Data from: Maternal investment increases with altitude in a frog on the Tibetan plateau

Reproducing females can allocate energy between the production of eggs or offspring of different size or number, both of which can strongly influence fitness. The physical capacity to store developing offspring imposes constraints on maximum clutch volume, but individual females and populations can trade off whether more or fewer eggs or offspring are produced, and their relative sizes. Harsh environments are likely to select for larger egg or offspring size, and many vertebrate populations compensate for this reproductive investment through an increase in female body size. We report a different trade-off in a frog endemic to the Tibetan Plateau, Rana kukunoris. Females living at higher altitudes (n = 11 populations, 2000–3500 m) produce larger eggs, but without a concomitant increase in female body size or clutch size. The reduced diel and seasonal activity at high altitudes may impose constraints on the maximum body size of adult frogs, by limiting the opportunity for energy accumulation. Simultaneously, producing larger eggs likely helps to increase the rate of embryonic development, causing tadpoles to hatch earlier. The gelatinous matrix surrounding eggs, more of which is produced by large females, may help buffer developing embryos from temperature fluctuations or offer protection from ultraviolet radiation. High-altitude frogs on the Tibetan Plateau employ a reproductive strategy that favours large egg size independent of body size, which is unusual in amphibians. The harsh and unpredictable environmental conditions at high altitudes can thus impose strong and opposing selection pressures on adult and embryonic life stages, both of which can simultaneously influence fitness.繁殖期雌性个体可在不同大小或数量的卵或子代产出间分配能量，而二者均会对适合度产生显著影响。母体储存发育中子代的生理能力会对最大窝卵体积形成限制，但雌性个体与种群可在产卵/产仔的数量与子代相对大小之间进行权衡。恶劣环境往往会倾向于选择更大的卵或子代体型，许多脊椎动物种群会通过增大雌性个体体型来弥补这类生殖投入。本研究在青藏高原特有蛙类昆都仑林蛙（Rana kukunoris）中报道了一种独特的生活史权衡策略：栖息于高海拔区域（n=11个种群，海拔2000~3500米）的雌性个体所产卵粒更大，但雌性体型与窝卵量并未随之增加。高海拔环境下昼夜与季节活动时长的缩减，会通过限制能量积累的机会，对成蛙的最大体型形成限制。与此同时，产出更大的卵粒或有助于提升胚胎发育速率，使蝌蚪更早孵化。由体型较大的雌性所分泌的卵周胶状基质，可帮助发育中的胚胎抵御温度波动，或为其提供紫外线辐射防护。青藏高原高海拔蛙类采用了一种与体型无关、倾向于产出大卵粒的繁殖策略，这在两栖动物中较为罕见。因此，高海拔地区严苛且不可预测的环境条件，会对成体与胚胎两个生命阶段同时施加强烈且方向相反的选择压力，而这两个阶段均会对适合度产生影响。