Saturday, 18 March 2017

Observable Evolution Over Nine Generations!

Plants pollinated by bumblebees become more fragrant.
Picture: UZH
Real-time divergent evolution in plants driven by pollinators | Nature Communications.

Until a few years ago, almost all creationists had no doubt at all; evolution simply didn't happen. All living things were created in a couple of days exactly as they are today. There was no debate; evolution didn't happen because it wasn't mentioned in the Bible and that was that.

This is still the position maintained by a large number of creationists who believe the world was created just a few thousand years ago, as we see it today, and nothing has changed since.

So, hopefully this paper, published open access a few days ago in Nature Communications, will come as a shock to these reality deniers because it shows how evolutionary change can be observed, generation by generation, over a period as short as just nine generations, under natural selection pressure from perfectly natural selectors simply going about their lives. The Zurich-based researchers have shown that different pollinating insects can induce evolutionary change in plants similar to the way human selection can produce 'domesticated' varieties of plants and animals.

The researchers, professor Florian Schiestl and doctoral student Daniel Gervasi used field mustard as their subject. Field mustard is a member of the brasicca (cabbage) family and is closely related to oilseed rape. It normally relies on pollinating insects to transfer pollen from the male stamens to the female stigmas of other flowers but, if this mechanism fails, they will self-pollinate. Self-pollination is far less efficient in the long term because it results in reduced genetic mixing.

They divided the plants into three groups - one pollinated only by bumble bees; one pollinated only by hoverflies and the third group pollinated only by human hand.

Plants of nine replicates (total sample size 323) at generation 11 were analysed using linear discriminant function analysis (bumblebee: blue circles, hoverfly: green squares, control hand pollination: black triangles; filled symbols are group centroids of replicates). The analysis comprised morphological traits (petal length and width, flower diameter, pistil length, plant height) and all floral volatiles. In the analysis, only replicates, not treatments were pre-defined. The graph shows that despite floral trait differences among replicates, replicates within treatments resemble each other more than replicates across treatments. The evolved differences are, therefore, better explained by consistent, pollinator-specific selection than by random drift (functions: 1–8 χ2=1,225.86, 2–8: 881.73, 3–8: 625.16, 4–8: 408.4, 5–8: 248.15, 6–8: 122.12, 7–8: 60.0, all P<0.001, 8: 20.32, P=0.06).*
Photo credit: The authors.
Abstract
Pollinator-driven diversification is thought to be a major source of floral variation in plants. Our knowledge of this process is, however, limited to indirect assessments of evolutionary changes. Here, we employ experimental evolution with fast cycling Brassica rapa plants to demonstrate adaptive evolution driven by different pollinators. Our study shows pollinator-driven divergent selection as well as divergent evolution in plant traits. Plants pollinated by bumblebees evolved taller size and more fragrant flowers with increased ultraviolet reflection. Bumblebees preferred bumblebee-pollinated plants over hoverfly-pollinated plants at the end of the experiment, showing that plants had adapted to the bumblebees’ preferences. Plants with hoverfly pollination became shorter, had reduced emission of some floral volatiles, but increased fitness through augmented autonomous self-pollination. Our study demonstrates that changes in pollinator communities can have rapid consequences on the evolution of plant traits and mating system.*


After just nine generations there were marked differences between the resulting diverged populations of plants:

  • The plants pollinated by bumblebees alone were larger and had more fragrant flowers with a larger UV component in their colouring. The bumblebees had clearly been selecting from the largest, most fragrant flowers with colour in the UV spectrum, visible to bees but not to humans. The result was that the descendant generations has inherited more of the genes for these characteristics and fewer of those for shorter plants and less fragrant, less colourful flowers. The flowers were also less liable to self-pollinate because, by and large, bumblebees are efficient pollinators.
  • The plants pollinated by hoverflies alone were smaller, had less fragrant colours and were more likely to self-pollinate because hover flies are less efficient pollinators than are bumblebees.

The traditional assumption is that evolution is a slow process [but] a change in the composition of pollinator insects in natural habitats can trigger a rapid evolutionary transformation in plants.

Professor Florian Schiestl. Author.
University of Zurich, Switzerland. Quoted in UZH News release, 14 March 2017.
As the authors point out, the worrying aspect o this finding is that, as bee populations decline due to disease and insecticide use, plants might well evolve accordingly to rely on less efficient pollinator species and on self-pollination, resulting in loss of reduced genetic mixing and eventually to lowered viability. A population of highly specialised pollinator species such as bumblebees is essential for maintaining biodiversity and vigour in plants.

Now, no doubt the slightly more 'sophisticated' creationists will rush to point out that this is merely something they call 'micro'-evolution and not something they pretend has a completely different underlying mechanism, 'macro-evolution', because there was no fundamental change in biological taxon involved, as though how the evolutionary change fits into a purely human taxonomic accounting method is anyone's guess.

Until recently, evolution was simply flatly denied as ever having happened, until, that is, this idiot denialism of the available evidence began to harm creationism rather than its intended target, science. As we discovered more and more extinct and living species it became more and more ludicrous to claim a wooden boat could be constructed large enough to accommodate two (or seven, depending on which chapter of Genesis you read) of them all. So, creationist propagandists abandoned their opposition to evolution per se and decided that it did happen after all, despite not being mentioned in the Bible, and at a phenomenal speed - under the direct guidance of their supposed creator god, of course. No-one witnessed this amazing spectacle going on all around them, but creationists now assure us it must have happened because otherwise the Bible would be wrong. Moreover, they had always believed in it because they had always had a perfect understanding of the Bible! Allegedly!

Strange how no-one noticed a pair of beetles evolving in just a few years to produce about half a million very different species, for example, but creationists seem quite happy to believe it happened while everyone overlooked it.

But, this brings us to another little problem for their god-guided evolution, as normally rolled out and dusted off to explain away the fact of evolution as demonstrated by this paper. (Just a grain of sand in the mountains of evidence for evolution by natural selection, by the way. No-one would cite this paper alone as the be-all and end-all final 'proof' of evolution).

Creationists will claim the resulting evolution was their creator god's will; it wasn't natural at all but 'divine', theistic evolution. However, scientists set up the experiment and the result, though faster than expected, was entirely predictable according to the Theory of Evolution by natural selection. It would have been frankly astonishing if there had not been an observable change eventually, given the high level of selection pressure applied.

The problem for creationists is, in setting up the experimental conditions, did the scientists summon creationism's god to come along to ensure the outcome was as expected? In other words, is creationism's god subservient to mankind and is it obliged to do our bidding? (Not my original observation, by the way, but one I have seen ignored by creationists in Facebook groups when used by Facebook user Arthur Paliden.)

Any creationists prepared to answer that here? Was this an example of evolution happening perfectly naturally and without the involvement of magic and divine intervention, or an example of creationism's obedient god dutifully doing the scientists bidding?

Further Reading:
UZH - Flies and bees act like plant cultivators

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2 comments :

  1. This is a good piece, and yet creationists will stay say, "But the flowers remain flowers!" You touch on this when you bring up "micro/macro" evolution. Nevertheless, what is your best response when you hear this charge from creationists that all these flowers are of the same "kind" -- that they remain flowers?

    ReplyDelete
    Replies
    1. Indeed. The fact that they need to pretend evolution is something else in order to attack it illustrates their ignorance and/or dishonesty.

      Delete

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