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By Jeff Kubina. Creative Commons. Some rights reserved.
Fish can hide in the open ocean by manipulating how light reflects off their skin, according to researchers at The University of Texas at Austin. The discovery could someday lead to the development of new camouflage materials for use in the ocean, and it overturns 40 years of conventional wisdom about fish camouflage.
The researchers found that lookdown fish camouflage themselves through a complex manipulation of polarized light after it strikes the fishes’ skin. In laboratory studies, they showed that this kind of camouflage outperforms by up to 80 percent the “mirror” strategy that was previously thought to be state-of-the-art in fish camouflage.
The study was published this month in the Proceedings of the National Academy of Sciences (PNAS). The research was funded by the U.S. Navy, which has an interest both in developing better ocean camouflage technologies and in being able to detect such strategies if developed by others.
“The open ocean represents a challenging environment for camouflage,” said Molly Cummings, associate professor of integrative biology in the College of Natural Sciences. “There are no objects to hide behind in three-dimensional space, so organisms have to find a way to blend in to the water itself.”
For the past few decades the assumption has been that the optimal camouflage strategy for open ocean fish is to reflect sunlight like a mirror. Many fish, including the lookdown, have reflective skin elements that can act like mirrors.
Such a strategy works well for certain aspects of light, such as color and intensity, which tend to be distributed homogenously in the region surrounding the fish. The mirror strategy is not optimal, however, when light is polarized, which occurs when individual waves of light align parallel to one another.
“In the polarized light field, there is a lot of structure in the open ocean,” said physicist Parrish Brady, a postdoctoral associate in Cummings’ lab. “Humans can’t see it, but more than 60 different species of fish have some degree of polarization sensitivity. They can perceive the structure in the light.”
The contours of the polarized light field in the open ocean environment are constantly changing except at noon, when the sun is directly overhead. A fish needs to do more than deploy the straight mirror strategy in order to stay camouflaged. Cummings hypothesized that perhaps nature had evolved a strategy to do just that.
She and Brady caught some lookdowns, which are known as good camouflagers. In tanks in the lab, they simulated the sun passing over the ocean during the course of a day, and they used a custom-built polarimeter to measure how the lookdowns reflected the polarized light.
They found that the lookdowns were able to manipulate their reflective properties in ways that were close to the theoretical optimum and far better than a standard mirror.
“The nifty thing is when we mimicked the light field when the sun is overhead, as it would be at noon, the fish just bounced back that light field,” said Cummings. “It acted like a mirror. Then we mimicked the light field when it’s more complex, and the lookdown altered the properties of the polarized light it was reflecting so that it would be a better blend into its specific background at different times of day.”
The lookdown’s “polaro-cryptic” mirror skin functions by selectively reducing the degree of polarization and transforming the angle of polarization of the reflected light depending on the conditions.
The researchers’ next task is to understand how the fish are accomplishing this feat.
Cummings said it might be an entirely passive process, with different elements of their skin automatically responding to the angle of the sunlight. Or, the lookdowns may aid in their camouflage by subtly altering their bodies’ orientation relative to the sun, or by neurologically ramping up certain processes.
What the researchers discover about these mechanisms will be of particular interest to the Navy, which at present isn’t as good as lookdowns at open ocean camouflage.
“From an evolutionary biologist viewpoint, I am always excited when evolution is one step ahead of humans,” said Cummings. “There is this problem out there — how to blend in to this environment, and though we haven’t quite solved it yet, an animal has. We can identify these basic biological strategies, and perhaps materials scientists can then translate them into useful products for society.”
Photograph by Eric Lemar/Shutterstock.
Scientists from the Hebrew University of Jerusalem and the Technion-Israel Institute of Technology have discovered why Heteroxenia corals pulsate. Their work, which resolves an old scientific mystery, appears in the current issue of PNAS.
One of the most fascinating and spectacular sights in the coral reef of Eilat is the perpetual motion of the tentacles of a coral called Heteroxenia (Heteroxeniafuscescens). Heteroxenia is a soft coral from the family Xeniidae, which looks like a small bunch of flowers, settled in the reef walls and on rocky areas on the bottom of the reef. Each “flower” is actually a living polyp, the basic unit which comprises a coral colony. Apparently, the motion of these polyps, resembling flowers that are elegantly spreading out and closing up their petals, is unique in the animal kingdom.
Except for the familiar swimming motion of jellyfish, no other bottom-attached aquatic animal is known to perform such motions. Pulsation is energetically costly, and hence there must be a reasonable benefit to justify this motion.
The perpetual motions of jellyfish serve them for swimming, predation and feeding. The natural explanation would be that that the Heteroxenia’s spectacular motions are used for predation and feeding, however several studies indicate that these corals do not predate on other animals at all. If predation is not the reason for pulsating, there must be another explanation to justify the substantial energetic expense by the Heteroxenia.
Maya Kremien found the answers to these questions, while working on her master’s research at the Interuniversity institute for Marine Sciences in Eilat under the supervision of Prof. Amatzia Genin from the Hebrew University and Prof. Uri Shavit from the Technion in a joint research funded by the National Science Foundation.
After watching several coral colonies with an underwater infrared-sensitive camera night and day, the researchers found their first surprising discovery: Heteroxenia corals cease to pulsate and take a half-hour break every single day in the afternoon hours. At this stage, the afternoon “siestas” remained unexplained.
The labs of Prof. Genin and Prof. Shavit conduct work on the interaction between biological processes of aquatic creatures and the water motions which surround them. Apparently aquatic animals affect the flow and at the same time are absolutely dependent on that flow. In order to solve the mystery of the Heteroxenia coral, the research team developed (as part of Ph.D. work by Tali Mass) an underwater measuring device called PIV (particle imaging velocimetry), which allows measurement of the flow field just around the coral very accurately. The system consists of two powerful lasers, an image capturing system and computation ability. A special set of lenses releases a sheet of light in short, powerful pulses so that the imaging system can capture pairs of snapshots of natural particles moving with the flow. The computational system then performs a mathematical analysis of the pairs of photos, producing a huge database of flow field maps, from which the flow speed, characteristics of solutes transport, and turbulent mixing intensity are calculated.
The measurements were performed at night with the support of divers who volunteered to assist the research team. It was found that if a diver lightly touched the coral, the polyps “close” and remain motionless for a few minutes, after which the coral returns to its normal pulsation activity. The researchers used this behavior in order to repeatedly measure the flow field around the Heteroxenia during pulsation and rest.
These measurements led to the research group’s next discovery. Analysis of the direction of water flow indicated that the motion of the polyps effectively sweeps water up and away from the coral tissues into the ambient water. Corals need carbon-dioxide during daytime and oxygen during nighttime, as well as nutrients (such as phosphate and nitrogen) during day and night. One of the challenges for coral colonies is to render their surrounding waters rich in essential commodities by efficiently mixing the water around them.
By using the sophisticated measuring system, the researchers calculated the mixing intensity of the water as a result of the coral’s pulsation. The unexpected discovery was that even though the polyps’ motions are uncoordinated (i.e. each polyp starts its period of motion at a different time), the accumulated effect of the polyps’ activity is a significant enhancement of the flow around the colony, particularly in the upward direction which sweeps water away from the coral, hence reducing the probability of re-filtration of the same water.
However, these findings still did not yet answer the question of why a coral would invest so much energy to move its tentacles. After receiving a permit from the Israel Nature and Parks Authority, the research team collected a few Heteroxenia colonies from the sea in order to run a series of laboratory experiments. All corals were returned back to their original location after the experiment terminated. The Hypothesis was that the pulsation motions enhance the coral’s photosynthesis rate.
Corals are among the most ancient creatures surviving on our planet. One of the “secrets” of their amazing survival abilities is that they “host” photosynthetic algae in their tissues. The symbiotic algae provides the coral with essential nutrients and lives off the waste of the coral.
In a previous study of the same research team (which the results of were also published in PNAS) it was found that the motion of water around corals is essential in order to enhance the efflux of oxygen from the coral tissues. Without water motion, the oxygen concentration in the coral tissues would rise and the photosynthesis rate would drop.
The answer to the question as to why the Heteroxenia pulsates was finally revealed through the lab experiments. First, the photosynthesis rate of a pulsating Heteroxenia was measured, and it was found to be on an order of magnitude higher than that of a non-pulsating colony. Next, in order to prove that the mechanism of pulsation is intended to sweep away oxygen, the researchers artificially increased the oxygen concentration in the measurement chamber so that even when the coral managed to mix water via pulsation, it was replacing oxygen-rich water with new water, which, unfortunately for the coral , was also rich in oxygen. And indeed it was found that the photosynthesis rate was low in this case, and even when the coral was constantly pulsating, the oxygen concentration remained high and photosynthesis remained low, as if the coral was at rest (i.e. not pulsating).
The elegant motion of Heteroxenia has been fascinating the scientific society and capturing the attention of researchers for nearly 200 years (Jean-Baptiste Lamarck, 1744-1829), yet it has not been explained. Now, in the study of Kremien, Genin and Shavit, it was found that the pulsation motions augment a significant enhancement in the binding of carbon dioxide to the photosynthetic enzyme RuBisCo, also leading to a decrease in photorespiration. This explanation justifies the investment of energy in pulsation — the benefit overcomes the cost. In fact, thanks to pulsation, the ratio between photosynthesis to respiration in Heteroxenia is the highest ever measured in stony and non-pulsating soft corals.
The findings of this study indicate that pulsation motions are a highly efficient means for sweeping away water from the pulsating body, and for an increased mixing of dissolved matter between the body and the surrounding medium. These two processes (expulsion of medium and mixing of solutes) may lead to future applications in engineering and medicine. Currently the research group is focusing on attempts to broaden the results of this study and on developing mathematical models which could serve various applicative purposes.
Source: Science Daily
Photograph by Aleks.K/Shutterstock.
Newcastle Researchers Leapfrog Ahead in World-First
University of Newcastle researchers have successfully developed a method to freeze frog embryonic cells in a world-first breakthrough that could slow the threat of extinction to hundreds of frog species.
The researchers have separated, isolated and frozen the embryonic cells of an Australian Ground Frog (the Striped Marsh Frog, Limnodynastes peronii), using cryopreservation techniques that will now allow for cloning.
This is the first time anyone in the world has successfully used slow-freezing techniques on amphibian cells, project leader at the University of Newcastle, Professor Michael Mahony, said.
“Almost 200 frog species have been lost in the past 30 years due to disease and a further 200 species face imminent threat – this is the worst rate of extinction of any vertebrate group,” he said.
“Amphibian eggs and early embryos, unlike human eggs and embryos, are large in size and have traditionally presented a challenge to researchers attempting to cryo-preserve and store frog genomes, as they would shatter during the freezing process.
“The new technique, developed by our University of Newcastle researchers, will act as an insurance policy to buy us time for species on the edge of extinction, as we search for answers to diseases and other threats.”
Professor Mahony said the development would have wider implications for other species facing extinction.
“Not only will it help us preserve the genetic diversity of frogs, but this discovery could also help in the conservation of other species with large embryonic cells, such as fish.”
The University of Newcastle is leading the world on research into amphibian protection. This latest discovery follows on from recent work with other universities on the Lazarus project, which generated live embryos using cells from an extinct Australian frog.
The technical work was led by Dr John Clulow and Professor Michael Mahony, alongside Ms Bianca Lawson and Mr Simon Clulow.
Courtesy of the University of Newcastle.
Two weeks ago, a group of sailors off the coast of New Zealand leaned over the side of their boat, dropped a contraption into the Pacific Ocean and watched it disappear. Using an app they’d downloaded to a smartphone, they logged a reading from the underwater device, along with their GPS location and the water temperature. In just a few minutes’ time, they had become the first participants in a new program launched by the UK’s Plymouth University Marine Institute which allows citizen scientists to help climatologists study the effects of climate change on the oceans.
Photo: Richard Kirby
Researchers writing in the Proceedings of the Royal Society A say they have developed a new robotic fish that has lateral line sensing capabilities.
The FILOSE team members have spent four years investigating fish lateral line sensing, which is a sensing organ found in aquatic vertebrates used to detect movement and vibration in the surrounding water. This organ essentially helps a fish’s orientation in the water. The team set out to understanding how a fish detects and exploits flow features in water, and then use their findings to develop efficient underwater robots based on biological principles.
Flow can be measured and characterized on many salient features that do not change. This “flowscape” is a flow landscape that helps fish and robots orient themselves, navigate, and control their movements in water.
Photo: Prof. Maarja Kruusmaa and FILOSE fish robot. Credit: Jelena Pijonkina
Photograph by Jan Lupton.
Citizen science surveys compare well with traditional scientific methods when it comes to monitoring species biodiversity – according to new research from the University of East Anglia.
Research published today in the journal Methods in Ecology and Evolution
shows that methods to record marine diversity used by amateurs returned results consistent with techniques favoured by peer-reviewed science.
The findings give weight to the growing phenomenon of citizen science, which sees data crowd-sourced from an army of avid twitchers, divers, walkers and other wildlife enthusiasts.
The field study compared methods used by ‘citizen’ SCUBA divers with those used by professional scientists, to measure the variety of fish species in three Caribbean sites.
The divers surveyed the sites using two methods – the ‘belt transect’, used in peer reviewed fish diversity studies, and the ‘roving diver technique’, used by the Reef Environmental Education Foundation (REEF) volunteer fish survey project.
Two teams of 12 divers made 144 separate underwater surveys across the sites over four weeks.
While the traditional scientific survey revealed sightings of 106 different types of fish, the volunteer technique detected greater marine diversity with a total of 137 in the same waters.
Dr Ben Holt, from UEA’s school of Biological Sciences, led the research in partnership with the Centre for Marine Resource Studies in the Caribbean and the University of Copenhagen, Denmark.
He said: “The results of this study are important for the future of citizen science and the use of data collected by these programs. Allowing volunteers to use flexible and less standardised methods has important consequences for the long term success of citizen science programs. Amateur enthusiasts typically do not have the resources or training to use professional methodology. Our study demonstrates the quality of data collected using a volunteer method can match, and in some respects exceed, protocols used by professional scientists.
“Enlisting the help of a large pool of volunteers helps professional researchers collect valuable data across many ecosystems.
“The popularity of SCUBA diving has resulted in monitoring of the underwater environment on a scale that was previously impossible. For example, the REEF method has been used by volunteers in more than 160,000 underwater surveys across the world. It would have cost many millions of pounds for professionals to have undertaken the same work.
“Very few, if any, scientific groups can collect data on the scale that volunteer groups can, so our proof that both methods return consistent results is very encouraging for citizen science in general.
“I think we will really see the value of volunteer schemes increase in future. We’re living in a world that’s changing very significantly. Environmental changes are having a big impact on ecosystems around us so we need to harness new ways of measuring the effect.
“For example Lion fish is an invasive species which was not in the Caribbean until roughly 10 years ago. They have now become a real problem in many areas and this invasion has been tracked using volunteer data. Following our study, scientists can have more confidence when using these data to consider the impact of threats, such as invasive species, on the wider natural communities.
“It is important to note that our study does not consider the abilities of the individuals performing the surveys and this is also an important consideration for any large scale biodiversity program. By addressing these issues we can make important steps towards enabling the large pool of volunteer enthusiasts to help professional researchers by collecting valuable data across many ecosystems.”
The research was carried out in under water sites close to South Caicos in the Turks and Caicos Islands.
Source: ‘Comparing diversity data collected using a protocol designed for volunteers with results from a professional alternative’ by B. Holt (University of East Anglia, UK), R. Rioja-Nieto (Centre for Marine Resource Studies, Caribbean, and the National Autonomous University of Mexico), A. MacNeil (Australian Institute of Marine Science), J. Lupton (Centre for Marine Resource Studies) and C. Rahbek (University of Copenhagen, Denmark) is published by Methods in Ecology and Evolution.
Photograph by Rodho/Shutterstock.
Mysterious glow of light found to correlate with coral stress prior to bleaching
Coral reefs not only provide the world with rich, productive ecosystems and photogenic undersea settings, they also contribute an economic boost valued at hundreds of billions of dollars. But their decline in recent years due to a variety of threats—from pollution to climate warming—has lent urgency to the search for new ways to evaluate their health.
A new study by Scripps Institution of Oceanography at UC San Diego scientists has revealed that fluorescence, the dazzling but poorly understood light produced by corals, can be an effective tool for gauging their health.
As described in the March 12 edition of Scientific Reports (a publication of the Nature Publishing Group), marine biologists Melissa Roth and Dimitri Deheyn describe groundbreaking research using fluorescence to test coral stress prompted from cold and heat exposures.
In experimental studies conducted at Scripps, Roth and Deheyn tested the common Indo-Pacific reef-building branching coral Acropora yongei under various temperatures. Branching corals are susceptible to temperature stress and often one of the first to show signs of distress on a reef. Roth and Deheyn found, at the induction of both cold and heat stress, corals rapidly display a decline in fluorescence levels. If the corals are able to adapt to the new conditions, such as to the cold settings in the experiment, then the fluorescence returns to normal levels upon acclimation.
While the corals recovered from cold stress, the heat-treated corals eventually bleached and remained so until the conclusion of the experiment. Coral bleaching, the loss of tiny symbiotic algae that are critical for coral survival, is a primary threat to coral reefs and has been increasing in severity and scale due to climate change. In this study, the very onset of bleaching caused fluorescence to spike to levels that remained high until the end of the experiment. The researchers noted that the initial spike was caused by the loss of “shading” from the symbiotic algae.
“This is the first study to quantify fluorescence before, during, and after stress,” said Deheyn. “Through these results we have demonstrated that changes in coral fluorescence can be a good proxy for coral health.”
Deheyn said the new method improves upon current technologies for testing coral health, which include conducting molecular analyses in which coral must be collected from their habitat, as opposed to fluorescence that can be tested non-invasively directly in the field.
Corals are known to produce fluorescence through green fluorescent proteins, but little is known about the emitted light’s function or purpose. Scientists believe fluorescence could offer protection from damaging sunlight or be used as a biochemical defense generated during times of stress.
“This study is novel because it follows the dynamics of both fluorescent protein levels and coral fluorescence during temperature stress, and shows how coral fluorescence can be utilized as an early indicator of coral stress” said Roth, a Scripps alumna who is now a postdoctoral scientist at Lawrence Berkeley National Laboratory and UC Berkeley.
Source: University of California – San Diego, via EurekAlert!, a service of AAAS.
Alburnoides manyasensis. Photograph courtesy of Davut Turan; CC-BY 3.0
The newly described species Alburnoides manyasensis, belongs the large carp family Cyprinidae that includes freshwater fishes such as he carps, the minnows, and their relatives. This is the largest fish family, and more notably the largest family of vertebrate animals, with the remarkable numbers of over 2,400 species. Cyprinids are highly important food fish because they make the largest part of biomass in most water types except for fast-flowing rivers.
The genus Alburnoides is widely distributed in Turkey in rivers and streams of basins of the Marmara, Black and Aegean seas, being absent only from the Mediterranean Sea basin. It is distinguished by small black spots located on each side of the fish, especially prominent on the anterior of the body. The description was published in the open access journal Zookeys.
Alburnoides manyasensisis is described from the Koca Stream drainage of Lake Manyas, Marmara Sea basin in Anatolia and is currently only associated with this specific locality. The name of the species is an adjective that is derived from the name of Lake Manyas to which the new species is possibly endemic. The new species inhabits clear fast running water with cobble and pebble substrates. It is a comparatively small representative of the family with maximum known body length of only 92 cm while the largest representative of the family, the giant barb (Catlocarpio siamensis) can reach up to the astonishing 3 m in length.
Original Source: Turan D, Ekmekci FG, Kaya C, Guclu SS (2013) Alburnoides manyasensis (Actinopterygii, Cyprinidae), a new species of cyprinid fish from Manyas Lake basin, Turkey. ZooKeys 276: 276: 85–02, doi: 10.3897/zookeys.276.4107
Algae eaters on a reef in Fiji.
Using underwater video cameras to record fish feeding on South Pacific coral reefs, scientists have found that herbivorous fish can be picky eaters – a trait that could spell trouble for endangered reef systems.
In a study done at the Fiji Islands, the researchers learned that just four species of herbivorous fish were primarily responsible for removing common and potentially harmful seaweeds on reefs – and that each type of seaweed is eaten by a different fish species. The research demonstrates that particular species, and certain mixes of species, are potentially critical to the health of reef systems.
Related research also showed that even small marine protected areas – locations where fishing is forbidden – can encourage reef recovery.
“Of the nearly 30 species of bigger herbivores on the reef, there were four that were doing almost all of the feeding on the seven species of seaweeds that we studied,” said Mark Hay, a professor in the School of Biology at the Georgia Institute of Technology. “We did not see much overlap in the types of seaweed that each herbivore ate. Therefore, if any one of these four species was removed, that would potentially allow some macroalgae to proliferate.”
The research has been published online ahead of print by the journal Ecology and will be included in a future print edition. The study was supported by the National Science Foundation (NSF), the National Institutes of Health (NIH) and the Teasley Endowment to Georgia Tech.
Macroalgae – known as seaweeds – pose a major threat to endangered coral reefs. Some seaweeds emit chemicals that are toxic to corals, while others smother or abrade corals. If seaweed growth is not kept in check by herbivorous fish, the reefs can experience rapid decline. Overfishing of coral reef ecosystems has decimated fish populations in many areas, contributing to overgrowth by seaweed, along with the loss of corals and their ability to recover from disturbance.
To determine which fish were most important – information potentially useful for protecting them – Hay and Georgia Tech graduate student Douglas Rasher moved samples of seven species of seaweed into healthy reef systems that had large populations of fish.
They set up three video cameras to watch the reef areas, then left the area to allow the fish to feed. They repeated the experiment over a period of five days in three different marine protected areas located off the Fiji Islands. In all, Rasher watched more than 45 hours of video to carefully record which species of fish ate which species of seaweed.
“The patterns were remarkably consistent among the reefs in terms of which fish were responsible for removing the seaweed,” said Rasher. “Because different seaweeds use different defense strategies to deter herbivores from eating them, a particular mix of fish – each adapted to a particular type of seaweed – is needed to keep seaweeds off the reef.”
Among the most important were two species of unicornfish, which removed numerous types of brown algae. A species of parrotfish consumed red seaweeds, while a rabbitfish ate a type of green seaweed that is particularly toxic to coral. Those four fish species were responsible for 97 percent of the bites taken from all the seaweeds.
“It’s not enough to have herbivorous fish on the reef,” said Hay, who holds the Harry and Linda Teasley Chair in Environmental Biology at Georgia Tech. “We need to have the right mix of herbivores.”
While just four fish species consumed the large seaweeds, Rasher observed a different set of species involved in what he termed “maintenance” – the removal of small algal growths before they have a chance to grow.
“Through our videos, we were able to observe both groups in action,” he said. “There was not only little overlap in which fishes ate the large seaweeds, but there was also little overlap between fishes that comprised the two groups.”
To help determine why certain fish ate certain seaweed, the researchers played a trick on the unicornfish. They removed chemicals from each seaweed species that the unicornfish avoided and coated them individually on a species of seaweed that the unicornfish were accustomed to eating. That caused the fish to stop eating the chemical-laced seaweed, suggesting that chemical defenses kept them from consuming some seaweeds.
The researchers also compared the quality of coral reefs in marine protected areas to those in areas where fishing has been allowed. There are an estimated 300 marine protected areas in the Fiji Islands, most governed by local villages that have considerable autonomy over reef management.
Surveying these larger areas, the researchers found strong negative associations between the abundance or diversity of seaweed on the reef and diversity of herbivorous fishes at the sites they studied.
They found that strict rules against fishing in certain protected areas had led to a regeneration of corals, and that the contrast to fished areas nearby – some just 500 meters apart – was dramatic. The protected reefs supported as much as 11 times more live coral cover, 17 times more herbivorous fish biomass and three times more species diversity among herbivorous fishes as the unprotected areas.
“What we noted in Fiji is that where reefs are fished, they look like the devastated reefs in the Caribbean,” said Hay. “There’s a lot of seaweed, there’s almost no coral and there aren’t many fish in these flattened areas. But right next to them, where fishing hasn’t been allowed for the past eight or ten years, the reefs have recovered and have high coral cover, almost no seaweed and lots of fish.”
Although both fished and protected areas had only seven percent coral cover ten years ago, today the protected areas have recovered.
“This really demonstrates the value of reef protection, even on small scales,” Rasher said. “There is a lot of debate about whether or not small reserves work. This seems to be a nice example of an instance where they do.”
Ultimately, the researchers hope to provide information to village leaders that could help them manage their reefs to ensure long-term health – while helping feed the local human population.
“Not fishing is really not an option for people in these communities,” Rasher said. “Giving the village leadership an idea of which species are essential to reef health and what they can do to manage fisheries effectively is something we can do to help them maintain a sustainable reef food system.”
Beyond the researchers already mentioned, the research also included Andrew Hoey from the ARC Centre of Excellence for Coral Reef Studies at James Cook University in Townsville, Australia.
This research was supported by the National Science Foundation (NSF) under grants OCE 0929119 and DGE 0114400, and by the National Institutes of Health (NIH) under grant U01-TW007401. The opinions expressed are those of the authors and do not necessarily represent the official views of the NSF or NIH.
Source: Georgia Tech
Photograph courtesy of Cody Clements
Posted February 13th, 2013. Add a comment
Photograph by David Desoer/Shutterstock
Have you ever wondered why, and how, shoals of fish are comprised of fish of the same size? According to new research by Ashley Ward, from the University of Sydney in Australia, and Suzanne Currie, from Mount Allison University in Canada, fish can use a variety of different sensory cues to locate shoal-mates, but they are able to use chemical cues to find other fish of the same size as themselves. Using these cues, they can form a group with strength in numbers. The work is published online in Springer’s journal, Behavioral Ecology and Sociobiology.
Forming groups is beneficial for animals. One important benefit is the reduction of individual risk from predators. Indeed when animals are in groups, predators are confronted by a number of almost identical prey animals, making it more challenging to select a target.
Dr. Ward said, “Fish typically form shoals with fish of the same size. The key question that motivated our study is this: How on earth does a fish know how big it is? For humans this is trivial – we can stand on a flat surface and see whether we’re taller or shorter than someone, or we can look in a mirror. These options don’t exist for fish, so how do they choose to associate with fish of the same size?”
The scientists explored which of their senses fish use both to assess the size of other individuals, and to determine how big they are themselves. They studied two freshwater shoaling fish species: three-spined stickleback and banded killfish. In a series of experiments, they exposed the fish to a variety of chemical cues – either from fish of the same species of varying sizes or a control, so-called ‘blank’ cue. Chemical cues are formed as fish constantly emit molecules into their surroundings.
Ward continued, “We know the sense of smell is well developed in fish and that they are sensitive to tiny differences in the chemical signature given off by others. So could they smell how big they are themselves and use this as a template to assess the size of others? It seems they can.”
Both species of shoaling fish preferred the chemical cues of same-sized fish than those of larger or smaller fish from their own species. This suggests that the fish were able to determine their own size relative to other fish of the same species, primarily through chemical self-referencing.
“Using chemical cues to locate similarly sized fish of the same species in the wild promotes the formation of shoals, which creates confusion for predators as well as more coordinated, and potentially efficient, patterns of behavior for both activity and nutrition,” concluded Ward.
Posted February 7th, 2013. Add a comment