Pregnancy replacement in mammals – all costs or hidden benefits for females?

许多行为过程的适应价值可能与非常具体的生物或社会情况有关。从不同哺乳动物分类群中报道的布鲁斯效应描述了妊娠终止（在该效应的原始定义中，非常早），以对抗新的未知雄性。它可能有很高的能量成本为女性，特别是如果一个更广泛的，机械性较低的终止妊娠的定义，也在怀孕的后期阶段应用。适应值一直被认为是新雄性未来潜在杀螨剂的对策（杀螨剂回避假说），但也考虑了实验室人为因素，因为在啮齿动物物种中，仅在实验室条件下报告了该效应。我们在Eccard et al. 2017中表明，在实验中，接近自然条件下的啮齿动物对中，在隔离的繁殖对中，当遇到新的雄性时，一半的测试雌性会更换怀孕，这引发了关于该过程的适应价值和生物学功能的问题。在拟议的项目中，我的目标是通过实验解开怀孕更换的潜在适应性和机制解释，重点是替代而不是终止妊娠。低人口密度迫使女性与他们的亲属繁殖，因此，在一个未知的男性移民的情况下，怀孕替代可能会让女性增加她的遗传异质性（避免近亲繁殖）。此外，这一过程可能是一种顺序择偶的机制，因此应该取决于原始和替代雄性的相对质量（雄性质量）。假设将在接近自然的条件下进行测试，并监测每只雄性的杀虫倾向。此外，将在精细的自动跟踪装置上跟踪动物的动态相互作用，以揭示妊娠替代的近端触发因素，例如配偶保护、骚扰、回避（行为、机械解释）。通过使用啮齿动物作为一个可管理的实验系统，该项目将促进我们对哺乳动物怀孕前置，女性生殖策略和性冲突的理解。

The adaptive value of many behavioural processes may relate to very specific biological or social situations. The Bruce effect reported from different mammalian taxa describes the termination of a pregnancy (very early, in the original definiton of the effect) in reaction to the confrontation to a new, unknown male. It probably has high energetic costs for the female, especially if a broader, less mechanistic definition of the pregnancy termination also in later stages of the pregnancy is applied. The adaptive value has been debated as a counterstrategy to potential future infanticide by the new male (infanticide avoidance hypothesis), but also lab artefacts were considered since in rodent species the effect was reported only from laboratory conditions. We showed in Eccard et al. 2017 that in rodent pairs under experimental, near natural conditions in isolated, breeding pairs half of the test females replaced pregnancies when encountering a new male, which raised questions about the adaptive value and biological function of the process.In the proposed project I aim to experimentally disentangle potential adaptive and mechanistic explanations for pregnancy replacements, focussing rather on the replacement then the termination of pregnancies. Low population density forces females to reproduce with their relatives, so that in the event of an immigration by an unknown male, a pregnancy replacement may allow the female to increase her genetic dissimilary to sire (inbreeding avoidance). Further, the process could be a mechanism of sequential mate choice and should thus depend on the relative quality of original and replacement male (male quality). Hypotheses will be tested in near natural conditions, and infanticidal tendencies of each male will also be monitored. Further, the dynamic interaction of the animals will be tracked on a fine scale, automated tracking devices to reveal proximate triggers of pregnancy replacement, e.g. mate guarding, harassment, avoidance (behavioural, mechanistic exlanations). By the use of rodents as a manageable, experimental system the project will advance our understanding of pregnancy preplacement in mammals, female reproductive strategies and sexual conflict.