/* */ Rosa Rubicondior: Creationist Failure News - How White Clover is Unlucky for Creationists

Sunday, 22 August 2021

Creationist Failure News - How White Clover is Unlucky for Creationists

White Clover, Trifolium repens
White clover’s toxic tricks traced to its hybridization | The Source | Washington University in St. Louis

If there is one thing that Creationists are good at, it is ignoring the facts that show their dogma to be wrong, so here is yet another research finding for them to ignore.

This time, the research concerns the ubiquitous white clover, Trifolium repens, which is abundant throughout temperate zones of the world to the extent that there can scarcely be a patch of grass anywhere that doesn't have its population of white clover, unless specifically treated with a herbicide.

One reason for the success of this species is that it is a tetraploid hybrid that arose as the chance hybrid between two specialised diploid parent plants, T. pallescens, which grows along the costal cliffs of Western Europe, and T. occidentale which grows in alpine habitats in central Europe. In normal reproduction, each gamete will have half the genome of the species, so the offspring will have half the genome of each parent, giving it the full genome of the species, but in the case of these tetraploid hybrids, a mistake in the production of germ cells results in each parent gamete containing the full genome. If a pollen with this full genome happens to fertilise an ovule with the same mistake, the result is a tetraploid hybrid containing the full genome of both parents.

These events are rare but by no means unknown in the plant world. Because the offspring has the full genome of both parents, it can only interbreed with another tetraploid hybrid but not with either of the parent species, and there is much greater opportunity for adaptation and exploitation of new biological niches than either parent species had. This particular hybrid is thought to have arisen some 20,000 years ago, so refuting the first Creationist claim - that new species can't arise by evolution and need to be specially created by magic. Hybridization and polyploidy to produce new species is actually commonplace in plants, and is an example of a speciation event rather than the gradual evolutionary process which is typical of animal species.
What the research team at Washington University in St Louis, have shown now is that the success of T. repens, is also partly due to its ability to produce cyanide as a deterrent toxin against insect herbivores, because the hybrid has inherited genes from two different parents, each of which contributed an essential component of the system which produces cyanide in response to being eaten.

Little did I know, when, as a child, I would lay on the banks of the river Evenlode in North Oxfordshire or on the village green of my home hamlet of Fawler, with my nose buried in a mat of white clover, that it might have been giving off small traces of cyanide!

Normally, because a system like this only works if both components are present, an opportunist creationist like Michael J. Behe would rush into print and make another million dollars telling his marks that this is an example of irreducible complexity and so is evidence of intelligent [sic] design.

Of course, like his other examples, it is nothing of the sort; it is an example of how complex systems can evolve when systems evolved for a one purpose are exapted for a different one, under the influence of nothing more magical than mutation and/or chance recombination and natural selection.

In this study, we showed that the genes that are required for cyanogenesis in white clover come partly from one of its parental species, and partly from the other. Whereas the two parental species have very narrow ecological niches — one grows only along Atlantic coastal cliffs in western Europe, the other only in alpine habitats of central Europe — white clover’s ecological success can be attributed at least in part to cyanogenesis.

Kenneth M. Olsen, lead author.
Professor of biology in Arts & Sciences
Washington University in St. Louis, Missouri, USA.
The researchers have found that the two components of the system came from the two different parent species and only occur together in the hybrid, T. repens. From the Washington University in St Louis, news release:
White clover releases toxic cyanide when its leaf tissues are damaged. This chemical defense, a response called cyanogenesis, helps it to deter insect pests. Research published in New Phytologist shows how white clover developed its anti-herbivory superpower with input from both of its seemingly innocuous parents.

“In this study, we showed that the genes that are required for cyanogenesis in white clover come partly from one of its parental species, and partly from the other,” said Kenneth M. Olsen, professor of biology in Arts & Sciences and lead author of the study.

“Whereas the two parental species have very narrow ecological niches — one grows only along Atlantic coastal cliffs in western Europe, the other only in alpine habitats of central Europe — white clover’s ecological success can be attributed at least in part to cyanogenesis,” he said.

For the new study, Olsen and his collaborators integrated high-resolution genetic maps with genome sequence analyses. They determined that each of white clover’s two diploid ancestors contributed one of the two chemical components required for cyanogenesis.
Although the research paper is regrettably behind a paywall, the summary can be read here. In it, the authors say:
  • We combined linkage mapping of the loci that control cyanogenesis (Ac, controlling production of cyanogenic glucosides; and Li, controlling production of their hydrolyzing enzyme linamarase) with genome sequence comparisons between white clover, a recently evolved allotetraploid, and its diploid progenitors (Trifolium pallescens, Trifolium occidentale).
  • The Ac locus (a three-gene cluster comprising the cyanogenic glucoside pathway) is derived from T. occidentale; it maps to linkage group 2O (occidentale subgenome) and is orthologous to a highly similar cluster in the T. occidentale reference genome. By contrast, Li maps to linkage group 4P (pallescens subgenome), indicating an origin in the other progenitor species.
  • These results indicate that cyanogenesis evolved in white clover as a product of the interspecific hybridization that created the species. This allopolyploidization-derived chemical defense, together with subsequent selection on intraspecific cyanogenesis variation, appears to have contributed to white clover’s ecological success as a globally distributed weed species.
What creationists now need to ignore is the fact that a new species has again been show to arise by an evolutionary process, this time by hybridization and then environmental select, and secondly, that a seemingly irreducibly complex system arose by combination of two pre-existing processes, much in the way that science says other 'irreducibly complex' processes/structures evolved.

No wonder the Deception Institute and it's chief propagandist, Michael J Behe, have abandoned the refuted notion of irreducible complexity and have moved on to the even more ludicrous notion of 'devolution' in their desperate attempt to convince their willing dupes that science is wrong about evolution and that biodiversity and life on Earth requires magic and a magician.
Reference:
Olsen, K.M., Goad, D.M., Wright, S.J., Dutta, M.L., Myers, S.R., Small, L.L. and Li, L.-F. (2021)
Dual-species origin of an adaptive chemical defense polymorphism.
New Phytol.
DOI:10.1111/nph.17654

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