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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 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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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).

Mentions: The covariation independent of the relative position between the bill and cranium was explored by a PLS analysis on the residual shape coordinates of the separate fit dataset, in which the two blocks were subjected to separate Procrustes fits. The correlation between the scores of the first PLSsep vector is strong (r = 0.867, Fig. 9) and the corresponding shape changes (Fig. 10) resemble shape changes displayed by the third dimension of PLSwhole (r = 0.915, not visualized). These differences in shape represent individuals with a long, straight bill, a decreased relative palatinum length and a downward positioned cranio-facial hinge as well as downward positioned orbits, in contrast to individuals with a short, curved bill, an elongated palatinum, an upward positioned cranio-facial hinge and upward positioned orbits (Fig. 10). The correlation between the scores of the second PLSsep vector was low (r = 0.518) and therefore, the corresponding shape changes are not visualized.


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

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

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).
Mentions: The covariation independent of the relative position between the bill and cranium was explored by a PLS analysis on the residual shape coordinates of the separate fit dataset, in which the two blocks were subjected to separate Procrustes fits. The correlation between the scores of the first PLSsep vector is strong (r = 0.867, Fig. 9) and the corresponding shape changes (Fig. 10) resemble shape changes displayed by the third dimension of PLSwhole (r = 0.915, not visualized). These differences in shape represent individuals with a long, straight bill, a decreased relative palatinum length and a downward positioned cranio-facial hinge as well as downward positioned orbits, in contrast to individuals with a short, curved bill, an elongated palatinum, an upward positioned cranio-facial hinge and upward positioned orbits (Fig. 10). The correlation between the scores of the second PLSsep vector was low (r = 0.518) and therefore, the corresponding shape changes are not visualized.

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.