Age Structure and Body Size of the Plateau Brown Frog (Rana kukunoris) in the Jiuzhaigou National Nature Reserve and Potential Climatic Impacts on Its Life History Variations.

Simple Summary: Knowledge of life history traits is crucial for understanding population dynamics, biodiversity declines, and conservation management decisions. Here, we quantified the age structure and body size of the plateau brown frog (Rana kukunoris) in the Jiuzhaigou National Nature Reserve (JNNR), providing the first data about the life history traits of this species in this region. Subsequently, we compared the maximum longevity, age at sexual maturity (ASM), average age, and average snout–vent length (SVL) with those of 28 reported populations, and we examined the climatic influences on these four key life history traits. Notably, the maximum longevity in the JNNR population is 8 years, reaching the reported maximum longevity of this species. As elevation increases, the average age and ASM also increase. However, the average SVL initially increases before decreasing when above an elevation of 3000 m, which does not support Bergmann's rule. Climatic factors, particularly temperature and UV-B, have discriminative effects on the life history variations of R. kukunoris. Our results will contribute to a deeper understanding of the diverse life history strategies and the related driving forces within a species. Jiuzhaigou National Nature Reserve (JNNR) is a renowned World Biosphere Reserve and UNESCO-designated World Nature Heritage Site. The age structure and body size of a population are crucial for assessing the quality of habitats in which a population lives and are essential for the vertebrate conservation and management, especially for amphibians. Unfortunately, information about the life history traits of amphibians is currently unavailable in JNNR. Herein, we first estimated the age structure and body size of Rana kukunoris, which is endemic to the Eastern Qinghai-Xizang Plateau. Then, we compared our data with 28 reported populations along an elevation gradient (1797–3450 m) and investigated how life history traits respond to climatic variations. Our results indicated the following: (1) For individuals from JNNR, the maximum longevity is 8 years, age at sexual maturity (ASM) is 2 years, suggesting a favorable ecological environment in JNNR. Notably, females are significantly larger than males due to the age factor. (2) The average age and ASM show a positive correlation with elevation. However, when the elevation exceeds 3000 m, the average SVL initially increases and then decreases due to the harsh environmental conditions at higher elevation. (3) Temperature and/or UV-B have a significant impact on the average age, ASM, and average SVL variations of R. kukunoris, suggesting adaptive potential of this species via life history variations in light of environmental changes. These accounts provide antecedent information about the life history traits of amphibians in JNNR, and provide insights into the driving factors of the life history variations of the plateau brown frog. [ABSTRACT FROM AUTHOR]