Meeting Abstract
Most aspects of oxygen sensing including hypoxia-inducible factor (HIF), AMPK, and nitric oxide signaling are ancient pathways that occur throughout the Pancrustacea. Tracheal respiratory systems have evolved independently several times in terrestrial Arthropoda, including in the Hexapoda within the Pancustacea. Tracheal ventilation occurs primarily due to intersegmental muscles altering body volume, re-purposing muscles used primarily for posture and locomotion. However, some aquatic juvenile insects utilize appendage muscles for external ventilation as in crustaceans. Both crustaceans and insects respond to hypoxia with increasing ventilation driven by central pattern generators in the nerve cord. The response reflects the location of the primary constraints on gas exchange, with crustaceans increasing external and insects increasing internal ventilation. In contrast to most vertebrates, Pancrustaceans decrease rather than increase heart function in response to hypoxia. Tracheal systems and air-breathing allow hexapods to achieve higher rates of oxygen consumption than crustaceans, and hexapods are generally more able to support locomotion with aerobic metabolism. However, the two systems seem to have similar capabilities to support metabolism during hypoxia as critical PO2 values that limit aerobic metabolism and performance in crustaceans and insects appear similar. All Pancrustaceans examined so far exhibit suppression of metabolism, feeding and growth in mild hypoxia. Both air-breathing crustaceans and hexapods can achieve high internal PO2 levels, and both have relatively low internal PCO2 and bicarbonate levels relative to vertebrates. Secondary evolution of air-breathing in crustaceans and water-breathing in hexapods are beautiful examples of convergent function within the constraints of phylogenetic history. Partially supported by NSF IOS 1122157 and 1256745.
