The reproductive success of many aquatic insects is highly dependent on where they deposit their eggs. Not all aquatic habitats are created equal, some are more favorable than others for larval development and it would be evolutionarily advantageous for an ovipositing female to differentiate between them and choose the most suitable for her offspring’s survival. Numerous studies have shown that many species with complex life-cycles representing a diverse array of taxonomic groups sort themselves non-randomly among habitat patches on the basis of colonization of higher quality habitats. In the case of dragonflies, insufficient evidence exists to support the hypothesis that this group can assess relevant indicators of patch quality and use those cues to select habitat.
We investigated whether female dragonflies actively avoid ovipositing in sites containing predatory fish that potentially inflict significant fitness costs via predation to their offspring. To test this hypothesis, 16 replicate mesocosms were set up and filmed to assess dragonfly oviposition events in two treatments: (1) fish (Lepomis cyanellus) and (2) fishless habitats. Nearly 1000 hours of video was recorded. Additionally, a development study was performed aimed to determine to what degree predation by Lepomis cyanellus affects survival and other fitness correlates of larval dragonflies
Results/Conclusions
Oviposition by 3 species of free-ranging dragonflies (Pachydiplax longipennis, Pantala flavenscens, Libellula incesta) of the family Libellulidae was observed in 16 sets of replicated experimental mesocosms. In addition, the larval performance of 3200 individuals of the species Erythemis simplicicolis and Pachydiplax longipennis was assessed in 32 replicated experimental mesocosms.
The results of the oviposition and larval development studies contradict each other. Though the presence of predatory fish drastically decreased larval survival and performance, adult dragonflies did not strongly discriminate between high and low quality habitats in terms of the number of oviposition events. However, even though oviposition events between treatments were similar, the number of abdomen dips per oviposition event differed between treatments. Assuming the number of dips is positively correlated to the number of eggs released (currently being assessed); more eggs were deposited in fishless mesocosms, suggesting that dragonflies may exhibit a form of bet-hedging when selecting habitat for their offspring. This result is inconsistent with those observed in many other colonizing aquatic organisms which strongly avoid predatory fish such as Lepomis cyanellus. We discuss alternative mechanisms of matching oviposition with habitat quality, and hypotheses regarding observed lack/variation in selectivity