Experimental warming decreases egg-development time in four libellulid dragonfly species

Background/Question/Methods

Increasing global temperatures have been correlated with shifts in phenological events, leading to the decoupling of species interactions. While many species have exhibited phenological responses to warming, the strength of these responses often varies between species. Phenological asynchronies between interacting species have been observed as a result. However our knowledge of how climate warming will impact these interactions is limited because we lack data on inter-specific variation. Larval odonates typically exhibit negative trends in egg development time and temperature, however it is unknown how much this response varies between species. We experimentally tested for species-specific responses in egg-hatching phenology with increasing water temperature. We compared the effects of water temperature (21^o, 24^o, 27^o and 30^oC) on time to hatching in eggs from four species of libellulid odonates that co-exist in ponds in eastern North America. We measured time to hatching across thermal treatments. 

Results/Conclusions

We found that temperature significantly affected egg-development time; as temperature increased egg development time decreased (P<0.001). However, there was no interaction between species and temperature on egg-development time (P=0.857). These results imply that egg-development time appears to be a highly conserved plastic trait within libellulid odonates that decreases predictably with increasing temperatures. This also indicates that advances in hatching phenology may not impact larval odonate interactions because the order of hatching dates will remain consistent even with increased climate warming. However, temperature also affects organism growth rates, body size and behavior—factors that can contribute to changes in trophic or competitive interactions, especially in size-structured feeding guilds. Therefore it is crucial that multiple factors be considered when predicting the effects of phenological change with increasing temperatures.