UMR CNRS 5558 Biométrie et Biologie Evolutive, Univ Lyon, Université Claude Bernard (Lyon I), Villeurbanne, France.
Department of Aquaculture and Fish Biology, Hólar University, Sauðrkrókur, Iceland.
J Anim Ecol. 2021 Feb;90(2):471-482. doi: 10.1111/1365-2656.13380. Epub 2020 Nov 29.
In an environment with limited resources, parents may trade-off the number of offspring produced against offspring mass. To maximize fitness under unpredictable environments, females must not only maximize mean annual reproductive success but also minimize between-year variation in reproductive success. Thus, preferred strategies of maternal allocation might be to maximize the mass of their offspring or to produce a number of offspring of variable body masses. Many social species have evolved in variable and unpredictable environments where only the social environment can be predicted. If mothers seem to alter their total reproductive allocation to offspring depending on their social environment, how the total expenditure is allocated between the different offspring is still unknown. Here, we analysed how climatic and social environments influence strategies of maternal allocation and how these strategies impact pup first-year survival in a wild population of Alpine marmots monitored between 1990 and 2016. We found that females acted as income breeders using resources immediately available for reproduction. Our results showed that the proportion of maternal mass allocated to offspring varied mainly with litter size. However, how maternal allocation is shared between pups depended on climatic and social environments. In general, mothers tended to have litters of greater average mass and small variability in favourable social environments or when resources are abundant and lighter average pup mass but high variability in unfavourable social environments or when resources are scarce. This variable allocation could correspond to dynamic bet-hedging such that mothers influence the variance of pup mass within the litter in response to poor current environmental conditions. Our analysis of first-year survival showed that females should maximize the body mass of their young whatever the conditions will be because pups of higher mass have higher survival, regardless of environmental conditions. When resources are scarce, this strategy might not be achievable for all pups so that mothers produced variable pups. In large litters, this strategy increased first-year survival. Because pup variability affects parental fitness, differential allocation between pups of the same litter could have large consequences on fitness and thus on reproductive strategies of social species.
在资源有限的环境中，父母可能会权衡生育的后代数量和后代质量。为了在不可预测的环境中最大限度地提高适应性，雌性动物不仅要最大限度地提高平均年度繁殖成功率，还要最大限度地减少繁殖成功率的年际变化。因此，母体分配的首选策略可能是最大限度地增加后代的质量，或者产生具有不同体质量的后代数量。许多社会物种在变化和不可预测的环境中进化，只有社会环境可以预测。如果母亲似乎根据社会环境改变其对后代的总繁殖分配，那么总支出在不同后代之间的分配方式仍不清楚。在这里，我们分析了气候和社会环境如何影响母体分配策略，以及这些策略如何影响在 1990 年至 2016 年间监测的野生阿尔卑斯山土拨鼠群体中幼崽的第一年存活率。我们发现，雌性动物作为收益繁殖者，利用可立即用于繁殖的资源。我们的结果表明，母体质量分配给后代的比例主要随窝仔数而变化。然而，母体分配在幼崽之间的共享方式取决于气候和社会环境。一般来说，在有利的社会环境或资源丰富时，母亲倾向于生育平均质量较大且变异性较小的窝仔；而在不利的社会环境或资源稀缺时，母亲倾向于生育平均质量较轻但变异性较高的窝仔。这种可变的分配可能对应于动态套期保值，即母亲根据当前环境条件的好坏，影响窝仔内幼崽质量的变异性。我们对第一年存活率的分析表明，无论条件如何，母亲都应该使幼崽的体重最大化，因为体重较大的幼崽存活率更高，而与环境条件无关。在资源稀缺的情况下，这种策略可能无法为所有幼崽实现，因此母亲会产生具有不同体质量的幼崽。在较大的窝仔中，这种策略提高了第一年的存活率。由于幼崽的变异性会影响亲代适应性，同一窝仔中幼崽之间的差异分配可能会对适应性和社会物种的繁殖策略产生重大影响。
