The Role of Social Group and Matriline on Fluctuating Asymmetry in Female Rhesus Macaques.

Fluctuating asymmetry (FA), or random deviations from symmetry, is typically thought to reflect stress during development. Therefore, FA has been used as a proxy for developmental instability in a wide variety of bilaterally symmetric organisms. The literature on FA explores a variety of environmental stressors that invoke mechanisms allowing developmental instability (temperature, food, etc.), but the role of heredity on developmental instability should not be discounted. We aimed to clarify the role of social group and matriline on FA, and thereby developmental stability, in female rhesus macaques. The Cayo Santiago macaques provide a unique opportunity to investigate the nuances of FA because of the wealth of information about the lives and deaths of each individual from the island. Further, in most cases, female rhesus macaques remain in the social group they were born into for their entire lives. We hypothesized that individuals in the same social group would exhibit similar levels of FA because they occupy similar geographical territory and are more closely related than females between social groups. Additionally, we hypothesized that individuals from higher ranking social groups will exhibit less FA than other social groups due to greater access to resources. Lastly, we hypothesized that individuals in the same matriline would exhibit more similar levels of FA to one another than other matrilines. We calculated craniofacial FA using 3D geometric morphometric techniques for 112 female macaques with known matrilines, 77 of which had known social groups. We used ANOVAs to compare mean FA between social groups and matrilines. No significantly different FA levels were observed between either (p=0.398 and p=0.752, respectively). These results indicate that genetic influence via relatedness may not have an impact on FA levels in a population and/or that FA is not distributed by social group or social group rank (though individual rank cannot be ruled out here). This work contributes to the FA literature by further parsing out the environmental and genetic influences affecting developmental instability.