Photosynthesis research on yellowtops: Macroevolution in progress.
Kutschera U, Niklas KJ.
Institut fur Biologie, Universitat Kassel, Heinrich-Plett-Str. 40, 34109 Kassel, Germany.
The vast majority of angiosperms, including most of the agronomically important crop plants (wheat, etc.), assimilate CO(2) through the inefficient C(3) pathway of photosynthesis. Under ambient conditions these organisms loose about 1/3 of fixed carbon via photorespiration, an energetically wasteful process. Plants with C(4) photosynthesis (such as maize) eliminate photorespiration via a biochemical CO(2)-pump and thus have a larger rate of carbon gain. The genus Flaveria (yellowtops, Asteraceae) contains not only C(3) and C(4) species, but also many C(3)-C(4) intermediates, which have been interpreted as evolving from C(3) to fully expressed C(4) metabolism. However, the evolutionary significance of C(3)-C(4)Flaveria-intermediates has long been a matter of debate. A well-resolved phylogeny of nearly all Flaveria species has recently been published. Here, we review pertinent background information and combine this novel phylogeny with physiological data. We conclude that the Flaveria species complex provides a robust model system for the study of the transition from C(3) to C(4) photosynthesis, which is arguably a macroevolutionary event. We conclude with comments relevant to the current Intelligent Design debate.
Oops. These guys must not have received the memo from the National Center for Selling Evolution (NCSE) saying True Scientists aren’t supposed to dignify Intelligent Design by calling it things like debate or controversy. After all, the evidence supporting NeoDarwinian evolution is already overwhelming. What does this make it, overwhelming ne plus ultra evidence? Or maybe new and improved overwhelming evidence? We already know the chance worshippers are consumed with thoughts of intelligent design. It’s unusually refreshing when they actually admit they’re thinking about it.
They also must have missed the memo stating that only knuckle dragging Young Earth Creationist hillbillies make a distinction between microevolution and macroevolution. The official party line is that there is no boundary. It’s all evolution and it’s all the same evolution just more of it. Oops again.
If it wasn’t seriously debatable they wouldn’t bother clutching at straws like this to build a case. And what a straw it is. C3 photosynthesis is used by agronomically important grasses such as rice and wheat while C4 is used by agronomically important grasses such as corn. The difference is that C4 grasses can survive in a
more arid hotter environment. The similarity is they’re all still grasses. Where’s the macroevolution in that?
C4 plants belong to numerous, phylogenetically not related monocotyledonous and dicotyledonous families. Moreover have C4 activities also been detected in the blue-green alga Anacystis nidulans as well as in some dinoflagellates.
Since the alternative C3 or C4 is accompanied by considerable changes of the leaf anatomy has it to be assumed that the genetic potential for both pathways is quite common in the plant kingdom and that, depending on the ecological needs, one way is chosen by a species while a related species may choose the other one.
A well-studied example is the genus Atriplex, where both ways are realized. The C3 plants belong to one phylogenetic group, the C4 plants to another. In some cases can hybrids of C3 and C4 species be generated.
In several plant species of the genera Zea, Mollugo, Moricandia, Flaveria, etc. occur both types of CO2 fixation within one plant. In younger plants is usually the C3-, in older ones the C4 pathway taken. The amount of C4 is controlled by environmental factors.
Bungles like missing the research quoted above kind of makes you wonder what the researchers and peer review were doing instead of looking at previously published work that shoots large gaping holes in the hypothesis. Triple ne plus ultra oops.
But we should at least give the authors credit for
trying real hard making a seriously deficient effort to present some of the legendary overwhelming evidence for macroevolution. In the meantime we concede that microevolution happens. We’re interested in how microevolution like this adds up to macroevolution of novel cell types, tissue types, organs, and body plans. I’m sure that how rice evolves into corn is an interesting bit of esoteric trivia for botanists but the debate – and there is most certainly a debate – is about how bacteria evolve into rice.