Can eye shape serve as a marker for sexual dimorphism in chicken? A geometric morphometric study of an indigenous chicken breed from India

Satish K. Pathak and Utkarsh K. Tripathi and Anuradha Kumari and Ajeet Singh (2025) Can eye shape serve as a marker for sexual dimorphism in chicken? A geometric morphometric study of an indigenous chicken breed from India. Морфологія, 19 (4). pp. 64-73. ISSN 1997-9665

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Abstract

Accurate sex determination in poultry is essential for successful breeding programs, efficient flock management, and economic optimization within the poultry industry. Traditional methods—such as vent sexing, feather sexing, and DNA testing—often present significant drawbacks. These techniques can be invasive, stressful for the birds, labor-intensive, or inconsistent in their accuracy, particularly in native or indigenous breeds where clear sexual di- morphism is lacking during early developmental stages. Kadaknath chickens, an indigenous and genetically distinct breed from India, are known for their unique black pigmentation. However, the subtle external differences between males and females at a young age make conventional sexing methods challenging. As a result, there is significant interest in identifying alternative, non-invasive, and accurate morphological markers for early sex differentiation in this breed. Objectives. To investigate whether eye shape can serve as a reliable, non-invasive morphological marker for sex determination in Ka- daknath chickens using geometric morphometric techniques. Methods. High-resolution lateral photographs of the right eye were captured from 16 clinically healthy adult Kadaknath chickens (9 males and 7 females), ensuring consistent imaging conditions. A total of 45 anatomically homologous landmarks were placed on each image to capture the overall shape and curvature of the eye. Geometric morphometric techniques were applied, beginning with Generalized Procrustes Analysis (GPA) to normalize the data by removing variations due to position, orientation, and scale. Principal Component Analysis (PCA) was conducted to identify the major axes of shape variation across individuals. Canonical Variate Analysis (CVA) and Discriminant Function Analysis (DFA) were used to assess the degree of sexual dimorphism and the classification accuracy of individuals based on eye shape. Results. PCA revealed that the first two principal components (PC1 and PC2) accounted for 81.35% of the total shape variation. The greatest morphological differences between sexes were observed in the ventrolateral and dorsolateral regions of the eye, suggesting localized shape changes linked to sex. CVA demonstrated statistically significant sexual dimorphism between males and females, with a Mahalanobis distance of 3.7794 and a Procrustes distance of 0.0388 (P < 0.0001), indicating clear separation in morphospace. DFA achieved perfect classification (100%) when applied to the original dataset and retained a reasonably high classification accuracy of 68.75% under leave one-out cross-validation, suggesting a strong sensitive model. Conclusions. The study provides compelling evidence that eye shape exhibits distinct and measurable sexual dimorphism in Kadaknath chickens. These results highlight the potential of geometric morphometric analysis of eye morphology as a non-invasive, low-cost, and visually based method for sex identification in this breed. Future research should focus on more extensive datasets and exploring three-dimensional (3D) imaging techniques to enhance shape characterization. Additionally, integrating machine learning algorithms with morphometric data may further improve the automation and accuracy of non-invasive poultry sexing trait in Kadaknath chickens, revealing marked morphological differences between sexes. These findings support the development of alternative, noninvasive sex determination methods for poultry with subtle sexual dimorphism.Key words: sexual dimorphism, Kadaknath, chicken, eye shape, geometric morphometrics.

Item Type:	Article
Additional Information:	DOI: 10.26641/1997-9665.2025.4.64-73
Uncontrolled Keywords:	sexual dimorphism, Kadaknath, chicken, eye shape, geometric morphometrics
Subjects:	Biology with the fundamentals of genetics Experimental medicine Morphology Metabolism
Divisions:	University periodicals > Morphology
Depositing User:	Аліна Чеботарьова
Date Deposited:	31 Mar 2026 08:27
Last Modified:	31 Mar 2026 08:27
URI:	http://repo.dma.dp.ua/id/eprint/9760

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