̽��ֱ�� of Cambridge - Edwige Moyroud

Flowers use adjustable ‘paint by numbers’ petal designs to attract pollinators

Anonymous — Fri, 13 Sep 2024 18:00:51 +0000

̽��ֱ��study, by researchers at the ̽��ֱ�� of Cambridge’s Sainsbury Laboratory also found that bees prefer larger bullseyes over smaller ones and fly 25% faster between artificial flower discs with larger bullseyes – potentially boosting efficiency for both bees and blossoms.

Patterns on the flowers of plants guide insects, like bees, to the centre of the flower, where nectar and pollen await, enhancing the plant's chances of successful pollination. Despite their importance, surprisingly little is known about how these petal patterns form and how they have evolved into the vast diversity we see today, including spots, stripes, veins, and bullseyes.

Using a small hibiscus plant as a model, researchers compared closely related plants with the same flower size but three differently sized bullseye patterns featuring a dark purple centre surrounded by white – H. richardsonii (small bullseye covering 4% of the flower disc), H. trionum (medium bullseye covering 16%) and a transgenic line (mutation) of H. trionum (large bullseye covering 36%).

They found that a pre-pattern is set up on the petal surface very early in the flower’s formation long before the petal shows any visible colour. ̽��ֱ��petal acts like a 'paint-by-numbers' canvas, where different regions are predetermined to develop specific colours and textures long before they start looking different from one another.

̽��ֱ��research also shows plants can precisely control and modify the shape and size of these patterns using multiple mechanisms, with possible implications for plant evolution. By fine-tuning these designs, plants may gain a competitive advantage in the contest to attract pollinators or maybe start attracting different species of insects.

These findings are published in Science Advances.

Dr Edwige Moyroud, who leads a research team studying the mechanisms underlying pattern formation in petals, explained: “If a trait can be produced by different methods, it gives evolution more options to modify it and create diversity, similar to an artist with a large palette or a builder with an extensive set of tools. By studying how bullseye patterns change, what we are really trying to understand is how nature generates biodiversity.”

Lead author Dr Lucie Riglet investigated the mechanism behind hibiscus petal patterning by analysing petal development in the three hibiscus flowers that had the same total size but different bullseye patterns.

3_hibiscus_bullseyes-2-01-01_sml.jpg

She found that the pre-pattern begins as a small, crescent-shaped region long before the bullseye is visible on tiny petals less than 0.2mm in size.

Dr Riglet said: “At the earliest stage we could dissect, the petals have around 700 cells and are still greenish in colour, with no visible purple pigment and no difference in cell shape or size. When the petal further develops to 4000 cells, it still does not have any visible pigment, but we identified a specific region where the cells were larger than their surrounding neighbours. This is the pre-pattern.”

These cells are important because they mark the position of the bullseye boundary, the line on the petal where the colour changes from purple to white – without a boundary there is no bullseye!

A computational model developed by Dr Argyris Zardilis provided further insights, and combining both computational models and experimental results, the researchers showed that hibiscus can vary bullseye dimensions very early during the pre-patterning phase or modulate growth in either region of the bullseye, by adjusting cell expansion or division, later in development.

Dr Riglet then compared the relative success of the bullseye patterns in attracting pollinators using artificial flower discs that mimicked the three different bullseye dimensions. Dr Riglet explained: “ ̽��ֱ��bees not only preferred the medium and larger bullseyes over the small bullseye, they were also 25% quicker visiting these larger flower discs. Foraging requires a lot of energy and so if a bee can visit 4 flowers rather than 3 flowers in the same time, then this is probably beneficial for the bee, and also the plants.”

̽��ֱ��researchers think that these pre-patterning strategies could have deep evolutionary roots, potentially influencing the diversity of flower patterns across different species. ̽��ֱ��next step for the research team is to identify the signals responsible for generating these early patterns and to explore whether similar pre-patterning mechanisms are used in other plant organs, such as leaves.

This research not only advances our understanding of plant biology but also highlights the intricate connections between plants and their environments, showing how precise natural designs can play a pivotal role in the survival and evolution of species.

For example, H. richardsonii, which has the smallest bullseye of the three hibiscus plants studied in this research, is a critically endangered plant native to New Zealand. H. trionum is also found in New Zealand, but not considered to be native, and is widely distributed across Australia and Europe and has become a weedy naturalised plant in North America. Additional research is needed to determine whether the larger bullseye size helps H. trionum attract more pollinators and enhance its reproductive success.

Reference
Lucie Riglet, Argyris Zardilis, Alice L M Fairnie, May T Yeo, Henrik Jönsson and Edwige Moyroud (2024) Hibiscus bullseyes reveal mechanisms controlling petal pattern proportions that influence plant-pollinator interactions. Science Advances. DOI: 10.1126/sciadv.adp5574

Flowers like hibiscus use an invisible blueprint established very early in petal formation that dictates the size of their bullseyes – a crucial pre-pattern that can significantly impact their ability to attract pollinating bees.

If a trait can be produced by different methods, it gives evolution more options to modify it and create diversity, similar to an artist with a large palette or a builder with an extensive set of tools

Edwige Moyroud

Bumblebees prefer bigger targets

Lucie Riglet

Artificial flower discs designed to mimic the bullseye sizes of the three hibiscus flowers

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Petals produce a 'blue halo' that helps bees find flowers

fpjl2 — Wed, 18 Oct 2017 09:54:15 +0000

Latest research has found that several common flower species have nanoscale ridges on the surface of their petals that meddle with light when viewed from certain angles.

These nanostructures scatter light particles in the blue to ultraviolet colour spectrum, generating a subtle optical effect that scientists have christened the ‘blue halo’.

By manufacturing artificial surfaces that replicated ‘blue halos’, scientists were able to test the effect on pollinators, in this case foraging bumblebees. They found that bees can see the blue halo, and use it as a signal to locate flowers more efficiently.

While the ridges and grooves on a petal surface line up next to each other “like a packet of dry spaghetti”, when analysing different flower species the researchers discovered these striations vary greatly in height, width and spacing – yet all produce a similar ‘blue halo’ effect.

In fact, even on a single petal these light-manipulating structures were found to be surprisingly irregular. This is a phenomenon physicists describe as ‘disorder’.

̽��ֱ��researchers conclude that these “messy” petal nanostructures likely evolved independently many times across flowering plants, but reached the same luminous outcome that increases visibility to pollinators – an example of what’s known as ‘convergent evolution’.

̽��ֱ��study was conducted by a multidisciplinary team of scientists from the ̽��ֱ�� of Cambridge’s departments of plant sciences, chemistry and physics along with colleagues from the Royal Botanic Gardens Kew and the Adolphe Merkele Institute in Switzerland.

̽��ֱ��findings are published today in the journal Nature.

“We had always assumed that the disorder we saw in our petal surfaces was just an accidental by-product of life – that flowers couldn’t do any better,” said senior author Prof Beverley Glover, plant scientist and director of Cambridge’s Botanic Garden.

“It came as a real surprise to discover that the disorder itself is what generates the important optical signal that allows bees to find the flowers more effectively.”

“As a biologist, I sometimes find myself apologising to physicist colleagues for the disorder in living organisms – how generally messy their development and body structures can seem.”

“However, the disorder we see in petal nanostructures appears to have been harnessed by evolution and ends up aiding floral communication with bees,” Glover said.

All flowering plants belong to the ‘angiosperm’ lineage. Researchers analysed some of the earliest diverging plants from this group, and found no halo-producing petal ridges.

However, they found several examples of halo-producing petals among the two major flower groups (monocots and eudicots) that emerged during the Cretaceous period over 100 million years ago – coinciding with the early evolution of flower-visiting insects, in particular nectar-sucking bees.

“Our findings suggest the petal ridges that produce ‘blue halos’ evolved many times across different flower lineages, all converging on this optical signal for pollinators,” said Glover.

Species which the team found to have halo-producing petals included Oenothera stricta (a type of Evening Primrose), Ursinia speciosa (a member of the Daisy family) and Hibiscus trionum (known as ‘Flower-of-the-hour’).

All the analysed flowers revealed significant levels of apparent ‘disorder’ in the dimensions and spacing of their petal nanostructures.

“ ̽��ֱ��huge variety of petal anatomies, combined with the disordered nanostructures, would suggest that different flowers should have different optical properties,” said Dr Silvia Vignolini, from Cambridge’s Department of Chemistry, who led the study’s physics team.

“However, we observed that all these petal structures produce a similar visual effect in the blue-to-ultraviolet wavelength region of the spectrum – the blue halo.”

Previous studies have shown that many species of bee have an innate preference for colours in the violet-blue range. However, plants do not always have the means to produce blue pigments.

“Many flowers lack the genetic and biochemical capability to manipulate pigment chemistry in the blue to ultraviolet spectrum,” said Vignolini. “ ̽��ֱ��presence of these disordered photonic structures on their petals provides an alternative way to produce signals that attract insects.”

̽��ֱ��researchers artificially recreated ‘blue halo’ nanostructures and used them as surfaces for artificial flowers. In a “flight arena” in a Cambridge lab, they tested how bumblebees responded to surfaces with and without halos.

Their experiments showed that bees can perceive the difference, finding the surfaces with halos more quickly – even when both types of surfaces were coloured with the same black or yellow pigment.

Using rewarding sugar solution in one type of artificial flower, and bitter quinine solution in the other, the scientists found that bees could use the blue halo to learn which type of surface had the reward.

“Insect visual systems are different to human ones,” explains Edwige Moyroud, from Cambridge’s Department of Plant Sciences and the study’s lead author. “Unlike us, bees have enhanced photoreceptor activity in the blue-UV parts of the spectrum.”

“Humans can identify some blue halos – those emanating from darkly pigmented flowers. For example the ‘black’ tulip cultivar, known as ‘Queen of the night’.”

“However, we can’t distinguish between a yellow flower with a blue halo and one without – but our study found that bumblebees can,” she said.

̽��ֱ��team say the findings open up new opportunities for the development of surfaces that are highly visible to pollinators, as well as exploring just how living plants control the levels of disorder on their petal surfaces. “ ̽��ֱ��developmental biology of these structures is a real mystery,” added Glover.

New study finds “messy” microscopic structures on petals of some flowers manipulate light to produce a blue colour effect that is easily seen by bee pollinators. Researchers say these petal grooves evolved independently multiple times across flowering plants, but produce the same result: a floral halo of blue-to-ultraviolet light.

̽��ֱ��disorder we see in petal nanostructures appears to have been harnessed by evolution and ends up aiding floral communication with bees

Beverley Glover

Tobias Wenzel/ Edwige Moyroud

Top: petals of Ursinia speciosa, a daisy, contain a dark pigment that appears blue due to 'disordered' striations. Bottom: close-up top and side view of microscopic striations.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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