Sequestered and Synthesized Chemical Defenses in the Poison Frog Melanophryniscus moreirae

Abstract

Bufonid poison frogs of the genus Melanophryniscus contain alkaloid-based chemical defenses that are derived from a diet of alkaloid-containing arthropods. In addition to dietary alkaloids, bufadienolide-like compounds and indolealkylamines have been identified in certain species of Melanophryniscus. Our study reports, for the first time, the co-occurrence of large quantities of both alkaloids sequestered from the diet and an endogenously biosynthesized indolalkylamine in skin secretions from individual specimens of Melanophryniscus moreirae from Brazil. GC/MS analysis of 55 individuals of M. moreirae revealed 37 dietary alkaloids and the biosynthesized indolealkylamine bufotenine. On average, pumiliotoxin 267C, bufotenine, and allopumilitoxin 323B collectively represent ca. 90 % of the defensive chemicals present in an individual. The quantity of defensive chemicals differed between sexes, with males possessing significantly less dietary alkaloid and bufotenine than females. Most of the dietary alkaloids have structures with branched-chains, indicating they are likely derived from oribatid mites. The ratio of bufotenine:alkaloid quantity decreased with increasing quantities of dietary alkaloids, suggesting that M. moreirae might regulate bufotenine synthesis in relation to sequestration of dietary alkaloids.

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

“…The large quantity of benzocaine was greater than the amount of bufotenine and almost as great as the amount of pumiliotoxin 267C , the most abundant skin alkaloid in this species (Jeckel et al. ). In identical experiments with a captive bred individual of the dendrobatid poison frog Dendrobates auratus and the nonalkaloid sequestering ranid frog Lithobates clamitans , benzocaine also rapidly accumulated in the skin in large amounts (Fig.…”

“…, Jeckel et al. ,b). In the bufonid poison frog Melanophryniscus moreirae , the amount of benzocaine in the skin following oral administration of 10 μL of liquid Orajel® containing 20% benzocaine (Church & Dwight Co., Inc., Ewing, New Jersey) was equivalent to almost 50% of the total amount of the naturally occurring chemical defenses (Fig.…”

“…On the basis of new data presented below, oral administration of lethal doses of benzocaine results in the accumulation of large amounts of benzocaine in euthanized individuals of both alkaloid-sequestering and nonalkaloid-sequestering frogs ( Fig. 2; for chemical profiles of individuals of these poison frog species euthanized by other means, see Daly et al 1987, Jeckel et al 2015a. In the bufonid poison frog Melanophryniscus moreirae, the amount of benzocaine in the skin following oral administration of 10 µL of liquid Orajel R containing 20% benzocaine (Church & Dwight Co., Inc., Ewing, New Jersey) was equivalent to almost 50% of the total amount of the naturally occurring chemical defenses ( Fig.…”

An Empirical Test Indicates Only Qualitatively Honest Aposematic Signaling Within a Population of Vertebrates

“…Several alternative explanations may potentially explain why we see qualitative, but not quantitative, honesty in R. imitator. First, unlike invertebrates, which generally sequester all their toxins at the larval stage, there is likely an ontogenetic disconnect between color production and toxicity in many vertebrate species (dendrobatids: Daly et al, 1994; other poison frogs: Jeckel et al, 2015;newts: Hanifin and Brodie, 2002;aposematic snakes: McCue, 2006). Together, these examples likely indicate a substantial difference from examined insect cases in which the resource-allocation framework is more plausible.…”

An experimental assessment of the antipredatory function of green dorsal coloration in poisonous Neotropical red‐bellied toads

“…The red‐bellied toads, genus Melanophryniscus (family Bufonidae), include 29 species (Frost, ) restricted to southeastern South America (Zank et al , ) and is the sister taxon of all remaining Bufonidae (Pramuk et al , ). These small toads are diurnal (Santos & Grant, ), sequester alkaloids from their diet (Daly et al , ; Jeckel, Grant & Saporito, ) and present ventral, and in many cases also dorsal, bright coloration patterns (usually red, yellow and white) against a dark background (Baldo et al , ). The bright conspicuous ventral colors are exhibited during the unken reflex when specimens are manipulated and supposedly during predation attacks (McDiarmid, ).…”