Challenges of dehydration result in a behavioral shift in invasive toads

The adaptive nature of invasive species facilitates their survival in conditions that differ markedly from their native range. Behavioral changes in invasive populations are poorly explored but offer a wide potential when combined with physiological traits. For amphibians invading xeric habitats, finding water is important to function optimally and avoid dehydration. The water-finding hypothesis postulates that survival can be enhanced through the increased behavioral ability to find water. We tested the water-finding hypothesis in guttural toads (Sclerophrys gutturalis) from their native range and an invasive population. Additionally, we tested if artificially elevated corticosterone levels, which increase during dehydration, affect behavioral traits linked to water balance. In a labyrinth experiment, we observed the toads’ ability to find water in different hydration states (100%, 90%, and 80%). We found that individuals from the invasive population took longer to engage in water-searching behavior and spent more time close to the water source after finding it. Toads from the invasive population were also more active, and at 90% hydration, their attempts to find water increased. Moreover, artificially increasing corticosterone in fully hydrated invasive toads increased water-finding success. Our experiments demonstrated that invasive toads show water-conservation behaviors that can optimize water balance and might facilitate survival in an invaded xeric environment. Additionally, we suggest a link between elevated corticosterone levels and water-finding success. Our results lend support to the importance of behavior in successful invasions and the modulation of water-finding behavior by corticosterone

Challenges of a novel range: water balance, stress, and immunity in an invasive toad

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