An evaluation of honest signalling of warning coloration in Peruvian poison frogs
A fundamental question concerning signal communication is whether the signal is honest. Aposematic species signal to predators that they are not worth attacking because they possess a secondary defense (spines, toxins, etc). However, it remains unclear whether individuals in these species signal honestly, with more conspicuous individuals possessing more effective defenses. The Neotropical poison frogs (family Dendrobatidae) are well-known vertebrate aposemes that are defended by alkaloid toxins acquired from their diet. Evidence for honest signalling is mixed within this family. Importantly, empirical evidence for a correlation between coloration and toxicity has been measured across species or populations, while the majority of theoretical work has been focused on this correlation across individuals within populations. In this study we test whether Ranitomeya imitator, a poison frog endemic to Peru, signals honestly. We examine conspicuousness and alkaloid content (both the diversity and quantity of alkaloid types) of contiguous territorial males using spectral reflectance and GC-MS. Additionally, we compare the alkaloid profiles of individual males to the distance between male territories to determine if spatial distribution accounts for a large portion of the variation in alkaloid profiles between males.
Male Ranitomeya imitator from this population possess mostly alkaloids of ant origin (e.g., decahydroquinolines). Alkaloid profiles from these males were similar, however alkaloid quantities varied substantially between males. We did not find evidence that male brightness correlated with overall toxicity within this population, indicating that honest signalling does not seem to be the norm in this population. As a result, we suspect that an ecological factor, likely the availability of alkaloid-containing arthropod prey items, may be driving male toxicity in this system.