Sole coloration as an unusual aposematic signal in a Neotropical toad

Daniela C Rößler,Stefan Lötters,Marcelo Menin,Johanna Mappes,Albertina P Lima,Heike Pröhl,Janne K Valkonen

doi:10.1038/s41598-018-37705-1

Abstract

Many animals have evolved remarkable strategies to avoid predation. In diurnal, toxic harlequin toads (Atelopus) from the Amazon basin, we find a unique colour signal. Some Atelopus populations have striking red soles of the hands and feet, visible only when walking. When stationary, the toads are hard to detect despite their yellow-black dorsal coloration. Consequently, they switch between high and low conspicuousness. Interestingly, some populations lack the extra colour display of the soles. We found comprehensive support that the red coloration can act as an aposematic signal directed towards potential predators: red soles are significantly more conspicuous than soles lacking red coloration to avian predators and the presence of the red signal significantly increases detection. Further, toads with red soles show bolder behaviour by using higher sites in the vegetation than those lacking this signal. Field experiments hint at a lower attack risk for clay models with red soles than for those lacking the signal, in a population where the red soles naturally occur. We suggest that the absence of the signal may be explained by a higher overall attack risk or potential differences of predator community structure between populations.

Highlights

Many animals have evolved remarkable strategies to avoid predation
While studying Neotropical harlequin toads (Atelopus spumarius sensu lato) we found a unique colour signal that drew our attention
The following observations are noteworthy: firstly, harlequin toads are slow walkers rather than leapers[22]; secondly, Atelopus skin secretions contain the potent tetrodotoxin and its derivatives[23], substances known as effective defence mechanisms in a wide array of aquatic and terrestrial animals including amphibians[24,25]

Summary

Introduction

Many animals have evolved remarkable strategies to avoid predation. In diurnal, toxic harlequin toads (Atelopus) from the Amazon basin, we find a unique colour signal. The toads are hard to detect despite their yellow-black dorsal coloration. They switch between high and low conspicuousness. Aposematism is efficient when predators learn to avoid conspicuous signals as a cue of defence. In the case of aposematic coloration, potential prey display bright colours, often red, orange or yellow, forming a strong contrast against the background[7,8,9]. Some populations of these toads display bright red foot soles which become a highly conspicuous signal (see Fig. 1A, Supplementary Video S1). Despite mostly being yellow-green and black, the dorsal pattern makes it hard to detect the toads on complex backgrounds[21] (see Fig. 1B).

Methods

Results

Discussion

Conclusion