Skin structure, coloration, and habitat utilization in typical and melanistic morphs of the grass snake (Natrix natrix).

Melanism is a polymorphic phenotype caused by the number and density of melanocyte cells producing melanin pigment in the skin and widely observed in snakes. The frequency of this coloration in populations is associated with its opposing fitness consequences and can be closely related to species-specific characteristics such as sex, reproduction, and nutrition, as well as environmental factors such as climate and geography. Although melanism is frequently seen in snakes, the skin structure of melanistic individuals has not been studied in detail. Also, the impact of the black phenotype on habitat use has not yet been clarified in this species. Here, we show a comparison of typical and melanistic morphs of the grass snake Natrix natrix population of Anatolia for the first time in terms of skin structure, habitat, and sex. We found that melanistic individuals, in which partial melanism is more abundant than total melanism, comprise 13% of the population. Melanocyte area of the skin is 1.4 times greater in melanistic compared to the typical individuals. The epidermis is thicker in typical morphs by 7.7%. Hinge regions between adjacent scales do not bare melanocytes in both morphs. As for habitat utilization, we revealed that melanistic individuals of the Isikli population tend to occur closer to water bodies than typical ones. Our data provide a new perspective on poorly known aspects of color polymorphism and habitat use of widely distributed, semi-aquatic Natrix natrix.

A study on the vertebral column of the dice snake Natrix tessellata (Serpentes, Natricidae) from Denizli (western Anatolia, Turkey).

The vertebral anatomy of snakes has attracted the attention of researchers for decades and numerous studies have been made for extinct and extant species. The present study investigated the morphological variations in vertebral structure among different vertebral regions in the dice snake Natrix tessellata, and provides a detailed anatomical and microstructural description of the vertebral column. Vertebrae were analyzed and compared using x-ray imaging, scanning electron microscopy, micro-computed tomography, and histological techniques. The vertebral column of N. tessellata is divided into three regions: precloacal, cloacal, and caudal. Unlike in many other tetrapods and snakes, the atlas of N. tessellata does not form a complete ring. It has a flat and roughly trilobate shape with a prominent middle lobe. The axis has two hypapophyses. The anterior precloacal region of the vertebral column has longer and more paddle-shaped hypapophyses, distinguishing it from the posterior and mid-trunk vertebrae. The anterior cloacal vertebrae have a short hypapophysis rather than a hemal keel, and the lymphapophysis extends outward, curving slightly. The cotyle and condyle of the caudal vertebrae exhibited a closer resemblance to a rounded shape, while the pleurapophysis extended ventrolaterally and curved ventrally near its distal end. Paired hemapophyses were present at the posterior-most point of the centrum instead of a hypapophysis. In light of previous fossil findings, our anatomical comparison of the vertebral and transverse processes indicates that the extant Natrix has a more flexible and less rigid spine than its ancestors. Overall, the vertebral differences among snake anatomical regions or taxa are a testament to the remarkable diversity and adaptability of these fascinating reptiles.