Meeting Abstract
Respiratory proteins serve for the transport and storage of oxygen. Two types of respiratory proteins occur in the Pancrustacea: hemocyanin and hemoglobin. The copper-containing hemocyanin evolved from phenoloxidases in the arthropod stemline. Hemocyanins were only known from the malacostracan crustaceans but have recently been also identified in Remipedia and Ostracoda. Hemoglobins are common in Branchiopoda, but rare in other crustacean classes. Respiratory proteins had long been considered unnecessary in insects because of the tracheal system. Only chironimids, some backswimmers and the horse botfly, which all live under hypoxic conditions, were known exceptions, which possess hemoglobin. However, recent data suggest that hemocyanins occur in most ametabolous and hemimetabolous insects. Phylogenetic analyses showed a close relationship of hemocyanins of insects and Remipedia, suggesting a close relationship of these taxa. In “higher” hemimetabolous insects (e.g., cockroaches and grasshoppers), hemocyanin function is restricted to the developing embryo while in adults oxygen is supplied solely by the tracheal system. The pattern suggests that hemocyanin was the oxygen transport protein in the hemolymph of the last common ancestor of the pancrustaceans, but has been lost several times independently in taxa. The loss was probably associated with miniaturization, a period of high oxygen availability (e.g. in the Carboniferous period), a change in life-style or morphological changes. Once lost, hemocyanin could not be regained. When a respiratory protein was again required, it evolved several times independently from cellular hemoglobins. It is unlikely that these cellular hemoglobins had a respiratory role, but may rather be involved in signaling or ROS defense. Supported by DFG BU 956/14.
