Alkali Tiger Beetle

Eunota togata globicollis - Salt Plains NWR, Oklahoma

I haven’t written much about my early October trip to Oklahoma, where I had hoped to confirm a hunch that the gorgeous Cicindela pulchra (Beautiful Tiger Beetle) would be found in the red clay/gypsum hill habitats of Woodward and Major Counties (the same place where I had found the much rarer Cylindera celeripes the previous June).  Unfortunately, a sudden cold snap and overcast skies conspired against me for the duration of that short, 5-day trip, reducing tiger beetle activity to near zero and sending me back to Missouri with little to show for my efforts — save a scorpion, a torpid Cicindela splendida, and some very beautiful ladie’s-tresses orchids in peak bloom.  I did have one moderately successful day, however, when I returned to Salt Plains National Wildlife Refuge in north-central Oklahoma, a place where I observed seven species of tiger beetles during my June trip.  An eighth species that I did not see on that trip, but which I had observed in previous years, was my goal this time, and despite the cold temperatures and cloudy skies I was fortunate to find several individuals of Eunota togata globicollis.  Occurring primarily on saline flats in the central and southern Great Plain, this subspecies was called the Alkali Tiger Beetle¹ by Erwin and Pearson (2008), who reserved for the nominate form (found in salt marshes and tidal flats along the Gulf Coast) the more descriptive name White-cloaked Tiger Beetle².  A third subspecies, E. togata fascinans (Salt Flat Tiger Beetle) is restricted to salt flats in central New Mexico and west Texas (Pearson et al. 2006) (you may remember this subspecies from my habitat partitioning post last month).

¹ In reality, I have come to consider the term ‘alkali’ as a bit of a misnomer, as it is saline soils specifically — not just those with high pH (alkaline) — that the species is fond of. Moreover, there are many species of tiger beetles in addition to this one that are associated with saline soils.

² Okay, I might as well just get all this off my chest. Pearson et al. (2006) gave common names to each species of tiger beetle in the U.S., but not subspecies. I think most non-taxonomists probably consider this a good thing, although it is not without its problems (some species already had multiple common names applied to them, forcing choices that are sure not to please everyone). Erwin and Pearson (2008) took this further and came up with common names for all of the subspecies as well, and like any good taxonomist they steadfastly applied existing common names only to nominate forms. Eunota togata, however, is an example where the original common name would have been better applied to one of the non-nominate subspecies. The species epithet togata means “cloaked” (being derived from the Latin word toga — a reference to the broad white band running along the elytral margins). Each of the two non-nominate forms are distinguished by the white band being more broadly expanded (indeed, almost entirely covering the elytra in subspecies fascinans), yet it is the nominate subspecies — the least “cloaked” of the three — that retains the original common name. A silly argument I suppose, but if we start applying the “prinicple of priority” to common names in the same manner as scientific names, then what have we gained? Of course, I am of the opinion that most insect groups are too diverse and their taxonomy still too unstable to warrant a rigid system of “official” common names. Is it really any easier to learn White-cloaked Tiger Beetle than Eunota togata? How about Mount Ashland Night-stalking Tiger Beetle instead of Omus cazieri? And this is not even considering what happens when category-level shifts occur. For example, the genus Tetracha was formerly called the Big-headed Tiger Beetles; however, its former subgenera were recently elevated to genus level. Erwin and Pearson, accordingly, applied the common name to the entire subtribe containing Tetracha and its relatives and applied a new common name, Metallic Tiger Beetles, to the new, more limited concept of Tetracha. Thus, in an ironic case of common name instability despite no change in scientific name, the Virginia Big-headed Tiger beetle (Tetracha virginica) became the Virginia Metallic Tiger Beetle. Are your eyes bugging yet? Common names may be appropriate for higher vertebrates, but can they really be used effectively for beetles and other insect groups where the increasing use of molecular tools is sure to result in additional, perhaps radical, shifts in taxonomy? There — I said it, and I feel a lot better!

This species is restricted to saline flats in the central/southern Great Plains.

Of the eight tiger beetle species that I’ve now observed at Salt Plains NWR, half of them (Cicindela fulgida, C. nevadica knausii, E. togata globicollis, and Habroscelimorpha circumpicta johnsonii) are true saline habitat specialists.  One of the other four species (Cicindela tranquebarica kirbyi) is also fond of saline habitats but also occurs commonly on dry, sandy soils as well, and two show a high affiinity for nearly any moist (Cicindela repanda) or moist to dry (Cicindela punctulata) soils with little regard for salinity.  Only Cicindela formosa, a denizen of dry, deep sands seems a little out of its element on the moist, salty mud at Salt Plains NWR — perhaps the few individuals I’ve observed here are incidental visitors, mistaking the white, barren expanses of salt-encrusted soil for the dry sand the species prefers during disperal searches.  This again brings up the question of habitat partitioning for competition avoidance among tiger beetle species sharing the same habitat.  Eunota togata globicollis is active during the spring and fall and, thus, temporally isolated from C. nevadica knausii and H. circumpicta johnsonii (both summer-active species).  The other saline specialist at Salt Plains NWR (C. fulgida) is active during the same seasons as E. togata globicollis; however, in my observations that species prefers the sparsely-vegetated zone at the edge of the saline flats, while E. togata globicollis prefers to stay out in the more open areas.  These observations mirror those of Melius (2010) for E. togata fascinans and the other seven species he noted in the Laguna del Perro area of New Mexico, and of Willis (1967), who recorded as many as 11 sympatric tiger beetle species in saline habitats in the central U.S.

Saline flats at Salt Plains NWR are home to eight species of tiger beetles.

Microhabitat selection and seasonal occurrence are not the only isolating mechanisms that can minimize interspecific competition among the different tiger beetle species at Salt Plains NWR.  Cicindela tranquebarica kirbyi is also a spring/fall species and doesn’t appear to display a preference for open versus vegetated areas, potentially allowing it to compete directly with both E. togata globicollis and C. fulgida.  However, C. tranquebarica kirbyi is a decidely larger species, while the other two are smaller, and correlated with such differences in overall size is the size of their mandibles.  Mandibular size directly correlated to prey size in a number of tiger beetle species (Pearson and Mury 1979), thus providing another mechanism for avoiding competition between these three co-occurring species. 

Photo details:
Beetles: Canon 100mm macro lens w/ 68mm Kenco extension tubes on Canon EOS 50D (manual mode), ISO 100, 1/250 sec, f/18-20, MT-24EX flash 1/4 power w/ Sto-Fen diffusers.
Landscapes: Canon 17-85mm zoom lens (22mm) on Canon EOS 50D (landscape mode), ISO 100, 1/100 sec, f/10, natural light.

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.

Melius, D. A. 2009. Post-monsoonal Cicindela of the Laguna del Perro region of New Mexico. CICINDELA 41(4):81-89.

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.

Pearson, D. L. and E. J. Mury. 1979. Character divergence and convergence among tiger beetles (Coleoptera: Cicindelidae). Ecology 60:557–566.

Willis, H. L.  1967.  Bionomics and zoogeography of tiger beetles of saline habitats in the central United States (Coleoptera: Cicindelidae).  The University of Kansas Science Bulletin 47(5):145-313.

Copyright © Ted C. MacRae 2010

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A “Really” Big-headed Tiger Beetle

Megacephala megacephala 3rd-instar larva. Photo © Artur M. Serrano.

In my recent summary of the latest issue of the journal Cicindela, I included a scan of the cover of that issue and its stunning image of the 3rd-instar larva of Megacephala megacephala¹ from Africa.  This otherwordly-looking, four-eyed beast was photographed with jaws agape at the entrance to its burrow in Guinea Bissau by Dr. Artur M. Serrano (University of Lisbon, Portugal).  I was grateful for his permission to post a scan of this spectacular image; however, he did even better and sent me high-resolution images of not only the larva (above) but the adult (below) as well.  This species is one of 13 assigned to the genus—presently restricted to Africa (though not always, see discussion below), where they are usually found in savanna-type habitats and are active during the crepuscular and nocturnal periods (Werner 2000).

¹ An example of a tautonym, i.e. a scientific binomen in which the genus and species names are identical. Familiar tautonymic binomina include the gorilla (Gorilla gorilla), green iguana (Iguana iguana), and European toad (Bufo bufo). Tautonyms are expressly prohibited in plant nomenclature (see Article 23.4 of the International Code of Botanical Nomenclature) but are permitted and, in fact, quite common in zoological nomenclature; Wikipedia lists 51 mammals, 82 birds, 15 reptiles & amphibians, 54 fish, and 33 invertebrates (though not Megacephala megacephla!).

Megacephala megacephala adult. Photo © Artur M. Serrano.

For those of you who see a strong resemblance by this species to another tiger beetle I featured recently, Tetracha floridana (Florida Metallic Tiger Beetle), this is not merely a coincidence.  Megacephala and Tetracha are quite closely related, and in fact the two genera, along with a handful of other closely related genera, are at the center of one of the longest-standing disputes in tiger beetle taxonomy (Huber 1994).  The genus Megacephala was established by Latreille (1802) for the species pictured here (originally described as Cicindela megacephala Olivier).  As additional taxa were found in Africa, Australia and the Western Hemisphere and assigned to Megacephala, several workers attempted to divide the genus into multiple genera (with New World taxa being assigned to Tetracha and a few other mostly South American genera); however, there was little agreement on how these genera should be defined and on what characters they should be based.  The debate was effectively swept under the rug in the early 20th Century when Walter Horn, one of the most influential cicindelophiles of all time, accepted a monotypic Aniara based on the strange South American species A. sepulcralis but reunited the world’s remaining taxa within the single genus Megacephala in his world catalogue (Horn 1910).  Horn’s use of Megacephala as a catch-all genus was followed by subsequent workers for almost a full century until Huber (1994) once again proposed restricting Megacephala to certain of the African species and resurrecting the genus Tetracha for the bulk of the New World fauna.  He also urged additional analyses to resolve the status of the remaining generic names and their composition, which subsequently saw increasing use as subgenera of Megacephala² and later as genera.

² Thus, as type-species for the genus, the species featured here became known as Megacephala (Megacephala) megacephala (Werner 2000)—a triple tautonym that translates to the “Big-headed, Big-Headed, Big-Headed” tiger beetle!  Perhaps it’s best that I’m not an African tiger beetle specialist; I probably would have been unable to resist the temptation to resurrect M. senegalensis and assign it as a subspecies of M. megacephala, just so I could refer to the nominate form as Megacephala (Megacephala) megacephala megacephala!

The reversal of Horn’s concepts now appears to be complete, with all seven former subgenera of Megacephala formally being accorded full generic status (Naviaux 2007). This classification is strongly supported by molecular analysis of nuclear 18S and mitochondrial 16S and cytochrome oxidase gene sequences (Zerm et al. 2007), with the resulting dendrogram indicating three monophyletic clades corresponding to the African/Palearctic (Megacephala and Grammognatha, respectively),  Western Hemisphere (Aniara, Metriocheila, Phaeoxantha and Tetracha) and Australian (Australicapitona and Pseudotetracha) genera³.  The African/Palearctic clade was found to occupy a basal position in the tree, while the Western Hemisphere and Australian clades were more derived.  These data support the hypothesis that the early evolution of the megacephalines took place during the break-up of the ancient Gondwana megacontinent, which began about 167 million years ago (middle Jurassic period) and sequentially disconnected Africa from South America and Australia.

³ One striking deviation from the current classification, however, was the support for nesting the single Aniara species within Tetracha, a placement that renders Tetracha paraphyletic and, thus, requires either its division into multiple genera or the sinking of Aniara as a distinct genus. The support for this placement was quite strong and mirrored the results of a broader molecular phylogenetic study of tiger beetles based on full-length 18s RNA data (Galian et al. 2002). The authors concede that this puzzling placement is not corroborated by numerous morphological, ecological and ethological characters that distinguish Aniara from all known Tetracha species.

REFERENCES

Galián J., J. E. Hogan and A. P. Vogler. 2002. The origin of multiple sex chromosomes in tiger beetles. Molecular Biology and Evolution 19:1792–1796.

Horn, W.  1910.  Coleoptera Adephaga, Fam. Carabidae, Subfam. Cicindelinae.  In P. Wytsman (editor).  Genera Insectorum.  Fascicle 82a.  Desmet-Vereneuil, Brussels, Belgium, pp. 105–208.

Huber, R. L.  1994.  A new species of Tetracha from the west coast of Venezuela, with comments on genus-level nomenclature (Coleoptera: Cicindelidae).  Cicindela 26(3/4):49–75.

Latreille, P. A. 1802. Histoire Naturelle, Générale et Particulière des Crustacés et des Insectes. Paris: F. Dufart 3 xii 13 + 467 pp.

Naviaux R. 2007. Tetracha (Coleoptera, Cicindelidae, Megacephalina): Revision du genre et descriptions de nouveaus taxons. Mémoires de la Société entomologique de France 7:1–197.

Werner, K.  2000.  The Tiger Beetles of Africa (Coleoptera: Cicindelidae).  Volume 1.  Taita Publishers, Hradec Kralove, Czech Republic, 191 pp., 745 figures.

Zerm, M., J. Wiesner, J. Ledezma, D. Brzoska, U. Drechsel, A. C. Cicchino, J. P. Rodríguez, L. Martinsen, J. Adis and L. Bachmann.  2007.  Molecular phylogeny of Megacephalina Horn 1910 tiger beetles (Coleoptera: Cicindelidae).  Studies on Neotropical Fauna and Environment 42(3):211–219.

Copyright © Ted C. MacRae 2009

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