Bite performance and morphology in a population of Darwin's finches: implications for the evolution of beak shape

Abstract

Summary Previous studies of the Medium Ground Finch, Geospiza fortis, have documented that selection is most severe under drought conditions, which generally favour beaks that are comparatively deep and narrow. Deep beaks are presumed to enhance a bird's ability to crack hard seeds, and narrow beaks have been proposed to enhance a bird's efficiency in manipulating seeds. In the present study, we make the first direct measurements of bite force in Darwin's finches. We used 147 G. fortis from Isla Santa Cruz, Galápagos, to document the influence of beak, head and body dimensions on bite force. Among the various beak dimensions, depth, width and shape were all significant predictors of bite force. Among the various head dimensions, width was the best predictor of bite force. Generally low predictive values of multiple regression models including all morphological variables, as well as positive allometric scaling of bite force on head width, suggest an important additional role for variation in muscle architecture or jaw biomechanics in bite force generation.

Multi-layered bird beaks: a finite-element approach towards the role of keratin in stress dissipation

“…A detailed description of this setup is available in the study of Herrel et al [32][33][34]. Secondly, DSPI was used to measure the displacements of the upper beak.…”

Possible human impacts on adaptive radiation: beak size bimodality in Darwin's finches

“…This intra-specific variation has a strong additive genetic basis (Keller et al 2001) and important fitness consequences. In G. fortis populations, for example, individuals with larger beaks can bite harder (Herrel et al 2005) and are known to eat harder seeds in the wild (Grant 1986;Price 1987). As would be expected for a heritable trait with fitness consequences, G. fortis beak size evolves owing to natural selection imposed by changes in food resources.…”

Life history as a constraint on plasticity: developmental timing is correlated with phenotypic variation in birds

“…Given that developmental and genetic variation in mandible traits are often linked to adaptive performance differences (Durell, 2000;Herrel et al, 2005), our results suggest there may be differences between species in functional trait variation. Although it's possible that the variation we are detecting could be due to developmental noise (Parsons, 1990), it's likely that differences in phenotypic variation within species, regardless of the mechanism, will have consequences for both ecological and evolutionary processes (Smith and Skulason, 1996;Bolnick et al, 2011).…”

“…Similarly, rabbits reared on different diets develop entirely different jaw, palate and cranial structures (Menegaz et al, 2009;Menegaz et al, 2010), whereas pigs reared in different locomotor environments differ in joint and bone structure (Hammond et al, 2010;Congdon et al, 2012). We focus on avian bills because variation in the length, depth and width of the bill has been tied to functional variation in avian foraging, both within and between species (Grant, 1979;Smith, 1987;Benkman et al, 2001;Herrel et al, 2005). Bill development (which is tied to skeletal development) is sensitive to environmental influence after hatching (Young and Badyaev, 2007;Solem et al, 2011).…”