Species introduced by human activities can alter the normal functioning of ecosystems promoting negative impacts on native biodiversity, as they can rapidly expand their population size, demonstrating phenotypic plasticity and possible adaptive capacity to novel environments. Twenty years ago, the guttural toad, Sclerophrys gutturalis, was introduced to a peri-urban area of Cape Town, with cooler and drier climatic characteristics than its native source population, Durban, South Africa. Our goal was to understand the phenotypic changes, in terms of physiology and immunity, of populations in native and novel environments. We evaluated body index (BI), field hydration level, plasma corticosterone levels (CORT), proportion of neutrophils: lymphocytes (N: L), plasma bacterial killing ability (BKA), and hematocrit (HTC) in the field, and after standardized stressors (dehydration and movement restriction) in males from the native and invasive populations. Toads from the invasive population presented lower BI and tended to show a lower field hydration state, which is consistent with living in the drier environmental conditions of Cape Town. Additionally, invasive toads also showed higher BKA and N:L ratio under field conditions. After exposure to stressors, invasive animals presented higher BKA than the natives. Individuals from both populations showed increased CORT after dehydration, an intense stressor for these animals. The highest BKA and N:L ratio in the field and after submission to stressors in the laboratory shows that the invasive population has a phenotype that might increase their fitness, leading to adaptive responses in the novel environment and, thus, favoring successful dispersion and population increase.

人类活动引入的物种可以改变生态系统的正常功能，从而对本地生物多样性产生负面影响，因为它们可以迅速扩大种群规模，表现出表型可塑性和可能对新环境的适应能力。二十年前，喉蟾蜍，Sclerophrys gutturalis，被引入开普敦的城郊地区，其气候特征比其本地来源人口南非德班凉爽干燥。我们的目标是了解原生环境和新环境中种群在生理和免疫方面的表型变化。我们在现场评估了身体指数 (BI)、野战水化水平、血浆皮质酮水平 (CORT)、中性粒细胞比例：淋巴细胞 (N: L)、血浆细菌杀伤能力 (BKA) 和血细胞比容 (HTC)，并在标准化后来自本地和入侵种群的雄性的压力源（脱水和运动受限）。来自入侵种群的蟾蜍表现出较低的 BI，并且倾向于表现出较低的田间水合状态，这与生活在开普敦较干燥的环境条件下是一致的。此外，在野外条件下，侵入性蟾蜍也表现出更高的 BKA 和 N:L 比。暴露于压力源后，入侵动物呈现出比本地动物更高的 BKA。来自两个种群的个体在脱水后表现出增加的 CORT，这对这些动物来说是一种强烈的压力。现场最高的 BKA 和 N:L 比率以及在实验室中提交给压力源后表明，入侵种群具有可能增加其适应性的表型，导致在新环境中的适应性反应，从而有利于成功的分散和种群增加。