Baby on board: olfactory cues indicate pregnancy and fetal sex in a non-human primate

Olfactory cues play an integral, albeit underappreciated, role in mediating vertebrate social and reproductive behaviour. These cues fluctuate with the signaller's hormonal condition, coincident with and informative about relevant aspects of its reproductive state, such as pubertal onset, change in season and, in females, timing of ovulation. Although pregnancy dramatically alters a female's endocrine profiles, which can be further influenced by fetal sex, the relationship between gestation and olfactory cues is poorly understood. We therefore examined the effects of pregnancy and fetal sex on volatile genital secretions in the ring-tailed lemur (Lemur catta), a strepsirrhine primate possessing complex olfactory mechanisms of reproductive signalling. While pregnant, dams altered and dampened their expression of volatile chemicals, with compound richness being particularly reduced in dams bearing sons. These changes were comparable in magnitude with other, published chemical differences among lemurs that are salient to conspecifics. Such olfactory ‘signatures’ of pregnancy may help guide social interactions, potentially promoting mother–infant recognition, reducing intragroup conflict or counteracting behavioural mechanisms of paternity confusion; cues that also advertise fetal sex may additionally facilitate differential sex allocation.

嗅觉线索在介导脊椎动物社会与繁殖行为的过程中扮演着不可或缺却常被低估的核心角色。这类线索会随信号发送者的激素状态发生波动，其变化与个体繁殖状态的多项关键特征高度同步并传递相关信息，例如青春期启动、季节更替，以及雌性个体的排卵时机。尽管妊娠会显著改变雌性的内分泌特征，且胎儿性别可进一步对该特征产生影响，但目前学界对妊娠与嗅觉线索之间的关联仍知之甚少。为此，我们以环尾狐猴（Lemur catta）——一种具备复杂繁殖信号嗅觉传递机制的原猴类（strepsirrhine）灵长动物——为研究对象，探究了妊娠与胎儿性别对其生殖器挥发性分泌物的影响。研究发现，妊娠期间母体会调整并抑制挥发性化学物质的表达，其中产雄性后代的母体其化合物丰度降低尤为显著。这类变化的幅度与已发表文献中记载的、对狐猴同类具有显著生物学意义的种内化学差异幅度相当。此类妊娠相关的嗅觉‘特征标记’或可用于调控社会互动，或能促进母婴识别、减少群体内部冲突，或是抵消父权混淆的行为机制；而能够传递胎儿性别的线索，还可能辅助实现性别分配的差异化调控。