Giant damselflies in a tropical forest: reproductive biologyof Megaloprepus coerulatus with notes on Mecistogaster (Zygoptera: Pseudostigmatidae)

The tropical forest of Barro Colorado Island, Panama, harbors three common species of giant damselflies which are atypical odonates in several respects. Adult pseudostigmatids can detect non-moving prey and feed on small web-building spiders, occasionally taking wrapped prey from webs. On BCI, females of all three species oviposit in randomly distributed, water-filled treeholes. Larvae of the large Megaloprepus coerulatus occupied larger treeholes than those of Mecistogaster linearis or M. ornatus. Males of the sexually dimorphic Megaloprepus held mating territories around water-filled treeholes for up to two months, defending them from conspecific males and permitting only females with whom they had mated to oviposit in the holes. Territorial males were significantly larger than non-territorial males and all but one of the 16 observed matings involved resident males. In addition, defended treeholes were larger than undefended holes that also contained Megaloprepus larvae. However, because larval habitats vary greatly in quality, environmental influences on body size may greatly reduce the opportunity for the population to respond directly to selection on body size. Neither Mecistogaster linearis nor M. ornatus held territories nor remained localized in an area. Both species of Mecistogaster were less sexually dimorphic in size and coloration than was Megaloprepus. Matings in Mecistogaster appear to result from random encounters in light gaps where both sexes forage on spiders.