Amphibians forgo aquatic life in response to alien fish introduction

Species with complex life cycles are good models to understand trade-offs between life in hostile and favourable habitats. Newts remain in breeding wetlands for a long period and are strongly affected by fish introduction; however, mechanisms of the exclusion observed in the field are still not well known. In particular, whether newts skip breeding and leave water for land in response to fish introduction and how aquatic shelter may influence their choice remain open questions. To investigate these questions, we experimentally studied the use of aquatic and terrestrial habitats during the breeding season of palmate newts, Lissotriton helveticus, in the presence and absence of goldfish, Carassius auratus. We determined the consequences of habitat choice on newt fitness by assessing sexual activity and number of eggs. There was a strong, significant avoidance of the aquatic environment in the presence of fish, particularly when no aquatic shelter was available. This escape from the water had an impact on reproduction: newts decreased their sexual activity and laid fewer eggs. The availability of shelters favoured coexistence but did not prevent a large proportion of the newts from leaving water and skipping reproduction. This study shows how the presence of fish and the absence of aquatic shelters can lead to newts forgoing aquatic life, thus improving our understanding of the mechanisms behind the coexistence and exclusion patterns found in the wild. More broadly, these data contribute to explaining aquatic versus terrestrial life in favourable and unfavourable environments.