Traditional discussions of speciation often ignores the underlords of biology.
Biological species concepts works perfectly for species that reproduce sexually.
However, the definition soon encounters hindrance when understanding evolutionary pathways of those organisms without partners.
Questions:
What factors lead to speciation among asexual species?
What construction of speciation should we use for asexually reproducing species?
How will understanding asexual speciation contribute to our current efforts to better understand the history of life on earth?
Just my opinion: biological species does not exist in asexual organisms.
there are about 35 definitions of species (I'll piost the link or paper when I find it in my mess), the last one, and the most used, says: "The species is what the taxonomist decides to be".
Excuse my English, I'm not a native speaker.
You might find these papers interesting:
http://euplotes.biology.uiowa.edu/web/sexpapers/2004/week5/MarkWelch.pdf
http://www.mta.ca/~raiken/Courses/4401/source%20material/Judson96.pdf
http://scholar.google.cz/scholar?q=info:oZ05HDSBIIsJ:scholar.google.com/&output=instlink&hl=cs&as_sdt=0,5&scillfp=8401704070291093927&oi=lle
http://onlinelibrary.wiley.com/doi/10.1002/9780470015902.a0001588.pub2/full
Peaceful Christmas,
Peter.
Hi Peter, thanks for the articles.
The idea of a species does become muddled when you exclude reproduction sexually as a prerequisites.
Due to the genetic similarities in the offspring's of asexually reproducing "species" it is difficult to establish a gradient for favorable traits that would favored by natural selection for a particular environment.
I believe, that in the case of asexual reproducing species, mutation and genetic drift would be the largest driving force for evolution. These two factors would lead to changes in gene frequency for a particular population.
@Peter for asexual reproducing species I think the concept of an "evolutionary species" would be appropriate classification.
This classification defines species as "evolutionary units, or groups of populations that share similar evolutionary lineages" How, these asexual reproducing organisms are evolving similarly in response to evolutionary factors, such as selection, mutation, and drift.
@Michael:
asexual organisms are de facto modified clones... each individual evolves individually since last common ancestor.
They might be grouped to "species" because of similar "selection, mutation, and drift", as you said.
Just my opinion, as usually,
Peter A.
Considering asexual organisms, whether you took into account the bacterial conjugation? This process is considered to be the bacterial equivalent of sexual reproduction, because it causes the exchange of genetic material.
http://en.wikipedia.org/wiki/Bacterial_conjugation
Certain bacteria, manipulating the proportion of sexes in insects, have extremely high frequencies of gene exchange:
Klasson et al., 2009, "The mosaic genome structure of the Wolbachia wRi strain infecting Drosophila simulans". PNAS; DOI: 10.1073/pnas.0810753106
Bacteria not only exchange conjugative plasmids, but can also transfer small molecules (i.e. proteins) via nanotubes:
G.P. Dubey, S. Ben-Yehuda, 2011, "Intercellular Nanotubes Mediate Bacterial Communication". Cell, 144 (4): 590; DOI: 10.1016/j.cell.2011.01.015
@Mariusz:
IMHO, Bacteria do exchange of genetic material with any other Bacteria,
so they experience "network evolution", not "tree evolution".
They can mate with evolutionary far distant mates, not close relatives.
Have a peaceful Christmas,
Peter.
I guess asexual species can bypass cladogenesis by ecological speciation through natural selection and/or drift, and I think we have to forget the need for reproductive isolation as a necessary condition to speciation, and maintain it as a sufficient condition only.
@Daniel:
You are right, but then the phylogeny would become a network (which it already is, to some extent). Nevertheless, there are about 35 definitions of species, so, e.g., for morphospecies you are absolutely right.
@Peter
Of course. Without good definition of "species" there is tough to discuss the existence of "speciation". The definition of the species in the case of micro-organisms should be different than for multicellular organisms. But even with the latter we are often in trouble...
@Peter
Yeah! 35 mln. years without sex, and extremely "hungry" for stranger's DNA... :-)
I have only just found this discussion. It is not only organisms that reproduce asexually that cause problems: those that appear to self-fertilise (with meiosis and gametes) cause the same difficulties, compounded when this happens sometimes, or in some populations but not others. It is worth remembering that the vast majority of species are defined by their anatomy or genetic constitution, and not by any examination of breeding success with other possible conspecifics. When populations are isolated from one another, and show differences, the decision as to whether to call them species, subspecies etc is essentially arbitrary, though molecular taxonomists often attempt to use the % difference in genomes to make decisions.
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