Ontogenetic habitat shifts reduce costly male–male interactions

Ontogenetic habitat shifts are predicted to increase the fitness and survival of individuals by allowing effective utilization of spatially distributed resources. Evidence supports nutritional requirements and predation pressure as drivers of habitat shifts. Likewise, intraspecific interactions are thought to lead to ontogenetic habitat shifts, however, empirical evidence is lacking. Here, we test if intraspecific male–male interactions are responsible for ontogenetic habitat shifts in Xanthagrion erythroneurum, a damselfly that undergoes developmental colour change. The juvenile males are yellow and change colour to red with sexual maturity. Field observations showed that the proportion of juvenile males is higher in adjacent woods than in primary mating arenas by ponds. We measured male–male interactions by the pond and in the woods, predicting the habitat switch would reduce male antagonistic interactions such as male aggression and male–male mating attempts. We showed that juvenile males receive less aggression in woods than at the pond mating arena. We conclude that lower population density and lower male encounter rates in the woods reduce the cost of male aggression for juvenile males. Our study provides evidence that stage-dependent habitat choice resulting from intrasexual antagonistic interactions may drive ontogenetic habitat shifts.