Plant Species Divisions Are As Distinct As Those of Animals

first_imgPlants were thought to speciate differently than animals.  Evolutionary taxonomists presumed that their species barriers were more fuzzy, with hybridization, polyploidy and other mechanisms blurring the lines between species.  Not so, claim three scientists from Indiana University writing in Nature.1  These perceptions may just be artifacts of the plants selected for study:Many botanists doubt the existence of plant species, viewing them as arbitrary constructs of the human mind, as opposed to discrete, objective entities that represent reproductively independent lineages or ‘units of evolution’  However, the discreteness of plant species and their correspondence with reproductive communities have not been tested quantitatively, allowing zoologists to argue that botanists have been overly influenced by a few ‘botanical horror stories’, such as dandelions, blackberries and oaks.  Here we analyse phenetic and/or crossing relationships in over 400 genera of plants and animals.  We show that although discrete phenotypic clusters exist in most genera (> 80%), the correspondence of taxonomic species to these clusters is poor (< 60%) and no different between plants and animals…. Contrary to conventional wisdom, plant species are more likely than animal species to represent reproductively independent lineages.   (Emphasis added in all quotes.)The authors ended with an interesting statement: “Botanists have been accused of poisoning Darwin’s mind about the nature of species and our results at least partly validate this accusation.”  They refer to Ernst Mayr’s 1982 book The Growth of Biological Thought; Mayr, a devotee of the biological species concept (i.e., a species is a reproductively isolated population), decried the botanists who presented plant species as a mess with no clear dividing lines.  These authors reiterate their finding in their conclusion: “In the majority of sexual plant taxa, discrete entities that correspond to reproductively independent lineages do exist at the species level and a useful classification would reflect this.”    Science News (Week of March 25, 2006; Vol. 169, No. 12, p. 180) reported on this story, calling it “Reality Botany.”1Rieseberg, Wood and Baack, “The nature of plant species,” Nature 440, 524-527 (23 March 2006) | doi:10.1038/nature04402.How much of what scientists think they know about nature might be subjective judgments based on sampling bias?  How much more fallible might be theories based on these judgments?    Their ending statement about Darwin is cryptic.  Are they saying that the early botanists poisoned Darwin’s mind and should be considered blameworthy for doing so, or are they joining in the poisoning conspiracy?  Probably the former; they seem to be affirming that plant species are just as much “units of evolution” that can have “reproductively independent lineages” despite crossing and apomixis (reproduction without gametes).  Whether distinct species can evolve is a separate question.  In any case, most plant species seem as distinct as animal species, so any problems with animal speciation apply equally well to plant speciation (see 02/28/2006 entry).(Visited 13 times, 1 visits today)FacebookTwitterPinterestSave分享0last_img

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