Riddle me this...
How do you increase the number of species without discovering new ones?
Riddle me this: How do you increase the number of known species of mosquitoes by nearly one hundred without any collecting trips or discovering even a single new species? While it may sound like a Big Bang theory resulting in something from nothing, it is merely the consistent application of concepts about kinds of living things.
Since a classic publication in 1953 by E. O. Wilson and William L. Brown, Jr., the conceptual case against recognition of subspecies has been strong. Unlike species hypotheses that make explicit and testable predictions about the distribution of attributes within and among kinds of living things, subspecies have always been nakedly arbitrary. A population differing by some degree in a trait, often on the order of 70 or 80%, is given a third formal name in addition to its Linnaean binomial. There are many occasions in biology when it is useful to point to partially differentiated populations, but this can be done with an informal designation such as the “blue eyed” population.
The option of naming partially diverged populations has been irresistible candy to individuals suffering from what has been called the mihi itch, that is, the desire to see your name in print behind a scientific name. Of all the reasons to name a species, or subspecies, this is perhaps the least defensible in the realm of science. Neal Evenhuis has provided a brief and witty history of this taxonomic affliction in an issue of Zootaxa.
In an unusually large-scale act of equal application of logic, Harbach and Wilkerson have reviewed every trinomial existing for mosquitoes, either elevating named subspecies to species status or reducing them to synonyms where in their opinion they belong. The result is the recognition of 96 species where only subspecies had existed in the literature. Elevating subspecies to species creates a challenge to entomologists to test their validity, either substantiating their status as unique kinds with explicit evidence or demonstrating with why they, too, ought to be synonyms.
Species hypotheses, done right, make predictions about the distribution of heritable attributes of species, specifying a unique combination of characters found among each and every individual within a species—and none beyond. Such cannot be said of subspecies that, instead, are based on traits whose frequency varies among populations and through time. Further, the degree of difference between populations prompting the application of a subspecies name is entirely arbitrary and without a scientifically or biologically defensible basis. It is possible to make poorly founded species hypotheses, of course, and this has and regrettably continues to be done. When species are hypotheses, such mistakes are easily detected and resolved. But to deny the rigor of species hypotheses done well because sloppy work exists is to rob science of the ability to recognize the objective kinds of organisms that have resulted from evolutionary history.
There has been a recent resurgence in the idea that species do not exist, that they too are arbitrary bits of more or less continuous genetic variability recognized by taxonomists as a matter of convenience. This is a misreading of the mission of taxonomy. Yes, taxonomists give names to entities in nature so that the rest of biology has a vocabulary with which to carry out and communicate research. But at its core, taxonomy is an historical science that recognizes what are hypothesized to be irreversibly unique kinds of organisms as evidenced by suites of characters consistently distributed among every member of a species—and reconstructs the pattern of relationships among these kinds based on shared-derived similarities or synapomorphies.
Taxonomy is so fundamental to credible biology that it operates under enormous pressure to provide certain services including making species known and identifiable. But taxonomy is done best, and ultimately provides the best service to biology, when it is pursued as a rigorous, independent science with the aim of discovering what species objectively exist and explaining the complex pattern of similarities and differences among species in the context of descent with transformation.
The more than 3,500 species of mosquitoes are a bit more scientific as a result of this sweeping act of rational nomenclature. Is every one of these newly elevated species an actual species? Time and evidence will tell. But at least they are now tied to assertions that can be tested by objective observations rather than being based on untestable, arbitrary criteria. That, in and of itself, is a significant step forward in our understanding of the diversity and evolutionary history of mosquitoes and should be a template for all higher taxa.
References
Harbach, Ralph E. and Richard C. Wilkerson (2023) The insupportable validity of mosquitoe subspecies (Diptera: Culicidae) and their exclusion from culicid classification. Zootaxa 5303, 184 pp.
Wilson, E. O. and W. L. Brown, Jr. (1953) The subspecies concept and its taxonomic application. Systematic Zoology 2: 97-111.
Evenhuis, Neal L. (2008) The “Mihi itch”—A brief history. Zootaxa 1890: 59-68.