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. 2009 Jan 7:6:2.
doi: 10.1186/1742-9994-6-2.

Functional morphology and integration of corvid skulls - a 3D geometric morphometric approach

Christoph Kulemeyer  1 , Kolja Asbahr, Philipp Gunz, Sylke Frahnert, Franz Bairlein
Affiliations

Functional morphology and integration of corvid skulls - a 3D geometric morphometric approach

Christoph Kulemeyer et al. Front Zool. .

Abstract

Background: Sympatric corvid species have evolved differences in nesting, habitat choice, diet and foraging. Differences in the frequency with which corvid species use their repertoire of feeding techniques is expected to covary with bill-shape and with the frontal binocular field. Species that frequently probe are expected to have a relatively longer bill and more sidewise oriented orbits in contrast to species that frequently peck. We tested this prediction by analyzing computed tomography scans of skulls of six corvid species by means of three-dimensional geometric morphometrics. We (1) explored patterns of major variation using principal component analysis, (2) compared within and between species relationships of size and shape and (3) quantitatively compared patterns of morphological integration between bill and cranium by means of partial least squares (singular warp) analysis.

Results: Major shape variation occurs at the bill, in the orientation of orbits, in the position of the foramen magnum and in the angle between bill and cranium. The first principal component correlated positively with centroid-size, but within-species allometric relationships differed markedly. Major covariation between the bill and cranium lies in the difference in orbit orientation relative to bill-length and in the angle between bill and cranium.

Conclusion: Corvid species show pronounced differences in skull shape, which covary with foraging mode. Increasing bill-length, bill-curvature and sidewise orientation of the eyes is associated with an increase in the observed frequency in probing (vice versa in pecking). Hence, the frequency of probing, bill-length, bill-curvature and sidewise orientation of the eyes is progressively increased from jackdaw, to Eurasian jay, to black-billed magpie, to hooded crow, to rook and to common raven (when feeding on carcasses is considered as probing). Our results on the morphological integration suggest that most of the covariation between bill and cranium is due to differences in the topography of the binocular fields and the projection of the bill-tip therein, indicating the importance of visual fields to the foraging ecology of corvids.

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Figures

Figure 1
Figure 1
Landmarks and semilandmarks. Lateral view of a corvid skull with landmarks (big dots) and semilandmarks (small dots) partitioned into two blocks: bill (green) and cranium (red).
Figure 2
Figure 2
First two dimensions of the PC scores. Two-dimensional plot of the principal component scores calculated from the Procrustes shape coordinates of the full landmark set.
Figure 3
Figure 3
Shape deformations according to the first two dimensions of the PCA. The sequence of surface representations (from left to right) as deformations of the average shape correspond to increasing scores in PC 1 (a) and PC 2 (b) in Figure 2. The surface morphs differ from its neighbors by equal multiples of the standard deviation of the actual variability. The first and last column is extrapolated by 2 (a) and 4 (b) standard deviations, respectively. (a): Major variation in PC 1 lies in the relative length and curvature of the bill, in cranium height, in the position of the foramen magnum and in the position and orientation of the orbits. (b): Major variation in PC 2 lies in the angle between bill and cranium, in the position of the foramen magnum, in the position and orientation of the orbits and in bill-curvature.
Figure 4
Figure 4
Multivariate regression of shape variables on log centroid size. Three-dimensional plot of the principal component scores. The colored lines are intraspecific regressions of the shape coordinates on log centroid size and thus estimate allometry within species. The dashed line is the regression of shape coordinates on log centroid size over all species.
Figure 5
Figure 5
First dimension of the PLSwhole scores. First dimension of the partial least squares scores calculated from two landmark blocks, bill and cranium, of the whole fit dataset.
Figure 6
Figure 6
Second dimension of the PLSwhole scores. Second dimension of the partial least squares scores calculated from two landmark blocks, bill and cranium, of the whole fit dataset.
Figure 7
Figure 7
Shape deformations according to the first PLSwhole dimension. The sequence of surface representations (from left to right) as deformations of the average shape correspond to increasing scores of the first PLSwhole dimension in Figure 5. The surface morphs differ from its neighbors by equal multiples of the standard deviation of the actual variability. The first and last column is extrapolated by 4 standard deviations. Major covariation between blocks lies in bill- and cranium-length and in the orientation of the eyes.
Figure 8
Figure 8
Shape deformations according to the second PLSwhole dimension. The sequence of surface representations (from left to right) as deformations of the average shape correspond to increasing scores of the second PLSwhole dimension in Figure 6. The surface morphs differ from its neighbors by equal multiples of the standard deviation of the actual variability. The first and last column is extrapolated by 4 standard deviations. Major covariation between blocks lies in the angle between bill and cranium and in the position of the foramen magnum. (b): Exemplary representation of the positional change of the foramen magnum. The dashed line represents the dorsal margin of the foramen magnum of the consensus.
Figure 9
Figure 9
First dimension of the PLSsep scores. First dimension of the partial least squares scores calculated from two landmark blocks, bill and cranium, of the separate fit dataset.
Figure 10
Figure 10
Shape deformations according to the first PLSsep dimension. The sequence of surface representations (from left to right) as deformations of the average shape of the two blocks, bill (a) and cranium (b), correspond to increasing scores of the first PLSsep dimension in Figure 9. The surface morphs differ from its neighbors by equal multiples of the standard deviation of the actual variability. The first and last column is extrapolated by 4 standard deviations. Major covariation between blocks lies in relative bill- and palatinum length (a) and in the relative position of the cranio-facial hinge (b).
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References

    1. Holyoak D. Comparative study of food of some British Corvidae. Bird Study. 1968;15:147–153.
    1. Roell A, Bossema I. A comparison of nest defense by jackdaws, rooks, magpies and crows. Behav Ecol Sociobiol. 1982;11:1–6.
    1. Bossema I, Roell A, Baeyens G. Adaptations to interspecific competition in 5 corvid species in the Netherlands. Ardea. 1986;74:199–210.
    1. Waite RK. Winter habitat selection and foraging behaviour in sympatric corvids. Orn Scand. 1984;15:55–62.
    1. Rolando A, Peila P, Marchisio M. Foraging behaviour and habitat use in corvids wintering on farmlands in northern Italy. Avocetta. 1998;22:56–64.

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