The water-to-air respiratory transition of amphibiotic dragonflies

The transition from water-breathing to air-breathing is perhaps one of the greatest achievements in animal evolution, as it allowed them to colonize land and occupy new environmental niches. Numerous studies have investigated the respiratory adaptations that must have accompanied this respiratory transition in vertebrates and crustaceans, and have reached the conclusion that water-breathing animals have adapted to low levels of blood CO₂ partial pressure (PCO₂) and HCO₃⁻ while air-breathers have adapted to high levels of PCO₂ and HCO₃⁻, and that all animals making this transition follow this trend. However, the insects originated on land as air-breathers, and certain lineages subsequently evolved water-breathing capacities to become aquatic. As a result, the insects must have faced and overcome different challenges during their invasion of water compared to vertebrates and crustaceans that were ancestrally water-breathing and secondarily became air-breathers. However almost nothing is known regarding the respiratory transition of insects, and it remains to be seen whether the conclusions based on vertebrates and crustaceans are applicable to insects. This thesis is the first to explicitly investigate the respiratory physiology of insects during the transition from water to air, in order to examine how similar or different it is to that of vertebrates and crustaceans making the same transition. By measuring the total CO₂ (TCO₂) content of dragonfly nymphs and adults, it was revealed that the magnitude of TCO₂ increase from water-breathing to air-breathing is very minor in these insects compared to that experienced by vertebrates and crustaceans. In addition, quantifying the acid-base status of dragonfly hemolymph showed that the change from water-breathing to air-breathing elicits modifications of the hemolymph chemistry that are not seen in vertebrates and crustaceans. The data presented in this thesis provide strong evidence that the respiratory transition of dragonflies from water to air is different from that observed in vertebrates and crustaceans, and questions the current consensus that all animals experience the same shift in blood PCO₂ and HCO₃⁻ during the transition from water to air.Science, Faculty ofZoology, Department ofGraduat