Should the Use of Subspecies Be Revived?

The last week has seen a spirited discussion of the pros and cons of splitting recognized genera into multiple, smaller genera. We’ve had 34 comments already. Check it out! And if you’re an advocate of splitting genera, that viewpoint has been getting the short end of the stick and could use more support.

As a tangent, the topic of subspecies has come up, and David Hillis has strongly argued for reviving its use. Here’s what he has to say:

First, I don’t think either species or subspecies are “clades.” Species are lineages (the branches on the tree of life). Sexual recombination among individuals results in tokogenetic relationships within species. Clades, on the other hand, are monophyletic groups of lineages on the tree of life. Rather than being defined by tokogenetic relationships, they are defined by phylogenetic relationships.

Traditionally, subspecies are geographical races of species. In other words, they are geographically distinct populations that nonetheless meet and interbreed at contact zones. Sometimes, these contact zones are very broad, as with broad-banded versus southern copperheads. If the contact zones are very narrow, and there is strong evidence that the contact zone is a genetic sink (there is no gene flow across the zone, because of strong selection against hybrids), then I agree that the two entities can be considered separate lineages, and hence species. But in many recent cases, as with the copperhead example, there is abundant evidence that the contact zone is NOT a sink, and that there is NO selection against hybrids. In this case, I disagree strongly with the authors who proposed to split these subspecies into distinct species. That is inconsistent with any lineage species concept…there is a huge area where these two forms intergrade, with no evidence of any loss of fitness. Thus, the two forms are geographical, intergrading races, or subspecies.

I think we will soon see a backlash against the splitting off of geographic races as species as well. Frank Burbrink (who was an author on the copperhead example I mentioned above) and I plan to write a pro/con article about this together, each arguing our respective points of view. Hopefully, this will re-kindle the conversation about subspecies.

Subspecies are unpopular right now because they were long abused in several ways. Inappropriate uses include (1) to describe non-geographic “varieties”; (2) to arbitrarily break up clines; and (3) to describe distinct, isolated lineages that clearly are species. But used in proper context to designate a geographically distinct race, they are certainly reasonable and often useful. They are rarely used in some groups, for several reasons: Groups like freshwater fishes have discrete ranges, so taxa don’t interbreed over broad areas. And many groups are too poorly studied to understand geographic variation. But in well-studied terrestrial groups (like herps), subspecies are perfectly reasonable and useful taxa to designate intergrading geographic races.

About Jonathan Losos

Professor and Curator of Herpetology at the Museum of Comparative Zoology at Harvard University. I've spent my entire professional career studying anoles and have discovered that the more I learn about anoles, the more I realize I don't know.

8 thoughts on “Should the Use of Subspecies Be Revived?

  1. I would agree with David’s summary of the traditional definition of subspecies, maybe add what Mayr (1969) defined them as, being distinct populations of a species where 75% of one population can be distinguished from 100% of the other.

    I think they are useful and I said in the other thread I have steered clear of them in my own work, however that is not so much because I do not believe in them or something but that I did not feel the family I specialise in (Chelidae) were well described enough to do so. During my career the number of species in the Chelidae has gone from about 40 species world wide to 67. I am aware of, through as yet to be published works, of another 12 or so. With several other populations being examined right now, literally gels came back last week. It was not till we got to a point such as this that we could start looking at things like subspecies.

    So my point here is that one interesting flow on effect of being able to start defining subspecies in a group is it is a measure of how well that group is now known. Looking at the turtles worldwide, those groups with many subspecies are well studied groups, eg Emys, Testudo, Trachemys, and more recently Emydura and Chelodina. So I think this is a benefit because it is a way of getting an idea of how we are going with understanding the relationships in a group. This is not a reason to describe subspecies, just an observation I made once it became possible in the species I work with.

    I think subspecies are important to recognise when there is genuine evidence they exist, David pointed out some of the abuses, I will add one more and that is to raise the value of morphs for the pet trade. I think some genuine evidence that a population is a subspecies needs to be presented to avoid the abuses. That is yes you are not describing a species but maybe at least have that mind set in that you present some good evidence when proposing it.

    Just some of my thoughts, Cheers

  2. A very interesting post and interesting replies.
    I have a question regarding sub species; can concept of reciprocal monophyly or coalescence be applied to sub species of a species to assess the phylgeographic affinities ?

  3. I think are two different problems.

    Separate races or variation between the populations into distinct species, clearly is a mistake.

    But by other hand, I can´t see the utility of describe subspecies. The question is:

    We want to recognize natural lineages? or name the variation within species, that is independent of the evolutionary history of lineages

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