# Tadpole Skin Secretions, Not Food or Temperature, Mediate Costly Cannibal‐Induced Plasticity in Invasive Cane Toad Hatchlings

## TL;DR

Invasive cane toad hatchlings speed up development when sensing cannibal tadpoles, but this leads to worse growth and survival later.

## Contribution

Identifies skin secretions from cannibal tadpoles as the cue for costly developmental plasticity in cane toad hatchlings.

## Key findings

- Cannibal tadpole skin secretions trigger costly developmental acceleration in cane toad hatchlings.
- Developmental acceleration from cannibal cues causes reduced growth and survival in later stages.
- Excess food cannot mitigate the negative effects of cannibal-induced developmental acceleration.

## Abstract

Hatchlings of invasive cane toads (
Rhinella marina
) in Australia respond facultatively to chemical cues of non‐feeding cannibalistic conspecific tadpoles by accelerating development, but consequently experience reduced growth, development and survival in the subsequent tadpole stage. Predation‐induced developmental acceleration of eggs or hatchlings is rare among amphibians, and the implications of and context‐dependent impacts of such developmental plasticity are poorly understood. For cane toads, the source and identity of the tadpole cue that induces this response are unknown. Additionally, it is unknown whether these carry‐over costs are due to accelerated early development per se or are specific to developmental acceleration induced by conspecific tadpole cues. Finally, it is unknown whether these costs can be mitigated by the availability of food resources at critical times during early development. We conducted laboratory experiments to investigate these issues. Our results show that (1) based on significant hatchling responses to skin swabs, the chemical that induces costly developmental plasticity is located in the skin of cannibalistic cane toad tadpoles, (2) carry‐over effects of early developmental acceleration are elicited only by cues from cannibal tadpoles because temperature‐induced developmental acceleration of hatchlings did not reduce subsequent growth, development or survival and (3) excess food availability during early development did not mitigate the carry‐over costs of exposure to cannibal tadpole cues. Thus, this developmental plasticity response, triggered by detection of chemicals exuded from the skin of conspecific tadpoles, causes unique negative carry‐over costs for younger larvae. However, we found that tadpole production of skin secretions is also plastic, with swabbed tadpoles inducing stronger responses in hatchlings than their unswabbed siblings. Finally, the carry‐over costs that follow cannibal exposure cannot be mitigated by favorable nutritional conditions.

Hatchlings of invasive cane toads respond to the risk of cannibalism by accelerating development but experience significant negative carry‐over effects on fitness in the tadpole stage. Our experiments demonstrate that this hatchling response is induced by chemicals located in the skin of older cannibalistic tadpoles. This response is unique to cannibal tadpole cues, and once initiated, cannot be reversed by favourable conditions such as a high nutrient environment.