World's Strongest Animal , The Tiny Copepod

The world's strongest animal, the copepod, is barely 1 mm long. It is also the world's fastest animal and the most abundant multicellular animal on the planet. So what is it that makes the copepod so successful?

"The copepods' evolutionary success should be seen in relation to their ability to flee from predators. Their escape jump is hugely powerful and effective," says Professor Thomas Kiørboe from the National Institute of Aquatic Resources at the Technical University of Denmark (DTU Aqua).

Together with researchers from DTU Aqua and DTU Physics and with the aid of high-speed video recordings, Thomas Kiørboe has been able to give a detailed picture of the copepods' escape jump. The powerful jump has made an incredible impression upon the researchers.

"They jump at a rate of half a metre per second, and that's within a few thousandths of a second," says Thomas Kiørboe, continuing: "It shows that copepods -- in relation to their size -- are more than 10 times as strong as has been previously documented for any other animal or even [human-made] motors..."

The results of the impressive escape jump have just been published in full in the Journal of the Royal Society Interface.

Fine-tuned swimming legs with superior gearing

The researchers have now concluded that the strength of the copepod is 10-30 times that measured in any other species, where the maximum force production is surprisingly constant.

"The explanation is that the copepod has two separate propulsion mechanisms," says Thomas Kiørboe, DTU Aqua.

While other species have just one mechanism for movement (e.g. a bird's wings, or a horse's legs), and due to the risk of 'material fatigue', there is a maximum limit on the force production in a propulsion mechanism that is used almost constantly.

The copepod has vibrating feeding limbs that create a feeding current, while at the same time allowing it to move or swim almost continously. In addition, it has 4-5 pairs of swimming legs or jumping legs, which allows it to jump in order to escape or to attack. These are used less frequently and very briefly. The muscles in the two systems are fairly similar, but the gearing of the jumping mechanism is tuned to short bursts of immense force.

"The copepod does not experience material fatigue, because it has two systems of movement at its disposal. The swimming legs, which it uses to jump, are finely tuned, and the copepod's hydro-dynamic design is optimised for high speeds, making the escape jump unusually forceful and fast," explains Thomas Kiørboe.

Highly developed senses

Even though the copepod is both blind and so tiny that the water feels as thick as syrup, it has managed to solve the engineering feat of fleeing quickly and efficiently from predators. The solution is the two propulsion mechanisms with different gearing. Its well-developed senses interpret extremely quickly signals from the ambient and sends the message on to the swimming legs. This is made possible by a nerve transmission system that is exceptionally rapid for an invertebrate animal, and which can be explained by the special design of the neural pathways. The streamlined, hydro-dynamic shape and pure muscular strength of the copepod is what explains its most powerful jump.

More information about DTU Aqua can be found at: http://www.aqua.dtu.dk/Adapted from materials provided by Technical University of Denmark (DTU). Original article written by Charlotte Malass, National Institute of Aquatic Resources at the Technical University of Denmark (DTU Aqua).

Like Escape Artists, Rotifers Elude Enemies by Drying Up and -- Poof! -- They Are Gone With the Wind

They haven't had sex in some 30 million years, but some very small invertebrates named bdelloid rotifers are still shocking biologists -- they should have gone extinct long ago. Cornell researchers have discovered the secret to their evolutionary longevity: these rotifers are microscopic escape artists. When facing pathogens, they dry up and are promptly gone with the wind.

"These animals have evolved a way to avoid parasites and pathogens by drying up and blowing away," said Paul Sherman, Cornell professor of neurobiology and behavior, who wrote the paper with lead author Chris Wilson, a Cornell doctoral candidate in Sherman's lab.

After drying up, bdelloids come back to life when re-exposed to fresh water. The Cornell study is featured on the cover of the Jan. 29 issue ofScience.

Bdelloid rotifers (pronounced DELL -- oyd ROW-tiff-ers) are tiny, freshwater invertebrates that have long puzzled scientists because, as completely asexual animals, they should have been extinguished by parasites and pathogens long ago in evolutionary time. Instead, the bdelloids have proliferated into more than 450 species. Asexual animals like rotifers reproduce by cloning and this makes for a fixed gene pool.

Many scientists believe that the function of sex itself is to shuffle genes around. They theorize that the fresh genetic combinations that which sex provides allow sexual animals to fend off relentlessly evolving parasites and pathogens.

The discovery that bdelloids can desiccate and wisp away with the wind helps resolve the mystery of their ancient asexuality and success.

"It also helps answer one of the deepest puzzles in evolutionary biology -- why sex is nearly ubiquitous," said Wilson.

To study the bdelloids' adaptations, Wilson infected populations of rotifers with deadly fungi and found that they all died within a few weeks.

He then tried drying out other infected populations for varying lengths of time before rehydrating them. He found that the fungi were far more sensitive to dehydration than the rotifers. The longer the infected populations remained dried out, the more successful they were at completely ridding themselves of fungi and eluding death.

In a second wave of experiments, Wilson placed dried, fungus-infected rotifers in a wind chamber. The scientists observed that the rotifers were able to disperse without the fungi and establish parasite-free populations. After just seven days of blowing around, there were as many fungus-free rotifer populations as there were after three weeks of dehydration without wind. So, by drying and drifting passively on the wind -- sometimes for hundreds of miles -- bdelloids can continually establish new, uninfected populations.

"These animals are essentially playing an evolutionary game of hide and seek," said Sherman. "They can drift on the wind to colonize parasite-free habitat patches where they reproduce rapidly and depart again before their enemies catch up. This effectively enables them to evade biotic enemies without sex, using mechanisms that no other known animals can duplicate."

The study was supported by Sigma Xi, the U.S. Department of Agriculture, Cornell and Cornell's Stephen H. Weiss Presidential Fellowship Fund.

Wilder Weather Exerts a Stronger Influence on Biodiversity Than Steadily Changing Conditions

An increase in the variability of local conditions could do more to harm biodiversity than slower shifts in climate, a new study has found.

Climate scientists predict more frequent storms, droughts, floods and heat waves as the Earth warms. Although extreme weather would seem to challenge ecosystems, the effect of fluctuating conditions on biodiversity actually could go either way. Species able to tolerate only a narrow range of temperatures, for example, may be eliminated, but instability in the environment can also prevent dominant species from squeezing out competitors.
"Imagine species that have different optimal temperatures for growth. In a fluctuating world, neither can get the upper hand and the two coexist," said Jonathan Shurin, an ecologist at the University of California, San Diego who led the project. Ecologists have observed similar positive effects on populations of organisms as different as herbacious plants, desert rodents, and microscopic animals called zooplankton.
Now a study of zooplankton found in dozens of freshwater lakes over decades of time has revealed both effects. Shurin and colleagues found fewer species in lakes with the most variable water chemistry. But lakes with the greatest temperature variations harbored a greater variety of zooplankton, they report in the journal Ecology Letters January 21.
Their study considered data from nine separate long-term ecological studies that included a total of 53 lakes in North America and Europe. In addition to sampling zooplankton, scientists had also taken physical measurements repeatedly each season for periods ranging from 3 to 44 years.
From these data, they calculated the variability of 10 physical properties, including pH and the levels of nutrients such as organic carbon, phosphorous and nitrogen. Temperatures and the amount of oxygen dissolved in the water at both the surface and bottom of each lake were also included. The authors also teased apart variation based on the pace of change with year-to-year changes considered separately from changes that occurred from season-to-season or on more rapid timescales.
Zooplankton populations respond quickly to changes because they reproduces so fast. "In a summer, you're sampling dozens of generations," Shurin said. "For mammals or annual plants, you would have to watch for hundreds or thousands of years to see the same population turnover."
At every time scale the pattern held: Ecologists found fewer species of zooplankton in lakes with fluctuating water chemistry and greater numbers of species in those with varying temperatures. The authors noted that the temperature variations they observed remained within normal ranges for these lakes. But some chemical measures, particularly pH and levels of phosphorous, strayed beyond normal limits due to pollution and acid rain.
Environmental variability through time could either promote or reduce biodiversity depending on the pace and range of fluctuations, the authors suggested.
"It may depend on the predictability of the environment. If you have a lot of violent changes through time, species may not be able to program their life cycles to be active when conditions are right. They need the ability to read the cues, to hatch out at the right time," Shurin said. "If the environment is very unpredictable, that may be bad for diversity, because many species just won't be able to match their lifecycles to that."
Shurin's 10 co-authors include scientists from environmental agencies in Canada, and universities and research institutes in Canada, Germany, Switzerland and the United States. The Natural Sciences and Engineering Research Council of Canada supported Shurin's work on this study.

Vitamin Bombs for Baby Fish

Scientists at SINTEF have set themselves the goal of exploiting the advantages of a special type of zooplankton on a large scale called Copepods.Both in Norway and among the international fish-farming community it is well known that copepods are a sort of "vitamin bomb" for fish fry.Copepods are a type of zooplankton and the nutritional value is regarded as being better than that of rotifers.At SINTEF Fisheries and Aquaculture in Trondheim two scientists, Gunvor Øie and Ingrid Overrein, believe that there is a lot to be learned about the developmental requirements of fish larvae by using copepods, -- thinking primarily of cod fry and of new marine species such as groupers and tuna, which are difficult to breed.The challenge they face has been to automate the processes of harvesting and purification. Large-scale production of fry requires large volumes of copepods. Large tanks are needed to produce sufficient eggs, and since the eggs lie on the bottom, it can also be difficult to harvest them.Financed by Innovation Norway and Norwegian cod fry breeders, the project has scaled up the size of its tanks, adopted new technology for harvesting eggs and, in the future, will attempt to optimise feeding, water quality and methods of filtering and washing the eggs."Every day, we collect eggs from a large 1000-litre tank. We take up an average of eight million eggs a day, and this is gradually improving. The challenge lies in improving their quality, so that they will hatch out and develop normally," says Ingrid Overrein, who believes that the Trondheim group is well placed in a global context to produce eggs from this species of copepods, which could well be important for the production of marine fish fry in the future."We think it is exciting to hear how it is going, every time he comes in with his chiller bag to pick up fish feed," smiles Gunvor Øie. "The testing that he does is valuable for us."All over the world, aquarists compete to get hold of rare species. The trouble is that there are very few producers. The mandarin is bred only in three or four places in Germany and one in the USA. This is due to the fact that the offspring of rare aquarium fish are difficult, not to say quite impossible, to start-feed until they are viable. Many people have tried, but have had to give up.In Orkanger, a half-hour's drive from Trondheim, there are tropical treasures that have aroused the interest of aquarists in both Europe and the USA.Thomas Engels' day job is as chef at Løkken Shipyard, but at night he is "midwife" to such exotic beauties as mandarins, cardinals, seahorses, the yellowhead jawfish Opistognathus aurifrons and the orange clownfish Amphiprion percula,Engels is in no doubt that, besides his craft skills, hundreds of hours of work, countless Internet searches, and much trial and error, the special feed he collects from SINTEF is behind the success in his aquarium.Gunvor Øie and Ingrid Overrein also believe in the copepods and in a growing international market. They have already been contacted by a German dealer in aquarium equipment who wants to cover the European market for copepod eggs."We want to continue our research in order to find out more about the benefits of copepods as feed for marine fish larvae. Once we have identified the optimal conditions for egg production, it would be natural for an industrial company to take over the production, harvesting, storage and distribution of the eggs," says Overrein."What makes aquarium breeding and the international market so interesting is that we are talking at small quantities that can be sold at high prices. The problems that have to be solved are also identical. Start-feeding cod is quite similar to start-feeding aquarium fish, and the two industries have a great deal to learn from each other," says Gunvor Øie.

Fish food fight: Fish don't eat trees after all, says new study

What constitutes fish food is a matter of debate. A high-profile study a few years ago suggested that fish get almost 50 percent of their carbon from trees and leaves, evidence for a very close link between the terrestrial and aquatic ecosystems.But new research from the University of Washington shows this is not likely to be true. Algae provide a much richer diet for fish and other aquatic life, according to research published this week in the Proceedings of the National Academy of Sciences."Are the fish made of maple? Our argument would be no, they're not, they're made of algae," says Michael Brett, a UW professor of civil and environmental engineering. "Other scientists have said that up to 50 percent of the carbon was coming from this terrestrial source. We're saying that's very unlikely."The results could be important not just to fish but to people seeking to boost fish populations."In terms of fishery production this means you've really got to focus on the algae," Brett said. "The terrestrial environment is still important, but for other reasons such as habitat."The new paper shows that algae are necessary ingredients for healthy zooplankton, the animals at the base of the aquatic food web. Brett's lab studies omega-3 fatty acids, the same ones touted in health studies. Fish can't produce the heart-healthy lipids, they just accumulate them from their diet. Brett's group looks at where exactly the omega-3's are coming from, largely from several groups of phytoplankton that can make these fats.After reading the fish food study published in 2004 in the journal Nature, "we were furrowing our brows and saying 'This doesn't make sense,'" Brett said, "because the terrestrial plants aren't producing these omega-3 molecules. Those results completely conflicted with the perspective that was coming out of our own area of research."The earlier study by the Institute for Ecosystem Studies in Millbrook, N.Y., was a large-scale experiment on three lakes in Michigan. Researchers fertilized these lakes with a labeled form of carbon dioxide sprinkled on the lakes' surfaces over more than a month. They then analyzed how much of that labeled carbon showed up in animals at each position in the aquatic food web. Even when terrestrial plant matter was only about 20 percent of the available food, they found, the animals appeared to be composed of about 50 percent land-based carbon.The UW study took a different approach. Brett and colleagues raised zooplankton in the lab, feeding them a diet of either pure algae, pure land-based carbon, or various mixtures of the two. They found that zooplankton fed a purely land-based diet survived and reproduced but were small and produced relatively few offspring. Zooplankton fed a diet of pure algae were 10 times bigger than their tree-fed twins and produced 20 times more offspring. Zooplankton fed a mixed diet were larger and produced more offspring as the proportion of algae in their diet went up. Even when zooplankton ate almost nothing but land-based carbon, nearly all their lipids came from algae."I think we were able to show that the terrestrial source is such low quality that it's inconceivable that it could be nearly as important as what that study suggested," Brett said.The research was funded by the National Science Foundation. Co-authors are Martin Kainz of the Danube University Krems in Austria and Sami Taipale and Hari Seshan of the UW.So why did the earlier study suggest that fish were eating land-based food? Brett believes the reason is those researchers discounted the idea of zooplankton migration, the daily movement down to deeper waters during the daytime to hide from predatory fish. Researchers sprinkled tagged food in the upper waters and assumed that any other food source must be land-based."The flaw was that there was an alternative source. They could have been getting half of their carbon from the lower depths in the lakes," Brett said.In recent years the earlier study has had a profound impact on the field of aquatic ecology but few scientists have critically assessed its results, Brett says. "What I would hope our paper would do is to really get people to open their eyes and say 'Does this really add up, and is there a simpler way to look at what is supporting fisheries production?'" University of Washington

'Lucky Luke' Of The Seas: How Ambush-feeding Zooplankton Capture Prey

Could you filter 100,000 cubic metres of syrup every day to find food in a concentration of two grains of rice per cubic metre?

This is what zooplankters, such as copepods, do every day, gathering microscopic food particles (algae etc.) from a volume of water approx. one million times their own body volume to survive. It is no trivial task as water – at copepod scale – has the consistency of syrup. On top of which, copepods are blind.
The question is how they do it? Knowing this is necessary to understand the mechanisms at play in the food chains in the sea on which the fish on our supper table ultimately depend.
“The challenge for the copepod is that a small body moving through water will pull a thick layer of syrup-like water with it. So how do you get to the prey, if it is being pushed away as you move in?” asks Professor Thomas Kiørboe, National Institute of Aquatic Resources, Technical University of Denmark (DTU Aqua), who, together with colleagues from DTU Aqua and DTU Physics, has been studying the prey capture techniques of two ambush-feeding species of copepods by means of high-speed video, a great deal of patience and a fraction of luck.
The results are published in the scientific journal Proceedings of the National Academy of Science (PNAS).
The Lucky Luke effect
“So far, we know of four ways in which zooplankters tackle the engineering feat of finding food in water which appears as thick as syrup. Our contribution has been to describe the mechanism at work for the last of these: How some copepods perform spectacularly precise and rapid surprise attacks on their single-cell prey after first having registered the prey by means of hydrodynamic signals,” explains Professor Thomas Kiørboe, DTU Aqua.
The solution for the ambush-feeding copepods builds on what Thomas Kiørboe calls the Lucky Luke effect:
“Our recordings show that the sub-mm copepods accelerate to a speed of 100 mm per second in a few milliseconds, while at the same time rotating perhaps 180 degrees. Like Lucky Luke who is faster than his shadow, the copepods jump forward so rapidly and with such precision that they, so to speak, shake the viscous boundary layer off, in that way getting close enough to their prey to capture it with their feeding limbs.”
The viscous boundary layer is the layer of water which the copepods pull with them when moving their bodies through the syrupy water. The larger the animals are and the faster they swim, the thinner it seems.
Takes muscle power
Ambush feeding, whereby feeders passively wait for their prey and capture it by means of rapid surprise attacks, has many advantages over a technique where they swim around looking for prey.
“Lying still, you expend less energy and also minimise the risk of being spotted and eaten by other predators. An ambush specialist such as Oithonatherefore has a low metabolic rate and far lower mortality rates than other copepods of the same size pursuing more active feeding strategies,” says the DTU Aqua professor.
So the question is, of course, why don’t all zooplankters avail themselves of these apparently superior tactics?
“To capture prey through surprise attacks you must be streamlined and have enough raw muscle power to move extremely fast through water. At the same time, pinpointing the prey before jumping requires highly developed sensing capabilities. Surprise attacks are therefore not the most widespread prey capture technique among small animals,” concludes Thomas Kiørboe.
Nerdish but necessary
Thomas Kiørboe happily admits that, to outsiders, studying the prey capture techniques of copepods may seem slightly nerdish. However, it provides knowledge which is essential to understanding important strategies and mechanisms in the marine food chains.
“We are developing so-called trait-based models, describing properties, or traits, of individuals rather than species, e.g. various feeding strategies. By understanding the mechanisms at play in the individual interaction, we can extrapolate to other species and situations, e.g. describing all zooplankters on the basis of five properties, rather than conducting detailed studies of each and every individual species in order to model and understand the food chains and their development under different conditions.”
I’ve got no strings …
The project on ambush-feeding copepods has involved scientists from DTU Aqua and DTU Physics. As part of the results, the scientists have, for the first time ever, been able to film and study the techniques of the attacking copepods.
“Previous studies of the prey capture techniques in copepods that feed by creating a scanning flow so that the food passes past their mouths have been conducted by attaching the copepod to a hair to hold it in position in front of the camera lens. It goes without saying that this is not possible when studying how they jump. As the camera can hold only 1 second of recordings when recording 2,000 pictures a second, you have to film at the precise second, in the right place. It has taken a great deal of patience, not to mention a fair bit of luck, which is probably why it has never been done before,” muses Thomas Kiørboe, DTU Aqua.
Journal reference:
Kiorboe et al. Mechanisms and feasibility of prey capture in ambush-feeding zooplankton. Proceedings of the National Academy of Sciences, 2009; 106 (30): 12394 DOI: 10.1073/pnas.0903350106
Adapted from materials provided by Technical University of Denmark (DTU), via AlphaGalileo.

Simple Eyes Of Only Two Cells Guide Marine Zooplankton To The Light

Researchers unravel how the very first eyes in evolution might have worked and how they guide the swimming of marine plankton towards light.

Larvae of marine invertebrates – worms, sponges, jellyfish - have the simplest eyes that exist. They consist of no more than two cells: a photoreceptor cell and a pigment cell. These minimal eyes, called eyespots, resemble the 'proto-eyes' suggested by Charles Darwin as the first eyes to appear in animal evolution. They cannot form images but allow the animal to sense the direction of light. This ability is crucial for phototaxis – the swimming towards light exhibited by many zooplankton larvae. Myriads of planktonic animals travel guided by light every day. Their movements drive the biggest transport of biomass on earth.
"For a long time nobody knew how the animals do phototaxis with their simple eyes and nervous system," explains Detlev Arendt, whose team carried out the research at EMBL. "We assume that the first eyes in the animal kingdom evolved for exactly this purpose. Understanding phototaxis thus unravels the first steps of eye evolution."
Studying the larvae of the marine ragworm Platynereis dumerilii, the scientists found that a nerve connects the photoreceptor cell of the eyespot and the cells that bring about the swimming motion of the larvae. The photoreceptor detects light and converts it into an electrical signal that travels down its neural projection, which makes a connection with a band of cells endowed with cilia. These cilia - thin, hair-like projections - beat to displace water and bring about movement.
Shining light selectively on one eyespot changes the beating of the adjacent cilia. The resulting local changes in water flow are sufficient to alter the direction of swimming, computer simulations of larval swimming show.
The second eyespot cell, the pigment cell, confers the directional sensitivity to light. It absorbs light and casts a shadow over the photoreceptor. The shape of this shadow varies according to the position of the light source and is communicated to the cilia through the signal of the photoreceptor.
"Platynereis can be considered a living fossil," says Gáspár Jékely, former member of Arendt's lab who now heads a group at the MPI for Developmental Biology, "it still lives in the same environment as its ancestors millions of years ago and has preserved many ancestral features. Studying the eyespots of its larva is probably the closest we can get to figuring out what eyes looked like when they first evolved."
It is likely that the close coupling of light sensor to cilia marks an important, early landmark in the evolution of animal eyes. Many contemporary marine invertebrates still employ the strategy for phototaxis.
Journal reference:
Jékely et al. Mechanism of phototaxis in marine zooplankton. Nature, 2008; 456 (7220): 395 DOI: 10.1038/nature07590
Adapted from materials provided by European Molecular Biology Laboratory, via EurekAlert!, a service of AAAS.

View to a krill: Secrets of plankton eyes

Biologists on Wednesday explained how the larvae of marine zooplankton can see with just two cells, using what is believed to be the world's simplest vision system.Zooplankton are tiny creatures such as copepods and krill that drift in the ocean's water columns, swimming up from the depths towards the light in order to graze on marine plants called phytoplankton near the surface.This movement, called phototaxis, is the biggest biomass displacement in the world.In a study published by the British-based journal Nature, European scientists looked at the larvae of the marine ragworm Platyneris dumerilii to try to explain how plankton are able to do the phototaxis trick.The larva has just two eye cells, consisting of a pigment cell and a light-sensitive cell, say the investigators.The cells are unable to form images but enable the plankton to sense the difference between light and dark and send appropriate signals to its swimming mechanism, say the investigators.First, the pigment cell absorbs light and casts a shadow over the photoreceptor cell. The shape of the shadow varies according to the position of the light source.The photoreceptor cell then converts this light signal into electricity, sending it in a signal along a nerve that connects to a band of cells endowed with thin hairs, called cilia, that beat to displace water.The basic but effective system could explain how the very first eyes in evolution may have worked, say the team from the European Molecular Biology Laboratory (EMBL) and the Max Planck Institute."For a long time, nobody knew how the animals do phototaxis with their simple eyes and nervous system," said EMBL's Detlev Arendt."We assume that the first eyes in the animal kingdom evolved for exactly this purpose. Understanding phototaxis thus unravels the first steps of eye evolution."