Genetic architecture of host use in a widely distributed, polyphagous butterfly (Lepidoptera: Papilionidae): adaptive inferences based on comparison of spatio-temporal populations

Abstract

Genetic variance-covariance structure of larval performance within and among spatio-temporal populations of the widely distributed, polyphagous tiger swallowtail butterfly, Papilio glaucus, is described. Performance traits were assessed for full-sibling families on three host species: Liriodendron tulipifera, Magnolia virginiana and Prunus serotina. Mean performance varied across hosts, indicating these hosts present unique developmental environments. Although full-sibling families significantly differed in plasticity of across-hosts response in three of the five spatio-temporal populations, additive genetic variation was mostly associated with P. serotina or pupal mass. The relative lack of heritable variation in rate and length of larval development on L. tulipifera and M. virginiana was consistent with an earlier study that established host-associated geographic differentiation of P. glaucus populations. Performance appeared relatively independent across hosts and thus genetic constraints cannot be casually invoked to explain persistence of local adaptation and host specialization in the face of extensive gene flow. I promote the hypothesis that gene flow among geographically distant populations is relatively restricted and that previously established, allozyme-based estimates of panmixia are confounded by effects of Pleistocene glaciations. Significant heterogeneity of variance-covariance structure among spatio-temporal P. glaucus populations supports an interpretation of restricted gene flow and relative evolutionary independence. Despite low precision of estimates of genetic parameters, local variance-covariance structure was remarkably consistent with expectations given the presumed evolutionary history of regional populations.