There are a number of subgroups within Bembidion subgenus Trepanedoris whose structure of gene flow and species boundaries are not understood. The morphological data indicates several forms within these subgroups, but whether this variation is indicative of separate species is not yet clear. One such subgroup, and a main focus of the Discovering Insect Species course, is the Bembidion acutifrons subgroup. In this subgroup, Bembidion canadianum is fairly distinctive (more on that later), but the rest of the subgroup is a bit more confusing.
Of particular interest in our class’s research is the variation in what is now called Bembidion acutifrons. There are two rather distinctive forms of Bembidion acutifrons: an eastern form with darker and generally larger adults, and very shiny males, which look like this:
This shiny form is what we were finding at Klamath Marsh. It is also the form found at the type locality of Bembidion acutifrons, Alamosa, Colorado. Here’s a picture of Alamosa National Wildlife Refuge, where we found shiny B. acutifrons in 2013:
However, west of the Cascades in Oregon and Washington is a form that is generally smaller, often paler, and with males that are heavily microsculptured and thus dull. The following two pictures shows a comparison of the left elytron between a shiny male (above) and a dull male (below).
We haven’t compared the genitalia of these two forms yet, and we have very limited DNA data. So far we only have sequences from one specimen from Saskatchewan (a shiny male) and one from Corvallis, Oregon (a dull male). These two specimens are less than 1% different in the genes COI, CAD, and topoisomerase I, but they do differ by three bases in the sequenced portion of 28S.
We have additional specimens from Colorado, Utah, and Klamath Marsh, OR, of the shiny form ready to be sequenced, and two more specimens of the dull form from Corvallis. We are rather eager to see what these additional data might say! We also need to start comparing the internal sac sclerites of the genitalia.