Environmental warming during development affects phenology and morphology in an aquatic insect (Odonata)

Background/Question/Methods

Climate change is altering the thermal conditions organisms experience during development, including development rates and survival. Additionally, in organisms with complex life-histories, warming can have carry-over effects influencing adult phenotypes.  Ectotherms are especially sensitive to changes in thermal conditions and previous research suggests that aquatic organisms may be more vulnerable to climate change than terrestrial species. We addressed how realistic warming scenarios affected growth and survival in larval dragonflies and how warming affected the phenology of emergence to the adult stage and adult morphology. We reared dragonfly larvae (Erythemis collocata) in an experimental array of aquatic mesocosms with three thermal treatments: ambient, medium (ambient + 2.5°C), or high (ambient + 5.0°C). All treatments track natural levels of temperature variation, and the two warmed treatments closely approximate predicted levels of warming in the region in 50 and 100 years, respectively. Odonates were reared in these conditions from August 2013, early in their larval development, until their emergence as adults in the following year (April-September 2014). Adults emerging from mesocosms were collected and measured. We compared date of emergence, survival, and adult morphology across the three treatments.

Results/Conclusions

Warming resulted in a phenological shift, with significantly earlier emergence into the adult stage for those larvae reared in the warmed treatments (P < 0.03). Dragonflies from the high treatment emerged an average of a month earlier than those from the ambient treatment. Larval survival was not significantly different between the treatments. Warming also affected the morphology of adults emerging from mesocosms. Adults emerging from the high treatment treatment had proportionally shorter forewings than adults emerging from the other two treatments (P < 0.01). Morphological changes and advancing phenologies in response to warming have implications for adult performance and may shape the level of connectivity between populations.  We will discuss how our results compare to previous work in another dragonfly species and how similarities and differences in their responses may affect interactions between co-existing species of odonates. We also discuss the implications of environmental warming for odonate populations and communities in the context of climate change over the next century.