INTERPOPULATION DIFFERENCES IN HOST PREFERENCE AND THE EVOLUTION OF LEARNING IN THE BUTTERFLY, BATTUS PHILENOR

The host-discrimination behavior of the adult female pipevine swallowtail butterfly (Battus philenor) was investigated for two populations, an east Texas population that uses two host species with different leaf shapes and a Virginia montane population that uses one host species with a single leaf shape. While Texas and Virginia females exhibited similar chemotactile responses after landing on various host species, butterflies from each population landed more frequently on certain host species used by that particular population. Despite this difference in searching behavior, Texas and Virginia populations were equally capable of learning to search for the leaf shape of a particular host species in artificial enclosure arrays. In addition, learning of leaf-shape preference was confounded equally when each population was introduced into arrays containing all the host species found in both populations. The lack of differentiation in learning of leaf-shape preference between populations that differ in host breadth and host preference argues against the specific hypothesis that learning of leaf-shape preference represents a local adaptation that permits foraging butterflies in the east Texas population to respond to seasonal changes in the relative quality or abundance of host species that differ in leaf shape. Three hypotheses are proposed to explain the apparent absence of interpopulation genetic variation in learning traits. One hypothesis supposes that learning of leaf-shape discrimination is mediated by the same physiological mechanisms that permit females to learn to discriminate among suitable and unsuitable conspecific plants. Selection for restriction of learning of leaf-shape preference in the Virginia montane population may therefore be constrained by selection for learning of other types of discrimination behavior.