Ecogeographical Adaptation Revisited: Morphological Variations in the Plateau Brown Frog along an Elevation Gradient on the Qinghai–Tibetan Plateau

Abstract

Several anurans have broad elevational and latitudinal distribution ranges; distinct species and populations may face various environmental and selection stresses. Due to their environmental sensitivity, adaptation is critical for the long-term persistence of anurans. Previous studies have tried to identify the ecogeographical pattern and its mechanism in anurans, suggesting different patterns, but the related explanatory mechanisms are yet to be generally supported and are suggested to be complicated. To explore the elusive mechanisms, we studied the morphological variation of the plateau brown frog (Rana kukunoris) along an elevational gradient on the eastern margin of the Qinghai–Tibetan Plateau. Using body size, extremity length, and the ratio between them (extremities/body size) as testing indicators, we examined potential ecogeographical adaptations and investigated how environmental and biological factors could shape the morphological development in R. kukunoris. We found that males and females showed different variations in body size and extremities along the elevational gradient, whereas both of them showed a decreasing extremities/body size ratio along elevation. Together with the strong correlations between environmental and biological factors and the morphometrics, we identified ecogeographical adaptation and a sexual difference in the selective pressures on the extremities and body size of the plateau brown frog. Our results imply that geographic variations in anuran morphological traits should be understood as an outcome of environmental and biological factors. Furthermore, ecogeographical adaptation in anurans can manifest as an interactive change between body size and extremities.

Morphological Variation and Its Environmental Correlates in the Taihangshan Swelled-Vented Frog across the Qinling Mountains

“…PC1, PC2 were regarded as fixed variables and sampling site as a random factor, age and sex were considered as covariates to control its impact on morphological traits. We also used the R package ‘hier.part’ to implement a hierarchical partitioning to estimate the independent contribution of each environmental variable on morphological variations [ 7 , 38 ]. Next, we used generalized additive models (GAMs) to examine environmental effects on variation in morphological traits [ 39 ].…”

“…Environmental changes can affect animals’ physiology [ 1 ], phenology [ 2 , 3 ], morphology [ 4 ], distribution [ 5 ] and life-history strategies [ 6 , 7 ]. The environmental variations across a species’ distribution range provide an opportunity to assess the adaptive potential of animals to environmental changes [ 4 , 8 , 9 ].…”

“…Notably, amphibians are particularly vulnerable to environmental stresses and changes due to their highly permeable skin, unshelled eggs, and low dispersal abilities [ 10 ]. Previous studies have explained how amphibians respond to environmental changes through different strategies, such as niche shift [ 11 , 12 , 13 ], phenological changes [ 2 , 14 ], and variations in morphological traits [ 7 , 15 , 16 ]. Morphological variations that, in particular, reflect a strong link between an organism’s fitness and processes in the community and ecosystem, can help us understand how amphibians respond adaptively to environmental stresses and changes [ 4 ].…”

“…The tendency in which increasing body size of organisms is associated with colder climates is a well-known ecogeographical rule, i.e., Bergmann’s rule [ 18 , 19 ]. Although there is no consensus on the generalization of Bergmann’s clines in amphibians [ 18 , 20 ], some studies found that decreasing temperature and precipitation promoted larger body size [ 7 , 21 ]. Furthermore, ultraviolet-B (UV-B) radiation can have diverse effects on amphibians [ 22 ].…”

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

“…As a typical explosive breeder, it breeds from March to May, with a breeding duration lasting for only 9-21 days [35]. The researches on the plateau brown frog have focused on activity characteristics [36][37][38], phylogenetic relationships [39][40][41], life history traits [35,[42][43][44], and morphological and molecular adaptations to the harsh plateau environment [45][46][47]. The plateau frog has been selected as an ideal model for understanding potential responses to climatic change, and research studies have been conducted on the age structure and body size variations of 28 populations of this species [42][43][44].…”