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Three Ways that Plants Defy Darwin’s Mechanism


Plants have no brains and limited mobility, yet they have mechanisms to thrive in place. One mechanism involves the prevention of inbreeding. The trick defies Darwin’s theory. Darwin had already called the origin of flowering plants (angiosperms) an “abominable mystery.” If he had known what Austrian scientists found, it likely would have brought on more of his notorious stomach aches.

News from Austria’s Institute of Science and Technology (IST) explains how flowering plants prevent inbreeding. As we know, inbreeding limits diversification and leads to genetic decay. When you think about it, a flower produces its own gametes: male pollen and female ova. Self-fertilization, though, would create all the associated problems of inbreeding for a plant species. People know better than to marry their relatives, but how can a blind flower, with no brain or eyes, recognize “self” so as to prevent fertilizing itself? It’s a trick that both gametes have to cooperate on. A mutation in the pollen that enables it to recognize self won’t help if the ovum doesn’t get a corresponding mutation. The Austrian IST researchers were curious about this and decided to take a look.

Plants “Evolved” a Solution

In “Recognizing others but not yourself: new insights into the evolution of plant mating,” they assume that plants “evolved” a solution. But is evolution really the answer?

Self-fertilization is a problem, as it leads to inbreeding. Recognition systems that prevent self-fertilization have evolved to ensure that a plant mates only with a genetically different plant and not with itself. The recognition systems underlying self-incompatibility are found all around us in nature, and can be found in at least 100 plant families and 40% of species. Until now, however, researchers have not known how the astonishing diversity in these systems evolves. A team of researchers at the Institute of Science and Technology Austria (IST Austria) has made steps towards deciphering how new mating types evolve in non-self recognition self-incompatibility systems, leading to the incredible genetic diversity seen in nature. The results are published in this month’s edition of Genetics. [Emphasis added.] 

The paper in Genetics, “Evolutionary Pathways for the Generation of New Self-Incompatibility Haplotypes in a Nonself-Recognition System,” is pretty abstruse and burdened with technical jargon. The problem, though, is easy to understand:

Self-incompatibility (SI) is a genetically based recognition system that functions to prevent self-fertilization and mating among related plants. An enduring puzzle in SI is how the high diversity observed in nature arises and is maintained.

Some plants use “self-recognition” (SR) systems; others use “nonself-recognition” systems (NSR). Here’s a garden example of an SR system:

In plants such as snapdragons and Petunia, when the pollen lands on the stigma, it germinates and starts growing. The stigma, however, contains a toxin (an SRNase) that stops pollen growth. Pollen in turn has a team of genes (F-box genes) that produce antidotes to all toxins except for the toxin produced by the “self” stigma. Therefore, pollen can fertlize [sic] when it lands on stigma that does not belong to the same plant, but not when it lands on the plant’s own stigma. It may seem like a harsh system, but plants can use this toxin-antidote system to ensure that they only mate with a genetically different plant. This is important as self-fertilization leads to inbreeding, which is detrimental for the offspring.

Lock and Key

Do you see a problem for neo-Darwinism? The stigma basically has a lock that the “self” pollen cannot unlock. The pollen, though, has a key that only works on other flowers’ locks. How could such lock-and-key systems arise in a single plant that will work on unrelated plants? They not only have to evolve the toxin and the antidote, but ensure that the key doesn’t work locally — only with unrelated plants. And that’s not the only conundrum. NSR systems use a different trick. The authors puzzle over how this one evolved:

In non-self recognition systems, the male (pollen) and female (stigma) genes work together as a team to determine recognition, so that a particular variation of the male- and female-genes forms a mating type. Non-self recognition systems are found all around us in nature and have an astonishing diversity of mating types, so the big question in their evolution is: how do you evolve a new mating type when doing so requires a mutation in both sides? For example, when there is a change in the female side (stigma), it produces a new toxin for which no other pollen has an antidote – so mating can’t occur. Does this means [sic] that there needs to be a change in the male side (pollen) first, so that the antidote appears and then waits for a corresponding change in the stigma (female side)? But how does this co-evolution work when evolution is a random process? Is there a particular order of mutations that is more likely to create a new mating type?

A Committee to the Rescue

To solve this Darwinian puzzle, they created an interdisciplinary group of specialists in evolutionary genetics, game theory and applied mathematics — a committee. “This project shows how collaboration between scientists with very different backgrounds can combine biological insight with mathematical analysis, to shed some light on a fascinating evolutionary puzzle,” one of them said hopefully. With enough free parameters in your model, you can always come up with possibilities. Let’s think through their proposed solution:

Through theoretical analysis and simulation, the researchers investigated how new mating types can evolve in a non-self recognition system. They found that there are different pathways by which new types can evolve. In some cases this happens through an intermediate stage of being able to self-fertilize; but in other cases it happens by staying self-incompatible. They also found that new mating types only evolved when the cost of self-fertilization (through inbreeding) was high. Being incomplete – i.e., having missing F-box genes that produce antidotes to female toxins — was found to be important for the evolution of new mating types: complete mating types (with a full set of F-Box genes) stayed around for the longest time, as they have the highest number of mating partners. New mating types evolved more readily when there was [sic] less mating types in the population. Also, the demographics in a population affect the evolution of non-self recognition systems: population size and mutation rates all influence how this system evolves.

The analytical model worked in the committee, but does it work in the real world? In a model, you can assume that beneficial mutations will arise on cue. Nature, however, doesn’t work that way. Their model didn’t compare very well with real flowers:

So although it seems like having a full team of F-box pollen genes (and therefore antidotes) is the best way for new mating types to evolve, this system is complex and can change via a number of different pathways. Interestingly, while the researchers found that new mating types could evolve, the diversity of genes in their theoretical simulations were fewer compared to what is seen in nature. For Melinda Pickup, this observation is intriguing: “We have provided some understanding of the system, but there are still many more questions and the mystery of the high diversity in nature still exists.

It was a fun exercise, in other words, but:

Back to the Drawing Board 

A similar difficult arises when asking how plants learned to cooperate with nitrogen-fixing bacteria. In Science, László G. Nagy puzzles about why the nitrogen-fixing root nodule (NFN) “arose repeatedly during plant evolution” — an “age-old mystery.” This symbiotic relationship, so important to human agriculture, is only found in four unrelated plant groups. Nagy calls on “convergent evolution” to explain this “patchy” appearance that doesn’t follow Darwin’s branching tree pattern, offering promissory notes that someday evolutionists will figure it out.

Teasing apart the possible mechanisms behind convergently evolved traits remains a substantial challenge even in the era of genomics. It nevertheless appears that case studies and models are emerging to explain the pervasive occurrence of convergence across the tree of life.

Beating the Heat

Plants are cleverer than Darwinians. With summer upon us, RIKEN scientists investigated “how plants beat the heat.” The solution involves more than what the mutation/selection mechanism can handle:

We all know how uncomfortable it is to be stuck outside on a sweltering hot day. Now, imagine how bad it would be if you were a soybean or tomato plant without any chance of moving inside. Eventually your leaves might become bleached of color due to chloroplast membrane damage, and if you did not get any relief, you might die. Fortunately for plants, they do have a natural defense against this type of stress that involves modifying plant fats that make up chloroplast membranes. When heat causes chloroplast membranes to destabilize, polyunsaturated fatty acids are removed from the membrane lipids, which stabilizes the membranes. The team at RIKEN found the gene responsible for this process, and they did so rather quickly because of their innovative approach.

Sure, they found a candidate gene and ran controlled experiments to see whether it could help a lab plant last longer in heat — and it did. They did not speculate about how it might have evolved, at least in the news item. 

A “Fundamental Failing”

But if evolutionists think neo-Darwinism could account for this beneficial trait, they need to remember what Douglas Axe says in his chapter in the new volume, Theistic Evolution. Axe again points out the “fundamental failing” with natural selection (as he did in his earlier book, Undeniable). It’s this: evolution is “clueless” about inventing things. Natural selection “shows up only after the hard work of invention has been done.”

The only inventions we know about by experience come from inventors. An invention is a “functional whole,” Axe says. The “hard work” of invention requires having a goal or plan, and then organizing components at multiple hierarchical levels to work together to fulfill that plan.

Self-recognition systems, mutual symbioses and heat stress prevention are amazing inventions. Why must we endure stories of how they “might have” evolved, when Darwinian mechanisms are already disqualified? Axe says that “the outcome of accidental causes is guaranteed to be a mess,” and so attributing the origin of functional wholes to accident is “completely out of the question.” Science should go with the cause we know is necessary and sufficient to account for inventions: intelligence.

Photo: Snapdragons, by Off2riorob (talk) [CC BY 3.0 ], from Wikimedia Commons.