DAVIDOWITZ, G.*; ROFF, D.A.; NIJHOUT, H.F.; Univ. of Arizona; Univ. of California, Riverside; Duke Univ.: The physiological regulation of the response to simultaneous selection on body size and development time in Manduca sexta

Selection experiments on physiological traits can provide important, yet under-appreciated insight into the mechanisms by which traits and organisms respond to selection. The physiological and endocrine systems are responsible for coordinating organism-wide post-embryonic growth and development. Selection acting on post-embryonic traits, such as life history traits, will, by necessity, operate on these coordinating systems. We provide an example of the physiological regulation of the response to selection of two important life history traits, body size and development time. Three factors regulate both peak larval size and larval development time in the tobacco hornworm Manduca sexta, growth rate, the timing of the onset of juvenile hormone decay and the timing of prothoracicotropic hormone (PTTH) and ecdysteroid secretion. On the basis of this understanding of the physiological regulation of these two life history traits, we provide a framework for predicting how these underlying physiological factors enable or constrain the response to simultaneous selection on body size and development time. This framework may help elucidate the response to selection of a fundamental life history tradeoff- that between age and size at maturity.