Effects of experimental warming on phenology and morphology of an aquatic insect (Odonata)

Background/Question/Methods

Developmental conditions often affect both phenology and plastic traits such as body size and morphology. Thermal conditions are especially important for ectotherms, whose development is largely regulated by environmental temperature. Understanding the potential effects of developmental temperature is crucial because body size and morphology affect multiple aspects of life history, including dispersal ability, while phenology can shape population performance and community interactions. Dispersal is a critical component of a species’ ability to shift its range in response to climate change, and changes in body size and morphology may alter the ability of organisms to complete the long-distance dispersal events necessary to track changing climatic conditions. We experimentally assessed how developmental temperatures experienced by larvae affected survival, phenology, and adult morphology of dragonflies (Pachydiplax longipennis).  Larvae were reared under 3 environmental temperatures: ambient, +2.5 degrees C, and +5 degrees C, corresponding to temperature projections for our study area 50 and 100 years in the future, respectively.

Results/Conclusions

We found clear effects of rearing environment on survival and phenology: dragonflies reared under the highest temperature conditions had the lowest survival rates, and emerged from the larval stage ~3 weeks earlier than control animals. We did not find an effect of rearing temperature on overall body size, but flight-related morphology (the ratio of thorax length to forewing length) was influenced by temperature. Dragonflies reared under experimentally warmed conditions (at both +2.5 and +5 degrees C above ambient) had shorter forewings in relation to thorax length, which may negatively influence flight capacity and dispersal ability. Although released adults were only rarely resighted, 5/7 individuals that were resighted at a pond distant from the release site had been reared under ambient conditions, suggesting that elevated rearing temperatures may adversely affect dispersal in this species.