Factors Contributing to Behavioral Variation in Two Species of Alouatta and Their Hybrids.

Abstract

Understanding the causes of behavioral variation is critical to the study of animal behavior. This dissertation focuses on explaining behavioral variation in two species of New World primates: Alouatta pigra and A. palliata. I take advantage of a natural hybrid zone that occurs between them to examine what factors correlate with differences in social behavior and activity/movement patterns across taxonomic categories. Particularly, if behavior is constrained by ancestry, then hybrids more similar to A. pigra will exhibit “pigra-like” behaviors, while hybrids more similar to A. palliata will exhibit “palliata-like” behaviors. In Chapter One, I first describe the social behavior of the purebred animals to confirm that differences do exist between them. I then compare the behavior of the purebreds to hybrids. I found that A. pigra females exhibit greater affiliation and stay in closer proximity, as well as engage in lower levels of agonism, when compared to A. palliata females. This behavior is mirrored between pigra-like and palliata-like females (categorized by morphological similarities to the parental species). In Chapter Two, I focus on activity budgets (resting, feeding, moving) and travel distance. Again, I describe the patterns found in purebred animals and compare them to the hybrids. I found some evidence that aspects of A. pigra and A. palliata activity patterns reflected an effect of ancestry. In the hybrid zone, this ancesty effect seemed to result in pigra-like animals being less affected by environmental disturbance than palliata-like animals. In Chapter Three, I incorporated genetic analyses in order to more confidently categorize the hybrids according to their genetic ancestry and to examine whether genetic relatedness affected the social behavior patterns described in Chapter One. I used multilocus microsatellite data to calculate a hybrid index ranging from 0 to 1 (0 = A. pigra and 1 = A. palliata) for each individual and a coefficient of relatedness for each dyad. I found that differences in kinship did not predict differences in proximity and affiliation. Degree of hybridity had an effect on hybrid behavior, with genetically pigra-like females spending more time in closer proximity and engaging in more affiliation than genetically palliata-like females.