Sex Differences and Size at Emergence Are Not Linked to Biased Sex Ratios in the Common Green Darner, Anax junius (Odonata: Aeshnidae)

ABSTRACT

Many species of dragonflies exhibit sexual dimorphism and biased sex ratios in adult populations. It is predicted that, in species with territorial adults, males should be larger than females at emergence. Larger male size should elevate foraging rate and lead to increased predation risk and higher male mortality during the larval stage. We tested these predictions for a territorial dragonfly, Anax junius, using laboratory and field experiments. We measured differences in growth and foraging activity between the sexes, determined sex ratios at emergence, and measured size at emergence for female and male dragonflies. Males gained more mass than females and males spent more time in motion and moved longer distances than females in foraging trials. Males were larger than females at emergence in natural populations, but sex ratios at emergence were not significantly different from 1:1. Sex-specific growth strategies in the larval stage did not result in biased sex ratios at emergence but may be important to the reproductive success of this territorial dragonfly.