Is the globally rare frosted elfin butterfly (Lycaenidae) two genetically distinct host plant races in Maryland? DNA evidence from cast larval skins provides an answer

Abstract

Frosted elfin butterfly caterpillars (Callophrys irus) eat either lupine (Lupinus perennis) or wild indigo (Baptisia tinctoria) legumes. Data from larval behavior, adult morphology, demographics, and phenology have led to the suggestion that lupine-feeding populations are genetically distinct from wild indigo-feeding populations. Frosted elfins are of conservation concern throughout their range in the eastern half of North America, and the possibility of host plant races—in which females pass genetically determined oviposition preferences to their daughters—complicates assessments of this vulnerable species. The maternal inheritance of mitochondrial DNA sequences makes CO1 an excellent gene to determine if genetically distinct host plant races have evolved in frosted elfins. In this paper, we extracted DNA using cast larval skins, a non-lethal, minimal-disturbance method appropriate for insects of conservation concern. Fifty eggs and caterpillars were taken from the field, reared in the lab until molting, and then returned to the plant on which they were found. Over 80 % of individuals had DNA successfully sequenced from their cast larval skins. The sequences allowed unequivocal identification. Neither the lupine-feeding nor wild indigo-feeding populations formed monophyletic clusters because many lupine-feeding and wild-indigo feeding individuals shared the same CO1 658 base pair sequence. An isolated population from the mountains of western Maryland was also not genetically distinct from a coastal population 345 km to the east. These results show the usefulness of using cast larval skins as a non-lethal source of DNA in listed species and suggest that frosted elfins are generalist feeders of lupine and wild indigo and are not comprised of two genetically distinct host plant races.