Oldest Horseshoe Crab Fossil Found, 445 Million Years Old

Daily Science Journal (Feb. 12, 2008) — Few modern animals are as deserving of the title “living fossil” as the lowly horseshoe crab. Seemingly unchanged since before the Age of Dinosaurs, these venerable sea creatures can now claim a history that reaches back almost half-a billion years.

Lunataspis aurora - fossil paratype specimen (about 25 mm wide) beside the dried carapace of a young modern horseshoe crab. (Credit: Left image courtesy of G. Young, The Manitoba Museum; right, D. Rudkin, Royal Ontario Museum)

In a collaborative research article published recently in the British journal Palaeontology, a team of Canadian scientists revealed rare new horseshoe crab fossils from 445 million year-old Ordovician age rocks in central and northern Manitoba, which are about 100 million years older than any previously known forms.

Palaeontologist Dave Rudkin from the Royal Ontario Museum, with colleagues Dr. Graham Young of The Manitoba Museum (Winnipeg) and Dr. Godfrey Nowlan at the Geological Survey of Canada (Calgary), gave their remarkable new fossils the scientific name Lunataspis aurora, meaning literally “crescent moon shield of the dawn” in reference to their shape, geological age and northerly discovery sites. Although they are more “primitive” in several aspects than other known horseshoe crabs, their resemblance to living forms is unmistakable.

The fossil horseshoe crabs were recovered in the course of fieldwork studies on ancient tropical seashore deposits, providing yet another important link to their modern descendants that are today found along warmer seashores of the eastern United States and the Indian Ocean.

This is particularly significant, explains Rudkin. “Understanding how horseshoe crabs adapted to this ecological niche very early on, and then remained there through thick and thin, can give us insights into how ocean and shoreline ecosystems have developed through deep time.”

Today, marine shorelines worldwide are being threatened by human activity, and although some horseshoe crab populations are endangered, their enviably long record on Earth indicates that they have successfully weathered many previous crises, including the mass extinction that saw the demise of the dinosaurs and many other life forms 65 million years ago.

“We do need to be concerned about horseshoe crabs and many of the other unusual life forms found on marine shores,” said Dr. Young. “Nevertheless, we can also be mildly optimistic that some of these things have demonstrated a toughness that may allow them to survive our abuse of these environments.”

Living horseshoe crabs are extensively studied, especially in the fields of ecology and medical research. The exciting discovery of these unusual early fossil relatives adds a new introductory chapter to their remarkable story.

David Rudkin is Assistant Curator in the Department of Natural History (Palaeobiology) at the Royal Ontario Museum, and holds an appointment to the Department of Geology, University of Toronto, as a Lecturer in palaeontology. Rudkin joined the former Department of Invertebrate Palaeontology at the ROM in 1975 and began working on fossils from the Burgess Shale in British Columbia.

Adapted from materials provided by Royal Ontario Museum.

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Blue-eyed Humans Have A Single, Common Ancestor

Daily Science Journal (Jan. 31, 2008) — New research shows that people with blue eyes have a single, common ancestor. A team at the University of Copenhagen have tracked down a genetic mutation which took place 6-10,000 years ago and is the cause of the eye colour of all blue-eyed humans alive on the planet today.

Variation in the colour of the eyes from brown to green can all be explained by the amount of melanin in the iris, but blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes. (Credit: iStockphoto/Cristian Ardelean)

What is the genetic mutation

“Originally, we all had brown eyes”, said Professor Eiberg from the Department of Cellular and Molecular Medicine. “But a genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a “switch”, which literally “turned off” the ability to produce brown eyes”. The OCA2 gene codes for the so-called P protein, which is involved in the production of melanin, the pigment that gives colour to our hair, eyes and skin. The “switch”, which is located in the gene adjacent to OCA2 does not, however, turn off the gene entirely, but rather limits its action to reducing the production of melanin in the iris – effectively “diluting” brown eyes to blue. The switch’s effect on OCA2 is very specific therefore. If the OCA2 gene had been completely destroyed or turned off, human beings would be without melanin in their hair, eyes or skin colour – a condition known as albinism.

Limited genetic variation

Variation in the colour of the eyes from brown to green can all be explained by the amount of melanin in the iris, but blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes. “From this we can conclude that all blue-eyed individuals are linked to the same ancestor,” says Professor Eiberg. “They have all inherited the same switch at exactly the same spot in their DNA.” Brown-eyed individuals, by contrast, have considerable individual variation in the area of their DNA that controls melanin production.

Professor Eiberg and his team examined mitochondrial DNA and compared the eye colour of blue-eyed individuals in countries as diverse as Jordan, Denmark and Turkey. His findings are the latest in a decade of genetic research, which began in 1996, when Professor Eiberg first implicated the OCA2 gene as being responsible for eye colour.

Nature shuffles our genes

The mutation of brown eyes to blue represents neither a positive nor a negative mutation. It is one of several mutations such as hair colour, baldness, freckles and beauty spots, which neither increases nor reduces a human’s chance of survival. As Professor Eiberg says, “it simply shows that nature is constantly shuffling the human genome, creating a genetic cocktail of human chromosomes and trying out different changes as it does so.”

Adapted from materials provided by University of Copenhagen.

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Why Don't Chimpanzees Like To Barter Food?

Daily Science Journal (Jan. 30, 2008) — For thousands of years, human beings have relied on commodity barter as an essential aspect of their lives. It is the behavior that allows specialized professions, as one individual gives up some of what he has reaped to exchange with another for something different. In this way, both individuals end up better off. Despite the importance of this behavior, little is known about how barter evolved and developed.

Researchers examined the circumstances under which chimpanzees, our closest relatives, will exchange one inherently valuable commodity (an apple slice) for another (a grape), which is what early humans must have somehow learned to do. (Credit: iStockphoto/Nicola Stratford)

This study is the first to examine the circumstances under which chimpanzees, our closest relatives, will exchange one inherently valuable commodity (an apple slice) for another (a grape), which is what early humans must have somehow learned to do. Economists believe that commodity barter is one of the most basic precursors to economic specialization, which we observe in humans but not in other primate species. First of all, the researchers found that chimpanzees often did not spontaneously barter food items, but needed to be trained to engage in commodity barter. Moreover, even after the chimpanzees had been trained to do barters with reliable human trading partners, they were reluctant to engage in extreme deals in which a very good commodity (apple slices) had to be sacrificed in order to get an even more preferred commodity (grapes).

Prior animal behavior studies have largely examined chimpanzees' willingness to trade tokens for valuable commodities. Tokens do not exist in nature, and lack inherent value, so a chimpanzee's willingness to trade a token for a valuable commodity, such as a grape, may say little about chimpanzee behavior outside the laboratory.

In a series of experiments, chimpanzees at two different facilities were given items of food and then offered the chance to exchange them for other food items. A collaboration of researchers from Georgia State University, the University of California, Los Angeles, and the U.T. M.D. Anderson Cancer Center found that the chimpanzees, once they were trained, were willing to barter food with humans, but if they could gain something significantly better -- say, giving up carrots for much preferred grapes. Otherwise, they preferred to keep what they had.

The observed chimpanzee behavior could be reasonable because chimpanzees lack social systems to enforce deals and, as a society, punish an individual that cheats its trading partner by running off with both commodities. Also because of their lack of property ownership norms, chimpanzees in nature do not store property and thus would have little opportunity to trade commodities.

Nevertheless, as prior research has demonstrated, they do possess highly active service economies. In their natural environment, only current possessions are "owned," and the threat of losing what one has is very high, so chimpanzees frequently possess nothing to trade.

"This reluctance to trade appears to be deeply ingrained in the chimpanzee psyche," said one of the lead authors, Sarah Brosnan, an assistant professor of psychology at Georgia State University. "They're perfectly capable of barter, but they don't do so in a way which will maximize their outcomes."

The other lead author, Professor Mark F. Grady, Director of UCLA's Center for Law and Economics, commented: "I believe that chimpanzees are reluctant to barter commodities mainly because they lack effective ownership norms. These norms are especially costly to enforce, and for this species the game has evidently not been worth the candle. Fortunately, services can be protected without ownership norms, so chimpanzees can and do trade services with each other. As chimpanzee societies demonstrate, however, a service economy does not lead to the same degree of economic specialization that we observe among humans."

The research could additionally shed light on the instances in which humans also don't maximize their gains, Brosnan said.

The laboratory experiments for this study was conducted at Georgia State's Language Research Center and the University of Texas M.D. Anderson Cancer Center, and the much of the conceptual work was done at UCLA's Center for Law and Economics.

Citation: Brosnan SF, Grady MF, Lambeth SP, Schapiro SJ, Beran MJ (2008) Chimpanzee Autarky. PLoS One 3(1): e1518. doi:10.1371/journal.pone.0001518 http://www.plosone.org/doi/pone.0001518

Adapted from materials provided by Public Library of Science, via EurekAlert!, a service of AAAS.

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You Are What You Eat: Some Differences Between Humans And Chimpanzees Traced To Diet

Daily Science Journal (Jan. 30, 2008) — Using mice as models, researchers at the Max Planck Institute for Evolutionary Anthropology traced some of the differences between humans and chimpanzees to differences in our diet.

Humans consume a distinct diet compared to other apes, like this chimpanzee eating an apple. Not only do we consume much more meat and fat, but we also cook our food. It has been hypothesized that adopting these dietary patterns played a key role during human evolution. (Credit: iStockphoto/Stephanie Swartz)

Humans consume a distinct diet compared to other apes. Not only do we consume much more meat and fat, but we also cook our food. It has been hypothesized that adopting these dietary patterns played a key role during human evolution. However, to date, the influence of diet on the physiological and genetic differences between humans and other apes has not been widely examined.

By feeding laboratory mice different human and chimp diets over a mere two week period, researchers at the Max-Planck-Institute for Evolutionary Anthropology in Leipzig, Germany, were able to reconstruct some of the physiological and genetic differences observed between humans and chimpanzees.

The researchers fed laboratory mice one of three diets: a raw fruit and vegetable diet fed to chimpanzees in zoos, a human diet consisting of food served at the Institute cafeteria or a pure fast food menu from the local McDonald's™ (the latter caused the mice to significantly gain weight). The chimpanzee diet was clearly distinct from the two human diets in its effect on the liver - thousands of differences were observed in the levels at which genes were expressed in the mouse livers. No such differences were observed in the mouse brains. A significant fraction of the genes that changed in the mouse livers, had previously been observed as different between humans and chimpanzees. This indicates that the differences observed in these particular genes might be caused by the difference in human and chimpanzee diets.

Furthermore, the diet-related genes also appear to have evolved faster than other genes - protein and promoter sequences of these genes changed faster than expected, possibly because of adaptation to new diets.

Citation: Somel M, Creely H, Franz H, Mueller U, Lachmann M, et al (2008) Human and Chimpanzee Gene Expression Differences Replicated in Mice Fed Different Diets. PLoS One 3(1): e1504. doi:10.1371/journal.pone.0001504 http://www.plosone.org/doi/pone.0001504

Adapted from materials provided by Public Library of Science, via EurekAlert!, a service of AAAS.

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Cats' Family Tree Rooted In Fertile Crescent, Study Confirms

Daily Science Journal (Jan. 29, 2008) — The Fertile Crescent of the Middle East has long been identified as a "cradle of civilization" for humans. In a new genetic study, researchers at the University of California, Davis, have concluded that all ancestral roads for the modern day domestic cat also lead back to the same locale.

Cats, with their penchant for hunting mice, rats and other rodents, became useful companions as people domesticated, grew and stored wild grains and grasses. Eventually, cats also became pets but were never fully domesticated. Even today, most domestic cats remain self-sufficient, if necessary, and continue to be efficient hunters, even when provided with food. (Credit: Michele Hogan)

Findings of the study, involving more than 11,000 cats, are reported in the January issue of the journal Genomics.

"This study confirms earlier research suggesting that the domestication of the cat started in the Fertile Crescent region," said Monika Lipinski, lead researcher on the study and a doctoral candidate in the School of Veterinary Medicine. "It also provides a warning for modern cat fanciers to make sure they maintain a broad genetic base as they further develop their breeds."

Leslie Lyons, an authority on cat genetics and principal investigator on this study, said: "More than 200 genetic disorders have been identified in modern cats, and many are found in pure breeds. We hope that cat breeders will use the genetic information uncovered by this study to develop efficient breed-management plans and avoid introducing genetically linked health problems into their breeds."

History of the modern cat

Earlier archaeological evidence and research on the evolutionary history of cats has suggested that domestication of the cat originated about 5,000 to 8,000 years ago in the Fertile Crescent, a region located today in the Middle East. This is the area around the eastern end of the Mediterranean, stretching from Turkey to northern Africa and eastward to modern day Iraq and Iran. This domestication of the cat occurred as humans transitioned from nomadic herding to raising crops and livestock.

Cats, with their penchant for hunting mice, rats and other rodents, became useful companions as people domesticated, grew and stored wild grains and grasses. Eventually, cats also became pets but were never fully domesticated. Even today, most domestic cats remain self-sufficient, if necessary, and continue to be efficient hunters, even when provided with food.

Cats and their gene pools spread rapidly around the world as ancient civilizations developed trade routes. Unlike other domesticated species, there has been little effort to improve on the cat for functional purposes. Instead, development of cat breeds has been driven more by preferences for certain aesthetic qualities like coat color and color patterns.

Today, there are 50 recognized cat breeds. Of that total, 16 breeds are thought to be "natural breeds" that occurred in specific regions, while the remaining breeds were developed during the past 50 years.

DNA of 11,000 cats

In this study, the UC Davis research team focused on:

• tracing the movement of the modern cat through the ancient world and to the Americas;
• measuring changes in genetic diversity as cats dispersed throughout the world; and
• measuring any loss of genetic diversity that might have occurred in the development of the older or more contemporary breeds.

The researchers collected samples of cheek cells from more than 11,000 cats. These cats represented 17 populations of randomly bred cats from Europe, the Mediterranean, Asia, Africa and the Americas, as well as 22 recognized breeds.

DNA samples of most breeds were obtained at cat shows or were sent in upon the lab's request by cat owners in the United States. The study was assisted by a host of collaborators from throughout the world. DNA, or deoxyribonucleic acid, is the hereditary material in humans, other animals and plants. It carries the instructions or blueprint for making all the structures and materials that the organism needs to function.

Genetic markers called "microsatellite markers," commonly used for DNA profiling, were used to determine the genetic relationships of cat breeds, their geographic origins and the levels of genetic loss that have resulted from inbreeding.

Findings

From the DNA analysis, the researchers found that the cats were genetically clustered in four groups that corresponded with the regions of Europe, the Mediterranean basin, east Africa and Asia.

They discovered that randomly bred cats in the Americas were genetically similar to randomly bred cats from Western Europe. They also found that the Maine coone and American shorthair -- two breeds that originated in the United States -- were genetically similar to the seven Western European breeds. This suggests that cats brought to the New World by European settlers have not had sufficient time to develop significant genetic differentiation from their Western European ancestors.

The study yielded many interesting breed-specific findings. For example, the researchers found that the Persian breed, perhaps the oldest recognized pure breed, was not genetically associated with randomly bred cat populations from the Near East, but rather was more closely associated with randomly bred cats of Western Europe.

In addition, the researchers found that, of the Asian cat breeds, only the Japanese bobtail was genetically clustered with Western cats, although it did retain some Asian influence.

Cats from the Mediterranean region were found to be genetically uniform, perhaps a result of the constant movement of ships and caravans during the early era of the cat's domestication, the researchers suggested.

Lesson for cat breeders

The study found that genetic diversity remained surprisingly broad among cats from various parts of the world. However the data indicated that there was some loss of diversity associated even with the long-term development of foundation cat breeds -- those breeds that provided the genetic basis from which modern pure breeds were developed.

The researchers note that, given the relatively short time span during which modern breeds are emerging, cat breeders should proceed cautiously as they develop their breeds, making sure to maintain a broad genetic base that will minimize introduction of genetically based health problems.

Funding for this study was provided by the National Institutes of Health, the Winn Feline Foundation and the George and Phyllis Miller Feline Health Fund. Also supporting the study were the Center for Companion Animal Health and the Koret Center of Veterinary Genetics, both within the UC Davis School of Veterinary Medicine.

Adapted from materials provided by University of California - Davis.

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