SEEM Seminar - Alice Baniel "Evidence of deceptive fecundity in a wild primate".

Sexual bulges in primates have long sparked debate about their function - do they reliably indicate female fertility, or do they deceptively blur it? Here, we provide evidence that female primates can manipulate sexual swellings to outwardly indicate their fertility while inwardly failing to conceive. Geladas (Theropithecus gelada) exhibit extreme sexual conflict with sexually selected infanticide. When new males take control of a group, they often kill dependent babies - a high cost for lactating females. Using 14 years of demographic and hormonal data from a population of geladas in Ethiopia, we demonstrate that after takeovers: lactating females immediately resumed external signs of fertility (e.g. sexual swellings); these swellings were much less likely to lead to conception; and all lactating females showed an increase in estrogen mediating both fertile ("true") and non-fertile ("false") swellings. Crucially, lactating females that showed sexual bulges after takeover were less likely to lose their babies to infanticide compared with those that failed. We propose a strategy whereby lactating females' sexual bulges probably range from deceptive (when babies are highly dependent) to probably honest (when babies could be successfully weaned). These results strongly support the idea that sexual bulges can deceptively confound fertility as a counter-strategy to sexual conflict.