Factors behind intraspecific variation in sensitivity to pathogens remain poorly understood. We investigated how geographical origin in two North European amphibians affects tolerance to infection by the chytrid fungus Batrachochytrium dendrobatidis (Bd), a generalist pathogen which has caused amphibian population declines worldwide. We exposed newly metamorphosed individuals of moor frog Rana arvalis and common toad Bufo bufo from two latitudinal regions to two different BdGPL strains. We measured survival and growth as infections may cause sub-lethal effects in fitness components even in the absence of mortality. Infection loads were higher in B. bufo than in R. arvalis, and smaller individuals had generally higher infection loads. B. bufo had high mortality in response to Bd infection, whereas there was little mortality in R. arvalis. Bd-mediated mortality was size-dependent and high-latitude individuals were smaller leading to high mortality in the northern B. bufo. Bd exposure led to sub-lethal effects in terms of reduced growth suggesting that individuals surviving the infection may have reduced fitness mediated by smaller body size. In both host species, the Swedish Bd strain caused stronger sublethal effects than the British strain. We suggest that high-latitude populations can be more vulnerable to chytrids than those from lower latitudes and discuss the possible mechanisms how body size and host geographical origin contribute to the present results.

对病原体敏感性的种内变异背后的因素仍然知之甚少。我们研究了两种北欧两栖动物的地理起源如何影响对壶菌 Batrachochytrium dendrobatidis (Bd) 感染的耐受性，这种真菌是一种通用病原体，导致全球两栖动物数量下降。我们将来自两个纬度地区的沼泽蛙 Rana arvalis 和普通蟾蜍 Bufo bufo 的新变态个体暴露于两种不同的 BdGPL 品系。我们测量了存活率和生长率，因为即使没有死亡，感染也可能对健康成分造成亚致死影响。 B. bufo 的感染量高于 R. arvalis，个体较小的感染量通常较高。 B. bufo 对 Bd 感染的死亡率很高，而 R. arvalis 的死亡率很低。 Bd 介导的死亡率与体型有关，高纬度地区的个体较小，导致北部的 B. bufo 死亡率较高。 Bd 暴露会导致生长减少，从而产生亚致死效应，这表明感染后幸存的个体可能因体型较小而导致健康状况下降。在这两种宿主物种中，瑞典 Bd 菌株比英国菌株产生更强的亚致死效应。我们认为，高纬度地区的人群比低纬度地区的人群更容易受到壶菌的影响，并讨论了体型和宿主地理起源对目前结果的影响的可能机制。