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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.


Related in: MedlinePlus

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.
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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.

Mentions: While the scores of PC 1 correlate positively with the log of centroid size (r = 0.927, Fig. 4) and thus reflect shape changes that are associated with differences in size, the scores of PC2 do not correlate with log centroid size (r = -0.08). Note that although rooks have higher scores in PC 1 than hooded crows, centroid size between these two species does not differ (ANOVA, p = 0.959). Thus, shape differences between rooks and hooded crows are not allometric. To explore the influence of size on skull shape, a multivariate linear regression was performed. The correlation between the vector of regression slopes and the first eigenvector of the PCA is very high (r = 0.998, Fig. 4), so that shape changes predicted by the multivariate regression with increasing centroid size resembles shape changes along PC 1. We also regressed the Procrustes shape coordinates on log centroid size for each species separately (Fig. 4). Figure 4 clearly shows that the relationship of size and shape differ markedly between species and thus from the regression vector over all species. As the number of studied individuals per species is small, shape changes that occur with increasing centroid size within species 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)

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

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

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.
Mentions: While the scores of PC 1 correlate positively with the log of centroid size (r = 0.927, Fig. 4) and thus reflect shape changes that are associated with differences in size, the scores of PC2 do not correlate with log centroid size (r = -0.08). Note that although rooks have higher scores in PC 1 than hooded crows, centroid size between these two species does not differ (ANOVA, p = 0.959). Thus, shape differences between rooks and hooded crows are not allometric. To explore the influence of size on skull shape, a multivariate linear regression was performed. The correlation between the vector of regression slopes and the first eigenvector of the PCA is very high (r = 0.998, Fig. 4), so that shape changes predicted by the multivariate regression with increasing centroid size resembles shape changes along PC 1. We also regressed the Procrustes shape coordinates on log centroid size for each species separately (Fig. 4). Figure 4 clearly shows that the relationship of size and shape differ markedly between species and thus from the regression vector over all species. As the number of studied individuals per species is small, shape changes that occur with increasing centroid size within species 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.


Related in: MedlinePlus