Hello,
I wanted to know what the difference was between a subspecies and a regional form. Do you know ?
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The difference between a subspecies and a regional form is that a taxonomist has said so, and enough people have gone along with a designation that one or the other designation is used for a group. We have discussed many times on this forum that there is no widely applicable and operational definition for āspeciesā, and there is even less meaning to the word āsubspecies.ā On the average, groups that are more distinct are more likely to be described as subspecies, and those that are less distinct are regional forms or variations, but as the wind changes these decisions can wobble.
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The ancient hominid impulse to gather might be a positive spin on the ways of taxonomists. if it sometimes seems petty thatās because itās Deep Human.
I am not a taxonomist, but Iāve been thinking about how to answer this from a biologistsā perspective and this is my opinion. First, not everyone agree that subspecies are actually a thing and here is a decent take on those arguments. Personally, I use specific rank very sparingly and only really assign it on my main study species because of the issues with that rank. Some people view subspecies are true-breeding incipient species meaning that if we run the evolutionary tape forward enough in time, things currently designated subspecies will likely become species. Yet we know there is lots of morphological adaptation to local conditions that leads to things like light colored morphs on the white sands of New Mexico, or dark colored morphs on certain lava flows. Are these subspecies or just regional variants? Currently Holbrookia maculata ruthveni, which is a light morph at White Sands is considered a subspecies, but in this case there is good genetic evidence that the lizards on the sands donāt have much gene flow with the nearby lizards off the sands and that the light-dark coloration difference is selected against when on the mis-matched substrate meaning that divergence is being favored on vs off the sand. So, in this case there actually IS evidence that the White Sands subspecies is valid (full disclosure, I still donāt ID it as such because Iām more of a lumper than a splitter..but thatās just me).
But back to the original question. What exactly is a regional form. Iām not aware of a formal definition, but having identified all of multiple species and having collected animals over broad geographic regions for many years (I apologize for sounding like Iām using the argument from authority, but logical fallacies are sometimes hard to avoid), I can say that some areas seem to have visual differences that make that region distinct. For example, Western Fence Lizards are very broadly distributed and can be distinguished from other fence lizards in part by the yellowish blush to their ventral surface. However, near the Nevada-Idaho border I came across a population where every one I caught had a much more intense orange on their bellies. I had never seen this before and nowhere else since. As far as I know this hasnāt been described in the literature, but when I mentioned it to a colleague who spent their whole career working in this species they confirmed there were other populations with this kind of coloration, but itās not a defining characteristic of the subspecies and other populations in the same subspecies lack this trait. So one definition of regional form might be sub-subspecies level of variation, which is sometimes called a ābiological raceā, though that term has seemingly fallen out of favor because of its usage outside of science.
Iām aware of other examples such as tendency to have certain spot here, or certain color there all of which occur WITHIN a subspecies, but not throughout the entire subspecies. They all amount to the same thingā¦.location-specific visual forms that may or may not be true breeding and therefore may not be defining characteristics quite unique enough to be considered incipient species, if you go in for that kind of thing. The difference: fuzzy at best.
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I agree with what @dlevitis has said.
I think this is why a phylogenic approach to classification (as in the abolishment of ranks) is favoured in seemingly more and more of the books I read and by my professors also.
Assuming we had all the information, phylogeny is basically applicable all the way down to the individual (itās essentially a giant family tree of life). Whenever itās practical (or an author wants to name something), phyla are named and perhaps given a taxonomic rank. āSpeciesā is probably the rank with the most rigid rules, but even there thereās a lot of flexibility. The rest is all arbitrary.
I think, it would make sense to define the difference between subspecies and regional forms as monophyletic vs. non-monophyletic: If the individuals of a region are morphologically similar because they are all more closely related to each other than to any other individuals of the species, call it a subspecies. If the individuals of a region are morphologically similar because of the environment (functional constraints), call it a regional form.
However, I donāt think that it is done that way nor that it really would be doable (or rather, resources would be better spent doing other stuff in most cases).
I personally really like the form ārankā because it names a morphological characteristic and doesnāt have to be monophyletic. It could be practical for studying ecological impacts on morphology, but sadly ICZN doesnāt officially accept them.
10 posts were split to a new topic: Subspecies of humans
I split off a series of posts to the thread linked above and closed it. Please keep the discussion here on the OPās general question of the difference between a subspecies and a regional form. Thanks.
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One way to clarify the situation is to ask: are there subspecies which are not regional?
If you count the wintering grounds of many birds, you can find substantial overlap of subspecies. I can often see three or more subspecies of juncos in one spot during winter. But of course their breeding grounds are geographically separated.
Domesticated organisms recognized as subspecies separate from their wild type forms can occur almost anywhere, but thatās human caused.
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