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<p>The presence and causes of geographical gradients in body size, often linked to climate, are well-documented in animals, but their applicability and drivers in ectotherms remain a subject of debate. Given amphibians’ reliance on external heat sources and their high sensitivity to water availability, it is logical to expect that their biological traits are influenced by environmental factors acting at microhabitat and macroclimatic scales. To better understand the causes of intraspecific body size variation in ectotherms, we collected body size data from male 26 populations and females 24 populations of <i>Rana kukunoris</i>, a frog endemic to the eastern Tibetan Plateau. These populations covered the majority of the distribution range of this species, allowing us to test environmental variables to determine whether they supported our three hypotheses. Our findings reveal significant climate-driven variation in male body length, with precipitation showing a negative correlation (-0.13&#xa0;mm per 1&#xa0;mm increase), while thermal regimes exhibited contrasting effects: body length increased with minimum temperature of the coldest month (+ 5.41&#xa0;mm/℃) but decreased with mean temperature of warmest quarter (-2.83&#xa0;mm/℃). These findings suggest that geographic variation in body size reflects a trade-off between water and heat balance. We propose that size-climate relationships emerge from the interplay between thermoregulatory abilities and the benefits inherent to reduced surface-to-volume ratios in larger species, which decrease the rates of evaporative water loss and favour heat retention.</p>

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Geographic variation of body size in a plateau anuran: evidence supporting the water availability and heat balance trade-off hypothesis

  • 期刊论文

  • 发表日期：

    2025年8月19日

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  • Tong L. Yu,
  • Chao F. Gu

摘要

The presence and causes of geographical gradients in body size, often linked to climate, are well-documented in animals, but their applicability and drivers in ectotherms remain a subject of debate. Given amphibians’ reliance on external heat sources and their high sensitivity to water availability, it is logical to expect that their biological traits are influenced by environmental factors acting at microhabitat and macroclimatic scales. To better understand the causes of intraspecific body size variation in ectotherms, we collected body size data from male 26 populations and females 24 populations of Rana kukunoris, a frog endemic to the eastern Tibetan Plateau. These populations covered the majority of the distribution range of this species, allowing us to test environmental variables to determine whether they supported our three hypotheses. Our findings reveal significant climate-driven variation in male body length, with precipitation showing a negative correlation (-0.13 mm per 1 mm increase), while thermal regimes exhibited contrasting effects: body length increased with minimum temperature of the coldest month (+ 5.41 mm/℃) but decreased with mean temperature of warmest quarter (-2.83 mm/℃). These findings suggest that geographic variation in body size reflects a trade-off between water and heat balance. We propose that size-climate relationships emerge from the interplay between thermoregulatory abilities and the benefits inherent to reduced surface-to-volume ratios in larger species, which decrease the rates of evaporative water loss and favour heat retention.