Maternal investment increases with altitude in a frog on the Tibetan Plateau

Abstract

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.

Elevation and latitude interact to drive life‐history variation in precocial birds: a comparative analysis using galliformes

“…Although we do not have data on offspring survival or condition in high‐elevation species, increased investment in eggs with elevation has been reported across a wide variety of taxa lacking post‐hatching parental care; for example, frogs and snails breeding at high elevations lay larger eggs relative to body size and have increased reproductive investment per egg, respectively (Berven ; Baur & Raboud ; Chen et al . ).…”

Lineage diversity, morphological and genetic divergence in Daphnia magna (Crustacea) among Chinese lakes at different altitudes

“…Therefore, the morphological variation we observed between Daphnia populations from the Qinghai-Tibetan Plateau and those from lowland China might be due to phenotypic plasticity in response to the different environmental conditions, such as temperature and predator pressures. Alternatively, the different morphology of high altitude D. magna populations, when compared with those from lowland China, might be due to the unique geographical and environmental conditions there (e.g., Chen et al, 2013;Lin et al, 2008). Individual D. magna with longer heads, wider and longer bodies are more likely to survive and reproduce in the harsher environments (i.e., extremely low temperature and strong ultraviolet radiation) of the Qinghai-Tibetan Plateau.…”

“…Individual D. magna with longer heads, wider and longer bodies are more likely to survive and reproduce in the harsher environments (i.e., extremely low temperature and strong ultraviolet radiation) of the Qinghai-Tibetan Plateau. Indeed, the frog Rana kukunoris Xie, 2000 in the Qinghai-Tibetan Plateau produces larger eggs than do those from the lowlands, which allows for increased rates of embryonic development leading to earlier hatching of tadpoles (Chen et al, 2013). The larger females of R. kukunoris in high-altitude habitats produce more gelatinous matrix surrounding the eggs, which could protect embryos from temperature fluctuations and ultraviolet radiation (Chen et al, 2013).…”

Geographic variation in maternal investment and trade-offs between egg size and clutch size in an endemic toad of the Qinghai-Tibet Plateau

“…Moreover, females living in higher-altitudes must store enough energy during the short activity period in order to survive the harsh and extended winter, which may become more difficult for larger individuals. Therefore, Chen et al (2013) 4 suggested that larger females at high altitudes may be costly.…”