Taxonomy is a dynamic science. It evolves over time. We collect new specimens, we develop new tools for studying biodiversity, and our theoretical approaches to describing the diversity of life change. All of these developments mean that the names of species and higher taxa change over time as our understanding of their limits and relationships change.
Stéphanie Boucher and I have just published a paper in the excellent taxonomic journal Zootaxa, in which we look back a century and revisit some little old flies from Ecuador. There’s a story to these flies, and we’re just the latest players in that story. And the story starts, not with entomologists heading out into the field with collecting gear, but with a group of French geographers, cartographers, mathematicians and military men . . .
1901: After a couple of years of planning and negotiating, a French naval expedition sailed for Ecuador. The expedition was the Mission du service géographique de l’armée pour la mesure d’un arc de méridien équatorial en Amérique du Sud. And as the name suggests, their primary objective was to chart a meridian arc crossing the equator. At that time, many military expeditions included a naturalist among the crew. In the case of the Mission, that position was occupied by Paul Rivet — a physician, anthropologist, and naturalist. Although Rivet’s main scientific interest was anthropology, he was also kind enough to collect large numbers of insects in the later years of the expedition.
1920: Theodor Becker (1840–1928) was a Danish-born, German entomologist who had a particular interest in higher flies. Like many taxonomists at that time, he wasn’t primarily employed as one — he was the Commissioner of Municipal Buildings in Liegnitz (now Legnica, Poland). But in addition to his day job, Becker made enormous contributions to describing and cataloging fly diversity. Becker took on the task of identifying and describing the higher flies from the French expedition. One of the families he tackled was the leaf-miner flies in the family Agromyzidae. Becker identified eight species of these pretty little flies, three of which he described as new species.
2014: Stéphanie Boucher found a few things that didn’t make sense in reading Becker’s species descriptions, so she did what taxonomists frequently have to do when the published literature doesn’t match up with real specimens — she contacted our colleague Christophe Daugeron at the Musée National d’Histoire Naturelle in Paris where Rivet’s specimens are housed and asked to borrow the specimens.
When the specimens arrived, we realized that some changes were required to Becker’s species. This isn’t that unusual in taxonomy, and it certainly doesn’t mean that Becker was a bad or sloppy taxonomist. It simply means that, a century later, we have a different view of what constitutes a “species” in these little flies. Becker tended to base his species on visible, external traits such as colour. At that time, many taxonomists tended not to delve into finer scale characters such as male genitalia, or ecological traits, such as host plants for leaf-miner flies. We now know, with the help of a lot more research, and a lot more specimens, that this is a wildly diverse family of flies, many of which look very similar externally. So, not surprisingly, we made a lot of changes to Becker’s species from the expedition.
In the end, we identified 14, not 8, species of Agromyzidae. And one of Becker’s species turned out to be a member of a completely different family — the Heleomyzidae (yes, that happens pretty regularly too).
Becker was exactly right about a few of the species. In three cases, though, he lumped together multiple species under a single name (one of his species is actually four very similar flies). He considered some of the Ecuadorian species to be the same as known European species, but we found distinct differences between them, usually in the very valuable male genitalia (that’s “valuable” in the taxonomic sense; they’re not actually worth very much at all). And three of the specimens turned out to belong to new species that Stéphanie described in the paper.
So what about that heleomyzid fly? Becker described a new species as Agromyza bipartita, but later authors weren’t convinced. They pulled it out of the Agromyzidae, but didn’t place it anywhere else (there are quite a few “homeless” species in taxonomy). When the specimens arrived from Paris we looked at the flies and I realized that Agromyza bipartita looked an awful lot like some South American heleomyzid flies in the genus Notomyza I’d recently been sorting. Fortunately, there was good material in our collection to compare it to and the mystery is now solved. Tentatively. Probably. Those weasel words are there because the specimen is a female, in poor condition, and it would take more, undamaged specimens to be more certain about its identity.
A hundred years ago, microscopes were simple, genetics was a brand new (re)discovery, phylogeny was not a tool we used, our understanding of speciation and reproductive isolation was pretty basic, and our understanding of global biodiversity was very different than it is today. All of those areas have undergone major advances in the past century, so it’s only reasonable to expect that taxonomy would change as well. When a few specimens of little old flies come out to see the light of day after so many decades, it’s not too surprising that they’re going to need a bit of an update.
Is this the end of the story? Not at all. That heleomyzid fly is still only tentatively classified. Plus three of the agromyzid species that Stéphanie recognized remain unnamed because we only had single specimens, either females or damaged males. There’s probably more, fresh, live material out there in the forests of Ecuador, waiting for the next Paul Rivet to wander by, sweep them up, and get them into a museum where taxonomists can find them and put a few more little mysteries to rest.
Reference and Sources
Evenhuis, N.L. 1997. Litteratura Taxonomica Dipterorum (1758–1930) being a selected list of the books and prints of Diptera taxonomy from the beginning of Linnaean zoological nomenclature to the end of the year 1930; containing information on the biographies and patronymic genera of the authors listed in this work; including detailed information on publication dates, original and subsequent editions, and other ancillary data concerning the publications listed herein. 2 volumes. Backhuys Publishers, Leiden. x + 871 pp.