Appendix 6 Tables from Testing predictions of inclusive fitness theory in inbreeding relatives with biparental care

Inclusive fitness theory predicts that parental care will vary with relatedness between potentially caring parents and offspring, potentially shaping mating system evolution. Systems with extra-pair paternity (EPP), and hence variable parent-brood relatedness, provide valuable opportunities to test this prediction. However, existing theoretical and empirical studies assume that a focal male is either an offspring's father with no inbreeding, or is completely unrelated. We highlight that this simple dichotomy does not hold given reproductive interactions among relatives, complicating the effect of EPP on parent-brood relatedness yet providing new opportunities to test inclusive fitness theory. Accordingly, we tested hierarchical hypotheses relating parental feeding rate to parent-brood relatedness, parent kinship and inbreeding, using song sparrows (<i>Melospiza melodia</i>) experiencing natural variation in relatedness. As predicted, male and female feeding rates increased with relatedness to a dependent brood, even controlling for brood size. Male feeding rate tended to decrease as paternity loss increased, and increased with increasing kinship and hence inbreeding between socially paired mates. We thereby demonstrate that variation in a key component of parental care concurs with subtle predictions from inclusive fitness theory. We additionally highlight that such effects can depend on the underlying social mating system, potentially generating status-specific costs of extra-pair reproduction.

广义适合度理论（inclusive fitness theory）预测，亲本抚育行为将随潜在抚育亲本与子代间的亲缘关系程度发生变化，进而可能塑造交配系统的演化轨迹。存在婚外父权（extra-pair paternity, EPP）、因而亲本与巢幼崽间亲缘关系存在变异的研究系统，为验证这一预测提供了宝贵契机。然而，现有理论与实证研究均假定，目标雄性个体要么是子代的生父且未发生近交，要么与子代完全无亲缘关系。我们指出，当亲属间存在生殖互动时，这一简单二分假定并不成立：这一情形不仅使得婚外父权对亲本-巢幼崽亲缘关系的影响更为复杂，同时也为广义适合度理论的验证提供了新的研究路径。据此，我们以存在自然亲缘关系变异的歌带鹀（Melospiza melodia）为研究对象，检验了一系列层级化假说，这些假说围绕亲本喂食速率与亲本-巢幼崽亲缘关系、亲本亲缘关系以及近交程度之间的关联展开。正如预测所示，即便控制巢幼崽数量这一变量，雌雄个体的喂食速率均随其与依赖抚育的巢幼崽间亲缘关系的提升而升高。雄性喂食速率随其失父权比例的升高呈下降趋势，同时随社会配对配偶间的亲缘关系提升（进而伴随近交程度的升高）而升高。由此，我们证实，亲本抚育核心组分的变异与广义适合度理论的精细预测相符。此外我们还强调，此类效应可能取决于物种自身的社会交配系统，进而可能产生与社会地位相关的婚外生殖适配成本。