Dušek Adam, Bartoš Luděk, Sedláček František
Department of Ethology, Institute of Animal Science, Praha, Czech Republic.
Department of Zoology, Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic.
PLoS One. 2017 Mar 22;12(3):e0173985. doi: 10.1371/journal.pone.0173985. eCollection 2017.
Litter size is one of the most reliable state-dependent life-history traits that indicate parental investment in polytocous (litter-bearing) mammals. The tendency to optimize litter size typically increases with decreasing availability of resources during the period of parental investment. To determine whether this tactic is also influenced by resource limitations prior to reproduction, we examined the effect of experimental, pre-breeding food restriction on the optimization of parental investment in lactating mice. First, we investigated the optimization of litter size in 65 experimental and 72 control families (mothers and their dependent offspring). Further, we evaluated pre-weaning offspring mortality, and the relationships between maternal and offspring condition (body weight), as well as offspring mortality, in 24 experimental and 19 control families with litter reduction (the death of one or more offspring). Assuming that pre-breeding food restriction would signal unpredictable food availability, we hypothesized that the optimization of parental investment would be more effective in the experimental rather than in the control mice. In comparison to the controls, the experimental mice produced larger litters and had a more selective (size-dependent) offspring mortality and thus lower litter reduction (the proportion of offspring deaths). Selective litter reduction helped the experimental mothers to maintain their own optimum condition, thereby improving the condition and, indirectly, the survival of their remaining offspring. Hence, pre-breeding resource limitations may have facilitated the mice to optimize their inclusive fitness. On the other hand, in the control females, the absence of environmental cues indicating a risky environment led to "maternal optimism" (overemphasizing good conditions at the time of breeding), which resulted in the production of litters of super-optimal size and consequently higher reproductive costs during lactation, including higher offspring mortality. Our study therefore provides the first evidence that pre-breeding food restriction promotes the optimization of parental investment, including offspring number and developmental success.
窝仔数是多胎（产仔）哺乳动物中最可靠的依赖状态的生活史特征之一，它表明了亲代投资情况。在亲代投资期间，随着资源可利用性的降低，优化窝仔数的倾向通常会增加。为了确定这种策略是否也受到繁殖前资源限制的影响，我们研究了实验性的繁殖前食物限制对哺乳期小鼠亲代投资优化的影响。首先，我们调查了65个实验家庭和72个对照家庭（母亲及其依赖的后代）中窝仔数的优化情况。此外，我们评估了24个实验家庭和19个对照家庭中减少窝仔数（一个或多个后代死亡）情况下的断奶前后代死亡率，以及母体与后代状况（体重）之间的关系和后代死亡率。假设繁殖前食物限制会表明食物可利用性不可预测，我们推测亲代投资的优化在实验小鼠中比在对照小鼠中更有效。与对照组相比，实验小鼠产仔数更多，后代死亡率更具选择性（与大小有关），因此窝仔减少率更低（后代死亡比例）。选择性的窝仔减少有助于实验性母亲维持自身的最佳状况，从而改善剩余后代的状况并间接提高其存活率。因此，繁殖前的资源限制可能有助于小鼠优化其综合适应性。另一方面，在对照雌性小鼠中，缺乏表明环境有风险的线索导致了“母体乐观”（在繁殖时过度强调良好条件），这导致产仔数超最佳规模，进而在哺乳期产生更高的繁殖成本，包括更高的后代死亡率。因此，我们的研究首次提供了证据，证明繁殖前食物限制促进了亲代投资的优化，包括后代数量和发育成功率。
