Sexual dimorphism in the caudal skull region of wistar albino rats: a geometric morphometric study

Abstract

Wistar albino rats are recognized as essential model organisms in biomedical research due to their anatomy and genetic homogeneity. Their relevance in morphological and developmental studies makes them ideal subjects for investigating skeletal variations, including sexually dimorphic traits. This study aimed to examine the shape variations in the caudal region of the skull in Wistar albino rats, and especially to investigate the morphological differences between the genders. A total of 60 rats (30 males and 30 female) were analysed using geometric morphometric techniques, with shape data collected with via landmark-based analysis using MorphoJ. Statistical analysis was performed with PAST software. Principal Component Analysis (PCA) identified significant sexual dimorphism, revealing distinct morphological differences between male and female rats. Comparative visual assessments showed that females had a wider foramen magnum and condylus occipitalis, a more dorsally positioned opisthocranion, and a laterally broader linea nuchae compared to males. Additionally, ANOVA confirmed the presence of significant sexual dimorphism, demonstrating that the morphological characteristics of the caudal skeleton varied distinctly between male and female Wistar albino rats. These results suggest that the caudal skull region can serve as a useful indicator of sexual dimorphism, with geometric morphometrics offering a reliable method for detecting sex-related skeletal differences. This study not only advances the understanding of sexual dimorphism in rodents but also provides a framework for further investigations in comparative anatomy and evolutionary biology.

Keywords

• Cranium
• Geometric morphometrics
• Principal component analysis
• Rattus norvegicus
• Shape analysis

References

1. Abdel-Rahman EH, Taylor PJ, Contrafatto G, et al (2009): Geometric craniometric analysis of sexual dimorphism and ontogenetic variation: A case study based on two geographically disparate species, Aethomys ineptus from southern Africa and Arvicanthis niloticus from Sudan (Rodentia: Muridae). Mamm Biol, 74, 361-373.
2. Afshan K, Rizvi SS R, Ali M, et al (2013): Geo-morphometric approaches to the study of sexual size dimorphism in muridrodents. Pak J Zool, 45, 1035-1040.
3. Afshar S, Farshid AA, Heidari R, et al (2008): Histopathological changes in the liver and kidney tissues of Wistar albino rat exposed to fenitrothion. Toxicol Ind Health, 24, 581-586.
4. Ağaç DK, Onuk B, Gündemir O, et al (2024): Comparative cranial geometric morphometrics among Wistar albino, Sprague Dawley, and WAG/Rij rat strains. Animals, 14, 1274.
5. Agrawal SS, Gullaiya S, Dubey V, et al (2012): Neurodegenerative Shielding by Curcumin and Its Derivatives on Brain Lesions Induced by 6‐OHDA Model of Parkinson′ s Disease in Albino Wistar Rats. Cardiovasc Psychiatry Neurol, 942981.
6. Batur B, Kiliçli İB, Yunus HA, et al (2025): Geometric morphometric analysis of plastinated brain sections using computer-based methods: Evaluating shrinkage and shape changes. Ann Anat, 257, 152351.
7. Becerra F, Echeverría AI, Casinos A, et al (2014): Another one bites the dust: Bite force and ecology in three caviomorph rodents (Rodentia, Hystricognathi). J Exp Zool Part A Ecol Genet Physiol boşluk + part a, 321, 220-232.
8. Berdnikovs S, Bernstein M, Metzler A, et al (2007): Pelvicgrowth: ontogeny of size and shape sexual dimorphism in rat pelves. J Morphol, 268, 12-22.

9. Bonfili N, Barbeito‐Andrés J, Bernal V, et al (2022): Morphological correspondence between brain and endocranial surfaces in mice exposed to undernutrition during development. J Anat, 241, 1-12.
10. Bookstein FL (1997): Morphometric tools for landmark data. Cambridge University Press, Cambridge.
11. Bro R, Smilde AK (2014): Principal component analysis. Anal Methods, 6, 2812-2831.
12. Caumul R, Polly PD (2005): Phylogenetic and environmental components of morphological variation: skull, mandible, and molar shape in marmots (Marmota, Rodentia). Evol, 59, 2460-2472.
13. Demiraslan Y, Demircioğlu İ, Güzel BC (2024): Geometric analysis of mandible using semilandmark in Hamdani and Awassi sheep. Ankara Univ Vet Fak Derg, 71, 19-25.
14. El-Sharkawy NI, Abd-Elhakim YM, Alklech AM (2021): Forensic toxicological study on adipocere formation in submerged cadavers of female albino rats intoxicated with cadmium. Forensic Sci Res, 6, 159-167.
15. Gürbüz İ, Demiraslan Y (2024): The Skull Shape Analysis of Wistar Albino Rats: A Geometric Morphometric Study. Kocatepe Vet J, 17, 132-141.
16. Hallgrimsson B, Mio W, Marcucio RS, et al (2014): Let's face it—complex traits are just not that simple. PLoS Genet, 10, e1004724.
17. Hammer Ø, Harper DA, Ryan PD (2001): Past: paleontological statistics software package for educaton and data anlysis. Palaeontol electronica, 4, 1.
18. Hayat NQ, Nadir S, Muneera MJ (2016): The effect of hypothyroidism on the body weight of adult albino Wistar rats. J Rawalpindi Med Coll, 20, 147-149.
19. Hedrich HJ (2020): Taxonomy and stocks and strains. In The laboratory rat. Academic Press, Cambridge.
20. Islam MM, Farag E, Mahmoudi A, et al (2021): Morphometric Study of Mus musculus, Rattus norvegicus, and Rattus rattus in Qatar. Animals, 11, 2162.
21. Johnson WL, Jindrich DL, Roy RR, et al (2008): A three-dimensional model of the rat hindlimb: Musculoskeletal geometry and muscle moment arms. J Biomech, 41, 610 - 619.
22. Kaya M, Çetinkaya MA, Besne D (2024): The quantitative evaluation of cardiac structures and major thoracic vessels dimensions by means of lateral contrast radiography in Wistar albino rats (Rattusnorvegicus). Ankara Univ Vet Fak Derg, 71, 81-87.
23. Kenawy HM, Nuñez MI, Morales X, et al (2023): Sex differences in the biomechanical and biochemical responses of caudal rat intervertebral discs to injury. JOR Spine, 6, e1299.
24. Kılıçlı İB, Batur B, Yunus HA, et al (2025): Geometric Morphometric Analysis Of Body Shape And Sexual Dimorphism in Colossoma macropomum. Ann Anat, 260, 152659.
25. Klingenberg CP (2011): MorphoJ: an integrated software package for geometric morphometrics. Molecular ecology resources, 11, 353-357.
26. König HE, Bragulla H (2007): Veterinary anatomy of domestic mammals: textbook and colour atlas. Schattauer Verlag, Stuttgart.
27. Korkmazcan A, Ünal B, Bakıcı C, et al (2025): Exploring skull shape variation and allometry across different chicken breeds. Ankara Univ Vet Fak Derg, 72, 1-7.
28. Kryštufek B, Janžekovič F, Hutterer R, et al (2016): Morphological evolution of the skull in closely related bandicoot rats: a comparative study using geometric morphometrics. Hystrix, 27, 163.
29. Küchler EC, de Lara RM, Omori MA, et al (2021): Effects of estrogen deficiency during puberty on maxillary and mandibular growth and associated gene expression – an μCT study on rats. Head Face Med, 17, 14.
30. Mortimer H (1937): Pituitary and associated hormone factors in cranial growth and differentiation in the white rat: a roentgenological study. Radiology, 28, 5-39.
31. Muraleva NA, Sadovoy MA, Kolosova NG (2011): The features of development of osteoporosis in senescence-accelerated OXYS rats. Adv Gerontol, 1, 171-178.
32. Nagar HK, Srivastava AK, Srivastava R, et al (2016): Pharmacological investigation of the wound healing activity of Cestrum nocturnum (L.) ointment in Wistar albino rats. J Pharm, 2016, 9249040.
33. Neto WK, Silva WA, Ciena AP, et al (2017): Aging induces changes in the somatic nerve and postsynaptic component without any alterations in skeletal muscles morphology and capacity to carry load of wistar rats. Front Neurosci, 11, 688.
34. Noble J, Cardini A, Flavel A, et al (2019): Geometric morphometrics on juvenile crania: Exploring age and sex variation in an Australian population. Forensic Sci Res, 294, 57-68.
35. Pogoda P, Kupfer A (2020): Sexual shape dimorphism in the cranium and pelvic girdle of northern spectacled salamanders, salamandrina perspicillata, investigated via 3d geometric morphometrics. Salamandra, 56, 113-122.
36. Rohlf FJ (2015): The tps series of software. Hystrix, 26, 9-12.
37. Rohlf JF (2018): TPS Util Ecology and Evolution. SUNY at Stony Brook.
38. Scholz J, LaLiberté C, van Eede M, et al (2016): Variability of brain anatomy for three common mouse strains. NeuroImage, 142, 656-662.
39. Semiz N, Deveci MZY (2024): Effects of common centaury (Centauriumerythraea) oil and laurel (Laurusnobilis) seed oil on full-thickness excisional skin wound healing in rats. Ankara Univ Vet Fak Derg, 71, 487-496.
40. Szadvári I, Ostatníková D, Durdiaková JB (2023): Sex differences matter: males and females are equal but not the same. Physiol Behav, 259, 114038.
41. Taylor PJ, Kumirai A, Contrafatto G (2004): Geometric morphometric analysis of adaptive cranial evolution in southern African laminate-toothed rats (Family: Muridae, Tribe: Otomyini). Durban Mus, 29, 110-122.
42. Toneva DH, Nikolova SY, Tasheva-Terzieva ED, et al (2022): Sexual dimorphism in shape and size of the neurocranium. Int J Leg, 136, 1851-1863.