The structure of the skin may evolve rapidly during a biological invasion, for two reasons. First, novel abiotic challenges such as hydric conditions may modify selection of traits (such as skin thickness) that determine rates of evaporative water loss. Second, invaders might benefit from enhanced rates of dispersal, with locomotion possibly facilitated by thinner (and hence more flexible) skin. We quantified thickness of layers of the skin in cane toads (Rhinella marina) from the native range (Brazil), a stepping-stone population (Hawaii), and the invaded range in Australia. Overall, the skin is thinner in cane toads in Australia than in the native range, consistent with selection on mobility. However, layers that regulate water exchange (epidermal stratum corneum and dermal ground substance layer) are thicker in Australia, retarding water loss in hot dry conditions. Within Australia, epidermal thickness increased as the toads colonized more arid regions, but then decreased in the arid Kimberley region. That curvilinearity might reflect spatial sorting, whereby mobile (thin-skinned) individuals dominate the invasion front; or the toads’ restriction to moist sites in this arid landscape may reduce the importance of water-conservation. Further work is needed to clarify the roles of adaptation versus phenotypic plasticity in generating the strong geographic variation in skin structure among populations of cane toads.

中文翻译：

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皮肤薄薄的入侵者：甘蔗蟾蜍种群中的皮肤结构在地理上的变异（Rhinella marina）

皮肤结构在生物入侵过程中可能会迅速发展，这有两个原因。首先，诸如水合条件之类的新型非生物挑战可能会改变决定蒸发水分流失速率的性状（例如皮肤厚度）的选择。其次，入侵者可能会受益于分散速度的提高，并且运动可能会因皮肤更薄（因此更柔软）而得到促进。我们从本地范围（巴西），垫脚石种群（夏威夷）和澳大利亚的入侵范围中量化了蟾蜍蟾蜍（莱茵兰滨海）中的皮肤层厚度。总体而言，在澳大利亚的蟾蜍蟾蜍皮比本地的更薄，这与对流动性的选择一致。但是，调节水交换的层（表皮角质层和真皮地面物质层）在澳大利亚较厚，可防止在炎热干燥条件下失水。在澳大利亚内部，表皮厚度随着蟾蜍在更多的干旱地区定居而增加，但随后在干旱的金伯利地区则减少。曲线的线性可能反映了空间的排序，从而使活动的（皮肤瘦弱的）个体主导了入侵前沿。或蟾蜍限制在此干旱景观中潮湿的地方，可能会降低节水的重要性。需要进一步的工作来阐明适应性与表型可塑性在甘蔗蟾蜍群体皮肤结构中产生强烈的地理变异方面的作用。