Morphological differentiation of Anura (Amphibia) in the late ontogenesis: analysis of Rana temporaria populations from the Carpathian region

The study is devoted to the morphological features of the common frog of the Carpathian region of Ukraine, namely the expression, directionality and structure of sexual differences of this species. The work uses data obtained as a result of the processing of the scientific collection of Rana temporaria (Linnaeus, 1758) from the territory of the Ukrainian Carpathians (Lviv, Ivano-Frankivsk, and Zakarpattia oblasts), which is housed at the National Museum of Natural History, National Academy of Sciences of Ukraine (Kyiv). A total of 381 common frog specimens were studied—233 males (L = 24.6–84.5 mm) and 148 females (L = 23.2–94.2 mm). It is shown that individual differences in linear dimensions and body proportions in a sample of common frog males and females are structured and clearly reflect the morphological differentiation of individuals according to the age criterion. In the late ontogenesis of the common frog, generalised sex-related differences extend with the increasing age of individuals: in juveniles SqMD = 2.36, in subadults SqMD = 4.77, and in adults SqMD = 22.08. At the same time, not only does the expression of sex-related differences increase, but also their orientation changes significantly. According to our data, this year’s juveniles (juvenis) are individuals that did not winter at all (0+). At the same time, males are reliably (t = 4.50; p < 0.001) larger in body length (24.6–37.5 mm; Lmean = 29.87 mm) than females (23.2–32.7 mm; Lmean = 26.40 mm). But already in the group of semi-adult (subadultus) frogs, the orientation of sexual dimorphism in terms of body length changes completely—females are reliably larger than males, which is even more pronounced in adult, sexually mature individuals. Males of tailless amphibians grow and physiologically mature faster than females, so they begin to reproduce 1–2 years earlier. Females, which grow more slowly and mature later, join the reproduction having a larger size and older age. It is shown that sexual differences begin to form in the subadultus group. The generalised differences (SqMD) by sex are significantly smaller than by age. Adult sexually mature females compared to males are characterised by larger values of 18 body parameters, except for shoulder length (H.) and elbow joint diameter (Cr.a.c.), which are most reliably larger in males. These features of the proportions of the limbs provide the male with reliable holding of the female during mating (amplexus).