Cast away: drift as the main determinant for larval survival in western fire salamanders (Salamandra salamandra) in headwater streams

Larval development and poor trophic resource availability: Local adaptations and plasticity in a widespread amphibian species

Theory predicts that, in organisms with complex life cycles, if the earlier-stage limiting factor induces weak later-stage phenotypes, the development of the later-stage trait should evolve to reduce carry-over effects. Local adaptations could thus favour decoupling of later stages. However, decoupling is not always possible. In this study, we used a widespread amphibian, the European fire salamander (Salamandra salamandra), to assess the role of local adaptations to environmental stressful conditions experienced at the larval stage. We exposed 150 larvae from different altitudes to two conditions: rich food and poor food condition. Conditions in early life stages can affect an individual's traits, either as a direct effect or mediated through outcomes in successive life stages. To distinguish between effects of rearing conditions and local adaptation, we searched for a causal model. The causal model detected effects of both food treatment and population origin (altitude) on all life stages. Larvae reared under rich food condition metamorphosed earlier, had higher growth rates and reached smaller size at metamorphosis. Significant differences occurred between larvae of different origin: low-altitude individuals performed poorly under the poor food treatment. Moreover, larvae from higher altitudes were slower with rich food and faster with poor food compared to those from lower altitudes. Our results underline that environmental conditions and local adaptation can interplay in determining the plasticity of larval stages, still adaptations can maximize the growth efficiency of early stages in oligotrophic environments, leading to divergent pathways across populations and environmental conditions.

Larval development and habitat usage of stream-breeding Fire salamanders in an urban environment

Urbanisation adversely affects the abiotic and biotic characteristics of watercourses, including freshwater streams that support the development of stream-breeding salamanders. We conducted a study over four years on an isolated fire salamander population inhabiting a stream valley northwest of Budapest, Hungary. Our aim was to understand aspects of larval development and habitat usage within this population. The maximum number of larvae was observed in April and the first weeks of May. Due to drifting caused by heavy rainfall, there was a mean decrease of 63.3% in the number of larvae. The abundance of larval salamanders within 16 stream segments showed strong temporal and spatial variation, and there was a strong relationship between larval abundance and the % cover of fine gravel substrate. Some of the larvae could escape drift by entering pools with slower water flow and shelter. Larvae were predominantly solitary in smaller pools but occasionally aggregated in high numbers in some segments. The first larvae with yellow spots (indicative of metamorphosis) appeared in June, and by early September, all larvae were metamorphosing. Our results show that in this urbanised environment, larval development through to metamorphosis is occurring, but increasing urbanisation and alterations to stream flow threaten the persistence of the local population.

A near-natural experiment on factors influencing larval drift in Salamandra salamandra

The larval stage of the European fire salamander (Salamandra salamandra) inhabits both lentic and lotic habitats. In the latter, they are constantly exposed to unidirectional water flow, which has been shown to cause downstream drift in a variety of taxa. In this study, a closed artificial creek, which allowed us to keep the water flow constant over time and, at the same time, to simulates with predefined water quantities and durations, was used to examine the individual movement patterns of marked larval fire salamanders exposed to unidirectional flow. Movements were tracked by marking the larvae with VIAlpha tags individually and by using downstream and upstream traps. Most individuals showed stationarity, while downstream drift dominated the overall movement pattern. Upstream movements were rare and occurred only on small distances of about 30 cm; downstream drift distances exceeded 10 m (until next downstream trap). The simulated flood events increased drift rates significantly, even several days after the flood simulation experiments. Drift probability increased with decreasing body size and decreasing nutritional status. Our results support the production hypothesis as an explanation for the movements of European fire salamander larvae within creeks.