Are species real?
deepreef at BISHOPMUSEUM.ORG
Mon Apr 10 08:31:23 CDT 2006
I didn't realize there was a broad perception that animal species are
somehow more "real" than plant species. I think the results of this recent
study are interesting and useful. However, I would frame it the other way:
that animal species are every bit as artificial as plant species are (rather
than both species being "real"). I don't buy the argument that the
existence of quantifiable character clusters means that species are
"real" -- for either plants or animals.
> -----Original Message-----
> From: Taxacom Discussion List [mailto:TAXACOM at LISTSERV.NHM.KU.EDU]On
> Behalf Of Steve Manning
> Sent: Monday, April 10, 2006 8:13 AM
> To: TAXACOM at LISTSERV.NHM.KU.EDU
> Subject: Are species real?
> Hi all,
> Apologies for past (and any present) glitches in trying to post the
> following, which is sent with the permission of Troy Wood, one of the
> co-authors. I thought this was worth the trouble however. Do you see any
> problems with the gist of the analysis?
> I also speculate that the fern low hybridization rate is related to at
> least some of them having so many chromosomes(?).
> BLOOMINGTON, Ind. -- Notoriously "promiscuous" plants like oaks and
> dandelions have led some biologists to conclude plants cannot be divided
> into species the same way animals are.
> That perception is wrong, say Indiana University Bloomington scientists in
> this week's Nature. Their analysis of 882 plant and animal species and
> 1,347 inter-species crossings -- the first large-scale comparison of
> species barriers in plants and animals -- showed that plant species are
> just as easily categorized as animal species.
> The study also yielded a surprise. The hybrid offspring of
> different animal
> species are more likely to be fertile than the hybrid offspring of plant
> "We found that not only are plants just as easily subdivided into species
> as animals when analyzed statistically, but plants are more likely to be
> reproductively isolated due to hybrid sterility," said evolutionary
> biologist Loren Rieseberg, who led the study. "Most plant species are
> indeed 'real.' The problem has been that botanists have been way
> over-attracted to the plant species that readily hybridize and where the
> hybrids perpetuate themselves asexually. While it's true that dandelions
> and blackberries pose problems, these horror stories only make up
> 1 percent
> of the whole."
> The scientists did find categorization problems with nearly half of the
> plant and animal species they surveyed.
> Rieseberg and his co-authors, doctoral student Troy Wood and postdoctoral
> research associate Eric Baack, examined hundreds of peer-reviewed papers
> reporting the measurement of various plant and animal characteristics, or
> reporting on the success or failure of hybridization of plant and animal
> species with similar species. The scientists culled the papers for
> information, grouped and combined data for each given species, and then
> looked at how often characteristics clustered in accordance with
> named species.
> The scientists found that while real, quantifiable clusters did exist in
> most groups of plants and animals, the one-to-one correspondence
> of species
> names and character clusters was quite low -- about 54 percent. One
> explanation for this, Rieseberg said, is that too many taxonomists are
> "splitters" -- they give too many species names to a single group of
> related organisms.
> After analyzing the hybridization data, the scientists found that only 30
> percent of the approximately 500 plant species they surveyed are able to
> produce fertile hybrids when mated with other species. By stark contrast,
> 61 percent of animal species surveyed are able to reproduce successfully
> with other species.
> The hybridization of animal species is often portrayed as rare
> and strange,
> or else the result of human-forced matings, as is the case with ligers
> (lion-tiger hybrids) and mules (horse-ass hybrids). It is not common
> knowledge that many bird and fish species successfully hybridize in the
> wild. The scientists found that birds were most likely to produce fertile
> hybrids when crossed with other bird species. Ferns, of all things, were
> least likely to generate fertile hybrids.
> Many of the hybridization papers that Rieseberg, Wood and Baack looked at
> reported crossings under laboratory conditions, and therefore the
> may not accurately represent what happens in nature. For example, two
> species that can hybridize may not actually do so, perhaps because they
> exist on different continents or because they prefer to mate with members
> of their own species. For that reason, the percentages of plant and animal
> species that hybridize in the wild are likely to be lower than those
> reported by the scientists.
> The Nature study is meant to address gaps in scientists' knowledge in two
> areas: the fundamental nature of species and the divisibility of plant and
> animal species using commonly accepted definitions of species. Debates in
> both areas began with the 1859 edition of Darwin's Origin of Species, and
> they have not yet been settled.
> "These discussions should have been settled earlier, but no one
> bothered to
> summarize the relevant literature, perhaps because it is so vast,"
> Rieseberg said.
> Over the past 50 years, numerous scientific papers have been published in
> which species are categorized by statistical analysis of observable traits
> (i.e., numerical taxonomy) and/or by the ease with which species can be
> hybridized (i.e., breeding studies). "After going through all this
> literature, we realized someone just needed to compile and
> analyze it all,"
> Rieseberg said.
> The scientists decided to use the mass of data to see whether taxonomists
> were doing a good job, and whether cross-species mating in the plant
> kingdom is especially likely to be successful.
> "The species concept debate has devolved from an empirical discussion into
> a philosophical one," Rieseberg said. "But this is fundamentally an
> empirical question. These data support the notion that species can be both
> units of evolution and products of evolution."
> Rieseberg holds the Class of '54 Chair and is a distinguished professor of
> biology at IU Bloomington. Troy Wood and Eric Baack also
> contributed to the
> report. It was funded primarily by a Guggenheim Fellowship grant.
> Supplementary support came from the MacArthur Foundation, the National
> Institutes of Health and the National Science Foundation.
> Dr. Steve Manning
> Arkansas State University--Beebe
> Mathematics and Science
> Professor of Biology
> P.O. Box 1000
> Beebe, AR 72012
> Phone: 501-882-8203
> Fax: 501-882-4437
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