Contextually conspicuous species are more likely to be venomous: Habitat-dependent aposematic colouration found...

Many animals use conspicuous colours to advertise their unprofitability to potential predators, a phenomenon known as aposematism. For example, conspicuous banded patterns in snakes are often highlighted as aposematic signalling of their venomous nature. However, aposematic colouration needs to be analysed while considering a species' environmental context, seen as species which seem conspicuous in isolation may be well camouflaged within their natural environment. Here, we collate images for 458 snake species from iNaturalist and use a novel metric quantifying the degree of conspicuousness of each species compared with its natural context to test the relationship between conspicuousness and the presence, potency and defensive properties of venom. We find that venomous species are significantly more contextually conspicuous compared with non-venomous species. However, while these results provide support for the link between the evolution of aposematism in relation to venom, we do not find an association with the potency or the pain-inducing capacity of venoms with the data used in this study, indicating that these traits may not be important drivers of the evolution of aposematism in snakes. Our novel approach demonstrates how incorporating the environmental context of a species can shed light on our understanding of the evolution of conspicuous colouration.