Comparative analysis of the cranium in domestic geese and ducks by osteometric and geometric morphometry methods

In this study, domestic geese, which are hybrids of Turkey's native breeds, and domesticated Aylesbury ducks, bred in Turkey, were selected to perform both species and sexual dimorphism comparisons based on cranial morphology. In accordance with this purpose, a total of 40 domestic goose samples (20 females and 20 males) and 40 domestic duck samples (19 females and 21 males) were collected. The skulls of all 80 specimens were prepared under appropriate laboratory conditions to expose the cranium bones. Osteometric and geometric morphometric analysis were conducted on these samples. Two dimensional osteometric measurements were obtained using digital caliper. These are statistically analyzed through ANOVA, discriminant function analysis (DFA), and multiple regression analysis. The skull was scanned using a 3D scanning device. Three-dimensional measurements were acquired using landmark placement. Subsequently, it was processed for statistical evaluation using principal component analysis (PCA) and ANOVA. Additionally, the Procrustes distances of the samples were assessed. The results revealed statistically significant interspecific differences and shape variations, predominantly in the neurocranial region, between the domestic goose and domestic duck groups (P<0.05). The cranium of domestic geese was found wider and higher compared to that of domestic ducks. Significant sexual dimorphism was also detected within the domestic goose group (P<0.05), with males exhibiting larger craniums than females. In domestic ducks, DFA revealed a distinction between sexes, and ANOVA indicated statistically significant differences in three linear measurements (P<0.05). However, no significant differences were observed in terms of shape variation or centroid size. Another objective of the study was, comparing osteometric and geometric morphometric methodologies. The strengths and limitations of each method were evaluated, and it was concluded that both approaches complement each other effectively. This conclusion is supported by the fact that the two dimensional osteometric and three dimensional geometric morphometric analysis yielded to a largely consistent results. Furthermore, findings that could not be fully explained by only a method were elucidated through the other, demonstrating the complementary nature of these analytical techniques.