Abstract
Chemical defences are widespread in nature, yet we know little about whether and how climatic and geographic factors affect their evolution. In this study, we investigated the natural variation in the concentration and composition of the main bufogenin toxin in adult Asian toads (Bufo gargarizans Cantor) captured in twenty-two regions. Moreover, we explored the relative importance of eight climatic factors (average temperature, maximum temperature, minimum temperature, average relative humidity, 20–20 time precipitation, maximum continuous precipitation, maximum ground temperature, and minimum ground temperature) in regulating toxin production. We found that compared to toads captured from central and southwestern China, toads from eastern China secreted higher concentrations of cinobufagin (CBG) and resibufogenin (RBG) but lower concentrations of telocinobufagin (TBG) and cinobufotalin (CFL). All 8 climatic variables had significant effects on bufogenin production (ri>0.5), while the plastic response of bufogenin toxin to various climate factors was highly variable. The most important climatic driver of total bufogenin production was precipitation: the bufogenin concentration increased with increasing precipitation. This study indicated that the evolution of phenotypic plasticity in chemical defences may depend at least partly on the geographic variation of defensive toxins and their climatic context.
Highlights
Chemical defences are widespread in nature, yet we know little about whether and how climatic and geographic factors affect their evolution
We aimed to explore the natural variation in chemical defences and its relationships with assorted climatic and geographic factors in adult Asian toads
We found that the concentrations and proportions of the main defensive chemicals in adult Asian toads from different geographical regions were highly variable
Summary
Chemical defences are widespread in nature, yet we know little about whether and how climatic and geographic factors affect their evolution. Asian toads can secrete and release highly antimicrobial and poisonous defensive toxins from large parotoid glands when they face an environmental risk[16] These toxins are important defences against predators and microorganisms[17,18,19]. Gamabufotalin (GB), telocinobufagin (TBG), bufotalin (BFL), cinobufotalin (CFL), bufalin (BL), cinobufagin (CBG) and resibufogenin (RBG) (Fig. 1) are the dominant components, representing more than 80% of the total amount of bufagenins[26] These compounds are considered major contributors to the role of toxins in defence[27]. This study is the first to determine the variation in chemical defences among Asian toads in different geographical regions and its relationship to climatic factors
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