Where siblings mingle: Ellipsoptera marginata vs. E. hamata

When Erwin & Pearson (2008) formally broke up the great genus Cicindela by elevating most of its former subgenera to full genus rank, it caused a bit of consternation amongst some North American cicindelophiles. The argument went something like, “Now we have all these new genus names to learn, and we’ll have to relabel and reorganize everything in our collections, and how do we know the names won’t change again, and we can’t even tell them apart in the field anyway, and blah blah…” Pardon me, but since when did taxonomy become more about slotting species into fixed, easy-to-learn categories and less about best reflecting dynamic knowledge of complex evolutionary relationships? In the case of Cicindela and its former subgenera, however, even these arguments don’t hold up to close scrutiny—tiger beetle enthusiasts in North America should have already been quite familiar with the former subgenera due to their inclusion in the widely accepted Pearson et al. (2006) field guide, many of which actually do present a unique suite of morphological/ecological characters that facilitate their recognition in the field, and I personally find that nomenclatural recognition of individual lineages helps my attempts to learn and understand them much more than dumping them into a large, all-encompassing genus based on superficial resemblance. As for insisting that names don’t change, well that has never been a tenet of taxonomy. Stable, yes, but fixed and immutable, no.

Ellipsoptera marginata male | Pinellas Co., Florida

Enough waxing philosophic. One of the more distinctive of the former subgenera is Ellipsoptera. Morphologically the genus is defined by details of male genitalia, but the 11 North American species are generally recognizable in the field by their relatively “bug-eyed” look and long legs (Pearson et al. 2006) and, as a group, seem ecologically tied to extreme habitats with sandy and/or saline substrates that are nearly or completely devoid of vegetation. Coastal marshes and mudflats, saline flats, sandy river banks, and deep sand ridges representing ancient coastlines are some of the habitats where species in this genus are most commonly encountered. Most of the species exhibit a fairly uniform facies but differ in the details of maculation and dorsal coloration, but two species that stand apart from the rest are E. marginata (Margined Tiger Beetle) and E. hamata (Coastal Tiger Beetle) due to the highly diffuse middle band of their elytra. These are both eastern coastal species and presumably represent sibling species that have diverged based on geographical range partitioning—E. marginata along the Atlantic Coast and E. hamata along the Gulf Coast. In the field, the two species are almost identical in appearance but nonetheless easily identifiable based on geographical occurrence. There is, however, a small stretch of coastline—the lower Gulf Coast of Florida—where the ranges of the two species overlap and geography alone isn’t sufficient for species determination.

Ellipsoptera hamata lacerata male | Dixie Co., Florida

Fortunately, despite their strong resemblance to each other, field identifications in areas where these species co-occur are still possible due to the presence of small but distinct sexual characters present in one species but absent in the other. Close examination is necessary to see the characters (or their absence), so it is best to net a few individuals and examine them in the hand or, as I have done here, look at them through the viewfinder of a camera. The photos in this post include the male and the female of both species, each showing the presence or absence of the distinguishing character.

Ellipsoptera marginata female | Dixie Co., Florida

In most tiger beetles, male individuals are distinguished by a number of secondary sex characters, but easiest to see in the field are the brush-like pads on the underside of the front tarsi (“feet”). Males of E. marginata and E. hamata are further distinguished from each other by the presence (E. marginata) or absence (E. hamata) of a distinct tooth on the underside of the right mandible. Photo 1 above shows a male E. marginata from Pinellas Co., Florida, and the tooth is easily seen in that relatively distant view. Photo 2 above shows a male E. hamata lacerata (Gulf Coast Tiger Beetle)—the Floridian subspecies, and while a small bump can be seen on the underside of the right mandible, it is not nearly as well developed into a distinct tooth as in E. marginata.

Ellipsoptera hamata lacerata female | Dixie Co., Florida

Female tiger beetles, on the other hand, lack the brush-like tarsal pads present in the males and are further distinguished by the “mesopleural coupling sulcus”—an area just behind the side of the pronotum that receives the male mandible during mating and is thus devoid of setae (compare the females in Photos 3 and 4 with the males in Photos 1 and 2). Neither E. marginata nor E. hamata females possess the mandibular tooth found in E. marginata males, but they can be distinguished from each other by their elytral apices. In E. marginata females (Photo 3), the elytra are curiously “bent” at the tips, forming a distinct indentation at the apex of the elytra where they meet, while female E. hamata (Photo 4) lack this indentation.

Are there other tiger beetle sibling species groups for which you would like to see comparative posts such as this one?

p.s. I completely neglected to mark yesterday’s 5th anniversary of Beetles in the Bush! I don’t know how I missed a milestone as big as five years—hopefully my ability to provide interesting content is faring better than my middle-aged memory!

REFERENCES:

Erwin, T. L. and D. L. Pearson. 2008. A Treatise on the Western Hemisphere Caraboidea (Coleoptera). Their classification, distributions, and ways of life. Volume II (Carabidae-Nebriiformes 2-Cicindelitae). Pensoft Series Faunistica 84. Pensoft Publishers, Sofia, 400 pp.

Pearson, D. L., C. B. Knisley and C. J. Kazilek. 2006. A Field Guide to the Tiger Beetles of the United States and Canada. Oxford University Press, New York, 227 pp.

Copyright © Ted C. MacRae 2012

About these ads

About Ted C. MacRae

Ted C. MacRae is a research entomologist by vocation and beetle taxonomist by avocation. Areas of expertise in the latter include worldwide jewel beetles (Buprestidae) and North American longhorned beetles (Cerambycidae). More recent work has focused on North American tiger beetles (Cicindelidae) and their distribution, ecology, and conservation.
This entry was posted in Cicindelidae, Coleoptera and tagged , , , , , , , . Bookmark the permalink.

14 Responses to Where siblings mingle: Ellipsoptera marginata vs. E. hamata

  1. This is great Ted, and happy blogoversary! Did you leave any room for cake after the Thanksgiving holiday?

  2. Jon Quist says:

    Good point toward the begining. If you’re going to get into the Adephaga, you’re gong to have a lot of taxanomic suprises. Look at the other ground beetles, Bembidion and their related genera, Pterostichus and their related genera, Clivina and their related genera: They all superficially look the same! You have to pay due respect with these groups when you “mingle” with their taxonomy. As far as family rankings go, there is a little more wiggle room (as long as you are reasonable). Even as a student of entomology, I chose which subgenera to rank as full genera before I knew about Pearson’s treatment, his and my classifications lined up exactly with the North American genera of tigers simply because I looked a little further than “superficial.” I’m no expert, either.

  3. I couldn’t agree more with your first paragraph! Taxonomy/classification should incorporate convenience and reality, but reality trumps convenience every time (at least, ever since people figured out that Darwin & Wallace were onto something with that whole “evolution” thing). It used to drive me nuts as a grad student in taxonomy when non-taxonomists would trot out the tired old question about why “we” keep changing the names of things for no good reason. And the top-of-my-head answer was always “Are you %#$#% kidding me?!?” Except I ALMOST always managed to keep that answer in my inside-my-head voice . . .

    • I probably shouldn’t admit it, but the forum thread that I linked to in the post was “the last straw” that caused me to give up as a contributing editor at BugGuide. I couldn’t justify the time I spent repeatedly dealing with the “taxonomy vs. utility” debate that resurfaced everytime I made even the slightest taxonomic change. Fortunately, the folks there now do a pretty good job of keeping the detractors at bay, so the site continues to be a pretty good reflection of current taxonomy.

  4. Mike Kippenhan says:

    Ted, You wrote “When Erwin & Pearson (2008) formally broke up the great genus Cicindela…”. Acutally, Rivalier broke it up in the 50′s. It was only the North Americans that utilized Cicindela (senso lato) and subjugated Rivalier’s genera to subgenric status.
    Mike

    • Yes, you are correct. Rivalier’s work was basically ignored in North America until Pearson et al. (2006) and then Erwin & Pearson (2008) essentially forced North American workers to deal with the more refined generic concepts.

      • mike kippenhan says:

        Ted, Not to nit pick, but I think you have to watch your phrasing. North American’s did not ignore Rivalier, we just considered his genra as subgenra. Pearson et al (2006) did not force anyone, as they also had them as subgenra. Nor do I think Erwin and Pearson forced us to “deal with a more refined generic concept”, I think it would be more accurate to say that many of us, myself included, were waiting for a major North American work to accept/utilize Rivalier’s classification. Freitag could have done it in 1999, but stayed the course. Why the North American’s never accepted it is a mystery to me? I think it was only with the introduction of molecular techniques that Rivaliers genera were shown to be valid (for the most part).

        • James C. Trager says:

          Also nit-picking, Mike, the plural of North American does not have an apostrophe. But your point is well-taken. Rank is arbitrary, and a monophyletic subgenus is as good as a monophyletic genus.

          And Ted – Great blogoversary post! (as usual). Your first paragraph is gold. I’d like to copy it and send it out (properly credited, of course) to my email list of volunteers and naturalist friends. OK?

        • Thanks, Mike. We can quibble about my phrasing, but keep in mind that, for this blog audience: 1) I tend to write with more color than I would for a dry (and less entertaining) journal article, and 2) my comments here pertain as much to avocational cicindelophiles as to professionals. The former have contributed significantly to North American cicindelid taxonomy (and are the ones with whom I engaged at BugGuide, prompting my remarks in the first place). One need only browse recent issues of the journal CICINDELA to see that many authors continue to use the genus Cicindela for species in these other genera.

Commentaria

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s