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Within a species there may be subspecies that are named using trinomial nomenclautre. For example the Grizzly Bear, Ursus arctos horribilis is a subspecies of the Brown Bear Ursus arctos.

The dictionary definitions of subspecies seldom expand beyond this:

A taxonomic category that ranks below species, usually a fairly permanent geographically isolated race.

I'm assuming redefining species into subspecies is not a completely arbitrary process as the definitions would imply, but is based on biology. What are the biological criteria for a group within a species to be "upgraded" to a subspecies?

fileunderwater
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James
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    This is the definition by ICZN which is equally un-informative "The species-group rank below species; the lowest rank at which names are regulated by the Code. (2) A taxon at the rank of subspecies." – WYSIWYG Sep 14 '15 at 13:34
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    @WYSIWYG The definitions are all very tortological rather than insightful. Of course it's below a species rank! What else could 'sub' mean in this context? There must be criteria that make some strains, or groups biologically different enough to be subspecies, but that threshold is apparently hard to come by if you're not 'in the know'. – James Sep 15 '15 at 00:19
  • The wikipedia article is more helpful, if accurate: "a polytypic species has two or more subspecies, races, or more generally speaking, populations that need a separate description" and "A monotypic species has no distinct population or races, or rather one race comprising the whole species. A taxonomist would not name a subspecies within such a species." – jzx Sep 15 '15 at 01:11
  • @jzx It sounds better until you realise that it's still missing that nugget of information; specifically what factors warrant the 'need' to be separately described? – James Sep 15 '15 at 01:14
  • To clarify, it might be better to refer to subspecies on equal footing as Ursus Arctos Brunneis (brown) and Ursus Arctos Horribilis, both of which would be members of species Ursus arctos. – jzx Sep 15 '15 at 01:17
  • I think the answer is that it is whatever taxonomists agree to. So we have Canis lupus familiaris to identify our lovable friends and C. lupus dingo for the baby eaters. These are holdovers from Linnaeus et.al. But in all seriousness, this comes from an eLS article on genetic differences of Chimpanzees. "The researchers also used demographic history models to identify the values of different population and evolutionary parameters for all four populations of subspecies (i.e. effective population size, divergence and rates and directions of migration)." It sounds like there are a lot of factors. – AMR Sep 15 '15 at 01:35
  • There are likely many changes to come, and a rethinking of classifications, as we learn more about genomes and have access to whole sequences for organisms, tools that were not available to taxonomists when many of the classifications were first made. – AMR Sep 15 '15 at 01:39
  • Your assumption is wrong. Subspecies taxonomy is highly arbitrary. There are no clear criteria. On the other hand species are frequently constituted by an array of loosely defined races. – Robert McFetridge Apr 12 '17 at 12:36
  • @RobertMcFetridge - Welcome to Biology.SE. Please provide references for your claims and explain answers in good detail. You can take a look at what is considered a good answer on this site here. – AlexDeLarge Apr 12 '17 at 13:44
  • @RobertMcFetridge - Welcome to Bio. I've converted this answer into a comment. AlexDeLarge has given fruitful details on how to improve your post. – AliceD Apr 12 '17 at 14:22
  • This post is related as it talks about the concept of species. – Remi.b Apr 12 '17 at 15:30

1 Answers1

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In practice, subspecies are often fairly loosely-defined, reflecting a degree of uncertainty and ambiguity at this level of taxonomy. There are systematists who take the view that subspecies-level classifications should not be used as they are not rigidly definable.

In general, a subspecies will fulfil the following criteria:

  • it will occupy a distinct geographic range from other subspecies within its species,
  • it will have limited gene flow to other subspecies within its species, while still being capable of interbreeding
  • it will have some recognizable shared character, used to distinguish it from other subspecies within its species

Subspecies classifications, and their usefulness, are discussed in the Turtle Taxonomy Working Group's 'Turtle Taxonomy: Methodology, Recommendations, and Guidelines', for those interested in further reading.

bshane
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  • Great answer, albeit not what I was hoping for! I'm with the systemists on this one. I can't understand the usefulness of unsystematic subspecies nomenclature. – James Sep 15 '15 at 12:24
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    There can be good pragmatic reasons to hold on to subspecies labels. For instance, imagine you're after old DNA samples from museum specimens, and the species falls into two subspecies, one in the Pacific Ocean and one in the Indian Ocean. However, the old specimens do not have a lat/long of collection associated with them. In that case, you can get geographic subsets of the museum's catalogue by searching based on subspecies, and there may not be any other useful way to get that geographic subset. – bshane Sep 16 '15 at 07:14
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    There are also conservation reasons for wanting a "subspecies" designation. If a species is cosmopolitan, but a local unique population is threatened, being a "subspecies" may provide for governmental protection. For instance, many freshwater fish species on the US endangered species list are subspecies. – Kara Apr 12 '17 at 13:06
  • Subspecies are useful becasue species are not uniform homogenous populations, subspecies, may gave different behaviors, gene ratios, morphology, ect. For example there are several subspecies of Canus lupus including dogs, dingoes, and a variety of wolves ranging from the high tundra to the equatorial desert with adaptations to those environments. – John Apr 12 '17 at 13:50