̽��ֱ�� of Cambridge - Paloma Gonzalez-Bellido

Scientists discover the secrets behind the cuttlefish’s 3D ‘invisibility cloak’

cjb250 — Thu, 15 Feb 2018 17:00:41 +0000

Cuttlefish and octopuses are remarkable creatures. They have the ability to change their appearance in a matter of seconds, camouflaging themselves from predators and enabling them to surprise their prey. However, unlike a number of reptiles and amphibians which merely change colour to blend into their surroundings, these cephalopods are also able to change the physical texture of their skin to match the coarseness of surrounding rocks, coral or seaweed.

“ ̽��ֱ��sea is full of strange and wondrous creatures, but there are few as bizarre and intelligent as octopuses and cuttlefish,” says Dr Trevor Wardill from the Department of Physiology, Development and Neuroscience at the ̽��ֱ�� of Cambridge. “We’ve seen dozens of examples of these animals suddenly appearing from nowhere, as if they have thrown off an invisibility cloak. How they do this has long remained a mystery.”

̽��ֱ��skin of these animals is covered in tiny muscular organs known as ‘chromatophores’ that change colour in response to a signal from the brain. It also has a second set of muscular organs that can be activated to create bumps known as ‘papillae’. When stimulated, each papilla can change the texture of the skin from flat to three dimensional. ̽��ֱ��papillae can serve several functions, including disguise.

Understanding the nervous system of these creatures and how they manipulate their skin has proved challenging, but now a team of scientists from the Marine Biological Laboratory and ̽��ֱ�� of Cambridge has begun to understand how this happens. Their results are published today in the journal iScience.

Image: European cuttlefish (Sepia officinalis). Credit: Roger Hanlon

̽��ֱ��researchers found that the instruction signal from the cuttlefish’s brain is routed through the stellate ganglion, a peripheral nerve centre. ̽��ֱ��stellate ganglion houses the giant axon system, so called because it is large enough to see with the naked eye. It also houses particular motor neurons that control the papillae on the mantle (the cuttlefish’s outer surface). This nerve circuitry is similar to that by which squids control skin iridescence.

̽��ֱ��giant axon system, due to its large size of up to 1mm, helped Nobel prize-winning Cambridge scientists Alan Hodgkin and Andrew Huxley, along with Australian scientist John Eccles, figure out how nerve impulses (action potentials) work.

Dr Paloma Gonzalez-Bellido, also from the ̽��ֱ�� of Cambridge, adds: “This discovery is really interesting from an evolutionary point of view. It opens up the question of which came first: was the common ancestor to cuttlefish and squid able to camouflage themselves using papillae or express iridescence, or possibly both?”

̽��ֱ��researcher team – including Lexi Scaros of Dalhousie ̽��ֱ�� and Roger Hanlon of the Marine Biological Laboratory – also looked in greater detail at the papillae to find out how they manage to hold their shape over a long period of time without a signal. They found that the papillae use a mechanism which they describe as being ‘catch-like’. It resembles the ‘catch’ mechanism found in bivalves, such as oysters, mussels, and scallops, which enables the bivalve shell to remain closed without expending much energy.

“There is still a big mystery, however, which is how these animals interpret the world around them and translate this into signals that change their appearance,” says Dr Wardill.

̽��ֱ��researchers say that understanding how cephalopods’ skin changes from a smooth, flat surface to a textured, 3D structure could help in the design of biologically-inspired materials that can themselves be assembled from flat materials.

“This research on neural control of flexible skin, combined with anatomical studies of the novel muscle groups that enable such shape-shifting skin, has applications for the development of new classes of soft materials that can be engineered for a wide array of uses in industry, society, and medicine,” adds Professor Roger Hanlon of the Marine Biological Laboratory.

̽��ֱ��research was largely funded by the US Air Force Office of Scientific Research and the UK Biotechnology and Biological Sciences Research Council.

Reference
Neural control of dynamic 3-dimensional skin papillae for cuttlefish camouflage. iScience; 15 Feb 2018; DOI: 10.1016/j.isci.2018.01.001

An international team of scientists has identified the neural circuits that enable cuttlefish to change their appearance in just the blink to eye – and discovered that this is similar to the neural circuit that controls iridescence in squids.

̽��ֱ��sea is full of strange and wondrous creatures, but there are few as bizarre and intelligent as octopuses and cuttlefish. We’ve seen dozens of examples of these animals suddenly appearing from nowhere, as if they have thrown off an invisibility cloak

Trevor Wardill

Lakshmi Sawitri via Wikimedia Commons

Lembeh81 5-12-11 - 43 cuttlefish 1 looking like sand

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

Yes

Licence type:

Attribution

Detect. Lock on. Intercept. ̽��ֱ��remarkable hunting ability of the robber fly

cjb250 — Thu, 09 Mar 2017 16:44:24 +0000

̽��ֱ��robber fly Holcocephala is a relatively small fly – at 6mm in length, it is similar in size of the average mosquito. Yet it has the ability to spot and catch prey more than half a metre away in less than half a second – by comparison to its size, this would be the equivalent of a human spotting its prey at the other end of a football pitch. Even if the prey changes direction, the predator is able to adapt mid-air and still catch its prey.

An international team led by researchers from the ̽��ֱ�� of Cambridge was able to capture this activity by tricking the fly into launching itself at a fake prey – in fact, just a small bead on a fishing line. This enabled the team to witness the fly’s remarkable aerial attack strategy. Their findings are published today in the journal Current Biology.

To read more, see our article on Medium.

See the world through the eyes of a robber fly in the Plant and Life Sciences Marquee at the Cambridge Science Festival, Saturday 18 March 2017.

Reference
Wardill, TJ et al. A novel interception strategy in a miniature robber fly with extreme visual acuity; Current Biology; 9 March 2017; DOI: 10.1016/j.cub.2017.01.050

A small fly the size of a grain of rice could be the Top Gun of the fly world, with a remarkable ability to detect and intercept its prey mid-air, changing direction mid-flight if necessary before sweeping round for the kill.

̽��ֱ��Robber Fly – Top Gun of the fly world

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

Yes

Killer flies: how brain size affects hunting strategy in the insect world

sc604 — Tue, 09 Feb 2016 09:10:36 +0000

As in economics, there is a law of diminishing returns in neuroscience – doubling the investment going in doesn’t equal double the performance coming out. With a bigger brain comes more available resources that can be allocated to certain tasks, but everything has a cost, and evolution weighs the costs against the benefits in order to make the most efficient system.

“Larger brains are specialised for high performance, so there’s a definite advantage to being bigger and better,” says Professor Simon Laughlin of the Department of Zoology, whose research looks at the cellular costs associated with various neural tasks. “But since most animals actually have very small brains, there must also be advantages to being small.” Indeed, there is strong selection pressure to have the minimum performance required in order to survive and it’s not biologically necessary to be the best, only to be better than the nearest competitor.

So does size matter? Do small insects with relatively few neurons have the same capabilities as much larger animals? “When an animal is limited, is it because their neural system just can’t cope? Or is it because they’re actually optimised for their particular environment?” asks Dr Paloma Gonzalez-Bellido from Cambridge’s Department of Physiology, Development and Neuroscience.

With funding from the US Air Force, Gonzalez-Bellido is studying the hunting behaviours of various flying insects – from tiny killer flies, slightly larger robber flies to large dragonflies – to determine how their visual systems influence their attack strategy, and what sorts of trade-offs they have to make in order to be successful.

Dragonflies are among the largest flying insects, and hunt smaller insects such as mosquitoes while patrolling their territories. They have changed remarkably little in the 300 million years since they evolved – most likely because they are so well optimised for their particular environmental niche.

“Other researchers have found that dragonflies are capable of doing complex things like internally predicting what their body is going to do and compensating for that – for instance, if they’re chasing a target and turn their wings, another signal will be sent to turn their head, so that the target stays in the same spot in their visual field,” says Gonzalez-Bellido. “But are smaller animals, such as tiny flies, capable of achieving similarly complex and accurate feats?”

Gonzalez-Bellido also studies the killer fly, or Coenosia attenuata. These quick and ruthless flies are about four millimetres long, and will go after anything they think they can catch – picky eaters they are not. However, the decision to go after their next meal is not as simple as taking off after whatever tasty-looking morsels happen to fly by. As soon as a killer fly takes off after its potential prey, it exposes itself and runs the risk of becoming a meal for another killer fly.

To help these predacious and cannibalistic flies eat (and prevent them from being eaten), they need to fly fast and to see fast. Insects see at speeds much higher than most other animals, but even for insects, killer flies and dragonflies see incredibly fast, at rates as high as 360 hertz (Hz) – as a comparison, humans see at around 60 Hz.

“For prey animals, the most important thing is to get out of the way quickly – it doesn’t matter whether they know exactly what’s coming, just that it doesn’t catch them,” says Gonzalez-Bellido. “Predators need to be both fast and accurate in their movements if they’re going to be successful – but for very small predators such as insects, there are trade-offs that need to be made.”

By making the ‘pixels’ on their photoreceptors (the light-sensitive cells in the retina) as narrow as possible, killer flies trade sensitivity for resolution. In bright light, they see better than their similar-sized prey, the common fruit fly. However, the cap on sensitivity and resolution imposed upon killer flies by their tiny eyes means that they can only see and attack things that fly close by.

While dragonflies, with their larger eyes and better resolution, can take their time and use their brain power to calculate whether a prey is suitable for an attack, killer flies attack before they’ve had a chance to determine whether it’s something they can actually catch, subdue or eat – or they risk missing their prey altogether. Once a killer fly gets relatively close to its potential prey, it has to decide whether to keep going or turn back – this is one of the trade-offs resulting from evolving such a tiny visual system.

In the early 2000s, Laughlin determined the energy efficiency of single neurons, by estimating the numbers of ATP molecules – the molecules that deliver energy in cells – used per bit of information coded. To do this he compared photoreceptors in various insects. Laughlin and his colleagues found that photoreceptors are like cars – the higher the performance, the more energy they require, and costs rise out of proportion with performance. “For any system, whether it’s in a tiny insect or a large mammal, you don’t want something which is over-engineered, because it’s going to cost more,” says Laughlin. “So what’s the root of inefficiency, and how did nature evolve efficient nerve cells from the bottom up?”

Researchers in the Department of Engineering are taking the reverse approach to answer questions about how the brain works so efficiently by looking at systems from the top down. “If you reverse engineer an animal’s behavioural strategy by asking how an animal would solve a task under specific constraints and then work out the optimal solution, you’ll find it’s often the case that animals are pretty close to optimal,” says Dr Guillaume Hennequin, who looks at how neurons work together to produce behaviour.

Hennequin studies how brain circuits are wired in such a way that they become optimised for a task: how primates such as monkeys are able to estimate the direction of a moving object, for example. “How brain circuits generate optimal interpretations of ambiguous information received from imperfect sensors is still not known,” he says. “Coping with uncertainty is one of the core challenges that brains must confront.”

Different animals come up with their own solutions. Both dragonflies and killer flies have systems that are optimal, but optimal in their own ways. It’s beneficial for killer flies to be so small, since this gives them high manoeuvrability, enabling them to catch prey that turns at speed. Dragonflies are much bigger, and can do things that killer flies can’t, but their size means they can’t turn or stop on a dime, like a killer fly can.

“By answering some of the questions around efficiency in brain circuits, large or small, we may be able to understand fundamental principles about how brains work and how they evolved,” says Laughlin.

Inset images: top to bottom: robber fly, dragon fly, killer fly; credit: Sam Fabian.

Cambridge researchers are studying what makes a brain efficient and how that affects behaviour in insects.

When an animal is limited, is it because their neural system just can’t cope? Or is it because they’re actually optimised for their particular environment?

Paloma Gonzalez-Bellido

Sam Fabian

Size comparison of robber fly, dragon fly, killer fly (left to right)

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

Yes