Meeting Abstract
Too much mechanistic detail impedes our ability to make general predictions of the response to simultaneous selection on multiple life history traits, whereas too few details may result in predictions that lack mechanistic support. Here we provide a framework that strikes a balance between the two showing how antagonism and synergism at the physiological level enables and constrains simultaneous selection at the phenotypic level of two life history traits, body size and development time. Previous work with the tobacco hornworm Manduca sexta has shown that these two life history traits are regulated by the interaction of the same three underlying physiological factors: growth rate, the timing of the cessation of juvenile hormone secretion and the timing of the secretion of the ecdysteroid hormones. After ten generations of selection on all four combinations of body size and development time (Big/Short, Big/Long, Small/Short, Small/Long) the three physiological and two life history traits differed significantly from the initial population. The three physiological factors explained 93% of the response of development time to simultaneous selection and 99% of the response of body size. When the two life history traits were under synergistic selection, the response to simultaneous selection was due largely to juvenile hormone and the ecdysteroids and constrained by growth rate. When the life history traits were under antagonistic selection, the response to selection was due primarily to the change in growth rate and constrained by the two hormonal traits. Evidence suggests that this framework has broad applicability to a diverse range of taxa including green algae, plants, amphibians and mammals and to other insects.
