title: Built to break: the antenna of a primitive insect, Petrobius brevistylis (Archaeognatha).
abstract: Jumping bristletails (Archaeognatha) have flagellate antennae with frequent breakpoints, structures destined to break when undue mechanical stress is applied. In natural populations of Petrobius brevistylis at least 67% of animals had broken antennae. In twenty-four trials, all antennae broke at a breakpoint under the animal's weight. Breakpoints consist of two cylinders of laminated cuticle, one stuck inside the other. For half the length of the breakpoint the cylinders are separated by a non-laminated layer of cuticle; thus a tripartite cuticle is formed. During a breakage, the two cylinders slide apart along that non-laminated middle layer that seems to act like a lubricant. While the cylinders pull apart, a thin cuticle unfolds that closes off the new tip of the antenna formed by the outer breakpoint cylinder. Later on, the cylinder is not replaced by a new terminal antennomere. Instead, the antennomere directly proximal to a breakpoint, i.e. the one that after the break forms the last antennomere, already possess the same complement of sensilla as the original terminal antennomere. This includes sensilla basiconica Type A and B found exclusively on these antennomeres and the original terminal antennomere. Breakpoints are common to Archaeognatha and Thysanura, insects that moult throughout their lifetime.
authors.affiliation: Biology Department, Mount Saint Vincent University, 166 Bedford Highway, Halifax, NS, Canada B3M 2J6. amalie.frohlich@msvu.ca
authors.forename: A
authors.initials: A
authors.lastname: Fröhlich
authors.forename: Z
authors.initials: Z
authors.lastname: Lu
mesh_terms: D000818:Animals; D057506:Arthropod Antennae / Q000254:growth & development / Q000648:ultrastructure*; D007313:Insecta / Q000254:growth & development / Q000648:ultrastructure*; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D009674:Nova Scotia; D058618:Sensilla / Q000254:growth & development / Q000648:ultrastructure; D013314:Stress, Mechanical