Hybridization of <i>Limenitis</i> in the Western Great Basin (Lepidoptera: Nymphalidae).

Abstract

The distribution and nature of sympatry and interaction of Limenitis weidemeyerii, Limenitis lorquini, and their "fridayi" hybrid were investigated in the southwestern Great Basin during 1996-1998. L. weidemeyerii is univoltine, L. lorquini is at least bivoltine, and "fridayi" showed a peak flight corresponding to the peak flight of L. weidemeyerii and the first brood of L. lorquini. This "Mono" hybrid zone extends from the Wassuk Range in western Nevada to several canyons on the east slope of the Sierra Nevada (Devils Gate Summit to Lee Vining Creek) in eastern California where these Limenitis inhabit streamside willow associations. L. weidemeyerii occurs as pure populations to the east and L. lorquini occurs to the north, west, and south of the hybrid zone. The hybrid zone has a general east to west gradient of decreasing proportions of L. weidemeyerii and increasing proportions of L. lorquini, hybrids are most common at intermediate locations. The trend varies somewhat, in part due to the convoluted axis of the hybrid zone with several subaxes and the geographical proximity of populations of one or the other parentals. Both parental phenotypes span the width of the hybrid zone and represent 28-90% of populations sampled within the hybrid zone. "Fridayi" is intermediate in size to L. weidemeyerii and L. lorquini and exhibits a range of superficial and genital phenotypes between the parental species. Field caught samples of "fridayi" are female deficient compared to field caught samples of non-hybrid Limenitis. The Mono hybrid zone appears to be maintained by hybrid inferiority balanced by continued dispersal of parentals into the zone. A shift in phenotypic proportions at some sites within the Mono hybrid zone has been apparent during the last 20 years. Another hybrid zone, the "Humboldt" hybrid zone, is known in northern Nevada in the Santa Rosa and Pine Forest ranges. This zone has not been well-studied, but appears phenotypically more stable than the Mono hybrid zone. Hybrids far outnumber parentals, and no sex-ratio skew is apparent. This zone, unlike the Mono hybrid zone, may be maintained by hybrid superiority with little or no dispersal into the zone by parentals. Due to the apparent stability of the Mono hybrid zone, an apparent reduction of gene flow through the hybrid zone, and at least some genetic incompatability. L. lorquini and L. weidemeyerii are considered separate species.