Temporal and geographic patterns of the great arctic butterfly (Oeneis nevadensis)

The biennial Great Arctic Butterfly (Oeneis nevadensis) of western North America completes its development in two years; adults emerge every other year. We gathered date and locality data from museum specimens, personal collections and biological surveys, and have analyzed the geographic pattern of biennialism in this species. There are numerous even-year records from broad region of the Cascade Mountains, from southern British Columbia to northern California. However, odd-year individuals have been occasionally collected throughout much of the range of this species, and in several locations the number of specimens suggests the existence of several permanent and sympatric odd-year populations. They could also indicate “mistakes” in development (one year or three years for maturation from egg to adult) but for several reason this seems unlikely. At Saddle Mountain (Clatsop County, OR), and in the south Coast Range of Oregon (Josephine County) the species has been collected only in odd-years. One specimen is known from the Blue Mountains of eastern Oregon; this population should be verified. Our assessment of the Great Arctic distribution lays the groundwork for future studies to test if biennialism contributes to genetic divergence and potentially speciation by creating a phylogeny for butterflies collected in different localities and years.