A new lineage of Bembidion?

On my recent field trip around the west, something occurred that has never happened to me before in North America:  I knew, in the field, that I had found a previously undiscovered species.  This has happened to me in South America (where more of the fauna is undescribed), but not here.  I’ve described a number of new species from North America, and know of many yet to be described, but the realization that those species were undescribed occurred in the lab, after examination under a good microscope, or by using DNA sequences.   On this recent trip I experienced the excitement of discovery twice while still in the field.

The first was in northern New Mexico.  We were collecting at night on the Red River, a river with an abundance of Bembidion along its shores.  Among the species there were B. scopulinum, B. petrosum, B. transversale, B. recticolle, B. gratiosum, one of the “B. curtulatum” species, B. planatum, B. incrematum, and others.   With beetles running quickly this way and that in the light of my headlamp, I did not have time to carefully look at each of the beetles I was sucking into my aspirator.

Red River, NM

Red River, NM

The next morning I was in our campsite, processing the live Bembidion captured the night before. I was shocked to see in my bin a brown Bembidion with small eyes, long appendages, and very small hind wings. I immediately knew that it was a species I had never seen before, one that was undescribed in the scientific literature.  I preserved some tissue from the specimen for DNA studies, and put the rest of the body in a killing vial with ethyl acetate. Here is what the single known male looks like:

An undescribed species of the Ocydromus complex of Bembidion

An undescribed species of the Ocydromus complex of Bembidion from New Mexico

I know that it is a member of the Ocydromus Complex of Bembidion, but I don’t know to which species it is related within that group.  When we sequence DNA from it we will have a very clear idea about its relatives, but for the moment they are a mystery.

The small eyes, pale color, long appendages, and flightless nature of this beetle suggests it lives in some cryptic habitat.  What that habitat might be I do not know, but we may have received a hint from another undescribed species found a few days later in Utah.

Nine days later we were collecting along Coal Creek, Utah, looking for two special Bembidion that I knew lived there:  an undescribed member of the genus Plataphus, related to Bembidion rufinum (“Bembidion sp. nr. rufinum“), and an oddly pale form of Bembidion mckinleyi (a species so far unreported south of Canada, but of which I had seen specimens in museums from several localities in Colorado and Utah).  John and I were splashing the gravel and sand banks of the river, and the Bembidion mckinleyi were common.  One of my splashes yielded a smallish pale brown Ocydromus Complex member, which I picked up and thought – well, that’s an odd looking thing, but it didn’t seem quite interesting enough to examine it with a hand lens.  Alas, we were getting very few of the B. sp. nr. rufinum.

We were about to leave, and John decided to do one last splash – this time on the small talus slope that was at the base of a rock cliff next to the river.  That splash yielded some small pale brown beetles I took to be B. sp. nr. rufinum, and so in excitement we did many more splashes on the talus, netting in total 37 more specimens.

Mini talus slopes along Coal Creek, UT

Mini talus slopes along Coal Creek, UT

But it wasn’t until I started processing specimens later that night at our campsite in Pine Valley, UT, that I realized those 37 specimens were not B. sp. nr. rufinum as I had thought, but instead matched the single small, pale brown Ocydromus complex member from the nearby gravel shore – and that this too was an undescribed species.

A second undescribed species of the Ocydromus complex of Bembidion

A second undescribed species of the Ocydromus complex of Bembidion from Utah

The 37:1 ratio of specimens found in the talus slope to those found on the adjacent gravel shore suggests that at this locality at least the talus slope is the microhabitat for these beetles.  This is very intriguing, as it is a habitat I have rarely examined.  Might there be a whole fauna associated with such talus?

Might this Coal Creek, Utah, species be related to the undescribed New Mexico species? Although the Coal Creek species isn’t as pale as the New Mexico species, and doesn’t have small eyes, it looks somewhat similar.  That the New Mexico species likely lives in a hidden environment, and talus slopes can provide cave-like habitats, increases the possible similarities.

Red arrow shows the location of the Red River, NM, species, and the black arrow shows the location of the Coal Creek, UT, species.

Red arrow shows the location of the Red River, NM, species, and the black arrow shows the location of the Coal Creek, UT, species.

It’s tempting to speculate that these are but two species of a larger, previously undetected lineage of Bembidion occurring in talus slopes and other similarly hidden habitats along rivers in the southwest USA.  The DNA sequences will give us a sense as to whether the two new species are related, and future field work targeted at talus and other cryptic environments will inform us about whether these are the only two species in such habitats, or two of many.

This entry was posted in Fieldwork, Revising Bembidiina, Taxonomic Process and tagged , , , , . Bookmark the permalink.

9 Responses to A new lineage of Bembidion?

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  2. Paolo Bonavita says:

    Ciao David,
    it’s impossible not to envy you and your beautiful and fruitful trip.
    The first new species, with small eyes, has the same facies (see the imagine on web) of Sinechostictus (Pseudolimnaeum) doderoi, an European and rare species that I find, near Rome (Italy), in cryptic habitat, f.e. in fresh and cold water (often in spring) inside the gravel (of small size).
    Best regards

    • Thanks, Paolo, for that very interesting information about S. doderi. Are they deep in the gravel? Do you know if these can also be found in talus slopes, or are there other bembidiines that can be found there in Europe?

      And, yes, I am very lucky to have been able to go on the trip!
      Best wishes,

      • Paolo Bonavita says:

        I found Sinechostictus (Pseudolimnaeum) doderoi, in a tipical site (a spring), until 2-4 cm in deep, in fine gravel (about 3-5 mm of diameter), in which the cold water pass through. In this site doseroi was the only species of Bembidiina. In other sites the same species occurs always in cold water (in flow at high altitudine), in very shaded shores, together other species with similar ecology (i.e. Sinechostictus decoratus). About other bembidiina in talus slopes I don’t know.
        Best wishes

  3. Jon Quist says:

    This is awesome. I’m glad this complex genus is being worked on, as I am a western ground beetle collector myself. Also, I’m glad I found your blog! Linked

    • Good to hear of another western carabid enthusiast! In what western regions do you collect?

      • Jon Quist says:

        I did some limited but productive pitfalling in Utah County which is where I used to live, but now I’m developing a collection of the Sierra Nevada Coastal Range fauna in CA, especially the Brennus snail eaters and Omus. I actively collect all the other Carabids too, but I don’t have many keys to identify my bugs with. Recently I’ve been getting Carabids from a friend in AZ who finds them in his traps as well. There are just so many to collect them all!

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