Department of Arctic and Marine Biology, Faculty of Biosciences, Fisheries and Economics, University of Tromsø, 9037 Tromsø, Norway.
Ecol Appl. 2012 Jul;22(5):1628-39. doi: 10.1890/11-2181.1.
Parental allocation strategies are of profound interest in life history because they directly impact offspring fitness and therefore are highly valuable for understanding population dynamics and informing management decisions. Yet, numerous questions about reproductive allocation patterns for wild populations of large mammals remain unanswered because of the challenges for measuring allocation in the wild. Using a nine-year longitudinal data set on life-history traits of mother-calf bison pairs, we identified sources of variation in relative maternal allocation (calf mass ratio on mother mass) and assessed the occurrence of reproductive costs associated with differential maternal allocation. We found that heavy mothers provided a lower allocation but still produced heavier calves than light mothers. Older females produced lighter calves and tended to decrease allocation as they aged, supporting the occurrence of reproductive senescence. Mothers that had produced a calf the previous year produced lighter calves and allocated less than mothers that did not lactate the previous year, revealing reproductive costs. However, greater maternal allocation did not reduce the probability of breeding in successive years, and the amount of allocation provided by a mother was positively correlated among the offspring she produced, illustrating individual heterogeneity. Although life-history studies are usually classified as either supporting costs of reproduction or individual quality, our study demonstrates that these contrasting evolutionary forces can shape variation within a single trait. Our work illustrates that many processes can coevolve within a population, emphasizing the need to integrate multiple concepts to better understand the evolution of life-history traits. With regard to management of bison herds, if the goal of culling programs is to select for animals with the best performance, this research suggests that managers should account for the condition and previous reproductive status of mothers when taking culling decisions on juvenile bison.
亲代分配策略在生活史中具有深远的意义，因为它们直接影响后代的适应性，因此对于理解种群动态和为管理决策提供信息具有重要价值。然而，由于在野外测量分配的挑战，许多关于大型哺乳动物野生种群的生殖分配模式的问题仍然没有得到解答。利用九年的野牛母子对生命史特征的纵向数据集，我们确定了相对母体分配（犊牛质量与母体质量的比例）的变异来源，并评估了与差异母体分配相关的生殖成本的发生情况。我们发现，体重较重的母亲提供的分配较少，但仍比体重较轻的母亲生出的犊牛更重。年龄较大的雌性产生的犊牛较轻，随着年龄的增长，她们的分配倾向于减少，支持生殖衰老的发生。前一年生育过犊牛的母亲所生育的犊牛较轻，分配的资源也较少，前一年没有哺乳的母亲则相反，这揭示了生殖成本的存在。然而，更大的母体分配并没有降低母亲在连续几年繁殖的概率，而且母亲在其生育的后代中提供的分配量之间存在正相关，这表明了个体的异质性。尽管生活史研究通常被归类为生殖成本或个体质量的支持，但我们的研究表明，这些相互矛盾的进化力量可以塑造单一特征内的变异。我们的工作表明，许多过程可以在一个种群中共进化，这强调了需要整合多个概念，以更好地理解生活史特征的进化。就野牛群的管理而言，如果淘汰计划的目标是选择表现最好的动物，那么这项研究表明，管理者在对幼年野牛进行淘汰决策时，应该考虑到母亲的状况和以前的生殖状态。
