Assessing the Multivariate Evolutionary Responses of Phenological Differentiation for Sibling Species: Biosystematics in the Macrosteles fascifrons Complex (Homoptera: Cicadellidae)

Abstract

A brief history of the concept of the Macrosteles fascifrons (Stal) complex (aster leafhoppers) in the literature is given. Taxonomic problems are discussed involving the use of the name M. fascifrons for vector work in the lower Nearctic, the origin of the holotype of Macrosteles severini Hamilton, 1983, and the taxonomic status of long-winged and short-winged Macrosteles cultures at the University of California, Berkeley. A method is presented for distinguishing, quantifying, and comparing the biologically inherent seasonal phenological differentiation between these two laboratory-reared sibling species in the complex. The results can be used in taxonomic decisions. Morphometric traits are used after variance information associated with species level differentiation is removed. The method generates a comparative indicator for the multivariate evolutionary pathway between spring and fall mean group phenotypes for each of two species reared under equivalent laboratory conditions over several generations. The relative slope of this phenological pathway is then compared between the species. Results on two Macrosteles spp. indicate seasonal phenological slopes are quite similar between sexes within a species but differ markedly between species. The quantitative genetic contributions of a set of traits imparting the phenological (plus sexual) differentiation is ascertained.