Male care and life history traits in mammals

Male care has energetic and opportunity costs, and is more likely to evolve when males gain greater certainty of paternity or when future mating opportunities are scarce. However, little is known about the substantial benefits that males may provide to females and offspring. Using phylogenetic comparative methods and a sample of over 500 mammalian species, we show that mammals in which males carry the offspring have shorter lactation periods, which leads to more frequent breeding events. Provisioning the female is associated with larger litters and shorter lactation. Offspring of species with male care have similar weaning mass to those without despite being supported by a shorter lactation period, implying that they grow faster. We propose that males provide an energetic contribution during the most expensive time of female reproduction, lactation, and that different male care behaviours increase female fecundity, which in turn helps males offset the costs of caring.

雄性抚育行为（Male care）存在精力与机会成本，且更易在雄性获得更高父权确定性（certainty of paternity），或未来交配机会稀缺的情况下演化。然而，学界对雄性可为雌性与后代提供的实质性益处知之甚少。本研究采用系统发育比较法（phylogenetic comparative methods），基于超过500种哺乳动物的样本开展分析，结果显示：雄性参与抚育后代的哺乳动物类群，其泌乳期（lactation periods）更短，进而繁殖事件发生更为频繁。为雌性提供抚育补给的雄性类群，其每胎幼崽数量更多且泌乳期更短。尽管泌乳期更短，但拥有雄性抚育的物种，其后代的断奶体重（weaning mass）与无雄性抚育的物种后代并无显著差异，这意味着前者的生长速度更快。我们提出假说：在雌性繁殖成本最高的泌乳阶段，雄性会提供能量支持；且不同的雄性抚育行为可提升雌性的繁殖力，进而帮助雄性抵消抚育行为所付出的成本。