Broadly speaking, I am most intrigued by the pattern and process of evolution in insect systems: How have tiny changes over millions of years led to the vast diversity of forms we see today?
My research targets several aspects of systematic entomology:
- Why do closely related taxa sometimes follow wildly different evolutionary trajectories?
- What factors have historically acted on these taxa to shape their extant geographic ranges?
- How can we detect and delimit new species? (And what species are hiding “under our noses”?)
To get at these questions, my dissertation work has focused on the pan-American ant genus Dorymyrmex. These so-called “pyramid ants” are a widespread and understudied group recognizable by the pointed tooth on their propodeum (the posterior part of the mesosoma / “thorax,” as illustrated below).
These ants are known for their ubiquity in arid and semi-arid habitats, which also lends them an interesting amphitropical distribution, meaning the bulk of their diversity and most populations are concentrated outside the tropics.
1. Why do closely related taxa sometimes follow wildly different evolutionary trajectories?
To examine the evolution of the major lineages of Dorymyrmex, my research in the Ward lab utilizes next-generation sequencing methods targeting thousands of ultra-conserved elements (UCEs) throughout the genome. The phylogeny indicates that two major species groups—Dorymyrmex sensu stricto (the flavescens group) and the former Araucomyrmex (tener group)—are distinctly separate from the third (pyramicus group). The pyramicus group has a strikingly younger crown group and its short branches are indicative of a rapid evolutionary radiation.
Other evidence supports this scenario as well. (1) The pyramicus group is the only species group found beyond the Southern Cone region of South America, and it has dispersed and radiated wildly successfully (see above map). Additionally, (2) the tener and flavescens groups are relatively distinct at the species level (see AntWeb photos at the top of this page), whereas there is often minimal phenotypic variation among pyramicus group species. Although this similarity has long been the greatest obstacle facing the taxonomic revision of Dorymyrmex, we are certain that many of these cryptic lineages are indeed distinct species based on polyphyly, non-overlapping geographic ranges, and/or ecological differences.
2. What factors have historically acted on these taxa to shape their extant geographic ranges?
In contrast to traditional latitudinal diversity gradient theory, which presumes life on earth is most diverse near the equator, Dorymyrmex ants have an amphitropical range (mainly around the tropics) as illustrated in the distribution map above. Such “inverse,” bimodal, or disjunct ranges are interesting case studies on A) the drivers of biodiversity in temperate regions and B) the historical biogeographic processes that resulted in a gap. The latter of these—historical biogeography—is a central focus of my dissertation.
Initial phylogenies of Dorymyrmex like the one above show that the only species found north of the Amazon basin are part of the pyramicus group, a rapidly radiating clade. How did the pyramicus group disperse beyond this enormous humid region to reach as far as Oregon and North Dakota?
The two most likely paths are Central America and the Caribbean. Dorymyrmex ants may have moved by “island-hopping,” either between isolated patches of suitable dry habitat in Central America, or between literal islands in the Caribbean. By tracing a heavily-sampled Dorymyrmex phylogeny, it is becoming clear that these ants actually used Central America as their means of dispersal.
Dorymyrmex is interesting on its own, but it is a system for understanding phenomena of general interest: This travel across Central America is estimated to have happened ~8 million years ago (Mya), before the Isthmus of Panama was even connected (~3 Mya). It is possible Dorymyrmex dispersed via flight, but it is also possible that the emergence of the isthmus is earlier and more complex than previously thought—a hypothesis backed up by other studies.
Dorymyrmex by Jill Oberski
3. How can we detect and delimit new species? (And what species are hiding in our backyards?)
Working just within the scope of North America—which is still quite a task!—I am characterizing new and existing species so that our Dorymyrmex ants have proper names and can be identified. This is important for a variety of reasons:
- Many scientific studies hinge on reliable taxonomic IDs for Dorymyrmex species, including ecological surveys and social insect behavior and physiology.
- These IDs are not only important to scientists, but also to farmers and hobbyists: Dorymyrmex ants can interfere with agricultural pest control measures because they are so widespread across the southern and plains states (and numerous where they do occur).
- There are several undescribed species of Dorymyrmex in North America, even in well-traveled places like southern California.
Currently, the taxonomy of Dorymyrmex is quite chaotic. Guided by the molecular phylogeny, and informed by morphology, geography, and ecology, I hope to develop an identification key for the Nearctic species, or at least a series of regional keys.
Jumping into the fire of the “pyramicus” group
“Since neither Mayr nor Forel appear to have seen Roger’s types there is little to indicate that their ‘typical pyramicus‘ is the same insect that Roger described or the same form to which that name is applied here. It behooves us to tread very softly in this matter, however, for if our version of the typical pyramicus is not identical with Roger’s Brazilian types, then we are faced with the necessity of resuscitating Buckley’s name insanus…
Since this looks suspiciously like stepping out of the frying-pan into the fire, I believe that most myrmecologists will be content to leave matters as they are in regard to the typical pyramicus.“
— William Steel Creighton, 1950. The Ants of North America.
(Bonus!) 4. Miscellaneous social quirks
Dorymyrmex ants are unique in the social insect realm as well: Some species exhibit temporary social parasitism, a relatively rare life strategy in which parasite queens infiltrate the nest of another Dorymyrmex species, kill their host queen, and chemically trick the host workers into raising their own parasite offspring. New evidence is also coming to light that supports the existence of inquiline Dorymyrmex, which are totally workerless and exist only as parasitic queens and males. (Stay tuned for more on that.)
Finally, one of my favorite things about Dorymyrmex is an amusingly clever (and rude?) behavior: They have been observed throwing stones into nearby nests of various Myrmecocystus ant species to discourage those ants from foraging. This bombardment is effective—it actually helps the Dorymyrmex colony more efficiently gather food from the surrounding area without competition (Möglich and Alpert 1979). I have yet to see this strategy in action myself, but I would like to. It seems remarkably human and relatable.
Ultimately, I hope to contribute to a better understanding of our planet’s immense biodiversity, and how evolutionary dynamics and long-term climate shifts transform the Earth and its fauna over time.
