Large-scale movement by a North American dragonfly as revealed through genetic and isotope proxies: A new approach to insect migration

Anax junius (Odonata: Aeshnidae) is a widespread North American dragonfly with a terrestrial adult stage and an aquatic larval stage. For more than a century, biologists have speculated that that A. junius may engage in large-scale movement, possibly via seasonal migration. The range and basis of that movement have proven resistant to analysis, an issue common to the study of all nonlocal dispersal by small-bodied organisms. Using a combination of population genetic and both stable and radiogenic isotopic techniques applied to a large group of individuals, a synergistic set of insights has been revealed. Intra-generational continental-scale movement is common. Long-distance movement is bidirectional, with apparent multigenerational spring and fall migrations. Population structure is almost completely absent. Such patterns are distinct from other known winged migrants and represent a novel basis for movement. These results and methodologies suggest that large-scale insect movement may be more common and variable than has been imagined to date, and that this movement may be studied more easily and inexpensively than heretofore without resorting to direct tracking of individuals.