The diversity of strategies by animals to avoid predation is fascinating. We studied diurnal, toxic harlequin toads, Atelopus spumarius sensu lato, from the Amazon basin. In this species complex, some populations have striking red soles of the hands and feet, visible only when walking (see video). When stationary, the toads are hard to detect. Consequently, these toads switch between high and low conspicuousness. Interestingly, some populations lack the extra colour display of the soles.
In a recent study, lead by Daniela Rößler and published in Scientific Reports, we found comprehensive support that the red coloration can act as an warning signal directed towards potential predators: red soles are significantly more conspicuous than soles lacking red coloration to bird predators and the presence of the red signal significantly increases detection. In line with this, 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 painted frog clay models with red soles than for those lacking the signal, in a population where the red soles naturally occur.
If advantageous, why red soles are absent in some Atelopus populations? Signal lack (evolutionary loss?) may be explained by a higher overall attack risk or potential differences of predator community structure between populations.Rößler, D.C., S. Lötters, J. Mappes, J.K. Valkonen, M. Menin, A.P. Lima & H. Pröhl (2019): Sole coloration as an unusual aposematic signal in a Neotropical toad. — Scientific Reports, 9: 1128.