How is the process of eclosion in Odonata influenced by environmental variables?

Lillyanne Kop

Dragonflies and damselflies (Order Odonata) are important organisms for both aquatic and terrestrial ecosystems. Despite the threats of climate change and urbanisation, conservation decisions are being made without key information about the ecology of Australian odonates. Although locations chosen for eclosion (the transition between aquatic nymph and terrestrial adult) are known to be an important factor for the survival of odonates, they are unknown for Australian species. Despite its implications for adult fitness, the influence of environmental variables (such as temperature and depth) on the timing of eclosion is also unknown. I explored these two aspects of eclosion using field sampling and a laboratory experiment. I collected wild odonate exuviae at ten Perth wetlands during summer to identify key features of eclosion habitat, including distance travelled, substrate quality and cover. The laboratory experiment manipulated warming (18 and 21 °C) and drying simultaneously for nymphs of two common damselflies, Ischnura aurora and Xanthagrion erythroneurum, to determine whether these variables influenced the nymph stage, which would result in changes to adult fitness (size) and the timing of eclosion. The study observed 360 exuviae and revealed that sites for eclosion were generally over (38%) or close to the water’s edge (37%), and prioritised heights of over a metre and a half above ground level (44%), regardless of distance from the water’s edge. Exuviae site selection was not influenced by ground vegetation cover, overhanging structures, texture or colour. The majority of exuviae (83%) were found on wooden substrates, especially Melaleuca spp. trees which provide shade and are commonly associated with wetlands. In the laboratory experiment 75 nymphs were collected, 35 of which were I. aurora and the other 40 were X. erythroneurum. X. erythroneurum displayed little response to either drying or warming and nymph condition did not influence adult fitness, or time to emergence. For I. aurora, temperature did not impact size or time to emergence, but drying increased time to eclosion by an average of 12 days and increased the size of both nymph (by 2 mm) and adult (by 4 mm). Furthermore, I. aurora nymph size partially explained adult condition, but did not influence time to eclosion. These results suggest that common damselfly species in Perth wetlands are likely resistant to warming impacts of climate change but ongoing drying in this region may affect adult fitness. However, negative effects of warming and drying on Melaleuca trees, and urbanisation on native riparian and emergent vegetation may limit sites for odonate eclosion. More research is needed to examine physiological aspects of fitness, responses of dragonflies and responses of rarer species to impacts of climate change.

How is the process of eclosion in Odonata influenced by environmental variables?

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