Population Genetic Evidence of Restricted Gene Flow Between Host Races in the Butterfly Genus Mitoura (Lepidoptera: Lycaenidae)

We surveyed variation in allozymes and in the mtDNA cytochrome oxidase subunit II (COII) gene in populations of three nominal species of hairstreak butterßies in the genus Mitoura in northern California. These species are separated on the basis of wing pattern and larval hostplant differences: M. nelsoni (Boisduval) larvae feed on incense cedar, Calocedrus decurrens (Torrey); M. muiri(Hy.Edwards) larvae feedoncypress,CupressusmacnabianaA.MurrayandC. sargentii Jepson; and M. siva (W. H. Edwards) larvae feed on juniper, Juniperus occidentalis Carrière. All three taxa were indistinguishable using allozyme allele frequency data. Genetic distances among populations of all three species were very small (NeiÕs (1978) unbiased D 5 0.000Ð0.007). Percent uncorrected mtDNA divergences were similarly small (P 5 0.2Ð1.1%) and haplotypes are shared among taxa. However, analysis of molecular variation and exact tests for population differentiation indicate that populations of M. muiri in the coast range are differentiated from other populations. We conclude thatdivergenceamong these three taxahasoccurredvery recently.We further suggest thepossibility that divergence is being driven by the evolution of larval host races, and that gene ßow is restricted between M. nelsoni and at least some populations of M. muiri. This restriction may result from the adultsÕ habit of mating preferentially on different host trees and through phenological differences in the timing of reproduction.