Molecular and morphological divergence in the butter ̄y genus Lycaeides (Lepidoptera: Lycaenidae) in North America: evidence of recent speciation

Lycaeides idas (Linnaeus) and L. melissa (W. H. Edwards) (Lepidoptera: Lycaenidae) are broadly sympatric in several regions of North America (Fig. 1) and are morphologically distinguishable by qualitative wing pattern differences (Tilden & Smith, 1986), quantitative differences in male genital morphology (Nabokov, 1949; Lane & Weller, 1994) and by ecological differences in habitat speci®city and hostplant associations (Ferris & Brown, 1981; Garth & Tilden, 1986; Scott, 1986; Tilden & Smith, 1986; Opler, 1992). Based on these characteristics, these species are further subdivided currently into 17 subspecies (12 in L. idas, ®ve in L. melissa) (Miller & Brown, 1981; Ferris, 1989), two of which have attracted the attention of conservation and evolutionary biologists: L. m. samuelis, the Karner Blue butter ̄y, is a federally endangered subspecies (US Fish and Wildlife Service, 1992; Lane, 1994); L. i. lotis, the Lotis Blue, has the same status but is now believed to be extinct (Arnold, 1993). Nabokov (1949) suggested that limited hybridization between L. idas and L. melissa may occur in isolated localities. In particular, populations in the Warner Mountains of north-eastern California may be of hybrid origin. We studied the evolutionary relationships among populations of these two species and investigated the hypothesis of hybridization by surveying variation in morphology and in two kinds of genetic markers. The entity we are calling idas was separated on genitalic grounds from the palearctic species L. argyrognomon by Higgins (1985) but is often referred to under that name in the older Nearctic literature. As currently de®ned, Lycaeides idas is a circumpolar, Holarctic, polytypic species while L. melissa is purely North American.