What is bred in the bone: Ecomorphological associations of pelvic girdle form in greater Antillean Anolis lizards

Abstract

Ecological niche partitioning of Anolis lizards of the Greater Antillean islands has been the focus of many comparative studies, and much is known about external morphological convergence that characterizes anole ecomorphs. Their internal anatomy, however, has rarely been explored in an ecomorphological context, and it remains unknown to what degree skeletal morphology tracks the diversity and ecological adaptation of these lizards. Herein, we employ CT scanning techniques to visualise the skeleton of the pelvic girdle in situ, and 3D geometric morphometrics to compare the form of the ilium, ischium, and pubis within and between ecomorphs. We examine 26 species of anoles representing four ecomorphs (trunk-ground, trunk-crown, crown-giant, twig) from three islands (Jamaica, Hispaniola, and Puerto Rico). The subtle variations in pelvic girdle morphology discovered are directly associable with all three parameters that we set out to focus on: phylogenetic relationship, specimen size, and assigned ecomorph category. Morphometric variation that correlates with size and/or phylogenetic signal varies between species and cannot be eliminated from the data set without markedly reducing its overall variability. The discovered patterns of skeletal variation are consistent with the demands of locomotor mechanics pertinent to the structural configuration of the microhabitat of three of the four ecomorphs, with the fourth having no discernible distinctive features. This manifests itself chiefly in the relative anteroposterior extent and anteroventral inclination of the ilium and pubis, which differ between ecomorphs and are postulated to reflect optimization of the direction of muscle vectors of the femoral protractors and retractors. Our investigation of the form of the pelvic girdle of anoles allows us to generalize our findings to entire ecomorph categories within a broad phylogenetic and biogeographic context. Differences in the form and configuration of the postcranial skeleton are directly related to ecological patterns.

Plasticity and evolutionary convergence in the locomotor skeleton of Greater Antillean Anolis lizards

“…We acknowledge that the ecomorph classification does not always rely on well-documented habitat use ( Poe and Anderson, 2019 ), but there is a very close concordance between classification based on habitat use ( Nicholson et al, 2012 ) and classification that also includes gross morphology, such as the total length of limbs, head size and tail length ( Losos, 2009 ). We quantified shape using 18 3D landmarks each on the pectoral and the pelvic girdle (partially adapted from Tinius and Russell, 2014 ; Tinius et al, 2018 ; Supplementary file 1A ), and measured the length of 15 limb elements of fore- and hindlimb, as well as the cortical thickness and bone diameter in virtual cross-sections of the four long bones ( Figure 1B ). We used the centroid size of the pelvic girdle as a proxy for body size.…”

Peer Review #2 of "Lower rotational inertia and larger leg muscles indicate more rapid turns in tyrannosaurids than in other large theropods (v0.2)"

“…In such interspecific comparisons, morphometrics establish correlation between general muscle origin size and locomotor ecomorphologies (Moen et al 2013(Moen et al , 2016Tinius et al 2018).…”

Enhanced locomotor performance on familiar surfaces is uncoupled from morphological plasticity in Anolis lizards

“…Studies of anoles transplanted to islands (Losos, Warheit, & Schoener, 1997) or colonizing new habitats (e.g., urban environments; Kolbe, Battles, & Avilés‐Rodríguez, 2016; Winchell, Reynolds, Prado‐Irwin, Puente‐Rolon, & Revell, 2016) suggest that changes in morphology and behavior that are concordant with such functional demands can evolve within a few generations. While ecomorphs also differ in the shape of pectoral (shoulder) and pelvic (hip) girdles (Herrel, Vanhooydonck, Porck, & Irschick, 2008; Tinius & Russell, 2014; Tinius, Russell, Jamniczky, & Anderson, 2018), it is not known to what extent this variation is functionally related to locomotion.…”