Age Structure of the Japanese Treefrog Dryophytes japonicas (Amphibia, Anura, Hylidae) in the Southern Part of Primorskii Krai (Russian Far East)

The results of study of the age structure of the population of the Japanese treefrog (Dryophytes japonicas) by skeletochronology are presented. The animals were captured in the vicinity of the town of Fokino and the settlement of Dunai (Primorskii krai, Russian Federation) in the second half of July 2022–2023. Cross sections of the finger phalanges were used as a registering structure. Preparations from 59 individuals (12 females and 47 males) were used for age determination. The body length of females ranged from 29.40 to 44.80 mm (on average, 38.50 ± 5.69), and males, 34.16–44.16 mm (on average, 38.30 ± 2.36). The age of females and males varied between one and four years (on average, 2.7±1.3) and between one and five years (on average, 2.2 ± 1.1), respectively. The modal age of females was four years (41.6% of all individuals studied) and males, 1–2 years (63.8%), respectively. The average age of males and females was not statistically significantly different. The body length depended on the age, in both females (r = 0.82, p < 0.05) and males (r = 0.54, p < 0.05). The life expectancy of females was 4.41 years (S = 0.744), and of that males, 3.76 years (S = 0.693). The growth of males stops after reaching sexual maturity. Females continue to grow after maturation; that is why the most adult individuals are the largest ones. The growth rate coefficient (k) was higher in males (2.22) than in females (0.89). The authors note that D. japonicas in the southern part of Primorskii krai is characterized by the minimum age of sexual maturity and lifespan among all populations studied.