Eutrophication Of Lake Constance Led To Genetic Changes In A Species Of Water Flea

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ScienceDaily (Mar. 18, 2009) — Ecological changes caused by humans affect natural biodiversity. For example, the eutrophication of Greifensee and Lake Constance in the 1970s and 1980s led to genetic changes in a species of water flea which was ultimately displaced.

Despite the fact that water quality has since been significantly improved, this species has not been re-established. This was demonstrated by researchers from Eawag and from two German universities (Frankfurt and Konstanz), who analysed genetic material from Daphnia eggs up to 100 years old.
Evolutionary biologist Nora Brede explains, animatedly: “In the laboratory, we were able to revive resting eggs over 40 years old isolated from Greifensee sediment.” For Eawag, this Jurassic Park-style method has a serious purpose: it makes it possible to determine retrospectively which Daphnia species was dominant in the lake around 1960, and whether the species that prevailed in the 1970s and 1980s became more tolerant of pollutants. Daphnia, which are crustaceans, can produce diapausing (resting) eggs – e.g. when food supplies are inadequate – which develop into a living organism when environmental conditions subsequently become more favourable. As these eggs are deposited in datable layers of anoxic sediments, their DNA can be analysed even after the passage of 100 years or more.
What makes this biological archive particularly interesting is the fact that conditions in the lake have undergone dramatic changes since 1960. In the 1970s and 1980s, inputs of phosphate detergents and fertilizer runoff led to eutrophication, with the development of algal blooms, including toxic cyanobacteria (blue-green algae). Fish died as a result of oxygen depletion.
As reported in the latest edition of the Proceedings of the National Academy of Sciences, the results of the genetic analysis of Daphnia eggs indicate that genetic diversity was also affected by the excessive nutrient levels. At the beginning of the 20th century, only one species of water flea (Daphnia hyalina) occurred abundantly in the two lakes studied. As eutrophication developed, this was displaced by another species (Daphnia galeata). In the transitional periods before and after peak nutrient inputs, hybrids also developed. However, although the lakes are now once again much cleaner (thanks to major efforts in the urban wastewater management sector), the original species has yet to recover.
According to Nora Brede, “This demonstrates that anthropogenic changes, such as eutrophication, can have major and not fully reversible effects on animal species.” In addition, the research project also showed how rapidly evolutionary processes can unfold in the animal kingdom. Brede comments: “In a mere 50 years, there have been measurable changes in the genome structure of a species, which is amazing, given that this is an extremely short period on the timescale of the Earth’s history.”
Biological archives such as the resting eggs of Daphnia in lake sediments are a valuable tool for investigating how organisms respond to changes in the ecosystem. Together with its partners, Eawag is therefore making the most of these opportunities to study and gain a better understanding of evolutionary processes. Research is focusing in particular on the question of how quickly plants and animals adapt genetically to the alterations in temperature associated with global climate change.
Journal reference:
Brede et al. The impact of human-made ecological changes on the genetic architecture of Daphnia species. Proceedings of the National Academy of Sciences, 2009; DOI: 10.1073/pnas.0807187106
Adapted from materials provided by EAWAG: Swiss Federal Institute of Aquatic Science and Technology, via AlphaGalileo.

Elephant Shark Genome Sequence Leads To Discovery Of Color Perception In Deep-sea Fish

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ScienceDaily (Mar. 18, 2009) — The elephant shark, a primitive deep-sea fish that belongs to the oldest living family of jawed vertebrates, can see color much like humans can.

This discovery, published in the March 2009 issue of Genome Research, may enhance scientists' understanding of how color vision evolved in early vertebrates over the last 450 million years of evolution.
"It was unexpected that a 'primitive' vertebrate like the elephant shark had the potential for color vision like humans. The discovery shows that it has acquired the traits for color vision during evolution in parallel with humans," said Byrappa Venkatesh, Ph.D., who with David Hunt, Ph.D., headed the research team responsible for this surprising discovery.
Dr. Venkatesh is a scientist at Singapore's Institute of Molecular and Cell Biology (IMCB), while Dr. Hunt is based at the Institute of Ophthalmology at University College London (UCL).
The research team found that the elephant shark had three cone pigments for color vision and, like humans, it accomplished this through gene duplication.
Dr. Venkatesh said that the finding underscores the research utility of the elephant shark, which IMCB scientists proposed in 2005 as a valuable reference genome to understand the human genome.
In a separate paper titled, "Large number of ultraconserved elements were already present in the jawed vertebrate ancestor," published in the journal Molecular Biology and Evolution in March 2009, the research team reported that they had discovered that the protein sequences in elephant shark were evolving at a slower rate than in other vertebrates.
This finding indicates that the elephant shark had retained more features of the ancestral genome than other vertebrates belonging to the same evolutionary tree and hence was a useful model for gaining insight into the ancestral genome, in which the human genome also has its roots.
In several scientific publications, Dr. Venkatesh's team has described research showing that the human DNA sequence was more similar to elephant shark than to any other fish.
Dr. Venkatesh added, "We expect the sequencing of the whole genome of the elephant shark to be completed by early 2010, the availability of which will then enable scientists to explore the important functional elements in both the human and elephant shark genome that have remained unchanged during the last 450 million years of evolution."
The findings reported in Genome Research and Molecular Biology and Evolution were generated less than two years after IMCB secured National Institutes of Health funding to sequence the whole genome of the elephant shark.
Journal references:
Davies, W.L., Carvalho, L.S., Tay, B., Brenner, S., Hunt, D.M. and Venkatesh, B. Into the blue: gene duplication and loss underlie colour vision adaptations in a deep-sea chimaera, the elephant shark Callorhinchus milii. Genome Research, 2009; 19: 415-426 DOI: 10.1101/gr.084509.108
Wang, J., Lee, A.P., Kodzius, R., Brenner, S. and Venkatesh, B. Large number of ultraconserved elements were already present in the jawed vertebrate ancestor. Molecular Biology and Evolution, 2009; 26: 487-490 DOI: 10.1093/molbev/msn278
Venkatesh, B., Kirkness, E.F., Loh, Y.H., Halpern, A.L., Lee, A.P., Johnson, J., Dandona, N., Viswanathan, L.D., Tay, A., Venter, J.C., Strausberg, R.L. and Brenner, S. Survey Sequencing and Comparative Analysis of the Elephant Shark (Callorhinchus milii) Genome. PLoS Biology, 2007; 5 (4): e101 DOI: 10.1371/journal.pbio.0050101
Venkatesh, B., Kirkness, E.F., Loh, Y.H., Halpern, A.L., Lee, A.P., Johnson, J., Dandona, N., Viswanathan, L.D., Tay, A., Venter, J.C., Strausberg, R.L. and Brenner, S. Ancient Noncoding Elements Conserved in the Human Genome. Science, 2006; 314 (5807): 1892 DOI: 10.1126/science.1130708
Adapted from materials provided by Agency for Science, Technology and Research (A*STAR), Singapore.

Animal Families With The Most Diversity Also Have Widest Range Of Size

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ScienceDaily (Mar. 18, 2009) — Somewhere out there in the ocean, SpongeBob SquarePants has a teeny-tiny cousin and a humongous uncle.

That's just what one would expect from a new analysis of body sizes across all orders of animal life that was conducted by researchers at the National Evolutionary Synthesis Center (NESCent), in Durham, N.C. and the University of North Carolina, Chapel Hill.
Researchers Craig McClain and Alison Boyer created a giant database on body sizes across all orders of animal life and found that phyla -- families of animals grouped together by a similar body plan -- with the greatest diversity of species were also those with the largest range of body sizes.
The sponges, Poriferans, were found to have some of the greatest diversity of both body size and species, ranging from microscopic to the size of an automobile. Molluscs (snails, squid, clams, chitons), and Arthropods (crabs, insects, lobsters, copepods) also showed great diversity. So did our family, the Chordates, which ranges from a half-inch fish in the swamps of Borneo to the truly leviathan 100-ton Blue Whale, with all the fishes, birds and mammals in between.
On the one hand, it may seem obvious that diversity in size and diversity in species go together, acknowledges marine biologist McClain, assistant director of science at NESCent. But it also says something a little more subtle about how new species arise and adapt to all the available niches in the environment.
"This really comes down to understanding the diversity of life on Earth," McClain said.
The group's findings appear online in Proceedings of the Royal Society B. The research was conducted in part at the Monterrey Bay Aquarium Research Institute, funded by the David and Lucile Packard Foundation, and the Smithsonian National Museum of Natural History. NESCent is a National Science Foundation collaboration of Duke, UNC and N.C. State that is housed in buildings Duke leases.
The Blue Whale, incidentally, is the largest animal ever, but the Chordate group doesn't boast the smallest. That distinction belongs to animals with names like mud dragons, brush heads, jaw worms, stomach hair worms and water bears that are so small they live between individual grains of sediment in the ocean. But this smallest group's range doesn't reach up to the largest body size.
This is a pattern that repeated itself several times in the data, McClain said. There are apparently physical limits to the range of sizes that can work for some body plans. In worms, for example, it is impossible to slither along if the girth and weight become too large. (The largest worm, Riftia pachyptila, from deep-sea vents, doesn't move.)
Within the range of sizes that works for a given body plan, evolution creates new species and new sizes, McClain said. What this sweeping analysis hasn't solved is the riddle about how different body sizes emerge. One theory says that body sizes arise through random natural variation. A second says that size diversity is driven by the availability of unused niches in the environment.
The finding also points to areas where more species might be waiting to be discovered. For example, the little-studied priapulid worms (aka "penis worms") have only 16 species on the books, but with a very large range in size. McClain's guess is that there may be more undiscovered species within that range of sizes. "There are groups that definitely don't have a lot of people studying them," he said.
Knowing something about a body plan's size constraints also might allow for a ballpark estimate of its number of species, McClain said.
Adapted from materials provided by Duke University, via EurekAlert!, a service of AAAS.

American Carnivores Evolved To Avoid Each Other, New Study Suggests

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ScienceDaily (Mar. 17, 2009) — How do the many carnivorous animals of the Americas avoid competing for the same lunch, or becoming each other's meal?

A possible answer comes from a new study by a pair of researchers at the University of California, Davis. Their large-scale analysis shows that it's not just chance that's at play, but avoidance strategies themselves that have been a driving force in the evolution of many carnivores, influencing such factors as whether species are active daytime or nighttime, whether they inhabit forests or grasslands, or live in trees or on the ground.
The Americas are home to more than 80 species of terrestrial carnivores, including cats, dogs, bears, weasels, skunks and raccoons. Commonly, 20 or more species can occupy the same region.
"For the most part, these overlapping species all share the same prey base -- other animals -- which includes each other," said Jennifer Hunter, who conducted the study for her Ph.D. dissertation in ecology.
Hunter and co-author Tim Caro, professor of wildlife, fish and conservation biology, first plotted the known ranges of all of the American carnivores on one big digital map. Assuming that wherever ranges overlapped, competition and predation between those species was possible, they then compared those animals' behavioral characteristics, body sizes and coloration. By analyzing this huge matrix of information, they were able to tease out broad patterns of strategies employed by each family.
For example, their map showed that the bear and dog families shared ranges with the greatest number of potential competitors. Most species in these families are omnivores, which helps reduce competition for a meat diet.
Raccoon family members, although small, run the lowest risk of becoming prey, because most live out of harm's way in trees.
One of their most surprising findings, Hunter said, was that the most petite carnivores, skunks, along with some weasels, lack an avoidance strategy. "When you look at all these overlays of ecology, these guys share all the same space at the same time with other carnivores."
How do these animals manage to survive? All skunks and a number of weasel species in this exposed group have facial or body coloring with an abrupt demarcation between white and dark. For skunks, this contrasting coloration almost surely warns predators of their noxious spray, Hunter explained, while with some weasel family members -- the notoriously aggressive badgers and wolverines, for example -- it may warn of ferocity.
The work provides a body of evidence for why these behaviors have evolved that could not have been obtained in the field, Hunter said.
The findings were published in the December issue of Ethology, Ecology and Evolution.
Partial funding for the study came from the National Science Foundation.
Journal reference:
Hunter J. and Caro T. Interspecific competition and predation in American carnivore families. Ethology, Ecology and Evolution, 2008; 20 (4): 295-324
Adapted from materials provided by University of California - Davis, via EurekAlert!, a service of AAAS.

Leatherback Turtle Threatened By Plastic Garbage In Ocean

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ScienceDaily (Mar. 16, 2009) — Leatherback turtles, the most widely distributed reptiles on Earth, are threatened with extinction themselves, in large part due to the carelessness of humans. A Dalhousie University professor addresses the threat of plastics to this endangered species.

They survived the extinction of the dinosaurs. They're descendants of one of the oldest family trees in history, spanning 100 million years. But today leatherback turtles, the most widely distributed reptiles on Earth, are threatened with extinction themselves, in large part due to the carelessness of humans.
We've seen reference to the dangers plastic poses to marine life, garbage that we humans directly and indirectly deposit in the oceans, but how clearly have we received the message? Not well enough according to a recent article in the journal Marine Pollution Bulletin co-authored by Dalhousie University's Mike James.
“We wanted to see if plastics ingestion in leatherbacks was hype or reality,” says Dr. James, senior species at risk biologist for Fisheries and Oceans Canada and adjunct professor with Dalhousie’s Department of Biology.
“It was a monumental effort that looked back at necropsies over the last century from all over the world,” he explains. (Necropsies are post-mortem examinations performed on animals.) “After reviewing the results of 371 necropsies since 1968, we discovered over one third of the turtles had ingested plastic.”
Since leatherbacks prefer eating jellyfish, it's widely believed they mistake bags or other plastics for their meals. Since jellyfish and marine debris concentrate where ocean water masses meet, leatherbacks feeding in these areas are vulnerable to ingesting plastic.
Once leatherbacks ingest plastic, thousands of spines lining the throat and esophagus make it nearly impossible to regurgitate. The plastic can lead to partial or even complete obstruction of the gastrointestinal tract, resulting in decreased digestive efficiency, energetic and reproductive costs and, for some, starvation.
“Plastics ingestion doesn’t always cause death, but there are clearly health risks to the turtles,” says Dr.James.
Fascinated by reptiles as a child, Dr. James developed a lifelong interest in turtles, from raising them as a kid, to his PhD research and now as a biologist and conservationist. He says there are simple ways to stop these ongoing threats.
“The frustrating, yet hopeful aspect is that humans can easily begin addressing the solution, without major lifestyle changes,” says Dr. James. “It's as simple as reducing packaging and moving towards alternative, biodegradable materials and recycling.”
Leatherback turtles are classified as critically endangered world-wide. The true population size is not precisely known, as only adult females come ashore for nesting in remote tropical locations. During the summer and fall, Canadian waters support the highest density of foraging leatherbacks in the North Atlantic.
Journal reference:
Mrosovsky et al. Leatherback turtles: The menace of plastic. Marine Pollution Bulletin, 2009; 58 (2): 287 DOI: 10.1016/j.marpolbul.2008.10.018
Adapted from materials provided by Dalhousie University, via Newswise.

Female Birds 'Jam' Their Mates' Flirtatious Songs

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ScienceDaily (Mar. 16, 2009) — When a single female is nearby, female antbirds will sing over the songs of their male partners in an apparent attempt to keep their messages from getting through, according to a new report published online on March 12th in Current Biology. Males respond to that interruption by singing a different tune.

The findings offer the first evidence that such "signal jamming" and "jamming avoidance" occur between mates, according to the researchers.
"In human terms, signal jamming is most commonly associated with attempts to scramble information in radio, radar, or cell phone signals," said Joseph Tobias of the University of Oxford. "The females in our study try to do a similar thing with the songs of their partner, but the overall situation is more analogous to a wife continually interrupting her husband to stop him from flirting with a single woman."
Social animals produce a wide range of communal displays, many of them remarkable feats of complex coordination, the researchers said. One example is the duets sung by pairs of Peruvian warbling antbirds. So far, scientists have disagreed about how temporal coordination between displaying individuals evolved, some seeing it as a cooperative signal of coalition quality, others as a selfish means to avoid signal overlap.
According to the research team, the new study provides the first evidence that the avoidance of signal overlap is sufficient to explain the coordination and complexity of communal signals.
In a series of playback experiments, the team found that resident pairs of antbirds sing coordinated duets when responding to rival pairs. But under other circumstances, cooperation breaks down, leading to more complex songs. Specifically, they report that females respond to unpaired sexual rivals by jamming the signals of their own mates, who in turn adjust their signals to avoid the interference.
Tobias said the females' attempts to jam their partners' songs are presumably intended to make the males less attractive, or to make it clear that they are "taken." He added that the results in antbirds may have broad implications for understanding how communal signals have developed over evolutionary time in many animals, and perhaps even in humans.
First, Tobias said, the findings reveal that group signals such as duets and choruses represent a subtle blend of cooperation and conflict. The balance between those two forces depends on the context. Their study also suggests that if there is some conflict in the system, then multiple singers can combine to produce rhythmic, precisely coordinated, and increasingly complex songs simply by avoiding overlap.
"Most evidence points to vocalizations in early humans having a function in both mate attraction and resource defense, so it seems plausible that 'signal jamming' and especially 'jamming avoidance' played a role in our evolutionary history. If so, our results may help to explain the first steps towards complex, coordinated group signals in humans, which themselves are the likely forerunners to modern music."
The researchers Joseph A. Tobias, and Nathalie Seddon, are of University of Oxford, Oxford, UK.
Journal reference:
Joseph A. Tobias, and Nathalie Seddon. Signal Jamming Mediates Sexual Conflict in a Duetting Bird. Current Biology, 2009; DOI: 10.1016/j.cub.2009.02.036
Adapted from materials provided by Cell Press, via EurekAlert!, a service of AAAS.

Human-generated Sounds May Be Killing Fish

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ScienceDaily (Mar. 13, 2009) — Anthropogenic, or human generated, sounds have the potential to significantly affect the lives of aquatic animals - from the individual animal's well-being, right through to its reproduction, migration and even survival of the species.

According to a new study marine animals could suffer detrimental effects ranging from a loss of hearing to increased stressed levels as a result of environmental noise - in ways not dissimilar to humans and land animals. The study also describes some recent well-controlled experimental studies while highlighting areas for future study.
"Human generated sounds in the marine environment may result in only small shifts in behavior for some animals, but immediate death in others. With the vast increase in production of sound in the marine environment due to human activity such as oil exploration, shipping and construction, the effect of human-generated sounds on the aquatic life becomes a growing issue", said Dr. Arthur Popper from the University of Maryland, USA.
Marine animals use sounds to communicate and to glean information about their environment. Unlike the "visual scene" developed by the animal's sense of sight, the "auditory scene" derived from sounds provides marine animals with a three dimensional view of the world and extends far beyond the visual scene.
Dr. Popper added, "The detection of the auditory scene plays a critical role in sound detection - along with the detection of communication signals. Anything in the environment that alters the organism's ability to detect and analyze its auditory scene has the potential to cause a detrimental impact on the life of the animal as well as the survival of the species".
Journal reference:
. The effects of human-generated sound on fish. Integrative Zoology, (in press)
Adapted from materials provided by Wiley - Blackwell, via AlphaGalileo.