N.Wells
Posts: 1836
Joined: Oct. 2005
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Denyse scores a bit of an "own-goal" with respect to plant evolution.
At http://www.uncommondescent.com/plants.....flowers , she quotes an article in Slate ( http://www.slate.com/article....er.html ), which in turn reports findings in Science last December ( http://www.sciencemag.org/content....ull.pdf ) about the New Caldonian plant Amborella, which is thought to be the most primitive living angiosperm | Quote | | Amborella is in a confused state when it comes to sex, as if transitioning from gymnosperm to angiosperm anatomy. It has separate male and female organs on the same plant, like a conifer. The male flowers have stamens only, but they don’t look like modern stamens—that is, with filaments topped with two pollen-bearing sacs. Instead, the two pollen sacs are carried on the edge of flat and broad petals that look very much like the scales in male conifer cones. But they also have flowers that look like hermaphrodites, with both carpels and stamens. These stamens, however, are sterile, making them staminodes. |
This is truly cool. Gymnosperms don't have flowers, so the male Amborella flower is sort of partway between gymnosperm cones and angiosperm flowers. However, the female flowers are much more flowerlike, in having both carpels and stamens (even if sterile). Amborella also has primitive xylem (with tracheids like gymnosperms, but without vessel cells, unlike other angiosperms).
The Science articles show all kinds of great stuff: massive horizontal gene transfer, suppression of gene duplication machinery in Amborella after the initial gene duplication, and yes, evidence for a whole-genome duplication shortly before the rest of flowering plants split from the Amborella lineage.
In contrast, Denyse opines cluelessly,
| Quote | Yet they became “instant winners in the survival game.”
Right. Same time. Next year. New theory.
We are obviously missing something. |
What she (not we) is missing is the importance of wholesale genome duplications, which she does not discuss beyond referring to it in the title of her piece. This is known to be really important in the evolution of flowering plants. The Slate article, as Denyse would have discovered had she bothered to read it and understand it, explains, | Quote | | Plants with multiple copies are called polyploids, and tend to be larger, have more complex flowers, and bear bigger fruits than their genomically less endowed relatives. Humans have shaped plant evolution by selecting polyploid plants for cultivation. Modern garden strawberries, for example, are octoploids, and some have berries so large they need to be cut in quarters to be eaten, while their wild relatives are diploid or at most tetraploid and have berries the size of a pea. Plant breeders often propagate garden flowers with doubled genomes to produce double the usual number of petals. In the era just before the amborella emerged, however, a doubled genome simply meant a new plasticity for basic forms and functions. That plasticity was critical to evolving leaves into colorful petals and into sepals, the leaves that protect unopened buds. Gene redundancy also was a factor in developing male and female organs in the same flower. |
The Science paper (which provided proof of whole-genome duplication through sequencing the entire genome, rather than just hypothesizing it) says, | Quote | | Previous examinations of plant genomes have shown that polyploidy has been a prominent feature in the evolutionary history of angiosperms and that WGD events have had major impacts on genome structure and gene family evolution |
Denyse concludes, | Quote | | If whole genome duplication performs such wonders, the world would doubtless look very different. |
Well, yes, if whole genome duplications had been important to angiosperm evolution we might anticipate that instead of having our comparatively uniform global forest of conifers and ferns, we might have ended up with a tumult of bizarre and diverse colorful plants with flowers and things called fruits and seeds, ranging from waterlilies to oak trees to sumacs to crabgrass to roses to bamboo to orchids to mangroves to strangler figs to pumpkins to turtle grass to coconut palms. Who could possibly imagine such a world?
Not incidentally, the Amborella line has not had any new whole-genome duplications, and ended up with just Amborella, while the Austrobaileyales lineage, which has been much more tolerant of genome duplications, ended up with arguably 400,000 species.
Lastly, the Science paper also discovered that | Quote | | ....genes involved in flower development [...] have homologs in other seed plants. The study concludes that orthologs of most floral genes existed long before their specific roles were established in flowering, and they were later co-opted to serve floral functions. |
No, no evolution here, at least not for those with intellectual blinders large enough to ignore pretty much everything in all the articles cited.
See also
http://newcaledoniaplants.com/amborel....chopoda
http://www.sciencemag.org/content....ull.pdf
http://www.sciencemag.org/content....ull.pdf
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