The Subulate Palpomere

As mentioned in my previous post, I outlined the state of the art in Trepanedoris research to the students in my Discovering Insect Species course.   Here’s the story I told them.  (As the class will be focusing on Trepanedoris in North America, my overview will only cover the New World species.)

Published research

I’ve already documented the published history of taxonomic research on Trepanedoris. In summary, according to the most recent revision of the group in North America plus minor notes since then, there are 13 species of subgenus Trepanedoris in Canada and the USA, arranged into two species groups:

• Bembidion fortestriatum species group
  • Bembidion anguliferum [California]
  • Bembidion concretum [Oregon to Alaska, east to Virginia and Newfoundland]
  • Bembidion fortestriatum [Oregon to Alaska, east to West Virginia and Newfoundland]
  • Bembidion pseudocautum [British Columbia to Nova Scotia, south to Connecticut and Illinois]
• Bembidion connivens species group
  • Bembidion acutifrons [northern California to Alaska, east to Manitoba and Colorado]
  • Bembidion scenicum [California, Utah]
  • Bembidion canadianum [Washington and British Columbia east to Quebec]
  • Bembidion clemens [California to Utah and New Mexico]
  • Bembidion connivens [California]
  • Bembidion elizabethae [Oregon to British Columbia]
  • Bembidion frontale [British Columbia east to Nova Scotia and south Kansas and Virginia]
  • Bembidion siticum [California to British Columbia, east to Nevada and Montana]
  • Bembidion ampliceps [California]

The fortestriatum species group is characterized by having the frontal furrows diverging toward the back of the head at a lesser angle than in the connivens group.  In the fortestriatum group, the frontal furrows end closer to the middle of the head (see yellow arrows, below).

In contrast, in the connivens group, the frontal furrows diverge at an increasingly greater angle toward the back, in some wrapping around the back of the eye, or at least getting closer to the eye as they go back:

There are also differences in male genitalia between the groups.  The most obvious is the shape of the apex, which has a notable hook in the fortestriatum group:

but not in the connivens group:

The 43

I began exploring Trepanedoris about a decade ago, but stopped that research in 2012 in anticipation of this course.  Before I stopped, my lab had extracted DNA from 43 specimens of Trepanedoris and sequenced several genes in each.   These genes include nuclear ribosomal gene 28S ribosomal RNA (“28S”), the mitochondrial gene cytochrome oxidase I (“COI”), and two nuclear protein-coding genes: the carbamoyl phosphate synthetase domain of the rudimentary gene (“CAD”), and topoisomerase I (“Topo”).

Here are most of those 43 vouchers, in all of their littleness and glory:

Below are the maximum likelihood trees from preliminary sequence data for each of the four genes.  The names used in the tree include my tentative name for the species to which each specimen belongs, plus a code for the state or province, plus the voucher number.  I’ve colored some of the specimens according to their taxonomic placement in my tentative scheme, but some specimens I left uncolored.  The classification use here is extremely fluid, and is only based upon these gene trees and just a little bit of morphological and geographic data.  As one example among many of things left unexamined are the male genitalia; photos have been taken, but I have not compared them, as I wanted to save that step for the class.

Based upon these gene trees an a little bit of morphological data, the starting point for the course is, tentatively, the following 17 North American species of Trepanedoris, with preliminary names:

• Bembidion fortestriatum species group
  • Bembidion anguliferum [California]
  • Bembidion concretum [Oregon to Alaska, east to Virginia and Newfoundland]
  • Bembidion fortestriatum [Oregon to Alaska, east to West Virginia and Newfoundland]
  • Bembidion sp. nr. fortestriatum  This is a high-elevation form that we have sequenced from the White Mountains of Arizona (“Hannagan”) and the Steens Mountains of Oregon (“Steens”).  We have collected similar large, wide, dark Trepanedoris from Colorado, Utah, and the Sierra Nevada of California. This may be a complex of many species, or they may just be high-elevation forms of B. fortestriatum (but I suspect not).  If different, the Colorado form at least will likely be called Bembidion cautum.
  • Bembidion pseudocautum [British Columbia to Nova Scotia, south to Connecticut and Illinois]
• Bembidion connivens species group
  • Bembidion acutifrons subgroup
    • Bembidion acutifrons [northern California to Alaska, east to Manitoba and Colorado]
    • Bembidion scenicum [California, Utah]
    • Bembidion canadianum [Washington and British Columbia east to Quebec]
  • Bembidion connivens subgroup
    • Bembidion clemens [Arizona, Utah, Colorado, New Mexico]
    • Bembidion “dark clemens” [California].  This may be a form of B. clemens, but adults have a different body shape than B. clemens from Arizona and are much darker; there are also molecular differences.  Genitalia have not been examined.
    • Bembidion “elizaclemens” [New Mexico].  This may be form of B. clemens, but adults are darker and of a slightly different form than B. clemens from Arizona, and the one specimen sequenced has very different 28S.  Genitalia have not been examined.
    • Bembidion connivens [California]
    • Bembidion elizabethae [Oregon to British Columbia]
  • Bembidion frontale subgroup
    • Bembidion frontale [British Columbia east to Nova Scotia and south Kansas and Virginia]
    • Bembidion siticum [California to British Columbia, east to Nevada and Montana]
  • subgroup unspecified
    • Bembidion ampliceps [California]
    • Bembidion “Lost Lake” [Oregon, California]

But there are obvious uncertainties with this view.  I will write more about various issues later, but I wanted to point out two particular issues:

Bembidion acutifrons:  there are two rather different forms of this species.  In Colorado and Saskatchewan males are very shiny, with almost no microsculpture, and are very dark, with dark brown legs, and have a very broad prothorax.  In contrast, males from western Oregon (e.g., Corvallis) and western Washington have dull elytra because of extensive microsculpture, and are much paler, with reddish legs and generally paler body; they also have a narrower prothorax.   If these are two different species, the dull, western one would probably have the name Bembidion microreticulatum Hatch.  Genitalia have not yet been examined, and more specimens need to be sequenced from other localities.  Most critical will be to acquire DNA-quality specimens of the dull, western form from localities distant from Corvallis, e.g., Washington state.

Bembidion fortestriatum:  If you look at the gene trees above, you will see that in each gene, the specimens of B. fortestriatum from Alaska and Ontario form a clade distinct from the Oregon and British Columbia specimens.  I suspect these will be different species, but I haven’t looked at morphological characters yet, and more extensive sampling is needed.

This, then, is the starting point for the class.  I am most excited to see what we discover during the next two months!

I’m a bit behind in posts about the Discovering Insect Species course, because so much has happened so quickly.  Last week we examined our catch from the local field trip and learned how to prepare specimens, and we learned the state of the art in Trepanedoris systematics.   On the weekend we went on our second field trip (this time for two full days), and then this week we are extracting DNA and amplifying DNA from two genes. Although I am tempted to jump in with the excitement of the field trip, I think it best to start with last week.

Preparing specimens

We warmed up to Trepanedoris by leaning how to mount them on points. This began by sorting beetles the students collected in Corvallis last week, and gluing them to little triangles of paper attached to insect pins.

Sorting the beetles to prepare

Pointing the beetles

This exercise not only taught them the basic preparation and labeling methods, but also allowed them to interact with specimens and look at them more closely. And it gave them a sense of satisfaction of a job well done.

Shannon is very excited about her excellently pointed beetles

On Thursday we mounted specimens from a locality in California (Arroyo Seco), from which John and I had collected many specimens last summer.  There appeared to be two common Trepanedoris species at this site; a shiny one that tended to be on the open mud near the shore, and a duller one that tended to be up in the reeds.

Identifying and sorting Trepanedoris

The students then took some of the specimens they had mounted, and used the keys from Lindroth’s 1963 work to see if they could identify them. For a group who had never seen a Bembidion before a few weeks ago, who had rarely if ever used a key to identify insects, and who had miserable lighting on their microscopes, they did very well.  Several of the students identified the shiny species at Arroyo Seco as Bembidion ampliceps, and others as B. connivens.   This fits my tentative naming of the two forms.

After giving the class an overview of previously published research on Trepanedoris, I then introduced them to the 43 specimens that my lab has previously sequenced for several genes.  I showed them the vouchers, pointed and labeled, and gave them cards showing various pictures of the specimens (habitus, head, pronotum, male genitalia).  As in our first class, they then tried to sort them into species based upon the pictures.

I then presented them with the gene trees from the four genes, and talked about my current views about Trepanedoris species, based upon the gene trees, combined with morphological and geographic data.  I’ll give an overview of my current views in the next post.