Mammals are mainly exposed to trace metals (TMs) via consuming contaminated food. Several studies have demonstrated relationships between metal concentrations in food and in animal tissues. However, potential effects of TMs on feeding behaviour of wildlife have been poorly documented under field conditions, despite experimental evidence showing that food selection is impacted by resource contamination. Here, we test the hypothesis that the diet of a generalist rodent, the wood mouse (Apodemus sylvaticus), is altered by soil TM contamination in the field. Wood mice were sampled in spring and in autumn along a gradient of soil contamination in the surroundings of a former smelter located in northern France. Available resources in the field were inventoried, and the diet of the animals was analysed using DNA "metabarcoding." We demonstrated that (a) relationship between the resource richness in the diet and their richness in the field was altered by soil metal contamination. Wood mice specialized their diet along the gradient of soil metal contamination for both plant and invertebrate resources in spring. We also showed that (b) preference for Salicaceae, a plant family accumulating metals, decreased when soil contamination increased. These results suggest that environmental TM pollution could act as a force modulating trophic interactions in terrestrial food webs, thereby affecting wildlife exposure to contaminants by trophic route.

Exposure of terrestrial mammals to chemical contaminants like trace metals (TMs) is considered to be mainly based on trophic transfer. Although relationships between TM transfer to animals and identity of contaminated food have been studied, the variation of the TM transfer with respect to diet diversity has been poorly documented. In this study, the oral exposure to TMs of wood mice Apodemus sylvaticus was investigated with respect to both the number of different items, i.e. diet richness, and the identity of items determined by metabarcoding from their stomach content, i.e. diet composition. The results showed that consuming Salicaceae, a known cadmium accumulator plant family, significantly increased exposure to cadmium and zinc.However, an increase in diet richness minimized exposure to cadmium when mice consumed Salicaceae items. This strongly suggests that TM accumulator items can lead to a high oral exposure to TMs but that such high exposure due to TM accumulator items can be "diluted" by diet richness due to other low accumulator items. Our results clearly indicate that both the presence of certain items in the diet and diet richness are important determinants of exposure to TMs in generalist animals, which matches the predictions of the "diet dilution hypothesis".

In recent decades, the Azé cave has begun to suffer from microorganism proliferation due to artificial lighting installations for touristic activity. The present work aims at understanding the origin of the Lampenflora and bacterial community populating inside the cave. We performed high throughput sequencing of the communities populating the outside, the entrance and the inside of the Azé cave. Our results indicated that 68.2–74.5% of the phototrophic community was represented by Eukaryotes, and 25.5 to 31.8% by cyanobacteria regardless of the sampled area. We observed a decrease of bacterial and phototroph species richness from the outside to the bottom of the cave. The phototrophic communities were significantly different in term of specific OTU richness but not in term of composition. For photosynthetic organisms, only 4 OTU were specific to the inside of the cave, representing less than 0.1% of the total OTUs. On the contrary, more than 400 bacterial OTUs were specific to the inside of the cave. These metabarcoding-based findings in the Azé cave revealed a complex community structure that is similar but less diverse in comparison to the outside.