Meeting Abstract

97.5  Wednesday, Jan. 7  Waiting to Exhale: Tracheal Air-filling in Embryos of Manduca sexta SPRAGUE, J. C.*; SMITH, J. N.; WOODS, H. A.; Univ. Montana; Univ. Montana; Univ. Montana jonathan1.sprague@umontana.edu

Insects exchange gases via branching tubes called trachea, which are air filled in larvae, pupae, and adults. In embryos, by contrast, tracheae are liquid filled and therefore nonfunctional. The transition from liquid- to air-filled tracheal tubes is a key event in ontogeny, but how it happens is unclear. Wigglesworth argued that air filling is a consequence of fluid absorption by tracheoles, which either draws outside air into the embryo or ruptures fluid inside the tracheal system. Here we describe a complementary mechanism in embryos of Manduca sexta. Time-lapse videos show that embryonic tracheal systems undergo rapid air filling about of the way through development. Air bubbles originate in sub-spiracular spaces, probably by nucleating onto increasingly hydrophobic tracheal cuticle. The bubbles expand rapidly (< a few seconds) to fill local tracheal trees and longitudinal branches between spiracles. Using several manipulative experiments, we show that expansion is driven in part by spring-like deformation of the eggshell. In turn, eggshell deformation is driven by earlier water loss. This mechanism couples local microenvironments around eggs to a key event in ontogeny, tracheal air-filling. Functionally, air filling in the embryonic stage may prepare the tracheal system for gas exchange during hatching or in the larval stage. Alternatively, it may have a respiratory function in the embryo itself. We are currently testing these alternatives by measuring metabolic performance of embryos during respiratory challenges.