Conflict over reproduction in a cooperative mammal: an experimental approach

生活在合作社会中的动物面临着内在的利益冲突，必须以某种方式解决，才能使社会正常运转。最根本的冲突涉及到再生产的分配。动物社会在“繁殖歪斜”的程度上差异很大，“繁殖歪斜”衡量的是群体成员之间繁殖分布的均匀性。人们提出了大量的进化模型来解释为什么社会会以这种方式变化。这些模型基于不同的原理，但却做出了相似或重叠的预测，其结果是，即使对这些模型进行了最好的测试，到目前为止也没有提供任何信息。区分这些模型并提供更丰富的生殖冲突理解的最佳方法是通过实验来操纵偏差的程度。我们将在一群自由生活的带状猫鼬身上进行第一次大规模的实验，我们已经研究了11年。这个物种是不寻常的，因为几乎所有的成年雌性（多达十只）在同一个洞穴里一起分娩，后代由两性成年照顾。我们在一项初步研究中表明，我们可以使用短效避孕注射剂来阻止正在繁殖的雌性在一次繁殖尝试中怀孕，从而暂时增加偏度，同时保持群体规模和其他变量不变。对操纵的行为反应，结合对母性、繁殖成功和群体亲缘结构的遗传分析，将使我们能够衡量共同繁殖的成本，确定哪些个体对繁殖的分配施加控制，并提供有关繁殖冲突中所采用的行为机制的信息。此外，我们的实验将首次测试繁殖分布的变化与个体社会行为的变化之间的因果关系方向，这是一个重要但未经检验的扭曲和合作模型假设。

Animals that live in cooperative societies face inherent conflicts of interest which must be resolved in some way for the society to function. The most fundamental conflict concerns the distribution of reproduction. Animal societies vary enormously in the degree of 'reproductive skew', which measures the evenness with which reproduction is distributed among group members. A large number of evolutionary models have been proposed to account for why societies vary in this way. These models are based on different principles but nevertheless make similar or overlapping predictions, with the consequence that even the best attempts to test the models have up to now been uninformative. The best way to distinguish the models and provide a much richer understanding of reproductive conflict is to manipulate the degree of skew experimentally. We will carry out the first experiment of this kind large-scale on a free-living population of banded mongooses that we have studied for the last eleven years. This species is unusual because nearly all adult females (up to ten) in each group give birth together in the same den, and offspring are cared for by adults of both sexes. We have shown in a pilot study that we can use short-acting contraceptive injections to block pregnancy in breeding females for a single breeding attempt, thereby temporarily increasing the degree of skew while keeping group size and other variables constant. The behavioural responses to the manipulation, combined with genetic analyses of maternity, reproductive success and the kin structure of the group, will enable us to measure the costs of co-breeding, determine which individuals exert control over the distribution of reproduction, and provide information on the behavioural mechanisms employed in reproductive conflict. Moreover, our experiment will test for the first time the direction of causality between variation in the distribution of reproduction and variation in individual social behaviour, a important but untested assumption of models of skew and cooperation.