Causes, consequences and evolution of inbreeding tolerance and avoidance in a cooperative mammal

众所周知，在野生种群中有时会发生近亲繁殖，这通常会导致适应性成本，但近亲繁殖的影响可能远不止近亲繁殖抑制。在最基本的层面上，近亲繁殖增加了群体成员之间的亲缘关系，这反过来又可能增加合作的好处。这个想法虽然有争议，但已经得到了相当多的理论支持。在合作繁殖的物种中，近亲繁殖的个体可能与其他群体成员关系更密切，因此可能比近亲繁殖的个体更有可能提供帮助或接受帮助。因此，近亲繁殖可能对社会群体内帮助行为的分布产生重要影响。此外，尽管近亲繁殖抑制的影响已经得到了很多研究，但对近亲繁殖的潜在原因却知之甚少。例如，人们对可能导致育种者之间高度亲缘关系的人口因素知之甚少。个体能够避免近亲繁殖的确切情况也尚不清楚。我们建议通过对一种高度合作的哺乳动物——带状猫鼬（Mungos mungo）的长期研究，利用丰富的多代数据来调查近亲繁殖的原因和后果。我们之前在这个系统上的工作已经揭示了在近亲繁殖的倾向和近亲繁殖的实现水平上有相当大的种内变异，这使得它非常适合研究近亲繁殖的自然史。因此，我们将利用一个庞大的现有分子数据集，在40个微卫星位点上对大约2000个个体进行基因分型，以构建一个长达17代的谱系。这将用于确定近亲繁殖和亲缘关系的水平，这反过来又将与近20年来连续收集的详细的基于个体的行为和表型数据联系起来。这些丰富的系谱和生活史数据将用于探索影响近亲繁殖行为的社会和遗传因素，确定雌性是否以及如何避免近亲繁殖，并确定帮助行为是否可以减轻近亲繁殖抑郁的代价。最后，我们将利用这个物种独特的“陪护”系统，在这个系统中，每一个后代都由一个成年人保护、喂养和梳理，来验证帮手优先照顾近亲繁殖的幼崽的假设。如果是这样，这将为我们对近亲繁殖促进合作繁殖哺乳动物亲缘选择的认识提供第一个实证证明。

It is well known that inbreeding sometimes occurs in wild populations, and that this usually incurs a fitness cost, but the impacts of inbreeding may go much further than inbreeding depression. At its most basic level, inbreeding increases relatedness between group members, which may in turn increase the benefits of cooperation. This idea, whilst controversial, has received considerable theoretical support. In cooperatively breeding species, inbred individuals may be more closely related to other group members and hence may be more likely to help, or to receive help, than their outbred counterparts. Consequently, inbreeding could have important impacts on the distribution of helping behavior within social groups. Furthermore, although the impacts of inbreeding depression have been much studied, the underlying causes of inbreeding are poorly understood. Little is known, for example, about the demographic factors that can lead to high levels of relatedness between breeders. The exact circumstances under which individuals are able to avoid inbreeding also remain unclear.We propose to investigate the causes and consequences of inbreeding using rich, multigenerational data from a long-term study of a highly cooperative mammal, the banded mongoose, Mungos mungo. Our previous work on this system has revealed considerable intraspecific variation in both the propensity to inbreed and the realised level of inbreeding, making it ideally suited to studying the natural history of inbreeding. Consequently, we will exploit a large existing molecular dataset of around 2000 individuals genotyped at 40 microsatellite loci to construct a pedigree up to 17 generations deep. This will be used to establish levels of inbreeding and relatedness, which in turn will be linked to detailed individual-based behavioural and phenotypic data collected continuously over almost two decades.This wealth of pedigree and life-history data will be used to explore the social and genetic factors that shape inbreeding behaviour, to establish if and how females avoid inbreeding, and to determine if whether helping behaviour can mitigate the costs of inbreeding depression. Finally, we will exploit the unique 'escorting' system of this species, in which each offspring is protected, fed and groomed by a single adult, to test the hypothesis that helpers preferentially direct care towards closely related, inbred pups. If so, this would provide the first empirical demonstration to our knowledge of inbreeding facilitating kin selection in a cooperatively breeding mammal.