Meeting Abstract

36.6  Thursday, Jan. 5  Hydraulic stress induced bubble nucleation and growth during pupal metamorphosis PRAKASH, Manu; Stanford University

Here I describe the role of physical fluid stress during pupal metamorphosis in flies. During early stages of pupation of larvae into adult flies, a physical gas bubble nucleates at a precise spatial and temporal location, as part of the normal development program in Diptera. Although its existence has been known for the last 50 years, the origin and control of this "gas nucleation" event has remained completely mysterious. Where does the driving negative pressure for bubble nucleation come from? How is the location of the bubble nucleation site encoded in the pupae? How do molecular processes control such a physical event? What is the role of this bubble during fly development? By developing imaging techniques including X-ray microscopy and bio-physical measurements for live insect pupal structures, here I elucidate the physical mechanism for the appearance and disappearance of this bubble. Via growth rate measurements of this bubble in a developing pupae subjected to variable fluid stress environments for three different species (Drosophila melangastor, Musca domestic, Sarcophaga bercaea), I directly measure the evaporative stress and the resulting negative pressure in the pupal cavity. The sharp increase in this negative pressure specifically encodes the exact timing of the nucleation event. Furthermore, controlled buckling of the main tracheal conduits breaks symmetry and thus govern the physical location of the nucleation site. Gaining physical insights into this hydraulic mechanism also allows us to finally predict the mechanics and inherent design of pupal shell architecture in various species.