# Interactive abiotic and biotic stressor impacts on a stream‐dwelling amphibian

## TL;DR

This study explores how abiotic and biotic stressors interact to affect the movement and stress responses of larval Pacific giant salamanders in a stream ecosystem.

## Contribution

The study reveals interactive effects of abiotic and biotic stressors on larval salamander behavior and identifies a potential physiological pathway for stress tolerance.

## Key findings

- Larval salamanders moved faster in the presence of trout chemical cues and sediment, with combined exposure increasing speed further.
- Low-flow summer conditions led to variable but not significantly higher heat-shock protein expression in larvae.
- Behavioral responses suggest interactive effects between abiotic and biotic stressors.

## Abstract

Organisms within freshwater and marine environments are subject to a diverse range of often co‐occurring abiotic and biotic stressors. Despite growing awareness of the complex multistress systems at play in aquatic ecosystems, many questions remain regarding how simultaneous stressors interact with one another and jointly impact aquatic species. We looked at multistress interactions in a protected stream ecosystem in Mendocino County, California. Specifically, we examined how diurnal temperature variation, turbidity, and predator cues altered the movement speed of larval Pacific giant salamanders (Dicamptodon tenebrosus). In a second experiment, we looked at how simulated low‐flow summer conditions impact the expression of heat‐shock proteins (HSPs) in the same species. Larvae moved almost one and a half times faster in the presence of chemical cues from trout and suspended sediment, and almost two times faster when both sediment and trout cues were present but were only marginally affected by temperature and visual cues from conspecifics. Interestingly, the order of stressor exposure also appeared to influence larval speed, where exposure to sediment and trout in earlier trials tended to lead to faster speeds in later trials. Additionally, larvae exposed to low‐flow conditions had more variable, but not statistically significantly higher, expression of HSPs. Our findings highlight the potential interactive effects of an abiotic stressor, sedimentation, and a biotic stressor, and predator chemical cues on an ecologically important trait: movement speed. Our findings also demonstrate the likely role of HSPs in larval salamander survival in challenging summer conditions. Taken together, these findings show that larval D. tenebrosus responds behaviorally to biotic and abiotic stressors and suggests a possible pathway for physiological tolerance of environmental stress. Consideration of multistress systems and their effects is important for understanding the full effects of co‐occurring stressors on aquatic organisms to guide appropriate conservation and management efforts based on ecologically relevant responses of organisms within an environment.

Despite growing awareness of the complex multistress systems at play in aquatic ecosystems, many questions remain regarding how simultaneous stressors interact with one another and jointly impact aquatic species. In this study, we examined how diurnal temperature variation, turbidity, and predator cues altered the movement speed of larval Pacific giant salamanders (Dicamptodon tenebrosus), and how simulated low‐flow summer conditions impact the expression of heat‐shock proteins (HSPs) in the same species. In these larvae, we observed behavioral responses suggestive of interactive effects between abiotic and biotic stressors, and physiological responses that suggest a pathway for tolerance of environmental stress.