Reproductive allocation in an ant reproducing by colony fission: experimental and theoretical studies
Thibaud Monnin (CNRS researcher, Institute of Ecology and Environmental Sciences of Paris (iEES-Paris), Sorbonne Université)
Social insects produce new colonies following two alternative strategies. Independent Colony Foundation (ICF) consists in the mother colony producing many queens that fly far away, start new colonies on their own and suffer high mortality (coloniser strategy). In contrast, colony fission consists in one (or a few) queen departing the mother colony with many workers (hence on foot in ants) and thus suffering low mortality (competitor strategy). We studied resource allocation during colony fission in the ant Cataglyphis cursor. Field observations showed that colonies that reproduced differed markedly in size. Larger colonies produced larger new colonies but did not produce more new colonies, and resource allocation among new colonies was highly biased in terms of both worker number and worker size. We tested whether C. cursor may adjust the number and size of new colonies to the intensity of competition by transplanting colonies in enclosure varying in colony density. These colonies produced fewer and larger new colonies than in the field, suggesting that they may indeed adjust resource allocation. Lastly, we used agent-based modelling to compare the success of colony fission with that of ICF. Our simulations show that the two strategies coexist under a wide range of parameter values because of a competition-colonization trade-off, and that environmental heterogeneity enhances coexistence conditions.