Dietary adaptations along the northern limit of distribution: what does the smooth snake Coronella austriaca eat in Norway? Metabarcoding of stomach content and visual analysis of faeces

Understanding how species survive at their poleward limits of distribution is of interest in species conservation, particularly in light of global warming and predictions of shifting distributions of both predators and prey species. How species adapt to high latitudes and to future climate changes will be impacted both by direct interactions with the environment, such as changing heat tolerances, but also indirectly through biotic interactions with prey and predators. The smooth snake Coronella austriaca in Norway provides an interesting case study of biotic interactions at range limits. The number of potential prey species of C. austriaca is lower in Norway than in southern latitudes. To investigate trophic adaptations at its poleward range limit we used metabarcoding sequencing to identify prey species in stomach samples of a museum collection of 17 preserved C. austriaca from Agder in southern Norway. Eight prey species were detected, four reptiles and four mammals. Field vole Microtus agrestis and common shrew Sorex araneus were the most common prey species, while bank vole Myodes glareolus and wood mice Apodemus sylvaticus were eaten by only a few smooth snakes. Slow worm Anguis fragilis was found in five samples and common lizard Zootoca vivipara in only three samples. DNA was also recovered from grass snake Natrix natrix in all but one sample, and DNA from European adder Vipera berus in one sample, indicating the role of ophiophagy. Visual analysis of 75 faeces from the Oslo region showed that A. fragilis was the most common prey species, followed by shrews. The main conclusion is that C. austriaca in Norway have a higher proportion of mammalian prey and snakes in their diet compared to populations in more southern latitudes.