Comparative histomorphology and histochemistry of the skin in different morphs of the Greek smooth newt Lissotriton graecus (Urodela: Salamandridae)

In the biphasic life cycle of the smooth newts, the aquatic larvae transform into terrestrial adults, the metamorphs. The Greek smooth newt Lissotriton graecus is characterised by facultative paedomorphosis in which 2 adult morphs can coexist. Paedomorphs are reproducing adults that live in an aquatic habitat and retain some larval characteristics. In this study, histological and histochemical characteristics of the skin of the L. graecus in all morphs were investigated: larvae, paedomorphs, and metamorphs. The most remarkable finding is that skin development in paedomorphic L. graecus, whose skin is a mosaic of larval and metamorphic features, is partially uncoupled from sexual maturity. Leydig cells in the epidermis and numerous clear/vacuolated cells in the skin glands are common features of adult skin, as is the relative thickness and keratinised surface of the epidermis. Our results provide new insights into this neglected field, given the gap in the existing literature on skin development in paedomorphic urodeles. The results of this study emphasise the importance of histological investigation of the possible uncoupling of sexual and somatic development in different organ systems to achieve a deeper understanding of the complex process of paedomorphosis.