Visual environment of rearing sites affects larval response to perceived risk

Abstract

1. Turbidity challenges the visual performance of aquatic animals. During development, environments with limited visibility may affect the fine-tuning of visual systems and thus the perception of, and response to, risk. While turbidity has frequently been used to characterise permanent aquatic habitats, it has been an overlooked feature of ephemeral ones.

2. Here, we use the natural diversity of ephemeral rearing sites (phytotelmata) in which the tadpoles of two poison frog species are deposited and confined until metamorphosis to explore the relationship between environments with limited visibility and response to perceived risk.

3. We sampled wild tadpoles of Dendrobates tinctorius, a rearing-site generalist with facultatively cannibalistic tadpoles, and Oophaga (formerly Dendrobates) pumilio, a small-phytotelm specialist dependent on maternal food-provisioning, to investigate how the visual environment in rearing sites influences tadpole behaviour. We hypothesised that turbid rearing conditions negatively impact both species’ ability to perceive risk, decreasing response strength to predatory visual stimuli. Using experimental arenas, we measured tadpole activity and space first on a black and white background, and then on either black or white backgrounds where tadpoles were exposed to visual stimuli of (potentially cannibalistic) conspecifics or potential predators.

4. When placed in a novel arena, the effects of rearing environment on D. tinctorius tadpoles were clear: tadpoles from darker pools were less active than tadpoles from brighter pools, and did not respond to either visual stimuli, whereas tadpoles from brighter pools swam more when paired with conspecifics versus odonate larvae, suggesting that tadpoles can visually discriminate between predators. For O. pumilio, tadpoles were more active on experimental backgrounds that more closely matched the luminosity of their rearing sites, but their responses to the two visual stimuli did not differ.

5. Larval specialisation associated with species-specific microhabitat use may underlie the observed responses to visual stimuli, which has implications for the stability of species interactions and trophic dynamics in pool communities. Together, our findings demonstrate that light availability of wild larval rearing conditions influences the perception of risk in novel contexts, and provide insight into how visually guided animals may respond to sudden environmental disturbances.