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Defending Darwinian view of speciation at PLOS

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At PLOSOne, What Is Speciation? Abstract:

Concepts and definitions of species have been debated by generations of biologists and remain controversial. Microbes pose a particular challenge because of their genetic diversity, asexual reproduction, and often promiscuous horizontal gene transfer (HGT). However, microbes also present an opportunity to study and understand speciation because of their rapid evolution, both in nature and in the lab, and small, easily sequenced genomes. Here, we review how microbial population genomics has enabled us to catch speciation “in the act” and how the results have challenged and enriched our concepts of species, with implications for all domains of life. We describe how recombination (including HGT and introgression) has shaped the genomes of nascent microbial, animal, and plant species and argue for a prominent role of natural selection in initiating and maintaining speciation. We ask how universal is the process of speciation across the tree of life, and what lessons can be drawn from microbes? Comparative genomics showing the extent of HGT in natural populations certainly jeopardizes the relevance of vertical descent (i.e., the species tree) in speciation. Nevertheless, we conclude that species do indeed exist as clusters of genetic and ecological similarity and that speciation is driven primarily by natural selection, regardless of the balance between horizontal and vertical descent. More. – B. Jesse Shapiro , Jean-Baptiste Leducq, James Mallet

Note “Comparative genomics showing the extent of HGT in natural populations certainly jeopardizes the relevance of vertical descent (i.e., the species tree) in speciation. Nevertheless, we conclude that species do indeed exist as clusters of genetic and ecological similarity and that speciation is driven primarily by natural selection, regardless of the balance between horizontal and vertical descent.”

If the relevance of vertical descent is jeopardized, and species exist only as “clusters of genetic and ecological similarity,” what does it mean to say that speciation is “driven primarily by natural selection”? In the context, natural selection means only—as Lynn Margulis put it—that not all the life forms that come into existence can survive and reproduce.

The Darwinian mechanism was always understood as natural selection acting on random mutation via common descent. That was evolution. Now it isn’t.

Darwinian evolution was supposed to produce awesome new levels of information. It doesn’t.

But expect at least a decade more of timely obfuscation.

See also: Speciation: Red wolf not “endangered”; a hybrid? Speciation is a topic well suited to a serious rethinking evolution meeting.

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One Reply to “Defending Darwinian view of speciation at PLOS

  1. 1
    Dionisio says:

    These recent models [80] and empirical work [83] have made some headway in resolving the paradox of gene sweeps but also raise new questions.

    How common are gene-sweeps relative to the genome-wide sweeps predicted by the Stable Ecotype Model?

    On what time scales do sweeps occur, and how does this affect speciation rates?

    More generally, can all life on Earth, including microbes and macrobes, be viewed on the same universal speciation spectrum?

    Later stages of speciation involve divergent natural selection and barriers to gene flow.

    The extent to which these barriers are ecological, behavioral, physical, or genetic remains an open research question.

    Just how much selection (on how many genes) and how much divergence across the genome is needed for speciation is an open question.

    Another important question is, for a given sample of organisms, what fraction of the genome is shaped by selection or drift within the individual, the species, or the multispecies [37]?

    What Is Speciation?
    B. Jesse Shapiro, Jean-Baptiste Leducq, James Mallet
    PLOS
    DOI: http://dx.doi.org/10.1371/journal.pgen.1005860

    Emphasis mine.
    Lots of details have been left out of the big picture here. What else is new?
    The story repeats: as outstanding questions get answered, new questions are raised.
    That’s not ‘gods of the gaps’ – That’s complex complexity. 🙂

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