Expression of fluctuating asymmetry in primate teeth: Analyzing the role of growth duration. Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of the Ohio State University By Sarah Abigail Martin, M.A. Graduate Program in Anthropology The Ohio State University 2013 Dissertation Committee: Dr. Guatelli-Steinberg, Advisor Dr. Scott McGraw Dr. Paul Sciulli Dr. Dawn Kitchen i Copyright by Sarah Abigail Martin 2013 ii Abstract This dissertation furthers our understanding of the association between growth duration and developmental noise (DN) by examining fluctuating asymmetry (FA) in a non-sexually selected and a sexually selected structure. FA occurs as small, random deviations from bilateral symmetry without any directionality between sides. Extended periods of growth may provide a ‘window of opportunity’ for growing body structures to accumulate perturbations resulting in elevated DN, manifested as FA. In comparison to other mammalian species, primates exhibit prolonged growth. Within the primate order, growth periods lengthen from prosimians to apes and humans. Although prolonged growth periods can be advantageous, lengthening of the growth period may provide the opportunity to accumulate deviations from symmetry. An association between growth duration and DN has yet to be studied across the primate order. This dissertation tested if and to what extent growth duration was associated with dental FA in primates. This potential association between growth duration and FA was first examined in the non-sexually selected first molar. First molar FA was compared between species based on crown formation times (CFTs) and life history (LH) schedules to test the hypothesis that species with prolonged CFTs or LH schedules would express greater first molar FA relative to species with shorter CFTs or LH schedules. The results generally lend support to the hypothesis; however, not all comparisons are statistically significant. ii An additional aim was to elucidate the mechanism(s) which underlie the association between FA and sexually selected structures. Sexually selected structures are prone to exhibiting elevated FA because they may be destabilized by directional selection. The primate canine has been given as one example of a sexually selected structure prone to expressing elevated FA. It is possible that the mechanisms believed to explain elevated canine FA in primates may not be associated with the destabilization of developmental processes but rather with the fact that males of sexually dimorphic species grow their canines for a longer period of time relative to their female counterparts. Two approaches were used in testing for an association between FA and sexual selection. First, canine FA was compared between males and females of a species. Generally, males of sexually dimorphic species expressed greater canine FA but not all comparisons were statistically significant. To further test this association, male canine FA was evaluated through linear regressions and controlled comparisons among males of different species. Linear regression results indicated that canine growth duration more closely predicted canine FA than variables representing sexual selection. Controlled comparisons that included great apes support the hypothesis that prolongation of growth is associated with elevated FA. An association between growth duration and FA is further supported in some but not all comparisons between males of different monkey species. Because anthropologists, and other scholars, use FA as an indicator of developmental stress, understanding what factors are associated with FA is essential to accurately intrepreting FA data. The results of this dissertation lend support to the hypothesis that growth duration contributes to dental FA in both a non-sexually selected and a sexually selected structure. iii DEDICATION I dedicate this dissertation to my mother, Christine, my father, Andrew, and my brother, Daniel. Without your love, support, and encouragement I would not have made it this far. iv ACKNOWLEDGEMENTS I wish to thank my advisor, Dr. Debbie Guatelli-Steinberg, for her intellectual support, encouragement, and enthusiasm. I am also grateful to my other dissertation committee members, Dr. Paul W. Sciulli, Dr. W. Scott McGraw, and Dr. Dawn Kitchen, for their guidance and support, as well as Dr. Gary Schwartz for providing unpublished data on dental growth of great apes. I would also like to extend my gratitude to my fellow graduate students who served as a source of support through our shared experiences. I thank everyone who provided access to the primate collections used in this dissertation: Judith Chupasko (Museum of Comparative Zoology, Harvard University), Lyman Jellema (Cleveland Museum of Natural History), Darrin Lunde (National Museum of Natural History), Bill Stanley (Field Museum), Martha Tappen (Tappen Collection, University of Minneapolis), and Eileen Westwig (American Museum of Natural History). This dissertation would not have been possible without the support from the Wenner-Gren Foundation (Grant #Gr8395), National Sigma Xi, and The Ohio State University’s Sigma Si Chapter, Critical Difference for Women Program, Graduate School, and Department of Anthropology. Finally, I am indebted to my family and friends for their love and support. I especially thank Daniel Martin, Bradley Vile, Denise Fickes, Christina Leach, Krystle Gnatz, Whitney and Matthew Senn, Jennifer Spence, Jennifer Everhart, and Jesse v Fuhrman for sharing in the joys and growing pains of life. Lastly, I thank my parents, Andrew and Christine, for always being a source of love, guidance, and support. vi VITA June 2000 .......................................................Lower Cape May Regional High School 2004................................................................B.S. Biological Sciences, Rowan University 2006................................................................M.A. Anthropology, The Ohio State University 2007-2011 ......................................................Graduate Teaching Associate, Department of Anthropology, The Ohio State University 2011-present ...................................................Lecturer, Department of Anthropology, The Ohio State University Publications Martin SA, Guatelli-Steinberg D Sciulli PW. (2011). Relationships among crown formation time, fluctuating asymmetry, and linear enamel hypoplasia in gibbons and gorillas. Presented at the 80th Annual Meeting of the American Association of Physical Anthropologists, Minneapolis, Minnesota. American Journal of Physical Anthropology 144 (S52): 207. Martin SA, Guatelli-Steinberg, D, Sciulli PW, Walker, PL. (2008). Brief Communication: Comparison of Methods for Estimating Chronological Age at Linear Enamel Formation on Anterior Dentition. American Journal of Physical Anthropology 135(3): 362-365. Fields of Study Major Field: Anthropology vii TABLE OF CONTENTS Abstract ............................................................................................................................ii Dedication ........................................................................................................................iv Acknowledgements ..........................................................................................................v Vita ...................................................................................................................................vii List of Tables ...................................................................................................................xiv List of Figures ............................................................................................................. ...xvii Chapter 1: Introduction ....................................................................................................1 Objectives ..................................................................................................................5 Hypotheses .................................................................................................................7 Hypothesis #1.......................................................................................................7 Hypothesis #2.......................................................................................................8 Hypothesis #3.......................................................................................................10 Significance................................................................................................................11 Chapter 2: Literature Review – Theoretical Context .......................................................14 Description and Causes of Fluctuating Asymmetry ..................................................18 Elevated Fluctuating Asymmetry: A Measure of Increased Developmental Noise ..............................................................................................................................20 Directional Selection, Fluctuating Asymmetry, and Sexually-Selected Structures ...26 Growth Processes and Fluctuating Asymmetry .........................................................31 viii Growth Duration and Fluctuating Asymmetry ..........................................................35 Filling in the Gaps ......................................................................................................38 Chapter 3: Literature Review – Estimating Fluctuating Asymmetry ..............................41