A diverse array of biologically active, lipid-soluble alkaloids have been discovered in amphibian skin. Such alkaloids include the following:  the steroidal samandarines from salamanders, the batrachotoxins, histrionicotoxins, gephyrotoxins, and epibatidine from neotropical poison frogs (Dendrobatidae), the pumiliotoxins, allopumiliotoxins, homopumiliotoxins, and decahydroquinolines from certain genera of anurans from four families (Dendrobatidae, Mantellidae, Bufonidae, and Myobatrachidae), a variety of izidines (pyrrolizidines, indolizidines, quinolizidines, lehmizidines), pyrrolidines, piperidines, various tricyclics (related in structures to the coccinellines), and spiropyrrolizidines from the first three of these four families, the pseudophrynamines from one genus of Australian frogs, and a variety of unclassified alkaloids as yet of undetermined structure. With the exception of the samandarines and the pseudophrynamines, all alkaloids appear to be derived from dietary sources. Although only a few of...

Alkaloids from amphibian skin: a tabulation of over eight-hundred compounds.

Indolizidine and quinolizidine alkaloids

Chapter Two - Naturally Occurring Cyclotryptophans and Cyclotryptamines

With few exceptions, aposematically colored poison frogs sequester defensive alkaloids, unchanged, from dietary arthropods. In the Neotropics, myrmicine and formicine ants and the siphonotid millipede Rhinotus purpureus are dietary sources for alkaloids in dendrobatid poison frogs, yet the arthropod sources for Mantella poison frogs in Madagascar remained unknown. We report GC-MS analyses of extracts of arthropods and microsympatric Malagasy poison frogs (Mantella) collected from Ranomafana, Madagascar. Arthropod sources for 11 “poison frog” alkaloids were discovered, 7 of which were also detected in microsympatric Mantella. These arthropod sources include three endemic Malagasy ants, Tetramorium electrum, Anochetus grandidieri, and Paratrechina amblyops (subfamilies Myrmicinae, Ponerinae, and Formicinae, respectively), and the pantropical tramp millipede R. purpureus. Two of these ant species, A. grandidieri and T. electrum, were also found in Mantella stomachs, and ants represented the dominant prey type (67.3% of 609 identified stomach arthropods). To our knowledge, detection of 5,8-disubstituted (ds) indolizidine iso-217B in T. electrum represents the first izidine having a branch point in its carbon skeleton to be identified from ants, and detection of 3,5-ds pyrrolizidine 251O in A. grandidieri represents the first ponerine ant proposed as a dietary source of poison frog alkaloids. Endemic Malagasy ants with defensive alkaloids (with the exception of Paratrechina) are not closely related to any Neotropical species sharing similar chemical defenses. Our results suggest convergent evolution for the acquisition of defensive alkaloids in these dietary ants, which may have been the critical prerequisite for subsequent convergence in poison frogs between Madagascar and the Neotropics.

/pdf/convergent-evolution-of-chemical-defense-in-poison-frogs-and-4ma5c1l1bx.pdf

Convergent evolution of chemical defense in poison frogs and arthropod prey between Madagascar and the Neotropics

The role of colours and colour patterns in behavioural ecology has been extensively studied in a variety of contexts and taxa, while almost overlooked in many others. For decades anurans have been the focus of research on acoustic signalling due to the prominence of vocalisations in their communication. Much less attention has been paid to the enormous diversity of colours, colour patterns, and other types of putative visual signals exhibited by frogs. With the exception of some anecdotal observations and studies, the link between colour patterns and the behavioural and evolutionary ecology of anurans had not been addressed until approximately two decades ago. Since then, there has been ever-increasing interest in studying how colouration is tied to different aspects of frog behaviour, ecology and evolution. Here I review the literature on three different contexts in which frog colouration has been recently studied: predator-prey interactions, intraspecific communication, and habitat use; and I highlight those aspects that make frogs an excellent, yet understudied, group to examine the role of colour in the evolution of anti-predation strategies and animal communication systems. Further, I argue that in addition to natural-history observations, more experiments are needed in order to elucidate the functions of anuran colouration and the selective pressures involved in its diversity. To conclude, I encourage researchers to strengthen current experimental approaches, and suggest future directions that may broaden our current understanding of the adaptive value of anuran colour pattern diversity.

/pdf/behavioural-ecological-and-evolutionary-aspects-of-diversity-4c0khmdavn.pdf

Behavioural, ecological, and evolutionary aspects of diversity in frog colour patterns

A naturally occurring erythro diastereomer of pumiliotoxin b

A Naturally Occurring Erythro Diastereomer (Ic) of Pumiliotoxin B (Ia).

Australian frogs of the genus Pseudophryne contain two distinct classes of alkaloids. The pseudophrynamine class (3a-prenyl pyrrolo[2,3-b]indoles) are unique to this genus of frogs of the family Myobatrachidae, while the pumiliotoxin-A class (8-hydroxy-8-methyl-6-alkylidene-1-azabicyclo[4.3.0]nonanes) also occur in dendrobatid frogs of the genera Dendrobates, Epipedobates, and Minyobates, in ranid frogs of the genus Mantella, and in bufonid toads of the genus Melanophryniscus. All seven species of Pseudophryne examined contain both classes of alkaloids. The pseudophrynamines were the predominant class in both species (Pseudophryne guentheri and Pseudophryne occidentalis) from Western Australia, while all of the eastern species (Pseudophryne australis, Pseudophryne bibronii, Pseudophryne coriacea, Pseudophryne corroboree, and Pseudophryne semimarmorata) contained significant amounts of both pseudophrynamines and pumiliotoxins. Pumiliotoxins, in particular pumiliotoxin B, were predominant in two eastern species (P. australis and a southern population of P. corroboree), while pseudophrynamines were dominant in P. bibronii, four of six populations of P. coriacea, one population of P. semimarmorata, and a northern population of P. corroboree. Structures are proposed for several new alkaloids of the pseudophrynamine class.

Alkaloids from Australian frogs (Myobatrachidae): pseudophrynamines and pumiliotoxins.

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A naturally occurring erythro diastereomer of pumiliotoxin b

A Naturally Occurring Erythro Diastereomer (Ic) of Pumiliotoxin B (Ia).

Alkaloids from Australian frogs (Myobatrachidae): pseudophrynamines and pumiliotoxins.