First characterization of toxic alkaloids and volatile organic compounds (VOCs) in the cryptic dendrobatid Silverstoneia punctiventris

Mabel Gonzalez,Andrés E Brunetti,Chiara Carazzone,Marco González-Santoro,Pablo Palacios-Rodriguez,Jack Hernandez-Restrepo,Adolfo Amézquita

doi:10.1186/s12983-021-00420-1

Abstract

BackgroundPoison frogs are known for the outstanding diversity of alkaloid-based chemical defences with promising therapeutic applications. However, current knowledge about chemical defences in Dendrobatoidea superfamily has two sources of bias. First, cryptic, brown-colored species have been neglected in comparison to those conspicuously colored, and second, there has been little interest in characterizing metabolites other than alkaloids mediating defensive functions. In an effort to contribute to fill the gap of knowledge about cryptic species and broadening the spectrum of compounds analyzed we have applied head-space solid phase microextraction coupled to gas chromatography and mass spectrometry (HS-SPME/GC-MS) for extracting amphibian alkaloids and volatile organic compounds (VOCs) from Silverstoneia punctiventris.ResultsUsing the skin from 8 specimens in 4 biological replicates we have found 33 different compounds. Twenty of them were classified as VOCs into 15 chemical classes including alkanes, alcohols, carbonyl compounds, methylpyridines, benzothiazoles, N-alkylpyrrolidines, pyrazines, and sesquiterpenoids, some of which were previously reported as repellents, defence compounds or defence pheromones in other organisms, and as sex pheromones in a treefrog. Interestingly, six of the remaining compounds were identified as alkaloids previously reported in other toxic/unpalatable dendrobatid frogs.ConclusionsThis is the first report of alkaloids and VOCs found in the Silverstoneia genus, which has been assumed for decades as non-chemically defended. This study establishes HS-SPME/GC-MS as a new application for a simultaneous approach to amphibian alkaloids and VOCs in poison frogs while opens up new research questions to assess the co-occurrence of both type of compounds and to investigate the evolutionary significance of a defence gradient that includes olfactory avoidance, unpalatability, and toxicity in dendrobatids. In addition, our results show that amphibian alkaloids could have a dual function (olfactory at distance, taste by contact) never explored before neither in Silverstonaeia nor in any other dendrobatid species.

Highlights

Poison frogs are known for the outstanding diversity of alkaloid-based chemical defences with promising therapeutic applications
Over 900 alkaloids have been characterized in amphibians [10,11,12], highlighting the chemical diversity found in Neotropical dendrobatid poison frogs which include more than 500 compounds classified in the following lipophilic families: batrachotoxins, histrionicotoxins, gephyrotoxins, pumiliotoxins, allopumiliotoxins, homopumiliotoxins, decahydroquinolines, pyrrolizidines, indolizidines, quinolizidines, lehmizidines, pyrrolidines, piperidines, tricyclics and pyridinic alkaloids [10]
Using Head-Space Solid Phase Microextraction (HS-SPME)/GC-MS in eight specimens of S. punctiventris we found 33 different compounds, seven of which were not annotated with available information in chemical libraries (Table 1)

Summary

Introduction

Poison frogs are known for the outstanding diversity of alkaloid-based chemical defences with promising therapeutic applications. Over 900 alkaloids have been characterized in amphibians [10,11,12], highlighting the chemical diversity found in Neotropical dendrobatid poison frogs which include more than 500 compounds classified in the following lipophilic families: batrachotoxins, histrionicotoxins, gephyrotoxins, pumiliotoxins, allopumiliotoxins, homopumiliotoxins, decahydroquinolines, pyrrolizidines, indolizidines, quinolizidines, lehmizidines, pyrrolidines, piperidines, tricyclics and pyridinic alkaloids [10]. Hydrophilic alkaloids, such as tetrodotoxins, have been found in two dendrobatid species [13, 14]. Many of these alkaloids possess toxic [2] or unpalatable function [21], but the evolutionary significance of toxicity versus unpalatability needs to be further explored [22]

Methods

Results

Discussion

Conclusion