Stress response of fire salamander larvae differs between habitat types

The larvae of the European fire salamander (Salamandra salamandra) can inhabit two different habitats: streams and ponds. Streams are characterized by lower predation risks and higher food availability. Thus, ponds are considered a less suitable habitat. To investigate the differential impacts of these two habitats on larval physiology, we measured the stress response of larvae. After successfully validating the measure of water-borne corticosterone release rates in fire salamander larvae, we measured the baseline and stress-induced corticosterone of 64 larvae from ponds and streams in the field. We found that larvae in ponds have a higher baseline and stress-induced corticosterone levels. Additionally, we performed a reciprocal transplant experiment (RTE) and tested whether larvae can adapt their stress responses to changing habitats. After two weeks, we did not find an increase in corticosterone levels when comparing stress-induced corticosterone values with baseline corticosterone values in larvae transferred into ponds, irrespective of their habitat of origin. However, larvae transferred into streams still exhibited an increase in the stress-induced corticosterone response in comparison with the baseline values. These results show that non-invasive hormone measurements can provide information on the habitat quality and potential adaptation and thus emphasize the potential for its use in conservation efforts.

Tonic immobility behaviour does not differ between fire salamander larvae from ponds and streams

Tonic immobility is an antipredator defence in which the prey animal remains motionless after physical contact with the predator, pretending to be dead. This behaviour has been observed among a variety of taxa but has received only little attention in amphibian larvae. During our field studies with fire salamander larvae, we observed that larvae from different habitats display tonic immobility after handling. In our study site, we find larvae in pond and stream habitats, that differ in several aspects such as their stress response and their risk-taking behaviour, likely caused by the very different habitat conditions. We measured the time that the tonic immobility behaviour was displayed but found no difference between larvae from the two habitat types. Likewise, we also found no correlation between the size of the larvae and the duration of displaying the behaviour. In conclusion, we found that fire salamander larvae show tonic immobility, but found no evidence that the different habitat conditions influence the tonic immobility behaviour.

Behavioural drivers of ecotone exploitation: activity of groundwater animals in spring

Abstract

Border habitats such as interfaces and ecotones are promising research targets being likely areas of high species richness and genetic and phenotypic diversity. Springs are intriguing habitats exploited by both subterranean and surface species. For subterranean species, springs can provide higher trophic resources but can be risky in terms of predation and UV radiation, while for surface species, springs can be safer but less productive environments. We coupled field surveys and laboratory experiments to understand how predation risk and physical constraints, like light occurrence, affect spring exploitation by both a subterranean (Niphargus thuringius) and a surface crustacean amphipod species (Echinogammarus stammeri). From March to May 2021, we surveyed multiple springs and evaluated the activity (both during day and night) of the amphipods and of their predators. Furthermore, in a subterranean laboratory, we reared 80 N. thuringius and 80 E. stammeri under safe and risky conditions with both constant darkness and diel light variation assessing their activity and survival. Risky conditions were represented by the occurrence of meso-predators alone or coupled with the presence of a top predator. In the field, N. thuringius activity was negatively related to the density of predators, while laboratory experiments revealed a main role played by light treatments and night period. E. stammeri activity in the field was higher close to surface while in laboratory conditions decreased during time. In laboratory conditions, predation risk negatively affected survival of both amphipods. Our findings reveal that physical constraints play a key role in affecting the exploitation of ecotones and can mediate antipredator responses, thus providing selective pressures for the exploitation of border environments.

Significance statement

Understanding environmental pressures acting on ecotones is a key point to verify if new adaptations may occur at the border between two distinct habitats. Using both field and laboratory approaches, we show that, in springs, the behaviour of subterranean invertebrates is affected by surface physical constraints which can mediate the effects of predation risk. Behavioural strategies to avoid predation, such as nocturnal activity, may promote spring ecotone exploitation by groundwater animals, such as amphipod crustaceans.

Demography and spatial activity of fire salamanders, Salamandra salamandra (Linnaeus, 1758), in two contrasting habitats in the Vienna Woods

Understanding population dynamics is vital in amphibian conservation. To compare demography and movements, we conducted a capture-recapture study over three spring seasons in two populations of Salamandra salamandra in the Vienna Woods. The study sites differ in topography, vegetation, and the type of breeding waters. Population density in a beech forest traversed by a stream was more than twice as high as in an oak-hornbeam forest with temporary pools. Movement distances were on average higher at the latter site whereas home range estimates were similar for both sites. The sexes did not differ significantly in the observed movement patterns at either site. Annual apparent survival was mostly high (~0.85), but the estimate for females from the low-density site was lower (~0.60), indicating a higher rate of emigration or mortality.