Meeting Abstract

S4.6  Monday, Jan. 5  Tracheal Systems and the Evolution of Insects VANDENBROOKS, J. M.*; KAISER, A.; HARRISON, J.F.; Arizona State University; Midwestern University; Arizona State University john.vandenbrooks@asu.edu

Most insects respire via an air-filled tracheal respiratory system. Tracheal systems appear in the three related clades of Ecdysozoa that achieve large size and terrestriality, and within all three higher subclades of Arthropoda, suggesting that the characteristics necessary for tracheation are fundamental to Ecdysozoa. However, the apparent evolution of multiple terrestrial arthropod clades from marine ancestors suggests independent evolution of tracheal systems in hexapods, myriapods and chelicerates. Members of all extant hexapod groups, including insects, possess tracheae, supporting a common terrestrial ancestor of this group. Insects may be excluded from marine environments because possession of a tracheal respiratory system limits physiological function in a marine environment. Possession of a tracheal system is a key characteristic in the evolution of flight, providing an important factor in the great biodiversity of insects. In addition, tracheal systems support the highest rates of oxygen consumption in the animal kingdom and tremendous tolerance to hypoxia/anoxia. However, accumulating data support the hypothesis that possession of a tracheal system limits insect body size, and that historical variation in atmospheric oxygen influenced maximal insect size. Larger insects have a greater fraction of their body devoted to tracheal system, perhaps to overcome gas exchange limitations associated with blind-ended tracheal tubes. Rearing studies under different oxygen levels in the lab have shown strong effects on insect respiratory structures, average body size, and development rates in a variety of insect groups, suggesting that changes in atmospheric composition in the past may have influenced insect ecology and evolution. Supported by NSF IBN 0419704 and EAR 0746352.