Eigensurface analysis, ecology, and modelling of morphological adaptation in the falconiform humerus (Falconiformes: Aves)

Abstract

Studies of morphological adaptation aim to quantify the relationship between an organism's form and its ecology. In the past such studies have been hampered by an over‐reliance on either qualitative observations or the collection of a few, marginally representative two‐dimensional linear measurements as morphological descriptors. Recent advances in morphometric data acquisition and analysis techniques now provide a means of accurately and comprehensively quantifying the morphological variation inherent in complex three‐dimensional (3D) surfaces across a specimen set. Using birds of prey as a model group, we examine how one of these new morphometric methods – eigensurface analysis – can be used to investigate adaptation. Virtual models of the humerus of 50 falconiform species from 29 genera were examined to identify the morphological correlates associated with different flight styles, habitats, and behaviours of these ecologically sensitive predators. Results indicate that strong, consistent, unique, and subtle modes of shape variation are associated with differences in flight speed (fast–slow), flight style (perch hunting, chasing, low flight, soaring flight, hovering), habitat (forested–open landscape) and migratory behaviour (long‐distance migrants–sedentary species). In each case, visual modelling of between‐groups transitions in morphology can be used to facilitate identification of features of the humerus, such as the size and extent of surface‐shape variation within specific regions of muscle attachment, that are important predictors of function and lifestyle. Eigensurface analysis‐based representations of 3D morphology, in combination with standard linear discrimination techniques and new shape modelling procedures, represent a way to statistically evaluate hypotheses of morphological adaptation. This approach can be used not only for bird taxa, but more broadly in studies of ecology and adaptation in many vertebrate, invertebrate, and plant species, in ways that cannot be duplicated either by visual observation or by the representation of form using linear measurements, 2D–3D landmark coordinate sets or sets of 2D–3D boundary outline semilandmarks. © 2012 The Trustees of the Natural History Museum. Zoological Journal of the Linnean Society© 2012 The Linnean Society of London, 165, 390–419.

Comparative analysis of vestibular ecomorphology in birds

“…So far, palaeoecological inferences on the flight abilities of fossil birds have been attempted based on wing morphologies (e.g. wing loading, aspect ratio), furcula morphology and the morphology of the forelimb skeleton (Viscor & Fuster, ; Simons, ; Close & Rayfield, ; Sievwright & MacLeod, ; Taylor, ). With further study, the labyrinth might provide additional insights into avian palaeoecology.…”

Sexual Dimorphism of the Human Tibia through Time: Insights into Shape Variation Using a Surface-Based Approach

“…A somewhat larger part of the shape can be captured by semi-landmark-based approaches [11] but still relatively large portions of the bone cannot be examined and some information is lost to analysis. To overcome such limitations for bone shape research, vertebrate palaeontologists have tested grids of points fitted to 3D models in carnivoran calcanei [13], aligned digitized surfaces using correspondence points in primate calcanei [14], and applied eigensurface analysis in avian humeri [15]. …”

A Quantitative and Comparative Analysis of the Muscle Architecture of the Forelimb Myology of Diurnal Birds of Prey (Order Accipitriformes and Falconiformes)

“…Modern birds are characterized by an extreme diversity in wing morphology that reflects aspects of their biology, such as flight ability (Rayner, ; Corvidae et al, ; Liu et al, ; Brewer and Hertel, ; Wang and Clarke, ), foraging strategies (Marchetti et al, ; Corvidae et al, ; Sievwright and Macleod, ; Hertel et al, ) migratory behavior (Lockwood et al, ; Hedenström, ), and sexual selection (Hedenström and Moller, ; Schultz et al, ). Nevertheless, the qualitative traits of the musculoskeletal system of the avian forelimb are highly conserved (Ashley, ; Norberg, ; Dial, ; Simons, ), thus we would expect the diversity in flight style to manifest as quantitative features.…”

“…Birds of prey are a highly diverse group that displays different flight styles, habitats, diet, and foraging behavior throughout the taxon (Sievwright and Macleod, ). Because of this, they make a good model to study the relationship between form and function of the wing myology and its implications for flight ability.…”