̽��ֱ�� of Cambridge - biophysics

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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Baby mantises harness mid-air ‘spin’ during jumps for precision landings

fpjl2 — Thu, 05 Mar 2015 16:48:31 +0000

̽��ֱ��smaller you are, the harder it is not to spin out of control when you jump. Miniscule errors in propulsive force relative to the centre of mass results in most jumping insects – such as fleas, leafhoppers and grasshoppers – spinning uncontrollably when they jump.

Until now, scientists worked under the hypothesis that such insects can’t control this, and spin unpredictably with frequent crash landings.

But new high-speed video analysis of the jumps of wingless, baby praying mantises has revealed a technique which actually harnesses the spinning motion, enabling them to jump with accuracy at the same time as repositioning their body mid-air to match the intended target – all in under a tenth of a second.

Researchers used a thin black rod distant from the platform on which the mantises sat as a target for them to jump at.

During the jumps, the insects rotated their legs and abdomen simultaneously yet in varying directions – shifting clockwise and anti-clockwise rotations between these body parts in mid-air – to control the angular momentum, or ‘spin’. This allowed them to shift their body in the air to align themselves precisely with the target on which they chose to land.

And the mantises did all of this at phenomenal speed. An entire jump, from take-off to landing, lasted around 80 milliseconds – literally faster than the blink of a human eye.

At first, scientists believed the mantis had simply evolved a way to mitigate the natural spin that occurs when such small insects jump at speed.

On closer inspection, however, they realised the mantis is in fact deliberately injecting controlled spin into the jump at the point of take-off, then manipulating this angular momentum while airborne through intricate rotations of its extremities in order to reposition the body in mid-air, so that it grasps the target with extreme precision.

For the study, published today in the journal Current Biology, the researchers analysed a total of 381 slowed-down videos of 58 young mantises jumping to the target, allowing them to work out the intricate mechanics used to land the right way up and on target virtually every time.

“We had assumed spin was bad, but we were wrong – juvenile mantises deliberately create spin and harness it in mid-air to rotate their bodies to land on a target,” said study author Professor Malcolm Burrows from Cambridge ̽��ֱ��’s Department of Zoology, who conducted the research with Dr Gregory Sutton from Bristol ̽��ֱ��.

“As far as we can tell, these insects are controlling every step of the jump. There is no uncontrolled step followed by compensation, which is what we initially thought,” he said.

In fact, when the researchers moved the target closer, the mantises spun themselves twice as fast to ensure they got their bodies parallel with the target when they grasped it.

For Sutton, the study is similar to accountancy, only with distribution of momentum instead of money. “ ̽��ֱ��mantis gives itself an amount of angular momentum at take-off and then distributes this momentum while in mid-air: a certain amount in the front leg at one point; a certain amount in the abdomen at another – which both stabilise the body and shift its orientation, allowing it to reach the target at the right angle to grab on,” he said.

̽��ֱ��researchers tested what would happen if they restricted the ability of the mantis to harness and spread the ‘spin’ to its extremities during a jump. To do this, they glued the segments of the abdomen together, expecting the mantis to spin out of control.

Intriguingly, the accuracy of the jump wasn’t impeded. ̽��ֱ��mantises still reached the target, but couldn’t rotate their bodies into the correct position – so crashed headlong into it and bounced off again.

̽��ֱ��next big question for the researchers is to understand how the mantis achieves its mid-air acrobatics at such extraordinary speeds. “We can see the mantis performs a scanning movement with its head before a jump. Is it predicting everything in advance or does it make corrections at lightning speed as it goes through the jump? We don’t know the answer between these extreme possibilities,” said Burrows.

Sutton added: “We now have a good understanding of the physics and biomechanics of these precise aerial acrobatics. But because the movements are so quick, we need to understand the role the brain is playing in their control once the movements are underway.”

Sutton believes that the field of robotics could learn lessons from the juvenile mantis. “For small robots, flying is energetically expensive, and walking is slow. Jumping makes sense – but controlling the spin in jumping robots is an almost intractable problem. ̽��ֱ��juvenile mantis is a natural example of a mechanical set-up that could solve this,” he said.

Professor Malcolm Burrows and Dr Gregory Sutton

High-speed videos reveal that, unlike other jumping insects, the juvenile praying mantis does not spin out of control when airborne. In fact, it both creates and controls angular momentum at extraordinary speeds to orient its body for precise landings.

As far as we can tell, these insects are controlling every step of the jump

Malcolm Burrows

Malcolm Burrows and Greg Sutton

A juvenile praying mantis

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