The Bembidion acutifrons story

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).

Left elytron of a shiny male, from Klamath Marsh, OR

Left elytron of a shiny male, from Klamath Marsh, OR

Left elytron of a dull male, from Corvallis, OR

Left elytron of a dull male, from Corvallis, OR

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.

This entry was posted in Fieldwork, Revising Bembidiina, Taxonomic Process, Z499 (Discovering Insect Species) and tagged , . Bookmark the permalink.

3 Responses to The Bembidion acutifrons story

  1. James C. Bergdahl says:

    Fascinating….I have hundreds of B. (T.) acutifrons in my collection from many types of still-water wetlands from the Puget Sound region of Washington and British Columbia, including many from the San Juan and Gulf islands. I have vouchers of this species in my collection identified by both George Ball and David Kavanaugh.

    Based on your awesome photos, my specimens are most definitely the “dull” type. I am sure you known – if the dull form is a separate species, it may have already been described as Bembidion microreticulatum Hatch, 1950 (Bousquet 2012: 622). (After the thorough work of Van Dyke, Casey, Hatch, Lindroth, etc, how many undescribed carabids are there left to be found in the Pacific Northwest anyway?)

    DeLorme’s Atlas for Washington State does not seem to mention “Stickney” Lake (Snohomish County), the type locality of B. microreticulatum, and I have no idea where it may be. I have intensively collected bogs, fens, and other wetland types in Snohomish and King counties for carabids and do have some B. acutifrons from that area. These counties, which were extensively glaciated during the Pleistocene, have thousands of very small yet significant wetlands that do not make it on to most maps. This region is the domain of the rare Sphagnum-bog beetles Agonum belleri (Carabidae) and Eanus hatchi (Elateridae).

    It is interesting that Lindroth (1963) decided to lump Hatch’s B. microreticulatum as Leconte’s B. acutifrons even though he is carabidology’s great mentor on the use of small variation in microsculpture as an aid to species determination, especially in Bembidion. It will be interesting to see how much variation (if any) in microsculpture your class finds between the sexes of these two forms – Lindroth (1963) frequently mentions these difference within Bembidion species, which adds some confusion in figuring out what is really going on regarding species boundaries.

    James Bergdahl
    Spokane, WA, USA

    • James:
      Re. “Bembidion microreticulatum”: yes, that would be the name, as I noted in a previous blog post.

      Re. Stickney Lake: it is west of I-5 just north of the I-5 / 405 northern junction.

      Re. microsculpture: it is often species specific, but there are also apparent single species with geographic variation within them.

  2. James C. Bergdahl says:

    I see now Stickney Lake is indicated in the DeLorme Atlas, but not listed in the index. I have probably been there before, but never collected carabids there since the lake is so heavily impacted by intense residential housing (at the time I was looking exclusively for intact Sphagnum communities, which have a very low tolerance land development by humans). Most of the lakes in that area and fairly small and very heavily impacted for housing development, such Lake Serene ~1 mile to the west. These impacts are now easily seen by using Google Earth, which is a great tool for searching for wetlands. I am curious if you have actually attempted to find B. microreticulatum at Stickney Lake? I suspect it is still there since, based on my collection, the species appears to have somewhat broad (eurytopic) habitat requirements. Looking for it at the public boat launch would probably be the first place to search given its easy access.

    I have records of B. “acutifrons/microreticulatum” from many wetlands, and many islands, in the Puget Sound area. By far the largest population I have documented, which is huge, is associated with the large wetland on Tumbo Island, Gulf Islands, British Columbia, which is a few mile north of the US border (48.794721, -123.065641). This wetland must provide near ideal habitat for this Trepanedoris species. Tumbo Island is now part of part of a National Park, but it was privately owned when I pitfall trapped there. They are also found in the obvious wetland on the adjacent Cabbage Island, however the structure of the Bembidion community there is significantly different and B. acutifrons of not nearly as common.

    Interesting sidebar: Stickney Lake is only a few miles northeast of Chase Lake (47.797494, -122.346883), which is the type locality for both Agonum belleri Hatch (Carabidae) and Eanus hatchi Lane (Elateridae). Both species are extreme Sphagnum specialists. Chase Lake bog is now owed by the Snohomish County School District. There is a bridge that bisects the bog, which is surrounded by suburbs. Amazingly there is still is classic Sphagnum community there, but it is probably much smaller in extent than what it once was before all the suburban impacts. I am pretty sure it was Paul Johnson who implied A. belleri was extinct at Chase Lake in 1980s, and online information on the beetle typically states it is now extinct at Chase Lake, but this is incorrect. I found them there in 1997. Eanus hatchi is one of the rarest beetles I have ever worked on, and I think it should be federally listed to as at least “threatened” status by US Fish & Wildlife. It is only known from 6 bogs is Seattle area. Very few specimens exist in collections; most of them are at OSU in Corvallis. I catalogued all of them in 1998. The vast majority of them were collected at Chase Lake by Mel Hatch, his colleagues and his students many years ago. I am unaware of any recent records of E. hatchi at Chase Lake; I did not find it there although I did add two new populations to records in the late 1990s. A. belleri is flightless, whereas E. hatchi is definitely capable of flight. One new E. hatchi population I found was obvious – an individual flew into my face and got stuck in my beard and was therefore hard not to notice! Most of the best Sphagnum bogs in Seattle area have been destroyed, however there are still some that are pristine.

    James Bergdahl
    Spokane, WA, USA

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