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Adaptation of anurans to the dry conditions and high predation risk in a West African savannah



Adaptation of anurans to the dry conditions and high predation risk in a West African savannah



Salamandra 33(2): 133-152



Adaptations of frogs to high temperature and unpredictable precipitation were investigated over more than five years in the savannah of the Comoe National Park, Ivory Coast (West Africa). So far, we found 35 anuran species in our research area. The following review article will present different strategies of minimization of stress under extreme climatic conditions in three frog species. Couples of Hemisus marmoratus dig into the ground near ponds. There they build a subterranean cave in which they lay their eggs. For a certain time period (from several days up to a few weeks), the female stays in the cave together with her tadpoles to provide the larvae with sufficient moisture. Thus the larvae can survive long periods of drought in between the unpredictable rainfalls. Then, after new precipitation, they reach the pond. Their shorter stay outside the pond reduces the risk of being killed by aquatic predators. Hoplobatrachus occipitalis use little rock pools on the river bank of the Comoe as spawning sites at the very beginning of the rainy season. The frogs judge the quality of the pools according to biotic (low risk of predation) and abiotic (low risk of desiccation) criteria and choose the most suitable for spawning. Thus, the frogs optimise the starting conditions for the survival of their tadpoles. Hyperolius (viridiflavus) nitidulus is sitting exposed to the sun on grassblades throughout the dry season (lasting up to four months). During this time, the frogs have to deal with high solar radiation load, evaporative water loss, and small energy reserves. Therefore, the frogs have developed extraordinary efficient ways to cope with the mentioned problems. The morphology of the skin during the rainy season, differs from that in the dry season. At the end of the rainy season, the number of iridophores increases and the guanin-pigments align in thin layers parallel to the surface of the skin. The effect of this is a total reflection of the radiated energy input. Only at the critical thermal maximum of over 43 degreeC, frogs use gland secretions of the skin for evaporative cooling.

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