Limited contamination by trace metals in city colonies of the ant Temnothorax nylanderi

Abstract

In urban environments, trace metals are a widespread class of pollutants that represents a major threat to organisms. Contamination levels in insects differ greatly among habitats, and a basic assumption is that individual contamination depends, at least in part, on environmental contamination. Ants are major actors in ecosystems, but surprisingly little information is available on trace metal contamination of ants in urban environments. Ants could be particularly sensitive to their local environment due to sedentary nesting but their social life could limit contamination. In this study, we assessed whether city colonies of the ant Temnothorax nylanderi differed from forest colonies in their trace metal contamination, and we tested whether larger colonies tolerate pollution better, then showing a lower level of contamination. We collected ant colonies and soil from five city parks in Paris and five forests around Paris, and we measured the concentration of five trace metals (cadmium, copper, iron, lead and zinc). We found that despite living in a more contaminated habitat for cadmium, copper, zinc and lead, city colonies were not more contaminated than forest colonies, except for lead. Interestingly, for lead, contamination decreased when colony size increased, suggesting that living in large groups limits pollutant contamination. Our results suggest that city colonies manage to cope with most trace metals. We argue that analysing whole colonies is important to take into account social life.