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Unanswered questions about the evolution of human gender abound and are salient across the anthropological disciplines and beyond. Did adult sex-typed behavioral tendencies actually evolve? If so, when? For what purpose? The best way to gain insight into the evolution of human gender is to understand the evolution and development of sex-typed behavior in comparative primate taxa. Captive research indicates that there are many proximate factors likely to shape the development of sex-typed behavior in non-human primates—prenatal and postnatal endocrinological experience, social experience, ecological factors, and their interactions. However, it is largely unknown how sex-typed behavior proceeds and is shaped by those factors in evolutionarily salient environments. This study investigated one—whether extrinsic sexually differentiated social interactions are likely influential in the development of adult sex-typed behavior in wild-living Lemur catta. Little is known about sex-typed development in this species or in strepsirrhines in general. This research therefore addresses an important phylogenetic gap in our understanding of primate sex-typed development. Behavioral observations were carried out on mixed cross-sectional sample of adult females (n=10), adult males (n=8), yearling females (n=4), yearling males (n=4), and newborn females (n=16) and males (n=14) at Beza Mahafaly Special Reserve in southwest Madagascar from September 2008 to August 2009. Twenty-three sex-typed behaviors were identified in adults using linear mixed effects models and models of group response profiles through time. Of those, only eight had a pre-pubertal developmental component. Infants did not exhibit any sex differences in behavior, but juveniles (prepubertal, weaned individuals) resembled adults in their (relatively few) patterns of expression of sex-typed behavior. Most adult sex-typed behaviors in this species apparently develop at or after puberty and may be under gonadal hormone control. Those that develop before puberty do not likely depend on extrinsic sexually differentiation social interactions for their development, because there is no clear evidence that infants and juvenile male and females are not treated differently by others according to sex. If sexually differentiated social interactions are important for sex-typed behavioral development in subadult ,italic>Lemur catta, they are likely intrinsically (rather than extrinsically) driven.
ContributorsMeredith, Stephanie Lynn (Author) / Nash, Leanne T. (Thesis advisor) / Reed, Kaye E (Committee member) / Schwartz, Gary T (Committee member) / Arizona State University (Publisher)
Created2012
Description
Fundamental hypotheses about the life history, complex cognition and social dynamics of humans are rooted in feeding ecology - particularly in the experiences of young animals as they grow. However, the few existing primate developmental data are limited to only a handful of species of monkeys and apes. Without comparative data from more basal primates, such as lemurs, we are limited in the scope of our understanding of how feeding has shaped the evolution of these extraordinary aspects of primate biology. I present a developmental view of feeding ecology in the ring-tailed lemur (Lemur catta) using a mixed longitudinal sample (infant through adult) collected at the Beza Mahafaly Special Reserve in southwestern Madagascar from May 2009 to March 2010. I document the development of feeding, including weaning, the transition to solid food, and how foods are included in infant diets. Early in juvenility ring-tailed lemurs efficiently process most foods, but that hard ripe fruits and insects require more time to master. Infants and juveniles do not use many of the social learning behaviors that are common in monkeys and apes, and instead likely rely both on their own trial and error and simple local enhancement to learn appropriate foods. Juvenile ring-tailed lemurs are competent and efficient foragers, and that mitigating ecological risks may not best predict the lemur juvenile period, and that increases in social complexity and brain size may be at the root of primate juvenility. Finally, from juvenility through adulthood, females have more diverse diets than males. The early emergence of sex differences in dietary diversity in juvenility that are maintained throughout adulthood indicate that, in addition to reproductive costs incurred by females, niche partitioning is an important aspect of sex differential feeding ecology, and that ontogenetic studies of feeding are particularly valuable to understanding how selection shapes adult, species-typical diets. Overall, lemur juvenility is a time to play, build social relationships, learn about food, and where the kernels of sex-typical feeding develop. This study of the ontogeny of feeding ecology contributes an important phylogenetic perspective on the relationship between juvenility and the emergent foraging behaviors of developing animals
ContributorsO'Mara, Michael Teague (Author) / Nash, Leanne T. (Thesis advisor) / Reed, Kaye E (Committee member) / Schwartz, Gary T (Committee member) / Sauther, Michelle L (Committee member) / Arizona State University (Publisher)
Created2012