Are olfactory traits in a pair-bonded primate under sexual selection? An evaluation of sexual dimorphism in Aotus nancymaae.

OBJECTIVES: Sexual selection has seemingly influenced chemical communication in numerous non-human primates, although it is unclear whether it has influenced strictly pair-living and pair-bonded taxa. The physical similarities between male and female owl monkeys suggest that disruptive selection has not played a role in this taxon. However, given their nocturnality, olfactory traits may show differing patterns of sexual selection than visual traits. If sexual selection has influenced chemical communication in owl monkeys, we expect larger scent glands and greater scent-marking in females given the high degree of paternal care, as has been proposed for callitrichines. MATERIALS AND METHODS: We evaluated sex differences in the qualitative and quantitative descriptions of the subcaudal and perianal glandular regions of captive male (n = 39) and female (n = 36) owl monkeys (A. nancymaae), and in the olfactory behaviors performed within breeding pairs (n = 16). RESULTS: Males had larger areas of secretion retained in the hairs covering the subcaudal gland, and females had more and darker secretion than males covering the perianal region. Males inspected the genital region of their partners more frequently than females did, but the sexes did not differ much in other investigative and marking behaviors. DISCUSSION: The observed sex differences and variation in olfactory traits are consistent with the hypothesis that sexual selection has influenced chemical communication in owl monkeys, with males having larger subcaudal glands and spending more time investigating odors. Still, sex differences in monogamous owl monkeys were less extreme than those in other, non-monogamous, taxa.

Chemical composition of glandular secretions from a pair-living monogamous primate: Sex, age, and gland differences in captive and wild owl monkeys (Aotus spp.).

Broadening our knowledge of olfactory communication in strictly monogamous systems can inform our understanding of how chemosignals may facilitate social and reproductive behavior between the sexes. Compared to other social and mating systems, relatively little is known about olfactory communication in strictly monogamous non-human primates. Furthermore, platyrrhines are not well represented in chemical analyses of glandular secretions. We conducted semi-quantitative headspace gas chromatography with mass spectrometry to investigate the chemical components of glandular secretions from the subcaudal and pectoral glands of a strictly pair-living platyrrhine, the owl monkey (Aotus spp.). In this study, the first chemical analysis of a wild platyrrhine population, our goals were to (1) conduct a robust analysis of glandular secretions from both captive and wild owl monkey populations and (2) identify whether biologically relevant traits are present in glandular secretions. We also compared and contrasted the results between two Aotus species in different environmental contexts: wild Aotus azarae (N = 33) and captive A. nancymaae (N = 104). Our findings indicate that secretions from both populations encode sex, gland of origin, and possibly individual identity. These consistent patterns across species and contexts suggest that secretions may function as chemosignals. Our data also show that wild A. azarae individuals are chemically discriminated by age (adult or subadult). Among the captive A. nanycmaae, we found chemical differences associated with location, possibly caused by dietary differences. However, there was no noticeable effect of contraception on the chemical profiles of females, nor evidence that closely related individuals exhibit more similar chemical profiles in A. nancymaae. Overall, our data suggest that glandular secretions of both wild and captive Aotus convey specific information. Future studies should use behavioral bioassays to evaluate the ability of owl monkeys to detect signals, and consider whether odor may ultimately facilitate social and sexual relationships between male and female owl monkeys.

Social monogamy, male-female relationships, and biparental care in wild titi monkeys (Callicebus discolor).

Titi monkeys (Callicebus spp.) are one of two primate genera that live almost exclusively in groups with one adult-size individual of each sex and exhibit extensive biparental care of offspring. We provide a quantitative description of infant care and pairmate behavior in natural groups of Callicebus discolor that contributes to a limited literature on the behavioral ecology of wild titi monkeys. We collected data during a 3-year period from two social groups living in primary tropical rainforest at the Tiputini Biodiversity Station in Amazonian Ecuador before and after the birth of five infants. In order to evaluate the potential social and energetic costs associated with biparental care of offspring, we examined the relationships between infant care, pairmate behavior, and adult activity budgets. We found that males were almost exclusively responsible for transporting, grooming, sharing food, and playing with infants. As predicted, we found that, following the birth of an infant, adults groomed their partners less, spent less time in contact, and that huddling between pairmates decreased. Contrary to our predictions, after the birth of an infant, females did not increase the time spent feeding, and males did not decrease the time spent moving nor increase their resting time. Overall, our data suggest that the pair may experience social costs during times of intense infant care but that any putative energetic costs associated with infant care are not mitigated by adjusting physical activity. Future studies should investigate energy intake and expenditure, and consider how the variation observed in pairmate social relationships may affect reproductive success.