Genetic and phenotypic population structure of the Coenonympha tullia complex (Lepidoptera: Nymphalidae: Satyrinae) in California: no evidence for species boundaries

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Abstract
Decisions regarding species status of taxa showing geographic replacement are explicit hypotheses about population structure. The structure of 21 populations of the Coenonympha tullia group from northern California, southwestern Oregon, and northern Nevada was analyzed for evidence of reproductive isolation. These samples included five subspecies (california, eryngii, ampelos, eunomia, and mono) nominally placed in three species (california, ampelos, and ochracea). We found very high intra- and inter-population variability in the "diagnostic" wing pattern characters used by previous authors. There is evidence of intergradation between eryngii and eunomia in southwestern Oregon, and between california and ampelos in the eastern Feather River drainage in California. A complex cline involving California, eryngii, and ampelos occurs in the Pit River drainage of northeastern California. The taxon mono appears distinct, apparently because of an absence of Coenonympha populations in the expected mono–ampelos contact area. Electrophoretic analysis of the same 21 populations showed very high intrapopulation genetic variability (expected heterozygosity = 13.5–20.4%, percentage of polymorphic loci (most common allele < 99%) = 35.5–58.8%; 14 alleles at the locus for phosphoglucose isomerase (one population with 11 alleles)). However, interpopulation (geographic) variability was extremely low. Standardized genetic variance among populations (FST, using Wright's formulation) in contact zones indicates that gene flow is probably uninterrupted between the subspecies california, eryngii, ampelos, and eunomia. FST values for the isocitrate dehydrogenase locus indicate that present-day gene flow is probably unimportant in maintaining similarity between ampelos and mono. The genetic population structure is reminiscent of highly vagile colonizing species, but this may be largely historical, due to post-Pleistocene range changes rather than high present-day interpopulation migration rates. We conclude that all California populations are conspecific. Only the subspecies mono is clearly separated from the others, at the level 0.034 (Nei's unbiased distance), approximating that of weak subspecies in other taxa. The North American entities should all be provisionally classified as subspecies of the holarctic species tullia unless evidence is found to support their separation.
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