656267.
Several studies of large mammals report no direct reproductive costs for females. Individual heterogeneity may hide fitness costs of reproduction, but mothers could also transfer some costs to their offspring. Using data on 442 lambs weaned by 146 bighorn sheep (Ovis canadensis) ewes at Ram Mountain, Alberta, we studied how reproductive effort varied with environmental and maternal conditions. During summer, lactating ewes should gain enough mass to survive the winter and to support their next gestation, while nursing their current lamb. We measured reproductive effort as summer mass gain by lambs corrected for maternal mass in June and maternal mass gain during summer. Females lowered their reproductive effort when population density increased and if they had weaned a lamb the previous year. A reduction in reproductive effort led to lower winter survival by lambs. Bighorn ewes have a conservative reproductive tactic and always favor their own body condition over that of their lambs. When resources are limited, ewes appear to transfer reproductive costs to their lambs, as expected from the much greater relative fitness consequences of a reduction in maternal than in offspring survival.
一些大型哺乳动物的研究报告表明，雌性没有直接的繁殖成本。个体异质性可能隐藏了繁殖的适应代价，但母亲也可以将一些成本转移给后代。利用在阿尔伯塔省拉姆斯山被 146 只大角羊（Ovis canadensis）母羊断奶的 442 只羔羊的数据，我们研究了繁殖努力如何随环境和母羊条件而变化。在夏季，哺乳期的母羊应该获得足够的体重来度过冬季并支持下一次怀孕，同时哺乳当前的羔羊。我们将羔羊在 6 月的夏季体重增加与母羊体重增加进行了校正，以此来衡量繁殖努力。当种群密度增加时，母羊会降低其繁殖努力，如果它们在前一年已经断奶了一只羔羊。繁殖努力的降低会导致羔羊在冬季的存活率降低。大角羊母羊采用保守的繁殖策略，总是优先考虑自己的身体状况，而不是羔羊的身体状况。当资源有限时，母羊似乎会将繁殖成本转移给羔羊，这与降低母羊而不是降低后代的存活率对其相对适应度的影响更大的预期相符。
