The starfish compound eye (red cups) is seen at the tip of the arm. Each red cup corresponds to a single optical unit, ommatidium, in an arthropod compound eye. Photograph courtesy of Dan-Erik Nilsson, Lund University.
A study has shown for the first time that starfish use primitive eyes at the tip of their arms to visually navigate their environment. Research headed by Dr. Anders Garm at the Marine Biological Section of the University of Copenhagen in Denmark, showed that starfish eyes are image-forming and could be an essential stage in eye evolution.
The researchers removed starfish with and without eyes from their food rich habitat, the coral reef, and placed them on the sand bottom one meter away, where they would starve. They monitored the starfishes’ behavior from the surface and found that while starfish with intact eyes head towards the direction of the reef, starfish without eyes walk randomly.
Dr Garm said: “The results show that the starfish nervous system must be able to process visual information, which points to a clear underestimation of the capacity found in the circular and somewhat dispersed central nervous system of echinoderms.”
Analyzing the morphology of the photoreceptors in the starfish eyes the researchers further confirmed that they constitute an intermediate state between the two large known groups of rhabdomeric and ciliary photoreceptors, in that they have both microvilli and a modified cilium.
Most known starfish species possess a compound eye at the tip of each arm, which, except for the lack of true optics, resembles arthropod compound eye. Despite being known for about two centuries, no visually guided behavior has ever been documented before.
How do fish swim? It is a simple question, but there is no simple answer.
Researchers at Northwestern University have revealed some of the mechanical properties that allow fish to perform their complex movements. Their findings, published on June 13 in the journal PLOS Computational Biology, could provide insights in evolutionary biology and lead to an understanding of the neural control of movement and development of bio-inspired underwater vehicles.
“If we could play God and create an undulatory swimmer, how stiff should its body be? At what wave frequency should its body undulate so it moves at its top speed? How does its brain control those movements?” said Neelesh Patankar, professor of mechanical engineering at Northwestern’s McCormick School of Engineering and Applied Science. “Millennia ago, undulatory swimmers like eels that had the right mechanical properties are the ones that would have survived.”
The researchers used computational methods to test assumptions about the preferred evolutionary characteristics. For example, species with low muscle activation frequency and high body stiffness are the most successful; the researchers found the optimal values for each property.
“The stiffness that we predict for good swimming characteristics is, in fact, the same as the experimentally determined stiffness of undulatory swimmers with a backbone,” said Amneet Bhalla, graduate student in mechanical engineering at McCormick and one of the paper’s authors.
“Thus, our results suggest that precursors of a backbone would have given rise to animals with the appropriate body stiffness,” added Patankar. “We hypothesize that this would have been mechanically beneficial to the evolutionary emergence of swimming vertebrates.”
In addition, species must be resilient to small changes in physical characteristics from one generation to the next. The researchers confirmed that the ability to swim, while dependent upon mechanical parameters, is not sensitive to minor generational changes; as long as the body stiffness is above a certain value, the ability to swim quickly is insensitive to the value of the stiffness, the researchers found.
Finally, making a connection to the neural control of movement, the researchers analyzed the curvature of its undulations to determine if it was the result of a single bending torque, or if precise bending torques were necessary at every point along its body. They learned that a simple movement pattern gives rise to the complicated-looking deformation.
“This suggests that the animal does not need precise control of its movements,” Patankar said.
To make these determinations, the researchers applied a common physics concept known as “spring mass damper” — a model, applied to everything from car suspension to Slinkies, that determines movement in systems that are losing energy — to the body of the fish.
This novel approach for the first time unified the concepts of active and passive swimming — swimming in which forcing comes from within the fish (active) or from the surrounding water (passive) — by calculating the conditions necessary for the fish to swim both actively and passively.
The paper, “A Forced Damped Oscillation Framework for Undulatory Swimming Provides New Insights into How Propulsion Arises in Active and Passive Swimming,” was authored by Patankar, Bhalla, and Boyce E. Griffith, assistant professor of medicine and mathematics at New York University.
The work was supported by the National Science Foundation (NSF).
Photograph by D. Ross Robertson and Carole C. Baldwin, CC-BY 3.0.
A new species of tiny blenniiform fish has been discovered in the biodiversity rich waters of the southern Caribbean. Haptoclinus dropi is only around 2 cm in length with a beautiful color pattern that includes iridescence on the fins. The proposed common name of the species is four-fin blenny, due to the division of the dorsal fin into four sections, which is a distinguishing feature of the genus and unique among blenniiform fishes. The study was published in the open access journal Zookeys.
This beautiful new species was discovered as a lucky bycatch during targeted specimen catching at 157-167 m depth off Curaçao as a part of the Smithsonian Institution’s Deep Reef Observation Project (DROP). The new species, Haptoclinus dropi, gets its name from the project’s abbreviation and is one of numerous new ray-finned fish species emerging from this project.
For DROP expeditions the Substation Curaçao‘s manned submersible Curasub was used to catch specimens. While generally used as tourist attraction because it travels at much greater depths than divers can reach, the Curasub is also used for scientific marine research. Targeted fish specimens are collected with the sub’s two flexible, hydraulic arms, but very often small non-targeted fish are also caught in the process.
“Below the depths accessible using scuba gear and above the depths typically targeted by deep-diving submersibles, tropical deep reefs are productive ocean ecosystems that science has largely missed. They are home to diverse assemblages of new and rare species that we are only just beginning to understand,” explains the lead author of the study Dr Carole Baldwin, Smithsonian Institution.
Source: Pensoft Publishers
Original Source: Baldwin CC, Robertson RD (2013) A new Haptoclinus blenny (Teleostei, Labrisomidae) from deep reefs off Curaзao, southern Caribbean, with comments on relationships of the genus.ZooKeys 306: 71–81, doi: 10.3897/zookeys.306.5198
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 Jeff Goddard; CC-BY 3.0.
The flora and fauna of the American west coast is generally believed to be well explored and studied. However, a new study and a taxonomic assessment of the octocorals from the north eastern Pacific Ocean proves such assumptions wrong, with two new beautiful and colorful species of soft corals alongside a new genus. The study was published in the open access journal Zookeys.
“It is remarkable that in a region previously thought to be as familiar and well known as the west coast of North America – with its numerous large urban centers and major marine laboratories – revisionary systematics are not only still possible, but essential for our understanding of global biodiversity,” comments the author of the study Dr Williams, California Academy of Sciences.
The paper describes four aspects of the North American west coast fauna, such as a new species of pale orange stoloniferous soft coral from San Diego, California. Also included is a revisionary assessment of a well-known soft coral previously misidentified as Gersemia rubiformis from the Pacific Northwest. Another new species of the soft coral Gersemia from the coast of British Columbia, Canada has been also described. This new species is found in colonies with beautiful pink to reddish coloration in life.
The study also defines a new genus named for a species previously placed in a tropical Indo-Pacific genus for the past century. The species for which the genus was erected inhabits the Gulf of the Farallones National Marine Sanctuary near San Francisco, California, as well as several other localities on the Pacific Coast. The remarkable diversity of octocorals accounts for around 3400 species described worldwide. Although the majority of octocoral taxa was described in the 19th and early 20th centuries, much of this colorful marine fauna is in fact only minimally studied and continues to surprise with new discoveries nowadays.
Williams GC (2013) New taxa and revisionary systematics of alcyonacean octocorals from the Pacific coast of North America (Cnidaria, Anthozoa). ZooKeys 283: 15. doi: 10.3897/zookeys.283.4803
A parasite attached to a bream. Photo by Dominique Roche.
Fish with parasites attached to their heads have a stronger preference for left or right when facing a T-intersection, giving them an edge when it comes to escaping predators, research from The Australian National University (ANU) has revealed.
A preference for one side is called lateralisation. Many human behaviours, such as being left-or right-handed when writing, are lateralised due to the body’s asymmetries and different wiring in the brain’s hemispheres.
“In addition to humans, many animals show lateralisation, including the bridled monocle bream we used in this study,” said lead author of the paper, Mr Dominique Roche, a PhD candidate in the ANU Research School of Biology.
“There has been some evidence that lateralisation is plastic, meaning it can change depending on the circumstances. For example, history has shown that some people born left-handed can become very adept at writing with their right hand if forced to do so in school. In fact, they often become more comfortable using their right hand in the long run.”
The bridled monocle bream is often parasitised by a large crustacean which attaches itself to one side of the fish’s head, just above the eye.
“We were interested in testing whether the ecological interaction of having this parasite attached to the fish’s head had any influence on lateralisation and whether it was changeable,” said Ms Sandra Binning, who collaborated with Mr Roche on the study.
The team caught bream with and without parasites from Lizard Island on the Great Barrier Reef and swam the fish in a maze that resembles a T-intersection, which forced the fish to choose to turn left or right.
“The population as a whole didn’t show a preference to turn one way or the other,” said Mr Roche. “However, at an individual level, some fish showed a turning preference, with parasitised fish showing a much stronger preference than their unparasitised counterparts. If they have a parasite, they definitely choose a side.”
When the parasite was removed, turning preference became much less pronounced, returning to the level of the unparasitised population.
“This is one of the first instances where lateralisation has been shown to be plastic and change so rapidly,” said Mr Roche.
“Having a preferred side gives the fish an advantage. Lateralised fish are quicker at responding to threats. We’ve shown previously that parasitised fish swim slower than unparasitised fish. Given that our parasitised fish don’t swim very fast, it makes sense that they need to react faster to predators to give themselves a head start and have a better chance of escaping.”
Interestingly, not all fish react the same to their parasite – some showed a preference to turn towards and some preferred to turn away.
“This is a good thing – the parasites are quite big and a predator could spot them easily,” said Ms Binning. “If all parasitised fish always turned towards their parasite, eventually predators would be able to anticipate their reaction, and parasitised fish would lose the advantage of reacting quickly.”
“This is a really exciting and interesting result,” said Mr Roche. “Fish are vertebrates like us, and determining whether important behaviours like turning can change ultimately helps us better understand humans and whether our own preference for using the right or left side of our body is plastic depending on circumstances and the environment around us.”
The research is published in the journal Behavioural Ecology and Sociobiology.
Source: Australia National University
Photograph courtesy of the University of Essex.
Unique university lecture held 18 metres underwater
Students at the University of Essex have taken their lectures to a whole new level – 18 metres under the sea in remote Indonesia to be precise.
The ground-breaking underwater marine biology lectures were the first of their kind, revolutionising the teaching, educational and learning experience during dives on tropical coral reef systems.
The lectures were held during the annual field trip to the Wakatobi Marine National Park in Indonesia, organised by the University’s School of Biological Sciences for its students.
The serious challenges threatening the future of the world’s coral reefs are the backbone of major research being carried out by the University’s internationally-recognised Coral Reef Research Unit (CRRU). Its on-going research, focused in this area of Indonesia, looks at the impact of climate change on coral reefs and how to work with nature to find a solution. More than half a billion people depend on coral reefs for food and income.
For the underwater lectures, Professor David Smith used specialised audio equipment so he could talk to students underwater, explaining exactly what they were seeing as they were seeing it. This was a world away from usual underwater communication involving basic slates to write on and hand signals.
“It was a fantastic experience as I was able to use the power of observation like never before,” explained Professor Smith. “I have been on thousands of dives over the years but this was a totally new experience as I was able to explain to students exactly what they were seeing and inject more passion and feeling into the whole lecture. It was very special and transformed the whole experience both for me and our students.”
Using a University of Essex special teaching grant, Professor Smith was able to buy an audio system which, to date, has never been used for formal lecturing and is only used by TV presenters and some professional divers. Professor Smith wore a full face mask which included a microphone and the students wore headsets so they could hear him talk. A hydrophone – an underwater microphone − was then positioned in the water which was linked to a control box and recorder on a boat.
With over 1,000 videos taken during the underwater lectures, adding up to 15 hours of footage, these will prove to be a valuable virtual field course resource for students who are not able to travel to Indonesia but can still get an insight into the experience whilst also providing a great “listen again” opportunity for participating students.
Second-year marine and freshwater biology student Tilly James said: “The underwater lectures were an invaluable part of the course as they enabled us to get a much better understanding of how all the components of the reef system were interacting with each other.
“It was an experience you simply cannot get with traditional lectures. Professor Smith was able to ask us questions throughout the dives, encouraging us as students to apply our theoretical knowledge in a much more practical setting.”
Source: The University of Essex, via AlphaGalileo.
Photograph by Aaron Norman.
New research has revealed that the evolution of the complex, weight-bearing hips of walking animals from the basic hips of fish was a much simpler process than previously thought.
Tetrapods, or four-legged animals, first stepped onto land about 395 million years ago. This significant change was made possible by strong hipbones and a connection through the spine via an ilium – features that were not present in the fish ancestors of tetrapods.
In a study published in the journal Evolution and Development, Dr Catherine Boisvert of the Australian Regenerative Medicine Institute at Monash University, MacQuarie University’s Professor Jean Joss and Professor Per Ahlberg of Uppsala University examined the hip structures of some of human’s closest fish cousins.
They found the differences between us and them are not as great as they appear – most of the key elements necessary for the transformation to human hips were actually already present in our fish ancestors.
Dr Boisvert and her collaborators compared the hip development – bones and musculature – of the Australian lung fish and the Axolotl, commonly known as the Mexican Walking Fish. The results showed that, surprisingly, the transition from simple fish hip to complex weight-bearing hip could be done in a few evolutionary steps.
“Many of the muscles thought to be ‘new’ in tetrapods evolved from muscles already present in lungfish. We also found evidence of a new, more simple path by which skeletal structures would have evolved,” Dr Boisvert said.
The researchers found that the sitting bones would have evolved by the extension of the already existing pubis. The connection to the vertebral column could have evolved from an illiac process already present in fish.
“The transition from ocean-dwelling to land-dwelling animals was a major event in the evolution of terrestrial animals, including humans, and an altered hip was an essential enabling step,” Dr Boisvert said.
“Our research shows that what initially appeared to be a large change in morphology could be done with relatively few developmental steps.”
Source: Monash University
Aquarists at ZSL London Zoo are launching an urgent worldwide appeal to find a female mate for the last remaining males of a critically endangered fish species.
The Mangarahara cichlid (Ptychochromis insolitus) is believed to be extinct in the wild, due to the introduction of dams drying up its habitat of the Mangarahara River in Madagascar, and two of the last known individuals are residing in ZSL London Zoo’s Aquarium.
And as if the situation wasn’t dire enough for this tropical fish species, the individuals at ZSL London Zoo are unfortunately both male.
The Curator of the Aquarium at ZSL London Zoo, Brian Zimmerman, along with colleagues at Zurich Zoo in Switzerland set about trying to find other Mangaraharan cichlids in zoos around the world – using international zoo and aquarium associations to reach as many experts and aquarists as possible, but had no luck finding surviving females.
The team at ZSL London Zoo are now launching a desperate appeal for private aquarium owners, fish collectors, and hobbyists to come forward if they have or know of any females in existence, so that a vital conservation breeding programme can be started for the species.
Launching the appeal, ZSL London Zoo’s Brian Zimmerman said: “The Mangarahara cichlid is shockingly and devastatingly facing extinction; its wild habitat no longer exists and as far as we can tell, only three males remain of this entire species.
“It might be too late for their wild counterparts, but if we can find a female, it’s not too late for the species. Here at ZSL London Zoo we have two healthy males, as well as the facilities and expertise to make a real difference.
“We are urgently appealing to anyone who owns or knows someone who may own these critically endangered fish, which are silver in colour with an orange-tipped tail, so that we can start a breeding programme here at the Zoo to bring them back from the brink of extinction.”
ZSL London Zoo is asking anyone with information about the cichlids to email the team at firstname.lastname@example.org
Source: London Zoo
Posted May 13th, 2013. 1 comment
Photograph courtesy of the University of Exeter.
Fish win fights on strength of personality
When predicting the outcome of a fight, the big guy doesn’t always win, suggests new research on fish.
Scientists at the University of Exeter and Texas A&M University found that when fish fight over food, it is personality, rather than size, that determines whether they will be victorious.
The findings suggest that when resources are in short supply personality traits such as aggression could be more important than strength when it comes to survival. The study, published in the journal Behavioral Ecology and Sociobiology, found that small fish were able to do well in contests for food against larger fish provided they were aggressive. Regardless of their initial size, it was the fish that tended to have consistently aggressive behaviour – or personalities – that repeatedly won food and as a result put on weight.
Dr Alastair Wilson from Biosciences at the University of Exeter said: “We wondered if we were witnessing a form of Napoleon, or small man, syndrome. Certainly our study indicates that small fish with an aggressive personality are capable of defeating their larger, more passive, counterparts when it comes to fights over food. The research suggests that personality can have far reaching implications for life and survival.”
The sheepshead swordtail fish (Xiphophorus birchmanni) fish were placed in pairs in a fish tank, food was added and their behaviour was captured on film. The feeding contest trials were carried out with both male and female fish. The researchers found that while males regularly attacked their opponent to win the food, females were much less aggressive and rarely attacked.
In animals, personality is considered to be behaviour that is repeatedly observed under certain conditions. Major aspects of personality such as shyness or aggressiveness have previously been characterised and are thought to have important ecological significance. There is also evidence to suggest that certain aspects of personality can be inherited. Further work on whether winning food through aggression could ultimately improve reproductive success will shed light on the heritability of personality traits.
This work was funded by a Biotechnology and Biological Sciences Research Council (BBSRC) David Phillips Fellowship. No fish were distressed or received physical injury during these experiments.
Source: The University of Exeter