Conspicuousness, color resemblance, and toxicity in geographically diverging mimicry: The pan-Amazonian frogAllobates femoralis

Abstract

Predation risk is allegedly reduced in Batesian and Müllerian mimics, because their coloration resembles the conspicuous coloration of unpalatable prey. The efficacy of mimicry is thought to be affected by variation in the unpalatability of prey, the conspicuousness of the signals, and the visual system of predators that see them. Many frog species exhibit small colorful patches contrasting against an otherwise dark body. By measuring toxicity and color reflectance in a geographically variable frog species and the syntopic toxic species, we tested whether unpalatability was correlated with between-species color resemblance and whether resemblance was highest for the most conspicuous components of coloration pattern. Heterospecific resemblance in colorful patches was highest between species at the same locality, but unrelated to concomitant variation in toxicity. Surprisingly, resemblance was lower for the conspicuous femoral patches compared to the inconspicuous dorsum. By building visual models, we further tested whether resemblance was affected by the visual system of model predators. As predicted, mimic-model resemblance was higher under the visual system of simulated predators compared to no visual system at all. Our results indicate that femoral patches are aposematic signals and support a role of mimicry in driving phenotypic divergence or mimetic radiation between localities.

Comment on Amézquita et al. (2017) “Conspicuousness, color resemblance, and toxicity in geographically diverging mimicry: The pan-Amazonian frogAllobates femoralis”

“…The fact that large amounts of benzocaine accumulate in the skin following oral administration of a lethal dose of that anesthetic casts doubt on Amézquita et al.’s () conclusions about frog toxicity. Injection of Allobates femoralis group skin extracts lacking naturally occurring skin alkaloids but containing large amounts of benzocaine are expected to elicit similar responses to those reported by Amézquita et al.…”

“…First, Amézquita et al. () did not analyze the chemical composition of the skin secretions they studied, so their conclusion that the inferred toxicity of samples was due to alkaloids is unfounded. Second, although not specified in Materials and Methods, Amézquita et al.…”

“…Second, although not specified in Materials and Methods, Amézquita et al. () euthanized frogs by buccal application of an undetermined quantity of 20% benzocaine in gel form (Benzotop, DFL Indústria e Comércio, Rio de Janeiro, RJ, Brazil; A.P. Lima, in litt.…”

“…In an attempt to circumvent this problem, Amézquita et al. () applied benzocaine to the buccal cavity of frogs, assuming this would prevent benzocaine from contaminating the skin secretions.…”

“…Chemical analysis of skins would have allowed Amézquita et al. () to detect benzocaine in their samples and either choose a different method of euthanasia (e.g., Shine et al. ; Lillywhite et al.…”