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

Reproducing females can allocate energy between the production of eggs of different size or number, both of which can strongly influence fitness. Environmental conditions often drive these reproductive tradeoffs, because of direct influences on offspring survival. Many vertebrates show positive relationships between female body size and altitude, resulting in the production of larger clutches at higher altitudes. We report a different tradeoff in the high-altitude endemic frog Rana kukunoris (n=11 populations, 2000-3500 m): females living at higher altitudes produce heavier clutches of larger eggs without a concomitant increase in female body size or clutch size. Reproduction at high altitudes thus favours current reproduction at a cost to short-term maintenance and growth. The harsh environmental conditions at high altitudes can impose strong and opposing selection pressure on egg and adult life history stages.

繁殖期雌性个体可将能量分配至不同大小或数量的卵的产出环节，二者均会对进化适合度产生显著影响。环境条件往往会驱动这类繁殖权衡，因其可直接影响子代存活率。许多脊椎动物的雌性体型与海拔呈正相关关系，故而在高海拔区域会产出更多的窝卵。我们在高海拔特有蛙类昆仑侧褶蛙（Rana kukunoris，样本覆盖11个种群，采样海拔范围2000~3500米）中发现了一种独特的繁殖权衡模式：栖息于更高海拔的雌性个体所产出的卵个体更大，单窝总卵重更高，但雌性自身体型与窝卵数并未随之增加。因此，高海拔环境下的繁殖更倾向于当前繁殖投入，却以短期的身体维持与生长为代价。高海拔区域严苛的环境条件，会对卵发育阶段与成体生活史阶段施加强烈且方向相悖的选择压力。