Morphological integration and evolutionary potential of the primate shoulder: Variation among taxa and implications for genetic covariances with the basicranium, pelvis, and arm

Morphology, evolution, and the whole organism imperative: Why evolutionary questions need multi‐trait evolutionary quantitative genetics

“…Most of this variation is likely associated with sexual dimorphism, and so accounting for those effects is essential. Likewise, we are looking for the effects of trait covariance independent of body size, and so size-correction is also necessary so that our estimates are not swamped by variance attributable to body mass (see Agosto & Auerbach, 2022;Grabowski, 2013;Grabowski et al, 2011;Rolian, 2009), even though this method does not entirely remove the effects of body size on trait covariances S1. AMIB, anterior margin of iliac blade; ASL, auricular surface length; AW, acetabular width; BFML, foramen magnum length; CLML, maximum length of clavicle; FAPD, anteroposterior diameter of femoral diaphysis; FHD, femoral head anteiroposterior diameter; FML, maximum length of femur; FMLD, mediolateral diameter of femoral diaphysis; FMW, foramen magnum width; GW, width of glenoid fossa of scapula; HDW, distal articular width; HEW, epicondylar width; HML, maximum length of humerus; LCH, lateral epicondyle height; LIH, lower iliac height; MCH, medial epicondyle height; NR, nuchal region; RAH, retroauricular height; RAPD, anterioposteiror diameter of radial diaphysis; RDA, mediolateral breadth of distal articular surface; RHDAP, mediolateral diameter of radial head; RMLD, mediolateral diameter of radial diaphysis; RMLS, length of radius; SBL, length of lateral border of scapula; SCM, sternocleidomastoid attachment; SNL, superior nuchal line; SSL, length of scapular spine; TAPD, anteroposterior diameter of tibial diaphysis; TDA, mediolateral breadth of tibial distal articulation; TFL, length of tibia; TMLD, mediolateral diameter of tibial diaphysis; TPB, mediolateral width of tibial plateau; VBA, superior vertebral border of scapula; VBB, inferior vertebral border of scapula.…”

“…As we reviewed in the previous section, studies have investigated genetic and evolutionary relationships across several, but not all, of the seven anatomical regions included in the analysis we present below. Most relevant to our study here, Agosto and Auerbach (2022) investigated these relationships between the basicranium, limb girdles, and the humerus and found evidence of potential genetic and evolutionary constraint between the basicranium and limb girdles in humans and other primates. While there is mutual evolutionary constraint among the limb girdles and basicranium, it is unknown how these may relate to traits of the upper or lower limbs.…”

“…As we and others have noted in recent years, however, examining morphological dimensions in isolation uses an implicit evolutionary model in which traits are genetically independent. In fact, most morphological complex traits, just as the environmental and functional variables thought to shape them, are interrelated and thus genetically non‐independent (e.g., Agosto & Auerbach, 2021, 2022; Green et al, 2017; Machado et al, 2018; Mallard et al, 2017; Rolian, 2009; Savell et al, 2016; Young et al, 2019).…”

“…One such distinction from historical precedent in biological anthropology is that researchers over the last 15 years have begun to apply quantitative genetic methods to disentangle the evolutionary processes responsible for shaping morphological variation (e.g., Agosto & Auerbach, 2021, 2022; Baab, 2018; Betti et al, 2013; Katz et al, 2016; Lewton, 2012; Madrigal & Willoughby, 2010; Rolian, 2009; Rolian et al, 2010; Roseman, 2016; Roseman & Auerbach, 2015; Savell, 2020; Savell et al, 2016, 2022; Schroeder & von Cramon‐Taubadel, 2017; Villamil, 2018; von Cramon‐Taubadel, 2019). Methods based on quantitative genetic evolutionary models (especially following Cheverud, 1984; Lande, 1979; Lande & Arnold, 1983) provide the only avenue for distinguishing trait responses to natural selection from the effects of stochastic and/or neutral evolutionary processes while also examining how those traits interact (covary) with each other, and how that covariance affects evolutionary outcomes.…”

“…Traits belonging to a single organism necessarily covary with each other beyond effects of scaling (e.g., are morphologically integrated), but the nature of these relationships must be observed when tested against specific evolutionary models. Indeed, evidence suggests that morphological variation in a single given trait is influenced by both the direct response of that trait to evolutionary forces acting upon it, as well as by the indirect responses of evolution acting on other traits with which the original trait covaries (Arnold, 1983; Hansen & Houle, 2008; Lande, 1979; Lande & Arnold, 1983; see examples in Agosto & Auerbach, 2022; Grabowski, 2013; Houle & Rossoni, 2022; Lewton, 2012; Love et al, 2022; Rolian, 2009, 2020a; Savell et al, 2016; Villmoare et al, 2011). With a quantitative genetic approach, we can explore potential evolutionary relationships that are not able to be examined using traditional trait‐by‐trait methods.…”