An assessment of skin temperature gradients in a tropical primate using infrared thermography and subcutaneous implants.

Infrared thermography has become a useful tool to assess surface temperatures of animals for thermoregulatory research. However, surface temperatures are an endpoint along the body's core-shell temperature gradient. Skin and fur are the peripheral tissues most exposed to ambient thermal conditions and are known to serve as thermosensors that initiate thermoregulatory responses. Yet relatively little is known about how surface temperatures of wild mammals measured by infrared thermography relate to subcutaneous temperatures. Moreover, this relationship may differ with the degree that fur covers the body. To assess the relationship between temperatures and temperature gradients in peripheral tissues between furred and bare areas, we collected data from wild mantled howling monkeys (Alouatta palliata) in Costa Rica. We used infrared thermography to measure surface temperatures of the furred dorsum and bare facial areas of the body, recorded concurrent subcutaneous temperatures in the dorsum, and measured ambient thermal conditions via a weather station. Temperature gradients through cutaneous tissues (subcutaneous-surface temperature) and surface temperature gradients (surface-ambient temperature) were calculated. Our results indicate that there are differences in temperatures and temperature gradients in furred versus bare areas of mantled howlers. Under natural thermal conditions experienced by wild animals, the bare facial areas were warmer than temperatures in the furred dorsum, and cutaneous temperature gradients in the face were more variable than the dorsum, consistent with these bare areas acting as thermal windows. Cutaneous temperature gradients in the dorsum were more closely linked to subcutaneous temperatures, while facial temperature gradients were more heavily influenced by ambient conditions. These findings indicate that despite the insulative properties of fur, for mantled howling monkeys surface temperatures of furred areas still demonstrate a relationship with subcutaneous temperatures. Given that most mammals possess dense fur, this provides insight for using infrared imaging in thermoregulatory studies of wild animals lacking bare skin.

To pair or not to pair: Sources of social variability with white-faced saki monkeys (Pithecia pithecia) as a case study.

Intraspecific variability in social systems is gaining increased recognition in primatology. Many primate species display variability in pair-living social organizations through incorporating extra adults into the group. While numerous models exist to explain primate pair-living, our tools to assess how and why variation in this trait occurs are currently limited. Here I outline an approach which: (i) utilizes conceptual models to identify the selective forces driving pair-living; (ii) outlines novel possible causes for variability in social organization; and (iii) conducts a holistic species-level analysis of social behavior to determine the factors contributing to variation in pair-living. A case study on white-faced sakis (Pithecia pithecia) is used to exemplify this approach. This species lives in either male-female pairs or groups incorporating "extra" adult males and/or females. Various conceptual models of pair-living suggest that high same-sex aggression toward extra-group individuals is a key component of the white-faced saki social system. Variable pair-living in white-faced sakis likely represents alternative strategies to achieve competency in this competition, in which animals experience conflicting selection pressures between achieving successful group defense and maintaining sole reproductive access to mates. Additionally, independent decisions by individuals may generate social variation by preventing other animals from adopting a social organization that maximizes fitness. White-faced saki inter-individual relationships and demographic patterns also lend conciliatory support to this conclusion. By utilizing both model-level and species-level approaches, with a consideration for potential sources of variation, researchers can gain insight into the factors generating variation in pair-living social organizations.

Non-monogamous copulations and potential within-group mating competition in white-faced saki monkeys (Pithecia pithecia).

Many primates display within-species variation in social organization and mating system. Individuals of these species may be confronted with both the challenges of between-group competition to exclude same-sex competitors as well as within-group competition for mating opportunities. Free-ranging white-faced saki monkeys (Pithecia pithecia) live in both male-female pairs and small multi-male, multi-female groups. Despite commonly held views that this species is monogamous, there are currently no published accounts of mating patterns in the genus Pithecia. I recorded copulations and sexual behavior from three free-ranging groups of white-faced sakis at Brownsberg Naturepark, Suriname over a period of 17 months. Groups displayed both monogamous and polygynandrous mating. Individuals in polygynandrous groups were not observed to mate more frequently with certain partners. Copulation harassment occurred in 8.6% of copulations (total N = 81) and was performed by both sexes. This harassment successfully prevented ejaculation in six out of seven instances and harassment by males resulted in male-male aggression on four occasions. Two cases of female-directed sexual aggression by males were also observed, which may indicate that males use sexual coercion to influence female mating behavior. Although based on a small number of groups, these data show that white-faced sakis display variability in mating system and that this variability is not directly dictated by social organization. Furthermore, groups with promiscuous copulations exhibit behaviors indicative of within-group mating competition.