Ample variation in body size is common in vertebrates over extensive geographical distances, or in isolated populations, where effective geographical barriers may cause dwarfism or gigantism. Here we study potential causes of extreme size reduction in continental populations of amphibians within a short geographical distance and in the absence of geographical barriers. Natterjack toads Epidalea calamita in Doñana National Park (Spain) experience up to 2.1‐fold difference in body mass in as little as 37 km. Studying six populations divergent in body size, we tested for genetic isolation of the dwarf populations using multilocus genotypes (16 microsatellites), and explored whether populations differ in trophic status (through stable isotope analysis), standard metabolic rate and growth pattern, senescence and age structure (conducting telomere length assays and skeletochronology). We also recorded advertisement calls across populations and experimentally tested for behavioural reinforcement of the body size variation through female preferences. Local dwarfism in these populations occurs in the absence of genetic isolation while maintaining relatively high effective population sizes. Dwarf populations, however, are exposed to drier and warmer climatic conditions, have different trophic status, show lower mass‐specific metabolic rate, and male advertisement calls with a higher dominant frequency. Juvenile growth differed among populations, reaching the adult stage at different body sizes. Altogether, our results suggest a significant influence of environmental conditions on the physiology and ecology of the Doñana E. calamita populations, mainly affecting toads between metamorphosis and sexual maturity. Further experimental and genomic studies focusing on these early life stages are necessary to dissect the relative roles of the environment and adaptive genetic differentiation on this phenomenon.

中文翻译：

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尽管缺乏基因隔离，但在近距离的两栖大陆人群中存在侏儒症

在广泛的地理距离内的脊椎动物中或在孤立的种群中，体型的足够大的变化很普遍，在这些种群中有效的地理障碍可能导致侏儒症或巨人症。在这里，我们研究了在短距离内且没有地理障碍的情况下两栖动物大陆种群极度缩小的潜在原因。Natterjack蟾蜍Epidalea calamita在西班牙多纳纳国家公园（DoñanaNational Park）中，仅37公里之内的体重差异就高达2.1倍。研究了六个不同体型的种群，我们使用多基因座基因型（16个微卫星）测试了矮种群的遗传分离，并探索了种群的营养状态（通过稳定同位素分析），标准代谢率和生长方式，衰老和年龄是否存在差异结构（进行端粒长度测定和骨骼年代学）。我们还记录了跨人群的广告致电，并通过实验测试了通过女性喜好增强体型的行为。这些人群中的局部侏儒症在没有遗传隔离的情况下发生，同时保持了相对较高的有效人群规模。但是，矮人人口 处于较干燥和温暖的气候条件下，营养状态不同，质量代谢率较低，男性广告主频较高。不同群体的少年生长情况不同，不同体型的成年阶段。总之，我们的结果表明环境条件对Doñana的生理和生态有重大影响E. calamita种群，主要影响变形和性成熟之间的蟾蜍。需要进一步的针对这些早期生命阶段的实验和基因组学研究，以剖析环境的相对作用以及对此现象的适应性遗传分化。