I managed to volunteer myself to lead the first discussion for Season 2, so thought I would write down a brief summary of the paper and a few of my thoughts on it as a spur to conversation. If you haven’t caught up with it, here’s the details of the paper we decided on for the first session
de Queiroz, Kevin. “The general lineage concept of species, species criteria, and the process of speciation.” (1998). in Howard, Daniel J., and Stewart H. Berlocher, eds. Endless forms: species and speciation. Oxford University Press, USA, 1998.
There are many species concepts, but one definition?
Everyone who has done an undergraduate course in biology has had the “species concept” discussion. Although species are fundamental units in biodiversity, and often the natural unit of comparison in evolutinary and ecological studies, bioloigsts spend quite a lot of their time arguing about exactly what constitutes a species. John Wilkins, who knows a thing or two about the debate, lists 26 species concepts that have at least one supporter. de Queiroz provides a summary of the more popular concepts, and the evidence they use to delimit species.
The huge number of species concepts available seems at first to be a barrier to the important tasks of delimiting species (alpha taxonomy) and working our how they came to be (the study of speciation). But, de Quieroz argues, all these concepts can be shown to share a single definition of species, and only differ in determining the types of evidence we should look to in deciding if a population fits that definition:
All modern species definitions either explicitly or implicitly equate species with segments of population-level evolutionary lineages.
For de Quieroz a species is a population, held together by some force, evolving through time, and all the existing species concepts already recognise this idea. In sexually reproducing organisms, it is reproduction itself that can pull partially-isolated populations in a single direction. de Quieroz doesn’t suggest similar forces that might apply in asexual species, but notes existing species concepts for these species presume such forces exist.
Linking species status to the speciation process
For me, the strongest and most interesting part of the general lineage species concept (GLSC) is the way it brings what we know about speciation, the study of the origin of species, into taxonomy, the process by which we identify and describe species. de Quieroz illustrates a hypothetical speciation proceeds something like this (this is actually my version, lifted from a powerpoint slide, so blame me if it’s misleading):

Some thoughts
- Applicability outside of living metazoans
- I only work on animals that are alive today. Can the GLSC be applied to asexual populations, or species that arise from hybridisation rather than simple splitting of lineages?Can we apply the GLSC to extinct species, where it’s very hard to know anything about the populations from which fossils come, and members of the same lineage could conceivably be separated by millions of years of evolution?
- Have we really embraced the GLSC
- For me,one of the major lessons of the GLSC should be to stop fighting over th One True Species Concept, and instead focus on gathering evidence that allows us to determine if populations are evolving independently. This idea is paid a lot of lip-service, but in practice species delimitation studies rely heavily on phylogenetic and population genetic methods. Is this really integrative?
January 30, 2013 at 5:16 pm
Oh, just for the record “The Atavism” is David Winter and he should probably work out how to set his name properly in a WP account.
Looking forward to the discussion
February 3, 2013 at 4:12 pm
Here’s a short 2007 paper by de Queiroz that provides a good table summary of the different species concepts: http://faculty.uca.edu/benw/biol4415/papers/DeQueiroz2007.pdf
February 4, 2013 at 11:01 am
With bacteria, viruses, and other microbes the definition(s) used for species or genus are also interesting. In some cases it is also impossible to define what a “population” is, and the degrees of isolation between populations form a wide spectrum. Some virologists have suggested we can define “species” of viruses simply by a genetic distance criteria. But it is clear that not all groups or types of viruses would best served by a one size fits all taxonomy/nomenclature system.
In the legal realm, where legislators and lawyers cannot be expected to understand the intricacies of population genetics and biodiversity, clear definitions are needed. An “endangered population” is less likely to get public support and legal protections than an endangered species. But likewise an endangered species of mammal is more likely to get attention than an endangered species of gymnosperm or bacteria. Making the legal definition of species conform to the currently accepted nomenclature/taxonomy definition within the group of organisms under discussion could allow different criteria for different types of organisms, without being completely arbitrary.
February 4, 2013 at 12:40 pm
Agreed–microbial species concepts are a whole other level of frustration when it comes to delimiting species, particularly due to the level of horizontal gene transfer…
Interesting point concerning legal definitions… do you know of a consistent overall legal definition of species? I’m guessing it varies among states and the federal level here in the U.S…
A quick google search turned up this: http://cnie.org/NLE/CRSreports/biodiversity/biodv-10.cfm
To quote: “Individual vertebrate populations can be listed as well as whole species, and listed vertebrates are protected on both public and private lands… [However,] individual invertebrate populations cannot receive protection. For example, the monarch butterfly occurs in two populations: one migrating to California and the other to Mexico for winter. Although the Mexico-wintering population is declining due to habitat destruction, it cannot receive protection under the ESA as long as the California-wintering population is abundant. The bald eagle, on the other hand, receives protection in all contiguous 48 States despite its numbers in Alaska.”
February 4, 2013 at 12:43 pm
A more recent (2005) article on legal definitions of species: http://lawlibrary.unm.edu/nrj/45/2/06_george_species.pdf
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