Complex patterns of geographic variation in heat tolerance and Hsp70 expression levels in the common frog Rana temporaria

1.We tested for geographical variation in heat tolerance and Hsp70 expression levels of Rana temporaria tadpoles along a 1500 km long latitudinal gradient in Sweden.2.Temperature tolerance of the hatchling tadpoles did not differ among populations, but they tolerated stressful hot temperatures better than 2 weeks older tadpoles.3.Among 2-week old tadpoles, the southern population tolerated 32 °C better than tadpoles from other populations. A parallel difference was found in Hsp70 expression, with the southern population showing the highest expression level. Nevertheless, at a highly stressful temperature (36 °C) the northern population showed highest tolerance.4.The heat shock pre-treatment increased heat tolerance of the tadpoles. The possible adaptive role of Hsp70 for thermal tolerance and climatic adaptation in R. temporaria tadpoles is discussed.