A male Pacific leaping blenny on the island of Guam. Photo: Courtney Morgans/UNSW.
One of the world’s strangest animals – a legless, leaping fish that lives on land – uses camouflage to avoid attacks by predators such as birds, lizards and crabs, new research shows.
UNSW researchers, Dr Terry Ord and Courtney Morgans, of the Evolution and Ecology Research Centre, studied the unique fish – Pacific leaping blennies – in their natural habitat on the tropical island of Guam.
Their study will be published in the journal Animal Behaviour.
“This terrestrial fish spends all of its adult life living on the rocks in the splash zone, hopping around defending its territory, feeding and courting mates. They offer a unique opportunity to discover in a living animal how the transition from water to the land has taken place,” says Dr Ord, of the UNSW School of Biological, Earth and Environmental Sciences.
The researchers first measured the colour of five different populations of the fish around the island and compared this with the colour of the rocks they lived on. “They were virtually identical in each case. The fish’s body colour is camouflaged to match the rocks, presumably so they aren’t obvious to predators,” says Dr Ord.
To see if background matching reduced predation, the researchers created realistic-looking models of blennies out of plasticine. “We put lots of these model blennies on the rocks where the fish live, as well as on an adjacent beach where their body colour against the sand made them much more conspicuous to predators,” says Dr Ord.
“After several days we collected the models and recorded how often birds, lizards and crabs had attacked them from the marks in the plasticine. We found the models on the sand were attacked far more frequently than those on the rocks.
“This means the fish are uniquely camouflaged to their rocky environments and this helps them avoid being eaten by land predators.”
The researchers then studied the body colour of closely related species of fish, some of which lived in the water and some of which were amphibious, sharing their time between land and sea.
“These species provide an evolutionary snapshot of each stage of the land invasion by fish,” says Dr Ord.
The similarities in colour between these species and the land-dwelling fish suggest the ancestors of the land-dwelling fish already had a colouration that matched the rocky shoreline before they moved out of the water, which would have made it easier for them to survive in their new habitat.
The Pacific leaping blenny, Alticus arnoldorum, is about four to eight centimetres long and leaps using a tail-twisting behaviour. It remains on land all its adult life but has to stay moist to be able to breathe through its gills and skin.
Originally published here: http://newsroom.unsw.edu.au/news/science/secrets-legless-leaping-land-fish
Posted December 3rd, 2013. Add a comment
The new species, a flasher wrasse, was named Parcheilinus rennyae in honor of ichthyologist Renny Hadiaty of the Indonesian Institute of Sciences (LIPI). (Photo courtesy of Conservation International)
By Jakarta Globe
Indonesian scientists working together with counterparts from the University of California have announced the discovery of a new species of fish in East Nusa Tenggara.
The new species was named Parcheilinus rennyae in honor of ichthyologist Renny Hadiaty of the Indonesian Institute of Sciences (LIPI).
“I’m deeply honored by this recognition, not only because it is such a beautiful fish species, but also because the lead author on the description is my close colleague and internationally renowned ichthyologist Gerald Allen,” said Hadiaty, the curator of fish collections at the Museum Zoologicum Bogoriense (MZB), in a statement released by Conservation International on Wednesday.
The description of the species — a flasher wrasse — was published in the year-end edition of aqua, International Journal of Ichthyology, the statement said.
Conservation International (CI) said that Hadiaty, in her 27-year career, has focused primarily on the taxonomy of freshwater fish in Indonesia, and has coauthored many papers with Allen, who now works for CI as a consultant.
The wrasse — a striking and colorful fish — is adding further conservation value to Komodo National Park and the surrounding reefs of southwest Flores, according to CI.
Tiene Gunawan, marine program director at Conservation International Indonesia, said that the new species therefore must be protected.
Although it is the seventeenth known species of flasher wrasse, CI said that the fish is unique in both its colors and the rounded shape of its dorsal and anal fins and tail.
“We’re delighted that one of our young local scientists, Ni Luh Astria Yusmalinda, was able to publish her first international journal paper based on her genetic analysis of this new species and its closest relatives,” Ngurah Mahardika, the hosting laboratory director of the Indonesian Biodiversity Research Center at Udayana University, said.
He also said that he deemed it particularly fitting that the new species be named after Renny and added that he hoped “this will highlight the spirit of strong scientific collaboration between Indonesian universities, conservation NGOs like Conservation International and the Indonesian Institute of Sciences.”
Flasher wrasses are popular among divers and underwater photographers because of their neon color patterns displayed as part of a daily mating ritual about one hour before sundown. Wrasses are brownish in hue the remainder of the day.
“We’re also hopeful that this new species will add to the tourism value of Komodo National Park and the surrounding reefs of southwest Flores,” Tiene Gunawan, marine program director at Conservation International Indonesia, said.
The scientists participating scientists were from the Indonesian Biodiversity Research Center, a collaborative initiative of Udayana University in Bali, the State University of Papua in Manokwari, Diponegoro University in Semarang, the University of California Los Angeles and Conservation International Indonesia.
Source: The Embassy of Indonesia
Posted November 22nd, 2013. Add a comment
Photograph by Jim Agronick/Shutterstock.
FORT LAUDERDALE-DAVIE, Fla. – The great white shark, a major apex predator made famous by the movie “Jaws,” is one of the world’s most iconic species capturing an extraordinary amount of public fascination. An intriguing question is what makes a white shark so distinctive? One way to address this is to explore the genetic makeup of this remarkable animal.
A new study by scientists from Nova Southeastern University’s (NSU) Save Our Seas Shark Research Centre and Cornell University published in final form today in the journal BMC Genomics now undertakes the first large-scale exploration of the great white shark’s genetic repertoire, and comes up with unexpected findings.
The researchers compared the transcriptome (i.e., the set of RNA sequences expressed by the organism’s genes) from the white shark heart to the transcriptomes from the best studied fish research model (the zebrafish) and humans to look for similarities and significant differences that might explain the distinctiveness of the white shark. So they had a common comparative base, the researchers compared gene products that had known functions in all three species.
Surprisingly, the researchers found that the proportion of white shark gene products associated with metabolism had fewer differences from humans than zebrafish (a bony fish).
Indeed, more broadly speaking, the researchers were also surprised to find that other aspects of the white shark heart transcriptome, including molecular functions as well as the cellular locations of these functions, also showed greater similarity to human than zebrafish. Like many first looks at complex scientific questions, the unexpected results of this study raises more questions than provides answers.
“It’s intriguing why there are these fewer differences in the proportion of gene products between white sharks and humans, than white sharks and zebrafish” said study co-author Mahmood Shivji, director of NSU’s Save Our Seas Shark Research Center and Guy Harvey Research Institute. “One possibility for the apparent greater similarity between white sharks and humans in the proportion of gene products associated with metabolism might be due partly to the fact that the white shark has a higher metabolism because it is not a true cold-bodied fish like bony fishes; however this explanation remains a hypothesis to be further tested.”
One of the notable biological properties of white sharks is that it is one of few fishes that is regionally warm-bodied, i.e., parts of its body (its viscera, locomotor muscles and cranium) are kept at a higher temperature than the surrounding water world – a property known as regional endothermy. This warm-body property is in turn associated with elevated metabolic rates compared to true cold-blooded bony fishes.
“Additional comparative data from other white shark tissues and/or from other endothermic shark species such as makos would be required to see if this general similarity in gene products holds”, said Michael Stanhope of Cornell, who co-led the study with Shivji. “Nevertheless, this preliminary finding opens the possibility that some aspects of white shark metabolism, as well as other aspects of its overall biochemistry, might be more similar to that of a mammal than to that of a bony fish.”
Another curious feature of the genetic repertoire of the white shark heart was that the transcriptome revealed a much lower abundance of a certain type of DNA sequence that occurs in repeated triplet form, than found in other vertebrates. Interestingly, in human genes that contain such repeated triplet sequences, an aberrant increase in their number has been linked to a variety of neurological disorders. It’s not known whether sharks are immune to neurological genetic diseases, but the fact that these DNA patterns occur in such low abundance in white shark genes may indicate a reduced chance of similar such disorders in this primitive vertebrate.
“Our results, along with other distinctive shark genome features reported by the very few studies in this area by others, are suggesting that we may be in for some surprises as we further explore sharks at their most fundamental level – their genes” said Shivji. “We’ve just scratched the surface in terms of investigating what makes these evolutionary marvels, and in many cases threatened species, tick.”
Originally published here: http://www.newswise.com/articles/great-white-shark-study-uncovers-unexpected-and-distinctive-features
The full study can be accessed from BMC Genomics:http://www.biomedcentral.com/1471-2164/14/697
Posted November 21st, 2013. Add a comment
Richard Bottom, left, and Iman Borazjani hope their research on how stingrays swim will lead to the design of new underwater vehicles. (Photo: Douglas Levere)
BUFFALO, N.Y. ─ Stingrays swim through water with such ease that researchers from the University at Buffalo and Harvard University are studying how their movements could be used to design more agile and fuel-efficient unmanned underwater vehicles.
The vehicles could allow researchers to more efficiently study the mostly unexplored ocean depths, and they could also serve during clean up or rescue efforts.
“Most fish wag their tails to swim. A stingray’s swimming is much more unique, like a flag in the wind,” says Richard Bottom, a UB mechanical engineering graduate student participating in the research.
Bottom and Iman Borazjani, UB assistant professor of mechanical and aerospace engineering, set out to investigate the form-function relationship of the stingray — why it looks the way it does and what it gets from moving the way it does.
They will explain their findings at the 66th Annual Meeting of the American Physical Society Division of Fluid Dynamics. Their lecture, “Biofluids: Locomotion III – Flying,” is at 4:45 p.m. on Sunday, Nov. 24, in Pittsburgh, Pa.
The researchers used computational fluid dynamics, which employs algorithms to solve problems that involve fluid flows, to map the flow of water and the vortices around live stingrays.
The study is believed to be the first time the leading-edge vortex, the vortex at the front of an object in motion, has been studied in underwater locomotion, says Borazjani. The leading-edge vortex has been observed in the flight of birds and insects, and is one of the most important thrust enhancement mechanics in insect flight.
The vortices on the waves of the stingrays’ bodies cause favorable pressure fields — low pressure on the front and high pressure on the back — which push the ray forward. Because movement through air and water are similar, understanding vortices are critical.
“By looking at nature, we can learn from it and come up with new designs for cars, planes and submarines,” says Borazjani. “But we’re not just mimicking nature. We want to understand the underlying physics for future use in engineering or central designs.”
Studies have already proven that stingray motion closely resembles the most optimal swimming gait, says Bottom. Much of this is due to the stingray’s unique flat and round shape, which allows them to easily glide through water.
Borazjani and Bottom plan to continue their research and study the differences in movement among several types of rays.
Posted November 18th, 2013. Add a comment
In spring 2012, the muddy seafloor at Station M was literally covered with the silvery bodies of dead salps (gelatinous midwater animals that feed on microscopic algae). This debris provided food for seafloor animals such as sea cucumbers. Image © 2012 MBARI
Animals living on the abyssal plains, miles below the ocean surface, don’t usually get much to eat. Their main source of food is “marine snow” — a slow drift of mucus, fecal pellets, and body parts — that sinks down from the surface waters. However, researchers have long been puzzled by the fact that, over the long term, the steady fall of marine snow cannot account for all the food consumed by animals and microbes living in the sediment. A new paper by MBARI researcher Ken Smith and his colleagues shows that population booms of algae or animals near the sea surface can sometimes result in huge pulses of organic material sinking to the deep seafloor. In a few weeks, such deep-sea “feasts” can deliver as much food to deep-sea animals as would normally arrive over years or even decades of typical marine snow.
For over 20 years, Smith and his fellow researchers have studied animals living on the abyssal plain at Station M — a deep-sea research site about 220 kilometers (140 miles) off the Central California coast. The muddy seafloor at Station M — 4,000 meters (13,100) feet below the surface — is home to a variety of deep-sea animals, from sea cucumbers and sea urchins to grenadier fish. In addition, a myriad of smaller animals and microbes live buried within the mud.
Researchers have long wondered how all these animals and microbes get enough food to survive. The slow trickle of marine snow sinking down from above does not provide nearly enough food to support all the organisms that live down there. However, in a new paper in the Proceedings of the National Academy of Sciences, Smith and his coauthors show that occasional feasts could provide enough food to support deep-sea communities for years at a time.
Smith and his colleagues used several instruments to study the amount of marine snow arriving at Station M, as well as its impacts on life in the deep. They suspended conical “sediment traps” above the seafloor to collect and measure the amount of marine snow falling through the water. They also used automated camera systems to take time-lapse photographs of the seafloor. This allowed them to track the behavior, numbers, and sizes of larger deep-sea animals such as sea cucumbers. Finally, they used a seafloor-crawling robot, the Benthic Rover, to measure the amount of oxygen being consumed by animals and microbes in the sediment. Such oxygen measurements allowed the researchers to estimate how much food these organisms were consuming.
Using data from 1989 to 2012, Smith and his colleagues compared the amount of marine snow arriving at Station M with estimates of populations of microscopic algae observed at the surface using satellites. During most years, the amount of food arriving at the seafloor reached a yearly peak in summer and fall, but remained relatively low.
However, during 2011 and 2012, the researchers observed three dramatic events that delivered huge amounts of relatively fresh food to the deep seafloor. The first took place from June to August 2011, when large numbers of diatoms (a type of microscopic alga) bloomed near the surface, then sank rapidly to the seafloor.
The second event occurred from March to May 2012, when salps — gelatinous midwater animals that eat algae — reproduced rapidly in surface waters. These salps became so abundant that they blocked the seawater intake of the Diablo Canyon nuclear power plant, located on the California coast east of Station M. When the salps in the surface waters at Station M died, they sank so quickly that they carpeted the seafloor, four kilometers below. During the third event, in September 2012, another algal bloom created so much dead algae that it clogged the researchers’ sediment traps, but was captured by a time-lapse camera.
The excess food that arrived on the seafloor during these feasts was not wasted. Instead, it was rapidly consumed by deep-sea animals and seafloor microbes, which used it to grow and reproduce. Some of the organic carbon from the food was released into the surrounding seawater by respiration. Most of the rest was incorporated into the deep-sea sediments, where it could be recycled by animals and microbes that feed on the mud. In this way, large, intermittent pulses of food could help sustain life in the deep for years or even decades.
Smith and his colleagues are still studying the biological effects of these extreme pulses of food. They have already seen changes in the numbers and types of deep-sea animals living at Station M that appear to result from the feasts of 2011 and 2012. They will be reporting these findings in a subsequent paper.
The researchers note that deep-sea feasts may be increasing in frequency off the Central California coast, as well as at some other deep-sea study sites around the world. Over the last decade, the waters off Central California have seen stronger winds, which bring more nutrients, such as nitrate, to the ocean surface. These nutrients act like fertilizer, triggering blooms of algae, which, in turn, sometimes feed blooms of salps. The fallout from all of this increased productivity eventually ends up on the seafloor.
The authors also note that the changes in ocean conditions that provided more food for deep-sea animals at Station M might be related to global warming. Alternatively, these changes could simply reflect naturally occurring long-term cycles in the ocean.
Originally posted by the Monterey Bay Aquarium Research Institute: http://www.mbari.org/news/news_releases/2013/feast&famine/feast&famine-release.html.
Posted November 12th, 2013. Add a comment
Common scalloped hammerhead shark, Sphyrna lewini (from Wikimedia Commons, photo by Barry Peters)
Discovering a new species is, among biologists, akin to hitting a grand slam, and University of South Carolina ichthyologist Joe Quattro led a team that recently cleared the bases. In the journal Zootaxa, they describe a rare shark, the Carolina hammerhead, that had long eluded discovery because it is outwardly indistinguishable from the common scalloped hammerhead. Through its rarity, the new species, Sphyrna gilberti, underscores the fragility of shark diversity in the face of relentless human predation.
Quattro, a biology professor in USC’s College of Arts and Sciences, didn’t set out to discover a new cryptic species, let alone one found exclusively in saltwater. When he started as an assistant professor at USC in 1995, he was largely focused on fish in the freshwater rivers that flow through the state before emptying into the western Atlantic Ocean.
He has wide interests that include conservation, genetic diversity and taxonomy. A driving force in his scientific curiosity is a desire to better understand evolution. As it turns out, South Carolina’s four major river basins — the Pee Dee, the Santee, the Edisto and the Savannah — are a source of particularly rich ore for mining insight into evolutionary history.
Glacial influence had limits
Quattro grew up in Maryland, earned a doctorate at Rutgers University in New Jersey, and completed a post-doc at Stanford University. “New Jersey and Maryland, in particular, had huge glacial influences,” said Quattro. “The areas where rivers now flow were covered with glaciers until 10,000 to 15,000 years ago, and as the glaciers receded the taxa followed them upstream.”
In contrast, rivers south of Virginia were not covered with glaciers. “In other words, these rivers have been around for quite some time,” Quattro said. “The Pee Dee and the Santee are two of the largest river systems on the East coast. And we just got curious — how distinct are these rivers from one another?”
Beginning with the pygmy sunfish, Quattro and colleagues examined the genetic makeup of fish species within the ancient freshwater drainage systems. They found the banded pygmy sunfish in all the South Carolina rivers — in fact, this widespread species is found in nearly all the river systems of the U.S. southeastern and Gulf coasts, starting from the plains of North Carolina, around Florida, and all the way to and up the Mississippi River.
But two species are much rarer. The bluebarred pygmy sunfish is found only in the Savannah and Edisto systems. The Carolina pygmy sunfish is found only in the Santee and Pee Dee systems. Both species coexist with the common banded pygmy sunfish in these river systems, but are found nowhere else in the world.
From an evolutionary standpoint, it’s a noteworthy finding. These rare species are related to the widespread species, yet the details of the inter-relationships — such as which predates the others and is thus an ancestral species — still defy ready description. The fact that a rare and a common species are located together in an ancient river system is important information in the ongoing struggle to clearly define evolutionary history. In the past, scientists drew taxonomic charts almost solely on the basis of physical structure (morphology) and available fossils. The genetic data revolution of recent decades is helping redefine biology in a much more precise manner, but the process is still in the early going.
From the river to the sea
Quattro has been doing his part by slowly moving down the river systems to the ocean, collecting genetic data the whole way down. In the freshwater rivers, he has examined pygmy sunfishes, other sunfishes and basses. Closer to the sea, he has looked at short-nosed sturgeon, which spend most of their time in the estuary (where the river meets the ocean), but do venture up the river to spawn. And further downriver still, he has looked at shark pups.
South Carolina is a well-known pupping ground for several species of sharks, including the hammerhead. The female hammerhead will birth her young at the ocean-side fringes of the estuary; the pups remain there for a year or so, growing, before moving out to the ocean to complete their life cycle.
In the process of looking at hammerheads, Quattro, his student William Driggers III and their colleagues quickly uncovered an anomaly. The scalloped hammerheads (Sphyrna lewini) that they were collecting had two different genetic signatures, in both the mitochondrial and nuclear genomes. Searching the literature, they found that Carter Gilbert, the renowned curator of the Florida Museum of Natural History from 1961 to 1998, had described an anomalous scalloped hammerhead in 1967 that had 10 fewer vertebrae than S. lewini. It had been caught near Charleston and, because the sample was in the National Museum of Natural History, the team was able to examine it morphologically and suggest that it constituted a cryptic species — that is, one that is physically nearly indistinguishable from the more common species.
After publishing the preliminary genetic evidence for the new, cryptic species in the journal Marine Biology in 2006, Quattro and colleagues followed up by making thorough measurements (of 54 cryptic individuals and 24 S. lewini) to fully describe in Zootaxa the new species, S. gilberti, named in Gilbert’s honor. The difference in vertebrae, 10 fewer in the cryptic species, is the defining morphological difference.
Apart from the satisfaction of discovery, Quattro has established locations and genetic signatures for a number of closely related, yet distinct, species in South Carolina’s rivers, estuaries and coastal waters. The results will go a long way in furthering efforts to accurately define taxonomy and evolutionary history for aquatic life.
His team’s work also demonstrates the rarity of the new species. “Outside of South Carolina, we’ve only seen five tissue samples of the cryptic species,” Quattro said. “And that’s out of three or four hundred specimens.”
Shark populations have greatly diminished over the past few decades. “The biomass of scalloped hammerheads off the coast of the eastern U.S. is less than 10 percent of what it was historically,” Quattro said. “Here, we’re showing that the scalloped hammerheads are actually two things. Since the cryptic species is much rarer than the lewini, God only knows what its population levels have dropped to.”
Originally published http://www.sc.edu/uofsc/stories/2013/joe_quattro_describes_new_species_hammerhead_shark.php#.Unz2r_msh8F.
Posted November 8th, 2013. Add a comment
Credit: Image courtesy of Polytechnic Institute of New York University
Brooklyn, New York— Recent studies from two research teams at the Polytechnic Institute of New York University (NYU-Poly) demonstrate how underwater robots can be used to understand and influence the complex swimming behaviors of schooling fish. The teams, led by Maurizio Porfiri, associate professor of mechanical and aerospace engineering at NYU-Poly, published two separate papers in the journalPLOS ONE.
These studies are the latest in a significant body of research by Porfiri and collaborators utilizing robots, specifically robotic fish, to impact collective animal behavior. In collaboration with doctoral candidate Paul Phamduy and NYU-Poly research scholar Giovanni Polverino, Porfiri designed an experiment to examine the interplay of visual cues and flow cues—changes in the water current as a result of tail-beat frequency—in triggering a live golden shiner fish to either approach or ignore a robotic fish.
They designed and built two robotic fish analogous to live golden shiners in aspect ratio, size, shape, and locomotion pattern. However, one was painted with the natural colors of the golden shiner, the other with a palette not seen in the species. The researchers affixed each robot to the inside of a water tunnel, introduced a live golden shiner fish, and observed its interactions with the robot. While the robot’s position remained static, the researchers experimented with several different tail-beat frequencies.
“When the fish encountered a robot that mimicked both the coloration and mean tail-beat frequency for the species, it was likeliest to spend the most time in the nearest proximity to it,” Porfiri said. “The more closely the robot came to approximating a fellow golden shiner, the likelier the fish was to treat it like one, including swimming at the same depth behind the robot, which yields a hydrodynamic advantage,” he explained.
While flow cues created by tail-beat frequency proved to be a critical trigger for shoaling behavior, coloration proved slightly dominant. “Even at tail-beat frequencies that were less than optimal for the live fish, the shiners were always more drawn to the naturally colored robot,” Porfiri added.
Robot speed and body movement were the main focus of another study, also published in PLOS ONE, in which Porfiri teamed with NYU-Poly postdoctoral fellow Sachit Butail and graduate student Tiziana Bartolini. This time, the subject was the zebrafish, and the robot was a free-swimming unit with the coloration, size, aspect ratio, and fin shape of a fertile female member of the species.
The researchers placed the robot in a shared tank with shoals of live zebrafish, aiming to determine if the fish would perceive the robot as a predator, and whether visual cues from the robot could be used to modulate the fishes’ social behavior and activity. The team used a remote control to drive the robot in a circular swimming pattern, while varying its tail-beat frequency. For comparison purposes, they also exposed the fish to the robot in a fixed position, beating its tail.
Experiments showed that while the zebrafish clearly did not perceive the swimming robot as one of their own—they maintained greater distance from the robot than they did to each other—the robot was still an effective stimulus for modulating their social behavior. When the robot was held still in the tank, the live fish showed high group cohesion, along with a strong polarization—meaning the fish were likely to be close to each other and oriented in the same direction. As the robot’s tail-beat frequency increased, it had a profound impact on the group’s collective behavior, causing a spike in the cohesion and a small but detectable decrease in polarization—the fish largely milled together and even matched their speeds to that of the robot as it reached a certain tail-beat frequency.
“This shows us that the fish are responding to more than one stimulus—it’s not just the flow cues, it’s the combination of visual and flow cues that influence the collective response,” Porfiri said.
Porfiri is a leading researcher in the field of ethorobotics—the study of robot-animal interaction. Studies like these advance multiple areas of science, including the development of an experimental animal model based on lower-order species such as fish, with robots providing a consistent, infinitely reproducible stimulus. The use of robots to influence collective animal behavior is also viewed as a potential means to protect marine wildlife, including birds and fish, in the wake of environmental hazard.
This research was supported by the National Science Foundation and the Mitsui USA Foundation.
Source: Polytechnic Institute of New York
Posted November 4th, 2013. Add a comment
A bat (Myotis nattereri) catches a worm, hung up by the scientists for it to find. (Credit: Lasse Jakobsen/SDU)
Oct. 29, 2013
Sperm whales weigh up to 50 tons, and the smallest bat barely reaches a gram. Nevertheless, the two species share the same success story: They both have developed the ability to use echolocation — a biological sonar — for hunting. Now Danish researchers show that the biosonar of toothed whales and bats share surprisingly many similarities — even though they live in very different environments and vary extremely in size.
Echolocation systems are one of Nature’s extremely successful specializations. About 1,100 species of bats and roughly 80 species of toothed whales use the technique — this is 25% of all living species of mammals. But why have such different animals as whales and bats both developed the same technique? The reason cannot be found in kinship, as bats and whales are no closer related to each other than all other mammals descended from the same land vertebrates for 200 million years ago.
The answer lies in convergent evolution — when almost identical features or developments happen in different species. Through evolution both bats and toothed whales have developed the same functional characteristics.
Researchers from the two Danish universities, Aarhus University and University of Southern Denmark, have now studied the acoustic properties of the technique behind echolocation in bats and whales in the wild. Previous studies of their abilities to locate and catch prey have primarily been based on laboratory tests, and the studies in the wild now provide a much more realistic picture of how the animals use echolocation.
The studies have been published in the scientific magazinePhysiology entitled “Functional Convergence in Bat and Toothed Whale Biosonars.” The authors of the study are Professor Peter Teglberg Madsen from Aarhus University and Professor Annemarie Surlykke from University of Southern Denmark.
“Our studies have shown that the sounds of bats and toothed whales are surprisingly similar. This is due to two things: First, all mammalian ears are developed in quite similar ways, and second, — which is the most surprising — the contradicting physical conditions in air and water along with the differences in size of the animals even out the differences, that you would expect in the sound frequency,” says Professor Annemarie Surlykke from University of Southern Denmark.
As a bat is much smaller than a whale and its prey is accordingly smaller, it needs to produce sounds with a very high frequency in order to achieve the same capacity to determine direction and size of its prey. However, the effect of the higher frequency will be partially cancelled out by the fact that the sound is transported five times as slowly and that the sound waves therefore are five times as short in air as in water.
The researchers conclude that bats and toothed whales produce signals for echolocation in the same frequency range, from 10 to 200 kHz.
The advantage of operating in water rather than air is that the whale’s “acoustic field of vision” is up to six times larger than the bat’s. The “acoustic field of vision” is the area where the animal can “see” their surroundings using echolocation. A sperm whale can echolocate prey up to 500 meters away, while a bat’s echolocation distance is only 2-10 meters.
Bats fly fast and cover approx. one echolocation distance per second. Therefore they often spend less than a second on detecting and catching their prey. Whales move more slowly and have a much greater echolocation distance. Thus they have more time to pick up information from the echoes and they have time to select their prey more carefully. This may explain why bats do not seem to be particularly picky with their prey, while toothed whales are much more selective about their food. The bat simply does not have the time to choose — it goes for fast food!
In the last part of the hunting phase, when they approach their prey both toothed whales and bats emit a series of buzzing sounds: Weak and short sound pulses at very short intervals — similar to strobe lights. It is a very complex mechanism that scientists do not yet fully understand. The animals control very carefully when they emit sounds and when they listen for echoes — and they adjust this exactly to their own and the prey’s speed. If they emit the buzzing sounds too fast they do not have time to listen for the echoes. If they do it too slowly they risk hitting obstacles on the fly.
“The mechanism must play a key role but we do not yet know exactly which one,” says Professor Peter Teglberg from Aarhus University and continues: “There is a need for further studies and fortunately new technologies make it possible to track animals in the wild, study their behavior and compare these results with the knowledge we have from the laboratory.”
Originally published http://www.sciencedaily.com/releases/2013/10/131029101617.htm.
Posted November 1st, 2013. Add a comment
Photo Credit: Nantawat Chotsuwan/Shutterstock
Oct. 30, 2013 — When it comes to choosing a mate, female guppies don’t care about who is fairest. All that matters is who is rarest.
Florida State University Professor Kimberly A. Hughes in the Department of Biological Science has a new study just published in the journal Nature that is the first to demonstrate a female preference for rare males using an experiment in a wild population, rather than a laboratory setting.
This study of genetic differences in male guppies is relevant to understanding variation in humans as well as in other organisms, Hughes said.
Hughes and her longtime collaborators studied guppies in Trinidad and found that male guppies with rare color patterns mated more — and lived longer — than the common males. The males’ color variations are genetic and not due to diet or temperature. And the males’ actual appearance didn’t matter to the females, who are tan in color and do the choosing of mates.
“No matter which color pattern we made rare in any group, they mated more and had more offspring,” Hughes said.
So, a male guppy common in one grouping, i.e., placed in a stream with many fish that look like him, is a dud to the females also in the stream. But, take that common male and place him in a different stream with only one or two others similar to him, and he’s suddenly rare — and a desirable mate.
In an earlier study, Hughes showed that male guppies with rare color patterns had a survival advantage compared to those with common patterns in natural populations. During a three-week study, also in Trinidad, 70 percent of common males survived, while 85 percent of rare males survived.
This new study, “Mating advantage for rare males in wild guppy populations,” reports the results of paternity analyses of the offspring produced by the females in that earlier field experiment.
Hughes approached this new, rare-male-as-mating-champ theory with the goal of ruling it out. She thought it was unlikely.
But, “We got a big, significant result,” she said.
Guppies (Poecilia reticulata) are an ideal species for this study, Hughes said, because the males’ color variations are so visible and because there is so much variation. Other fish show color variation but not as widely as the guppy.
“These guys are sort of the champions of variation,” she said.
And it’s not that the rare males are simply trying harder to land a female. All male guppies do elaborate mating rituals, fanning out their fins and pursuing a mate.
The next question to answer, Hughes said, is why. Why do female guppies go for the rarest male in a particular population? It’s possible that in choosing a mate who appears unknown to her, a female guppy is trying to avoid procreating with a relative, which can lead to genetic disorders in offspring.
The guppy question speaks to a longstanding puzzle within evolutionary biology: Why are individuals within species so genetically diverse?
Understanding why species are genetically diverse is key to understanding human variation in disease susceptibility, for maintaining healthy crop and livestock populations and for preserving endangered species, Hughes said.
Hughes’ collaborators in this study are Anne E. Houde of the Lake Forest College Department of Biology in Lake Forest, Ill., and Anna C. Price and F. Helen Rodd of the Department of Ecology and Evolutionary Biology at the University of Toronto in Toronto, Ontario, Canada. Their work was supported by grants from the National Science Foundation and the Natural Sciences and Engineering Research Council of Canada.
Originally published here.
Posted November 1st, 2013. 1 comment
A new as-of-yet unnamed species of humpback dolphin is shown off the coast of northern Australia. (Credit: Guido Parra)
Oct. 29, 2013 — A species of humpback dolphin previously unknown to science is swimming in the waters off northern Australia, according to a team of researchers working for the Wildlife Conservation Society, the American Museum of Natural History, and numerous other groups that contributed to the study.
To determine the number of distinct species in the family of humpback dolphins (animals named for a peculiar hump just below the dorsal fin), the research team examined the evolutionary history of this family of marine mammals using both physical features and genetic data. While the Atlantic humpback dolphin is a recognized species, this work provides the best evidence to date to split the Indo-Pacific humpback dolphin into three species, one of which is completely new to science.
“Based on the findings of our combined morphological and genetic analyses, we can suggest that the humpback dolphin genus includes at least four member species,” said Dr. Martin Mendez, Assistant Director of WCS’s Latin America and the Caribbean Program and lead author of the study. “This discovery helps our understanding of the evolutionary history of this group and informs conservation policies to help safeguard each of the species.”
The authors propose recognition of at least four species in the humpback dolphin family: the Atlantic humpback dolphin (Sousa teuszii), which occurs in the eastern Atlantic off West Africa; the Indo-Pacific humpback dolphin (Sousa plumbea), which ranges from the central to the western Indian Ocean; another species of Indo-Pacific humpback dolphin (Sousa chinensis), which inhabits the eastern Indian and western Pacific Oceans; and a fourthSousa species found off northern Australia yet to be named (the formal adjustment of the naming and number of species occurs through a separate and complementary process based on these findings).
“New information about distinct species across the entire range of humpback dolphins will increase the number of recognized species, and provides the needed scientific evidence for management decisions aimed at protecting their unique genetic diversity and associated important habitats,” said Dr. Howard Rosenbaum, Director of WCS’s Ocean Giants Program and senior author on the paper.
Working to bring taxonomic clarity to a widespread yet poorly known group of dolphins, the authors assembled a large collection of physical data gathered mostly from beached dolphins and museum specimens. Specifically, the team examined features from 180 skulls covering most of the distribution area of the group in order to compare morphological characters across this region.
The researchers also collected 235 tissue samples from animals in the same areas, stretching from the eastern Atlantic to the western Pacific Oceans, analyzing both mitochondrial and nuclear DNA for significant variations between populations.
The humpback dolphin grows up to 8 feet in length and ranges from dark gray to pink and/or white in color. The species generally inhabits coastal waters, deltas, estuaries, and occurs throughout the Indian and Pacific oceans to the coasts of Australia. The Atlantic humpback dolphin is considered “Vulnerable” according to the IUCN Red List, whereas the Indo-Pacific dolphin species Sousa chinensis is listed as “Near Threatened.” Humpback dolphins are threatened by habitat loss and fishing activity.
Originally published http://www.sciencedaily.com/releases/2013/10/131029143000.htm.
Posted October 29th, 2013. Add a comment