[Mass spectrum of salamander alkaloids]

A skin secretion metabolome analysis of the Greek Dodecanese Lycian salamanders: Preliminary evidence of dietary alkaloid sequestration in urodeles

Lyciasalamandra species, like most amphibians, secrete a wide array of compounds from their granular and mucous skin glands, including the internally synthesized samandarine alkaloids, making their skin a complex organ performing a variety of functions. Lyciasalamandra helverseni and L. luschani basoglui are insular endemics of the Dodecanese islands of SE Greece, bearing distinct isolated populations, with well-documented phylogenetic profiles. Here, we employ a metabolomics approach, utilizing UPLC-ESI-HRMS/MS data of the skin secretions sampled from a number of specimens found in the islands of Karpathos, Kasos and Kastellorizo, in an effort to reveal aspects of their chemistry and diversity across populations. The results indicated statistically significant variation between all taxa examined, based on various secreted compounds. The underlying factors of variation highlighted by the multivariate analysis were differences in samandarine and other alkaloid content as well as in animal size. Metabolite annotation, based on dereplication tools and most importantly HRMS and HRMS/MS spectra, yielded a number of known samandarine alkaloids, reported for the first time in the currently studied Lyciasalamandra species. We also present documentation for novel members of the samandarine alkaloid family, as well as preliminary evidence for a possible dietary alkaloid sequestration. This work can set the basis for further research of this often-neglected endemic species of the Salamandridae, as well as the structural investigation of the samandarine alkaloid group.

Toxin variation among salamander populations: discussing potential causes and future directions

Amphibians produce defensive chemicals which provide protection against both predators and infections. Within species, populations can differ considerably in the composition and amount of these chemical defenses. Studying intraspecific variation in toxins and linking it to environmental variables may help us to identify the selective drivers of toxin evolution, such as predation pressure and infection risk. Recently, there has been a renewed interest in the unique toxins produced by salamanders from the genus Salamandra: the samandarines. Despite this attention, intraspecific variation has largely been ignored within Salamandra-species. The aim of this study was to investigate whether geographic variation in profiles of samandarines exists, by sampling 4 populations of Salamandra atra over its range in the Dinaric Alps. In addition, we preliminary explored whether potential variation could be explained by predation (counting the number of snake species) and infection risk (cultivation and genomic analyses of collected soil samples). Salamanders from the 4 populations differed in toxin composition and in the size of their poison glands, although not in overall toxin quantity. Nor predation nor infection risk could explain this variation, as populations barely differed in these variables. Sampling over a much broader geographic range, using better estimators for predation and infection risk, will contribute to an improved understanding of how environment may shape variation in chemical defenses. Nevertheless, as the 4 populations of S. atra did differ in their toxin profiles, we propose that this species provides an interesting opportunity for further ecological and evolutionary studies on amphibian toxins.

Functional colour genes and signals of selection in colour-polymorphic salamanders

Coloration has been associated with multiple biologically relevant traits that drive adaptation and diversification in many taxa. However, despite the great diversity of colour patterns present in amphibians the underlying molecular basis is largely unknown. Here, we use insight from a highly colour-variable lineage of the European fire salamander (Salamandra salamandra bernardezi) to identify functional associations with striking variation in colour morph and pattern. The three focal colour morphs-ancestral black-yellow striped, fully yellow and fully brown-differed in pattern, visible coloration and cellular composition. From population genomic analyses of up to 4,702 loci, we found no correlations of neutral population genetic structure with colour morph. However, we identified 21 loci with genotype-phenotype associations, several of which relate to known colour genes. Furthermore, we inferred response to selection at up to 142 loci between the colour morphs, again including several that relate to coloration genes. By transcriptomic analysis across all different combinations, we found 196 differentially expressed genes between yellow, brown and black skin, 63 of which are candidate genes involved in animal coloration. The concordance across different statistical approaches and 'omic data sets provide several lines of evidence for loci linked to functional differences between colour morphs, including TYR, CAMK1 and PMEL. We found little association between colour morph and the metabolomic profile of its toxic compounds from the skin secretions. Our research suggests that current ecological and evolutionary hypotheses for the origins and maintenance of these striking colour morphs may need to be revisited.

Isolation and Identification of Alkaloids from Poisons of Fire Salamanders ( Salamandra salamandra)

Fire salamanders ( Salamandra salamandra) are conspicuously colored amphibians secreting a skin poison that contains unique steroid alkaloids such as samandarine (1) and samadarone (2), exhibiting toxic as well as antimicrobial activities. Because of their antipredatory and anti-infectious functions, alkaloids from Salamandra poison are of interest with regard to the threat that the lethal fungus Batrachochytrium salamandrivorans ( Bsal) poses to salamanders. Nevertheless, reliable data on the biological activity of Salamandra alkaloids are scarce, in part due to the difficulty to obtain and study those substances. Thus, isolation of pure salamander alkaloids is an important task that might directly contribute to the understanding of Bsal infections. Here we present a noninvasive isolation procedure for samandarine (1) and O-acetylsamandarine (3), as well as for two new alkaloids, O-3-hydroxybutanoylsamandarine (4) and samanone (6), using HPLC. For the first time, high-field NMR data are presented for these alkaloids. Analysis using GC/MS and ESI⁺-MS, provided important information on the structural variability of these salamander alkaloids.

Skin mucosome activity as an indicator of Batrachochytrium salamandrivorans susceptibility in salamanders

Recently emerged fungal diseases, Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal) are an increasing threat to amphibians worldwide. In Europe, the threat of Bsal to salamander populations is demonstrated by the rapid decline of fire salamander populations in Germany, the Netherlands and Belgium. Although most European urodelans are susceptible to infection in infection trials, recent evidence suggests marked interspecific differences in the course of infection, with potentially far reaching implications for salamander conservation. As a salamander's skin is the first line of defense against such pathogens, interspecific differences in innate immune function of the skin may explain differential susceptibility. Here we investigate if compounds present on a salamander's skin can kill Bsal spores and if there is variation among species. We used a non-invasive assay to compare killing ability of salamander mucosomes of four different species (captive and wild Salamandra salamandra and captive Ichtyosaura alpestris, Cynops pyrrhogaster and Lissotriton helveticus) by exposing Bsal zoospores to salamander mucosomes and determining spore survival. In all samples, zoospores were killed when exposed to mucosomes. Moreover, we saw a significant variation in this Bsal killing ability of mucosomes between different salamander host species. Our results indicate that mucosomes of salamanders might provide crucial skin protection against Bsal, and could explain why some species are more susceptible than others. This study represents a step towards better understanding host species variation in innate immune function and disease susceptibility in amphibians.

Variability of alkaloids in the skin secretion of the European fire salamander (Salamandra salamadra terrestris)

The two major alkaloids, samandarine and samandarone, were identified in the skin secretion of individual specimens from two populations of the European fire salamander (Salamandra salamandra terrestris) by gas chromatography/mass spectrometry. High intraspecific variability in the ratio of both alkaloids was observed, but also in individual specimens over a period of 4 months suggesting separate metabolic pathways of the compounds. Alkaloid synthesis appears to take place also in liver, testes and ovaries, whereas the larvae of the salamanders are entirely free of alkaloids.