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

Abstract

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.

Geographical Variation in Body Size and the Bergmann’s Rule in Andrew’s Toad (Bufo andrewsi)

“…Environmental variations can impose pressures on an animal’s physiology [ 1 , 2 , 3 ], phenology [ 4 , 5 , 6 ], morphology [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ], distribution [ 20 ], and life-history strategies [ 21 , 22 , 23 , 24 , 25 , 26 ]. The ecogeographic patterns of covariation between biological traits and environmental variables [ 27 ] provide opportunities to assess the adaptions of animals in response to the selection pressures imposed by significant variations in temperature, precipitation, and associated microclimate variations [ 28 , 29 ].…”

An amphibian toxin phenotype is sexually dimorphic and shows seasonal concordant change between sexes

“…amphibians, which overwhelmingly exhibit female-biased sexual size dimorphism (Shine, 1979;Lindenfors et al, 2007;Mori et al, 2017;Pogoda and Kupfer, 2018). A defining trait of amphibians is the presence of poison glands, but few studies have evaluated whether or not toxin phenotypes are sexually dimorphic (Mebs and Pogoda, 2005;Daly et al, 2008;Saporito et al, 2010;Stokes et al, 2011;Jeckel et al, 2015;Preißler et al, 2019;De Meester et al, 2021). Previous evaluations have focused on poison gland morphology and arrangement (Aoto, 1950;Staub and Julie, 1997;Chen et al, 2017;Zamora-Camacho, 2022) without addressing sexbased differences (Mailho-Fontana et al, 2019) and the few studies that have addressed poison composition and quantities found that anurans (family Dendrobatidae) exhibit sex-based differences due to diet (Saporito et al, 2006;Daly et al, 2008;Saporito et al, 2010;Jeckel et al, 2015).…”

“…Previous evaluations have focused on poison gland morphology and arrangement (Aoto, 1950;Staub and Julie, 1997;Chen et al, 2017;Zamora-Camacho, 2022) without addressing sexbased differences (Mailho-Fontana et al, 2019) and the few studies that have addressed poison composition and quantities found that anurans (family Dendrobatidae) exhibit sex-based differences due to diet (Saporito et al, 2006;Daly et al, 2008;Saporito et al, 2010;Jeckel et al, 2015). In addition, urodeles (genus Salamandra) possess, overall, a similar alkaloid composition (Preißler et al, 2019), but show distinct quantities of component toxin between sexes (Mebs and Pogoda, 2005;De Meester et al, 2021).…”