RESEARCH ARTICLE Morphological integration of anatomical, developmental, and functional postcranial modules in the crab-eating macaque (Macaca fascicularis) Mark A. Conaway 1 | Lauren Schroeder 1,2 | Noreen von Cramon-Taubadel 1 1 Buffalo Human Evolutionary Morphology Lab, Department of Anthropology, University at Buffalo, Buffalo, New York 14261 2 Department of Anthropology, University of Toronto Mississauga, L5L 1C6, Ontario, Canada Correspondence Noreen von Cramon-Taubadel, Department of Anthropology, University at Buffalo, Buf- falo, NY 14261, USA. Email: noreenvo@buffalo.edu Funding information SUNY Research Foundation Abstract Objectives: Integration and modularity reflect the coordinated action of past evolutionary proc- esses and, in turn, constrain or facilitate phenotypic evolvability. Here, we analyze magnitudes of integration in the macaque postcranium to test whether 20 a priori defined modules are (1) more tightly integrated than random sets of postcranial traits, and (2) are differentiated based on mode of definition, with developmental modules expected to be more integrated than functional or ana- tomical modules. Materials and Methods: The 3D morphometric data collected for eight limb and girdle bones for 60 macaques were collated into anatomical, developmental, and functional modules. A resampling technique was used to create random samples of integration values for each module for statistical comparison. Results: Our results found that not all a priori defined modules were more strongly integrated than random samples of postcranial traits and that specific types of modules did not present consistent patterns of integration. Rather, girdle and joint modules were consistently less integrated than limb modules, and forelimb elements were less integrated than hindlimbs. Discussion: The results suggest that morphometrically complex modules tend to be less integrated than simple limb bones, irrespective of the number of available traits. However, differences in inte- gration of the fore- and hindlimb more likely reflects the multitude of locomotory, feeding, and social functions involved. It remains to be tested whether patterns of integration identified here are primate universals, and to what extent they vary depending on phylogenetic or functional factors. KEYWORDS covariance, integration, modularity, postcranium 1 | INTRODUCTION Although many permutations of definitions exist, in general, morpho- logical integration refers to the “coordinated variation of functionally and developmentally related features of organisms” (Hallgrímsson et al., 2009; p 355). While the concept of coordinated trait variation harks back to the earliest quantitative studies of morphology (Klingenberg, 2013), the foundations of the modern concept of integration were laid by the seminal work, Morphological Integration, by Everett Olson and Robert Miller (1958). Their work set a precedent for the use of statistical correlation as a means of quantifying integration, which would later be specified to statistical comparison of variance/covari- ance and correlation matrices (Rolian and Willmore, 2009). The key aspect of the definition cited above is the coordination of morpho- logical trait variation. While generally measured in terms of trait co- variance, the coordination here refers to the interaction between functional, developmental, and evolutionary processes that create covariation (Hallgrímsson et al., 2009). Olson and Miller (1958) tested the hypothesis that highly correlated groups of traits would be equiva- lent to a priori defined so-called F-groups, created based on perceived Am J Phys Anthropol. 2018;1–10. wileyonlinelibrary.com/journal/ajpa V C 2018 Wiley Periodicals, Inc. | 1 Received: 3 August 2017 | Revised: 23 February 2018 | Accepted: 26 February 2018 DOI: 10.1002/ajpa.23456