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

Kulemeyer C, Asbahr K, Gunz P, Frahnert S, Bairlein F - Front. Zool. (2009)

Bottom Line: 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).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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institut fur Vogelforschung, "Vogelwarte Helgoland", An der Vogelwarte 21, 26386 Wilhelmshaven, Germany. christoph.kulemeyer@uni-oldenburg.de.

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.

No MeSH data available.


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.
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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.

Mentions: To assess the covariation between the bill and cranium, we performed a PLS analysis on the residual shape coordinates of the whole fit dataset, in which the entire landmark set was subjected to one Procrustes fit. The relationship between the functional units is plotted as scores returned by PLSwhole in Figure 5 and 6. These graphs illustrate how well shape and relative position of one block is predicted by shape and relative position of the other (and vice versa). The PLSwhole vectors were visualized as surface deformations in Figure 7 and 8. The correlation between the scores of the first dimension is strikingly high (r = 0.923, Fig. 5) and represents the direction of integration shared by all species. Shape changes of PLSwhole 1, visualized in Figure 7, represent the difference between individuals with a long bill and cranium, an upward positioned foramen magnum as well as sidewise oriented orbits and individuals with a short bill and cranium, a downward positioned foramen magnum and forward oriented orbits.


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

Kulemeyer C, Asbahr K, Gunz P, Frahnert S, Bairlein F - Front. Zool. (2009)

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.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2651141&req=5

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.
Mentions: To assess the covariation between the bill and cranium, we performed a PLS analysis on the residual shape coordinates of the whole fit dataset, in which the entire landmark set was subjected to one Procrustes fit. The relationship between the functional units is plotted as scores returned by PLSwhole in Figure 5 and 6. These graphs illustrate how well shape and relative position of one block is predicted by shape and relative position of the other (and vice versa). The PLSwhole vectors were visualized as surface deformations in Figure 7 and 8. The correlation between the scores of the first dimension is strikingly high (r = 0.923, Fig. 5) and represents the direction of integration shared by all species. Shape changes of PLSwhole 1, visualized in Figure 7, represent the difference between individuals with a long bill and cranium, an upward positioned foramen magnum as well as sidewise oriented orbits and individuals with a short bill and cranium, a downward positioned foramen magnum and forward oriented orbits.

Bottom Line: 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).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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institut fur Vogelforschung, "Vogelwarte Helgoland", An der Vogelwarte 21, 26386 Wilhelmshaven, Germany. christoph.kulemeyer@uni-oldenburg.de.

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.

No MeSH data available.