656More New Information on Nomada - Red-haired, Depressa, Lehighensis Groups
- May 4, 2009
All: Below is a continuation of some of our work on the eastern members of the genus Nomada based on COI m-DNA work by Molly Rightmyer, Cory Sheffield, and Sean Brady. In this section we explore the N. depressa, red-haired species, and N. lehighensis groups.
OK, first let’s set the stage here.
There are bees that have the unique feature of an unusually extensive pseudopygidial area in the females. Additionally, that pseudopygidial area has very, very short dense hairs, somewhat similar to what you might find in the foveae of Andrena females. Most of those specimens have traditionally been called N. depressa although there are several other names on the books that are rarely used and won’t be gone into here (at this point we think they are the same as the general N. depressa thing).
OK, now let’s travel to Molly, Sean, and Cory’s CO1 tree. Shall we?
Here a couple of interesting things are apparent. First all of the specimens are found internal to the “red-haired group” (N. composite, N. inepta, etc.). However, interestingly, one small part of the N. depressa group is above the large N. composite batch of specimens and the remainder below.
Now, let’s take a look at the specimens themselves.
All of them have the following characteristics that don’t seem to vary:
Strongly carinate cheeks, red hairs on the labrum and clypeus of the females, females with 3-5 thick dark red setae, moderately long mandibles…in other words the basic body form is very similar
Notice that I didn’t say they all had extensive pseudopygidial areas!
What varies a lot is size, degree of abdominal maculations, presence of extensive pseudopygidial area, extent of red on thorax
So, to help deal with all this variation and to see if there were patterns within the larger concept of N. depressa, I took each group within the molecular tree created from the CO1 material collected by Molly Rightmyer, Cory Sheffield, and Sean Brady. However, note that the groups are separated by much less than 0.5% and traditionally a value of 2% is used to separate species. In doing so, there is the one group of large pseudopygidial individuals that comes out above N. composita in the tree and 9 groups below N. composita. I put together an Excel sheet that documents the differences within those groups. One general issue with this process is that these groups don’t have that many specimens associated with them so it’s often not clear if there is more variation out there than we can document. Additionally, because the differences among groups are so small group membership and even the groups themselves would be expected to morph back and forth with the inclusion of additional specimens or the removal of others.
By doing that it’s clear that there are morphological patterns within these groups. Male and female patterns are different, of course, but they almost always match in a relative way. So, for example Group 2 is a group of individuals from several areas that have a limited amount of very light colored (pale yellow to ivory) maculations on the abdomen. On the other hand Group 4 is made up of very large individuals that have very extensive amounts of yellow on their tergites and only a tiny strip of pseudopygidial area along the T6 rim, they also have a few prominent red hairs on their sternites. Of interest is a single member of what matches Group 4 in Group 3 (again these groups are so close genetically, that it would be easy for a wrong association to occur).
Another pattern is that these groups cover large geographic areas. The Smokies alone has 6 of the 10 groups, so one can’t say that these patterns are mere geographic matters. My best guess is that there may be host/Nomada parings going on that has led to associative mating with some genetic component to it. The variation we see in color perhaps acts as a cue to members of a host group to come hither. Wouldn’t it be nice if someone pursued those investigations?
OK, so what do we do with all of this in terms of what is and is not a species? My suggestion is to, for right now, to separate these individuals into just 2 species. So the large pseudopygidial areas would be one (this includes the molecular group that comes out above N. compsita and doesn’t seem to have any obvious morphological traits to separate it from the others) and the one without a pseudopygidial area would be another. The rest of the variation I think is too unclear to ascribe to species status at this point. We will look at what name should be given to the non-pseudopygidial species by looking through the other red-haired molecular specimens and types…so more on that later.
N. gracilis = N. inepta = N. xanthura - The red-haired species
Cory Sheffield has recently published this synonymy. He has a nice series of females identified as N. inepta and a short series of males identified as N. gracilis (all Canada specimens). They all closely match their descriptions in Mitchell and in each the opposite sex is undescribed. The only addition is a branch off the N. inepta group that has 2 Canadian specimens (one of which I can’t seem to find) that has a distinctly different maculation pattern, but is otherwise the same). The type of N. xanthura falls right into this group but at the end with the most extensive markings or maculations on the abdomen. Given the amount of variation we are finding in markings on the abdomen within a species group there is no reason at this point to consider N. xanthura anything other than a more colored version of N. gracilis.
N. lehighensis = N. townesi?, N. ulsterensis?
This is another N. depressa like situation (hmmm, maybe this isn’t that unusual) in that there is a basic core morphological “look” to the group as a whole with lots of variation in size and maculations that appear to have genetic components.
So, here is the core look and feel to this group. The gestalt is that of what we would call a red-haired species, but without the red hair; females have 2-5 thick dark red setae on the hind tibia; females have a fairly wide but coarsely haired pseudopygydium, a bit hard to describe but nowhere near the extent of N. depressa; the scutellum of males and females are either without a central depression or only a very slight one, appears pillow shaped; female maculations go from none to moderate amounts; cheeks subcarinate
Like N. depressa the internal groupings are all less than 0.5%. However, despite very low genetic differences there is quite a bit of variation explained by the groups themselves. This is particularly true of the abdominal maculations, which varies from zero in some groups to moderate in others, but also can include variation in the shape and color of the scutellum and likely other things as well.
Like the N. drepressa situation, my thought right now is to not split these into a number of species, but keep them as one group. The type of N. lehighensis matches these specimens nicely, the types of N. townesi and N. ulsterensis haven’t been compared but key out to what the males appear to be. All types have undescribed sexes.sam