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Geological game changer: When continents connected

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One of the cichlid fish from Guatemala, Thorichthys meeki, collected by LSU Curator of Ichthyology Prosanta Chakrabarty for the study that refuted the date in which the Isthmus of Panama was formed.
Credit: Courtesy of Prosanta Chakrabarty, LSU

 

New study shakes up understanding of when continents connected

A long-standing fact widely accepted among the scientific community has been recently refuted, which now has major implications on our understanding of how Earth has evolved.

Until recently, most geologists had determined the land connecting North and South America, the Isthmus of Panama, had formed 3.5 million years ago.

But new data shows that this geological event, which dramatically changed the world, occurred much earlier. In a comprehensive biological study, researchers have confirmed this new information by showing that plants and animals had been migrating between the continents nearly 30 million years earlier.

“This means the best-dated geological event we ever had is wrong,” said Prosanta Chakrabarty, LSU Associate Professor in the Department of Biological Sciences and Curator of Ichthyology at the LSU Museum of Natural Science. His research on the evolution of freshwater and marine organisms in Central America was part of the study with colleagues at the Smithsonian Tropical Research Institute, American Museum of Natural History and University of Gothenburg, which included living and extinct mammals, birds, plants, fish and invertebrate animals published by the Proceedings of the National Academy of Sciences.

The researchers found large pulses of movement among these plants and animals between North and South America from 41 million, 23 million and eight million years ago. These coordinated spikes in migration imply that geological changes in Central America, such as landmass formation and new freshwater corridors, were aiding migration for many kinds of plants and animals.

“Before, South America was thought of as an island with no communication until 3.5 million years, so the only way to explain such high biodiversity was to say that it accumulated extremely fast. Now, with a longer history, we know that processes and patterns took a lot of time to form,” said Christine Bacon, lead author of the study and associate researcher at the University of Gothenburg. “Our results change our understanding of the biodiversity and climate, both at the regional and global levels.”

Even after the reported geological closure, geminate marine species, those close relatives found on opposite sides of the narrow isthmus, also provide evidence that this landmass between North and South America is more like a sponge where organisms can periodically pass rather than a solid barrier. The current expansion of the Panama Canal has yielded new fossils that have informed these observations.

“Now we know that the closure of the Isthmus of Panama, which is supposed to be one of the biggest deals in geology, is just one part of a really complicated puzzle of how the continents came together,” Chakrabarty said.

He and colleagues at LSU mapped the evolution of two major families of fishes in Central America — cichlids, which include many aquarium fish, and poeciliids, which include guppies and swordtails. They collected samples of fishes from every country in Central America and sequenced the DNA to determine the genetic relationship between species. Matching the skeletal structure of fish found in the fossil record, they calibrated the DNA-based evolutionary tree and determined the age of each species.

Because freshwater fish can only migrate when a new passage way opens to a river or lake, there must have been dry land with freshwater running through it, Chakrabarty said. Therefore, their arrival in Central America signifies early geological changes.

“The cool thing is there are so many freshwater fish species that are essentially stuck in one place until the land changes, so they can tell us about the history of the Earth,” he said.

The formation of the Isthmus of Panama had large-scale effects on the planet. It divided the Atlantic and Pacific oceans, thus changing sea levels and ocean currents. This affected global temperatures possibly causing periods of glaciation.

“The geology of this whole region is so complicated, and it’s amazing to me that the biology can inform us of that,” he said. Chakrabarty has been conducting research on Central American freshwater fish for about 15 years. He has received more than $1 million in National Science Foundation funding for this work. He and his lab have collected fish species from every country in Central America and have expanded the specimen collection at LSU to South America, the Greater Antilles and much of Asia. He is currently researching the evolution and migration of freshwater fish between South America, Central America and the Greater Antilles that may have began 50 to 60 million years ago.

Materials provided by Louisiana State University

Originally published here: www.sciencedaily.com/releases/2015/06/150609213351.htm

Posted June 12th, 2015.

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Longest ever tiger shark tracking reveals remarkable, bird-like migrations

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This is the tiger shark from a side view.
Credit: Courtesy of Nick Filmalter/Danah Divers

Tiger sharks are among the largest and most recognizable sharks on the planet, yet many of their habits remain mysterious because they are long-distance travelers that are hard to track. But a new study, reported in the June 9 issue of the journal Scientific Reports, has yielded the first ever continuous, two or more-year satellite tagging tracks for the animals. This study reveals remarkable, and previously unknown, migration patterns more similar to birds, turtles and some marine mammals than other fishes.

Long believed to be mainly a coastal species, the tiger sharks, in fact, made more than 7,500 kilometer, round-trip journeys every year between two vastly different ecosystems — the coral reefs of the Caribbean and the open waters of the mid-North Atlantic. Furthermore, they returned reliably to the same overwintering areas each year, a discovery with significant conservation implications.

The study was led by James Lea and Brad Wetherbee, Ph.D., co-first authors, and senior author, Mahmood Shivji, Ph.D., all of whom work out of Nova Southeastern University’s (NSU) Guy Harvey Research Institute in Florida. Renowned marine artist and conservationist Guy Harvey, a Ph.D. fisheries ecologist, is also an author on the paper and co-led the project’s tagging work, which took place near Bermuda, in collaboration with the Bermuda Shark Project.

‘As apex predators, the presence of tiger sharks — and other large sharks — is vital to maintain the proper health and balance of our oceans,’ said Dr. Shivji, who is professor at NSU and also the director of NSU’s GHRI. ‘That’s why it’s so important to conserve them, and understanding their migratory behavior is essential to achieving this goal.’

Background

The details of the movements and migrations of tiger sharks and most other large shark species have been a mystery because they are difficult to track for more than a few months because of tag or other logistic limitations. For this project, the tags the team attached to sharks near Bermuda lasted in many cases more than two years, and in some cases more than three years, sending satellite position data each time an animal surfaced.

One tiger shark, named Harry Lindo, traveled more than 44,000 kilometers (27,000 miles), the longest track distance documented for a tiger shark and possibly the longest ever published for a shark.

‘It is truly remarkable,’ said Harvey of the animal’s travels.

Tiger Shark Highway

The researchers were able to show that adult male tiger sharks in the Atlantic repeatedly spend their winters in Caribbean island locales including the Bahamas, Turks and Caicos Islands, and Anguilla. Then, during summers, they travel far into the North Atlantic, often more than 3,500 kilometers and as far north as Connecticut, though well offshore in nearly the middle of the ocean.

‘These repeated journeys were very unexpected,’ said Lea, who also works out of the Marine Biological Association of the United Kingdom, ‘The tiger shark has traditionally been considered a coastal species, and it is rare among sharks to so easily and habitually switch between the two vastly different environments.’

Remarkably, the sharks followed the same pattern each year and returned to almost the same small area in the Caribbean each time.

‘Even though they’ve got a whole range of islands to choose from, it seems like each animal has its favorite winter spot,’ said Shivji.

For the tiger sharks, the migrations are something like a ‘highway road trip,’ on their way to definite destinations. Bermuda is a handy spot for tiger shark tagging because it is the equivalent of a popular highway exit — lots of animals stop off there for a break while heading north or south. But for the most part the animals travelled directly between their migration destinations, meandering around only after arriving.

Why They Go

What makes the tiger sharks so committed to particular areas is still an open question. At the south end, the story may be fairly simple. Female tiger sharks are common in the Caribbean in the winter, so the Caribbean may just be the best place for male tiger sharks to find dates, although this is just an educated guess.

Why they go so far north is more complicated. How far they go seems to be guided by avoidance of colder temperatures — information that offers one example of how migration research can help to predict the implications of climate change for sharks.

‘There’s got to be something really good up there to make the sharks undertake such massive, repeated swims, but exactly what is a puzzle,’ said Shivji.

One possibility is that they go to feed on young loggerhead turtles that also migrate north — indeed when the researchers examined stomachs of some tiger sharks killed by long liners in the region, they found turtle remains. But then there are also turtles much farther south.

Great White Similarities

The only other instance where researchers have found a broadly similar, repeated migration pattern between coastal and distant open water regions is with the warm-bodied, great white and salmon sharks in the Pacific Ocean. White sharks migrate in the winter from the California and Baja coasts to a mid-Pacific open water area dubbed the ‘White Shark Café.’

‘We joke that tiger sharks, not being media stars like white sharks, wouldn’t be comfortable in a ‘café’ and prefer to hang-out in their ‘truck-stop’ in the mid-Atlantic,’ says Wetherbee, who is also based at the University of Rhode Island.

Conservation Implications

Tiger sharks are nearing threatened status, in part because of targeting for the soup fin trade. One of the most important implications of the new research, therefore, is for conservation.

‘Understanding how these animals use the oceans is the first step toward effective conservation,’ said Harvey. ‘Protecting migratory species is a great challenge because they can be found in such a wide area. Protecting the areas where animals, such as tiger sharks, spend the most time is a tractable goal once those areas have been identified.’

Guided in part by early access to the GHRI team’s data about the importance of the Bahamas habitat to the tiger shark’s annual migratory pathways, The Bahamas government established a shark sanctuary in 2011 prohibiting commercial shark fishing in their territorial waters.

How to Follow Sharks

All of the satellite tracks for tiger sharks in this study, as well as ongoing tracks for other species including mako sharks, oceanic whitetip sharks and marlins, can be found online at http://www.ghritracking.org

Source: Nova Southeastern University

Originally published here: www.sciencedaily.com/releases/2015/06/150609213349.htm

Posted June 10th, 2015.

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Why some threatened corals swap ‘algae’ partners

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This image shows Caribbean star coral (Orbicella faveolata) with individual coral polyps showing different levels of bleaching during a warm summer bleaching event in summer 2014. Image taken off northern Florida Keys.
Credit: Rivah Winter

A new research study showed why threatened Caribbean star corals sometimes swap partners to help them recover from bleaching events. The findings are important to understand the fate of coral reefs as ocean waters warm due to climate change.

The University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science research team placed colonies of Caribbean star coral (Orbicella faveolata) in a heated tank for one to two weeks to replicate ocean conditions that would lead to both mild and severe coral “bleaching” — when corals turn white as a result of the loss of symbiotic algae living in their tissues. The corals, collected from waters off Miami, were then allowed to recover at two different water temperatures, below and above the local average, to see if they recovered with the same or different algal partners.

“Since ‘symbiont shuffling’ occurs in only some cases, we wanted to understand what drives this process and whether it could help corals adjust to climate change,” said Ross Cunning, a UM Rosenstiel School alumnus and lead author of the study. “We discovered that partner switching in Caribbean star corals is dependent upon the severity of the bleaching event and the temperature during recovery.”

The researchers discovered that severe bleaching and warmer water recovery temperatures caused corals to shuffle their symbionts in favor of more heat-tolerant algae, which belong to a group of symbionts called clade D, while mild bleaching and cooler recovery drove shifts toward the less heat-tolerant algae, in clade B. The study, published in the June 3 issue of the journal Proceedings of the Royal Society B, suggests that increases in heat-tolerant symbionts in the Caribbean star coral are greatest when bleaching is more severe and the recovery environment is warmer.

Corals depend on symbiotic algae to survive and build coral reefs. Increased ocean temperatures due to climate change can cause these symbiotic algae to be expelled from the coral, an event known as bleaching, which often leads to death. Climate change is one of the main threats to the Caribbean star coral (O. faveolata), which was were recently listed as a ‘threatened’ species under the U.S. Endangered Species Act.

“These findings help resolve a long-standing debate over why some corals switch partners after bleaching, while others do not,” said Andrew Baker, UM Rosenstiel School associate professor of marine biology and ecology and a Pew fellow in marine conservation. “They show that, as the oceans continue to warm and bleaching events become more severe, we might expect heat-tolerant symbionts to become a common feature of recovering reefs. Corals that can ‘buddy up’ with different algae might be more resistant to bleaching in the future.”

Two more recent studies, also conducted in Baker’s Coral Reef Futures lab at UM, showed how corals modify their symbionts in response to environmental changes. The first, published earlier this year in the journal Global Change Biology, showed how changes in symbiont partners following bleaching directly increased corals’ thermal tolerance. The second, published in the May issue of the journal Ecology, showed that, in addition to changing the types of algae they partner with, corals also fine-tune the number of algae they contain to deal with an ever-changing environment.

“Together, these studies suggest that that the rate of warming, timing between bleaching events, and severity of each bleaching event, will play an important role in determining coral survivorship,” said Baker. “We need to better understand these changes in order to accurately predict coral reef futures.”

Source: University of Miami Rosenstiel School of Marine & Atmospheric Science

Originally published here: www.sciencedaily.com/releases/2015/06/150604100915.htm

Posted June 8th, 2015.

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Sisters act together: Cichlid sisters swim together in order to reach the goal

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Cichlid fish in the Lake Tanganyika.

Credit: Stefanie Schwamberger

The manner and routes of dispersal vary with the species and the ecological conditions. Many fish form shoals to avoid predation. Shoaling with familiar conspecifics affords the fish an even greater advantage by increasing the benefit for relatives. This promotes the continuation and future spread of an individual’s own genetic information.

Franziska Lemmel-Schädelin, Wouter van Dongen, Yoshan Moodley and Richard Wagner from the Konrad Lorenz Institute of Ethology studied Neolamprologus caudopunctatus, a species of cichlid fish endemic to Lake Tanganyika, Africa’s second largest and the world’s second deepest freshwater lake. Lake Tanganyika has a surface volume of about 33,000 m², which corresponds to the size of Belgium. The researchers studied the influence of sex and size on dispersal and shoaling behavior.

Females dispersed longer distances than males

Lemmel-Schädelin and her field assistants carried out a number of dives in October and November 2008 to study the dispersal behavior and relationships of over 900 cichlids. The divers collected DNA samples from the dorsal fins and documented the body size and sex of the fish. An analysis of the data showed that over the course of their lives the females dispersed farther from their parental nesting sites than males.

“To avoid inbreeding and resource competition, it is usual among many animals for one sex to disperse farther from their place of birth than the other. Male-biased dispersal is more frequently the norm among mammals, with females remaining near the original nesting area. Among the cichlids we studied, on the other hand, it appears to be the females that disperse,” says ethologist Lemmel-Schädelin.

Kin-shoaling promotes the spread of an individual’s own genes

The researchers discovered another phenomenon while studying the familial relationships within the shoals. Small — and therefore probably younger — females tend to shoal with female siblings. Small males do not, instead preferring to shoal with non-sibling males. Larger — and therefore older — fish no longer exhibit this preference for kin-shoaling.

Richard Wagner explains this behaviour as follows: “Females disperse around eleven times as far from their parental nests than males. This naturally involves a certain risk for the females. We observed that females tended to shoal with their female siblings. They probably do so in order to minimize the risks of long-distance dispersal and to increase the chance of at least one member of the family making it.”

“Cichlid research is especially interesting from an evolutionary perspective,” says Lemmel-Schädelin. “Africa’s three largest lakes — Lake Victoria, Lake Tanganyika and Lake Malawi — are home to cichlids that are believed to have emerged from a limited source population. The ancestral animals followed the rivers to enter these lakes, where they found a number of ecological niches in which they began to develop in different directions. This makes it possible here to look at evolution in action, so to speak, and to research the emergence of new species and a rich repertoire of different behavior’s,” Lemmel-Schädelin explains.

Source: Veterinärmedizinische Universität Wien

Posted June 2nd, 2015.

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Genetic analysis of the American eel helps explain its decline

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American Eels of the upper St. Lawrence grow slowly but attain larger sizes (top) compared with eels in coastal areas (bottom).
Credit: Guy Verreault/Current Biology 2015

The American eel has been a concern for the U.S. Fish and Wildlife Service since 2007, when it was first considered for, but failed to receive, Endangered Species Act protection. The numbers of these slender, slimy, ancient fish in freshwater areas have been decreasing rapidly due to dams, pollution, and overfishing, but scientists have been puzzled as to why the fish can’t recolonize. Now, a new look at eel genetics published on May 28 in Current Biology finds that there are differences between eels that feed in freshwater and eels that feed in brackish environments that were previously thought to be genetically interchangeable.

Both freshwater and brackish American eels are the same species, but they vary in size and have very different growth rates and life spans. Once a year, sexually mature eels from both groups migrate thousands of miles to spawn in the Sargasso Sea (located in the North Atlantic Ocean east of Bermuda). The offspring are carried off by the current to their new homes. It’s been thought that young American eels can detect whether they’ve ended up in brackish or freshwater habitats and acclimate accordingly. But this new study suggests that eels are predisposed to survive in these environments, depending on what genes they inherited.

“People have considered these differences in growth and age to be 100 percent due to phenotypic plasticity, independent of the genotype,” says lead author Scott Pavey, a postdoctoral fellow at the Integrated Biology Institute of Laval University in Quebec, Canada. “But what we found is that genes affect whether an eel can survive freshwater or brackish environments.” This helps explain why some conservation efforts to preserve the freshwater eel haven’t been successful, as more plentiful brackish eels cannot easily change their traits to survive in freshwater environments.

Pavey, in collaboration with ecologist Louis Bernatchez and colleagues, used new sequencing technologies to screen the eel genome in 45,000 places. The analysis identified 99 genes that differ between freshwater and brackish eels, including those associated with growth rate, heart development, and smell. It’s unknown whether this type of genetic differentiation exists in other, non-eel marine species with high levels of phenotypic plasticity.

The question remains, though, as to why eels would have such a strange approach to survival. The fish is considered evolutionarily ancient, so they must be doing something right. “It’s a different strategy, a kind of hedging your bets,” speculates Pavey. His team is now working to publish and release the entire genome of the eel. This will provide an important tool for other researchers to conduct similar studies on different aspects of eel ecology.

Source: Cell Press

Originally published here: www.sciencedaily.com/releases/2015/05/150528124204.htm

Posted May 29th, 2015.

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