Missing Link News - A Triple Whammy for Half-Baked Creationists. How Sweet!

Mystery of sweetpotato origin uncovered, as missing link plant found by Oxford research | University of Oxford

Here is one of those scientific discoveries that should have every Creationist covering their eyes and ears and looking the other way, or simply invoking some wackadoodle conspiracy theory in order to dismiss it. What they won't do, is incorporate the new knowledge and adjust their opinion accordingly.

Their problem is because the discovery shatters three of their most cherished dogmas:

1. 'Macro-evolution' (i.e. a new taxon arising) is impossible.
2. No new information can arise by mutation.
3. There are no transitional forms.

The discovery is one of the parent species of the sweetpotato, Ipomoea batatas, an important food crop whose ancestry was unknown.

The problem was that the sweetpotato is a hexaploid plant, having six copies of each chromosome, instead of the usual two, in other words, its entire genome has been trebled. Polyploidy is common in plants and is a common way new species arise because a polyploid individual cannot normally interbreed with either of its parents. The problem was that there were no suitable candidate species for the parents of the sweetpotato - until now.

The normal way a polyploid species arises is because of a failure in the normal process which reduces the genome by half in each the gametes, which results in a gamete having the entire genome. If two of these gametes (pollen and ovule) happen to form a zygote, a tetraploid individual can be the result. The mystery was how a hexaploid species arose in the case of the sweetpotato. The assumption was that a tetraploid gamete from a tetraploid plant in which the reduction stage had failed must have fused with a diploid gamete from a diploid plant in which the reduction had also failed.

The problem was that there were no known tetraploid members of the Ipomoea genus so there was no known intermediate stage between diploidy and hexaploidy.

The University of Oxford news item explains:

How the sweetpotato evolved has always been a mystery. Now, we have found this new species in Ecuador that is the closest wild relative of sweetpotato known to date and is a fundamental piece of the puzzle to understand the origin and evolution of this top-ten global food crop.

Professor Robert Scotland, Lead author
Department of Plant Sciences
University of Oxford, UK.

Years of careful taxonomic research by a team led by Robert Scotland, Professor of Systematic Botany at Oxford Plant Sciences, and funded by the UK's Biotechnology and Biological Sciences Research Council, has concluded with the discovery of a new species that is sweetpotato’s closest wild relative, Ipomoea aequatoriensis.

This species, which most likely played a key role in the origin of the crop, is the latest in a series of discoveries by the Oxford team and collaborators at USDA and the International Potato Centre Peru, and one that represents an ‘extraordinary discovery in untangling the evolution’ of the plant, according to the researchers.

The search for the tetraploid ancestor of sweetpotato has been going on for almost a century, but it is only today with the combination of rigorous taxonomic study and the latest DNA analysis techniques that we have been able to definitively identify it. This will enable a better understanding of sweetpotato’s origin and contemporary diversity.

Tim Wells, joint first author
Department of Plant Sciences
University of Oxford, UK.

[…]

Using the latest techniques, the researchers found the missing part of the puzzle between the sweetpotato, which is a hexaploid (having three copies of its genome) and its closest relative, which is a diploid (having one copy). Biologists believed there had to be a tetraploid, which has two copies of the genome, but until Ipomoea aequatoriensis - which is tetraploid - was identified, none had been found.

In the summary to their open access paper published in the journal, New Phytologist, the authors summarise their findings thus:

Copyright: © 2022 The authors.
Published by John Wiley & Sons, Inc.

Summary

• The origin of sweetpotato, a hexaploid species, is poorly understood, partly because the identity of its tetraploid progenitor remains unknown. In this study, we identify, describe and characterize a new species of Ipomoea that is sweetpotato’s closest tetraploid relative known to date and probably a direct descendant of its tetraploid progenitor.
• We integrate morphological, phylogenetic, and genomic analyses of herbarium and germplasm accessions of the hexaploid sweetpotato, its closest known diploid relative Ipomoea trifida, and various tetraploid plants closely related to them from across the American continent. We identify wild autotetraploid plants from Ecuador that are morphologically distinct from Ipomoea batatas and I. trifida, but monophyletic and sister to I. batatas in phylogenetic analysis of nuclear data.
• We describe this new species as Ipomoea aequatoriensis T. Wells & P. Muñoz sp. nov., distinguish it from hybrid tetraploid material collected in Mexico; and show that it likely played a direct role in the origin of sweetpotato’s hexaploid genome. This discovery transforms our understanding of sweetpotato’s origin.

Muñoz-Rodríguez, P., Wells, T., Wood, J.R.I., Carruthers, T., Anglin, N.L., Jarret, R.L. and Scotland, R.W. (2022)
Discovery and characterization of sweetpotato’s closest tetraploid relative.
New Phytologist; DOI: 10.1111/nph.17991

Copyright: © 2022 The authors. Published by John Wiley & Sons, Inc.
Open access
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

So, here we have an example of 'macro-evolution' in that a new species has arisen by hybridization from two related species - one tetraploid and one diploid - to give a stable population of hexaploid plants that can only breed within itself but not with either parent species (the definition of a species, even by Creationist's limited taxonomy). Necessary for the speciation to occur was a mutation which doubled, then tripled the entire genome, giving the lie that mutations are invariably detrimental because it involves a loss of information, to give new information to produce a valuable food crop, and we have the missing 'transitional' form in one of the ancestral tetraploid species, the newly discovered Ipomoea aequatoriensis.

As I said, there is a great deal there for Creationists to ignore or find another way to cope with the cognitive dissonance between reality and what their dogma says the reality should be.

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