Tuesday, 30 March 2021

Evolution News - Solving Darwin's "Abominable Mystery"

Research into the flower preferences of pollinating moths may have delivered a vital clue to the simple factors needed for the emergence of new species.
Pioneering pollinator study offers clues to Darwin’s “abominable mystery”

With characteristic intellectual honesty, Charles Darwin was always quick to acknowledge difficulties for his theory of evolution by natural selection, one of which he called an 'abominable mystery' in a letter to his close friend, botanist and explorer Dr Joseph Hooker in 1879. He wrote:
The rapid development as far as we can judge of all the higher plants within recent geological times is an abominable mystery... Nothing is more extraordinary in the history of the Vegetable Kingdom, as it seems to me, than the apparently very sudden or abrupt development of the higher plants. I have sometimes speculated whether there did not exist somewhere during long ages an extremely isolated continent perhaps near the South Pole.
This 'mystery' had been used by Scottish botanist William Carruthers, keeper of botany at the British Museum, to argue for divine intervention in a 1876 lecture to the Geologists Association.

Now researchers Kelsey J. R. P. Byers and H. D. Bradshaw Jr., working at the Department of Biology, University of Washington, Seattle, WA, USA think they have gone some way to solving this mystery. The press release by the John Innes Centre explains:
Strong coevolutionary relationships between plants and animal pollinators have long been recognised as a potential driver of high rates of speciation in the 275,000 extant flowering plants.

Shifts between pollinators, such as bumblebees, hummingbirds, hawkmoths and bats, often coincide with plant speciation events.

Each of these pollinator “guilds” is attracted by a different set of floral traits such as colour, patterns, scent, shape, and nectar reward, collectively known as a pollination syndrome.

So far, the detailed genetics of traits involved in pollinator shift-driven speciation remain unclear except in a few developing model systems.

In a new study researchers set out to engineer a pollinator switch in the lab that could mirror the origin of a new species in nature.

They selected a species in the genus Mimulus (monkeyflowers) section Erythranthe where the evolution of hawkmoth pollination from hummingbird pollinated ancestors has not occurred.

They made genetic changes to two flower colour genes – effectively synthesising a new Mimulus species with lower levels of the red pigment anthocyanin and yellow carotenoid pigments. These changes were based on observations in nature that most hummingbird-pollinated flowers are red and not easily visible to hawkmoths whose visual sensitivity does not extend to longer, red-light wavelengths. Hawkmoth-pollinated flowers, in contrast, are usually white or pale and highly reflective, adapted for detection by the crepuscular and nocturnal hawkmoths.

Researchers tested the attractiveness of the four resulting colour phenotypes – red, yellow, pink and white – using lab-reared hawkmoths with no previous exposure to flowers.

We expected the hawkmoths to show some preference between colours, but their preferences were extremely strong. Our study shows that changes in flowering plant pollination syndrome can proceed through relatively few genetic changes, and this further suggests that only a few simple genetic changes might be required for the origin of a new species...

We have shown that the critical steps towards the origin of a new, experimentally synthesised hawkmoth-pollinated plant species can be predicted based upon a fundamental knowledge of pollination syndromes and genetics.

Dr Kelsey Byers, First author
John Innes Centre
Formerly, University of Washington, Seattle, WA, USA.
Hawkmoths strongly preferred “derived” non-red colours – yellow, pink, and white – over the ancestral red favoured by hummingbirds and visited these pale coloured flowers more often and for longer total periods over the experimental period.

The study found that just these two simple genetic changes engineered by the researchers were required to affect the preference of hawkmoth pollinators.

“We expected the hawkmoths to show some preference between colours, but their preferences were extremely strong,” said first author Dr Kelsey Byers of the John Innes Centre and formerly based at the University of Washington (Seattle, WA, USA) where this research took place.

“Our study shows that changes in flowering plant pollination syndrome can proceed through relatively few genetic changes, and this further suggests that only a few simple genetic changes might be required for the origin of a new species,” she added.

Charles Darwin – fascinated by what he described as the “abominable mystery” of diverse flowering plant species – famously predicted that the Malagasy star orchid (Angraecum sesquipedale) which has a white flower and 35cm nectar spur, must be pollinated by a (then undiscovered) hawkmoth with a 35cm proboscis. Exactly such a hawkmoth pollinator was discovered decades after his prediction, confirming his hypothesis.

This study likewise inspires a prospective approach to the understanding of plant speciation by pollinator shift – one of making predictions and testing them experimentally using new trait combinations synthesised in the lab. This contrasts with the classic retrospective approach which involves comparing related plants with different pollinators for differences in key floral traits and the effects of these on pollinator preference.

“We have shown that the critical steps towards the origin of a new, experimentally synthesised hawkmoth-pollinated plant species can be predicted based upon a fundamental knowledge of pollination syndromes and genetics,” said Dr Byers.

So far, the experiments have been confined to the laboratory using lab-reared insects and one potential future direction of the research is to test the hypothesis in nature with wild insects to determine if a novel species could persist in the external environment.
The research was published, open access, in the journal, Frontiers in Ecology & Evolution yesterday:
Diversification of the ca. 275,000 extant flowering plant species has been driven in large part by coevolution with animal pollinators. A recurring pattern of pollinator shifts from hummingbird to hawkmoth pollination has characterized plant speciation in many western North American plant taxa, but in the genus Mimulus (monkeyflowers) section Erythranthe the evolution of hawkmoth pollination from hummingbird-pollinated ancestors has not occurred. We manipulated two flower color loci and tested the attractiveness of the resulting four color phenotypes (red, yellow, pink, and white) to naïve hawkmoths (Manduca sexta). Hawkmoths strongly prefer derived colors (yellow, pink, white) over the ancestral red when choosing an initial flower to visit, and generally preferred derived colors when total visits and total visit time were considered, with no hawkmoth preferring ancestral red over derived colors. The simple flower color genetics underlying this innate pollinator preference suggests a potential path for speciation into an unfilled hawkmoth-pollinated niche in Mimulus section Erythranthe, and the deliberate design of a hawkmoth-pollinated flower demonstrates a new, predictive method for studying pollination syndrome evolution.

Even in the early days of our understanding of evolutionary biology, creationists such as William Carruthers were trying to use 'problems' that Darwin himself admitted to, as evidence for divine magic in the development of life on Earth, tacitly admitting that the TOE was a major problem for their favourite notion. The intellectual dishonesty of this gap-filling tactic, with its dependence on a false dichotomy, but saving them from the trouble of providing their own evidence for their own notions, or risking it being picked apart by rivals, never seemed to feature in their thinking, or trouble their consciences. Much the same with today's Creationists, that their target marks could be depended on to assume "science doesn't know" was synonymous with "God did it".

Now, as we can see by this piece of research, these gaps just keep on being filled and never once is a god or evidence of the role of magic ever found.

Creationism is not a problem for science; science is a problem for Creationism.





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