Love is in the air : sociality and pair bondedness influence sifaka reproductive 1 signalling

15 Social complexity, often estimated by group size, is seen as driving the complexity of vocal 16 signals, but its relation to olfactory signals, that arguably arose to function in nonsocial realms, 17 remains underappreciated. That olfactory signals also may mediate within-group interaction, may 18 vary with social complexity, and may promote social cohesion underscores a potentially crucial 19 link with sociality. To examine that link, we integrated chemical and behavioural analyses to ask 20 if olfactory signals facilitated reproductive coordination in a strepsirrhine primate, the Coquerel’s 21 sifaka (Propithecus coquereli). Belonging to a clade comprising primarily solitary, nocturnal 22 species, the diurnal, group-living sifaka represents an interesting test case. Convergent with 23 diurnal, group-living lemurids, sifakas expressed chemically rich scent signals, consistent with 24 the social complexity hypothesis for communication. These signals minimally encoded the sex of 25 the signaler and varied with female reproductive state. Likewise, sex and female fertility were 26 reflected in within-group scent investigation, scent marking, and over-marking. We further asked 27 if, within breeding pairs, the stability or quality of the pair’s bond influenced the composition of 28 glandular signals and patterns of investigatory or scent-marking behaviour. Indeed, 29 reproductively successful pairs tended to show greater similarity in their scent signals than did 30 reproductively unsuccessful pairs, potentially through chemical convergence. Moreover, scent 31 marking was temporally coordinated within breeding pairs and was influenced by past 32 reproductive success. That olfactory signalling reflects social bondedness or reproductive history 33 lends support to recent suggestions that the quality of relationships may be a more valuable 34 proxy than group size for estimating social complexity. We suggest that olfactory signalling in 35 sifakas is more complex than previously recognized and, as in other socially integrated species, 36