JCM NATURAL HISTORY LOG

The genes that are most beneficial to males are the most disadvantageous for females, and vice versa. However, this genetic conflict between the sexes is important in maintaining genetic variation within a species, researchers at Uppsala University have shown in a study on fruit-flies published in the open access journal PLoS Biology.

Males and females of many species often look quite different from one another. These differences are thought to have evolved because the sexes often have needs and strategies that do not coincide. For example, in fruit-flies, females may do best by concentrating their efforts in acquiring resources to lay more eggs, while males benefit by increasing their mating and fertilization success.

Such differences generate a sexual “conflict of interests,” and since as a general rule each characteristic of an organism is regulated by the same set of genes in the two sexes, this conflict takes place at the genetic level. Using a combination of behavioral studies and genomic technology, researchers Paolo Innocenti and Ted Morrow have succeeded in getting a first insight into which genes are influenced by this type of sexual conflict.

“Our study shows that genes whose expression is beneficial to males are also detrimental to females, and vice versa,” says Ted Morrow who led the study.

Their work also shows where in the genome these sexual conflict genes are, and that they are abundant in the sex-determining X-chromosome, something previously predicted by theory. These results indicate that a genotype that is optimal for both sexes does not exist.

The full article can be found at: http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.1000335

A synopsis can be found at:  http://www.plos.org/press/plbi-08-03-InnocentiSynopsis.pdf

A genetic study has found that small domestic dogs probably originated in the Middle East more than 12,000 years ago. Researchers writing in the open access journal BMC Biology traced the evolutionary history of the IGF1 gene, finding that the version of the gene that is a major determinant of small size probably originated as a result of the domestication of the Middle Eastern gray wolf.

Melissa Gray and Robert Wayne, from the University of California, Los Angeles, led a team of researchers who surveyed a large sample of gray wolf populations. She said, “The mutation for small body size post-dates the domestication of dogs. However, because all small dogs possess this variant of IGF1, it probably arose early in their history. Our results show that the version of the IGF1 gene found in small dogs is closely related to that found in Middle Eastern wolves and is consistent with an ancient origin in this region of small domestic dogs.”

Previous archeological work in the Middle East has unearthed the remains of small domestic dogs dating to 12,000 years ago. Sites in Belgium, Germany and Western Russia contain older remains (13,000-31,000 years ago), but these are of larger dogs. These findings support the hypothesis put forward by Gray and colleagues that small body size evolved in the Middle East.

Reduction in body size is a common feature of domestication and has been seen in other domesticated animals including cattle, pigs and goats. According to Gray, “Small size could have been more desirable in more densely packed agricultural societies, in which dogs may have lived partly indoors or in confined outdoor spaces.”

The article discussed is:  Gray MM, Sutter NB, Ostrander EA, Wayne RK: IGF1 Haplotyping supports a Middle
Eastern Origin for small dogs.  BMC Biology 2010, 8:16.

A trio of biologists, including two from East Carolina University, have discovered in Peru the first confirmed species of monogamous amphibian, Ranitomeya imitator, better known as the mimic poison frog — a finding that provides groundbreaking insight into the ecological factors that influence mating behavior.

To the left:  A family group of Ranitomeya imitator amphibians, better known as mimic poison frogs. Credit: Photo courtesy of Jason Brown.
The scientists’ work, which is to be published in the April issue of The American Naturalist, may be the most solid evidence yet that monogamy can have a single ecological cause.

“We were able to tie the evolution of monogamy and the evolution of biparental care to variation in a single ecological factor, and that’s rare,” said Kyle Summers, an ECU biology professor whose specialties include evolutionary ecology and evolutionary genetics. Summers authored the study with Jason L. Brown, a former ECU graduate student now a researcher at Duke University, and Victor Morales of Ricardo Palma University in Lima, Peru.

Analyzing data on 404 frog species, the biologists found a strong association between the use of small pools for breeding, and the evolution of parental care, including intensive parental care involving egg-feeding and the participation of both parents. The researchers then focused in on the mating and parenting habits of two similar frog species, the mimic poison frog and the R. variabilis, more commonly known as the variable poison frog, that differed mainly in the size of the breeding-pool.

They theorized that the differences in parental care and mating system between these otherwise similar species stemmed from the relative availability of resources in the breeding pools. The tadpole of the mimic poison frog grows up in much smaller, less nutrient-dense water pools that form in the folds of tree leaves. They are ferried there after hatching by males, who monitor them in the months following birth. About once a week, the male calls for his female partner, who lays non-fertile eggs for the tadpoles to eat.

The variable poison frog, however, raises its tadpoles in larger pools. Here, as with most amphibians, rearing of the young is handled mostly by the male.

To test their theory, scientists moved tadpoles from both species into differently sized pools. Tadpoles in larger pools thrived while tadpoles in smaller pools did not grow.

This, the scientists said, means that tadpoles living in the larger, more nutrient-rich pools don’t need the work of two parents as much as their smaller-pond counterparts. Species that raised tadpoles in smaller ponds were more likely to require the skills of both parents. In turn, this likely favored parents who remained devoted only to the offspring that they had produced together.

The researchers used genetic analysis based on techniques similar to the DNA-based forensic methods used for paternity cases to investigate the mating system of the mimic poison frog. Surprisingly, the all but one of the families investigated were completely genetically monogamous. Many animals thought to practice social monogamy have been found through genetic testing to be less faithful than previously believed. Monogamy “turns out to be relatively rare, eve in birds and mammals — particularly in mammals — and reptiles,” Summers said. “Finding a frog that has a monogamous mating system was pretty novel for us.”

The biologists’ work already has attracted attention from scientific and popular media, both international and national. While the idea that ecological factors — say, scarcity of resources — have contributed to monogamous behavior in humans and other animals is well accepted, Summers cautioned against drawing inferences about human behavior from the findings.

“People are interested in whether there are parallels between mating systems of other species and our own,” he said. “Of course, the human situation is so different from other species. It’s somewhat perilous to over interpret the similarities. You can’t just translate it.”

Citation: Brown, J. et al. 2010. A Key Ecological Trait Drove the Evolution of Biparental Care and Monogamy in an Amphibian. The American Naturalist 175: 436–446.

A puzzle that has baffled scientists for centuries — why some birds appear to be male on one side of the body and female on the other — has been solved by researchers.

The research, which involved studying rare naturally occurring chickens with white (male) plumage on one side and brown (female) plumage on the other, sheds new light on the sexual development of birds.

It was previously thought that sex chromosomes in birds control whether a testis or ovary forms, with sexual traits then being determined by hormones.

The researchers, however, identified differences between male and female cells that control the development of sexual traits. The scientists have named the phenomenon, cell autonomous sex identity (CASI).

The study from The Roslin Institute at the University of Edinburgh, which receives key funding from the Biotechnology and Biological Sciences Research Council, is published in the journal Nature.

The findings, which are scientifically revolutionary in the field, may also be relevant to why males and females differ in behaviour and in susceptibility to disease.

They could also lead to improvements in poultry production — identification of some of the molecular differences between male and female cells should lead to better tests for sexing embryos prior to hatch. It might even be possible to devise ways of obtaining the growth characteristics of male birds in females, with improvements in feed efficiency and productivity that could contribute to future food security.

Dr Michael Clinton, who led the study, said: “This research has completely overturned what we previously thought about how sexual characteristics were determined in birds. We now believe that the major factors determining sexual development are built into male and female cells and derive from basic differences in how sex chromosome genes are expressed. Our study opens a new avenue for our understanding of sexual development in birds.

“It also means we must now reassess how this developmental process occurs in other organisms. There is already some evidence that organs such as the heart and brain are intrinsically different in males and females and birds may provide a model for understanding the molecular basis for these gender differences.”

Citation: Zhao D. et al. 2010.Somatic sex identity is cell autonomous in the chicken. Nature 464, 237-242.

Two Dartmouth biologists have found that brown anole lizards make an interesting choice when deciding which males should father their offspring. The females of this species mate with several males, then produce more sons with sperm from large fathers, and more daughters with sperm from smaller fathers. The researchers believe that the lizards do this to ensure that the genes from large fathers are passed on to sons, who stand to benefit from inheriting the genes for large size.

The male of this species can be two to three times the mass of the female, but the females seem to be in control of the genetic destiny. (Credit: Photo by Joseph Mehling '69)

The study is published in the March 4 issue of Science Express, the advance online publication of the journal Science.

“This species has figured out a clever way to pass on genes with gender-specific effects on fitness,” said Bob Cox, the lead author on the paper and a post-doctoral researcher at Dartmouth. “Usually, when natural selection pulls genes in different directions for each gender, the species faces an evolutionary dilemma. But these lizards have solved this puzzle, they’ve figured out how to get the right genes into the right gender.”

By manipulating opportunities for females to mate with males of different sizes, the researchers determined that females prefer larger males. But, when the choice of partners was limited to small males, females minimized the production of sons.

The researchers explain that the genes that make males more fit are often different from the genes that benefit females, which presents a conundrum because males and females share most of their DNA. The valuable traits for one gender are not always the same for the other. “In an evolutionary sense, what’s good for the goose is not always good for the gander,” said Cox.

In these lizards, however, mothers can enhance the fitness of their offspring by manipulating their gender depending on the size of the father. To demonstrate this, Cox and Calsbeek measured the survival rates of sons and daughters over eight months when released to their natural habitat in The Bahamas.

“As we predicted, the survival of the male offspring increased if they had large fathers,” said Calsbeek. “But, we found that the survival of the daughters was not influenced by the size of the father. This suggests that the genetic benefits of large size are specific to sons.”

How do females control the gender of their progeny? “That’s the big question at this point,” said Cox. The researchers will continue their studies to learn more about the mechanisms involved in this most fundamental of all evolutionary processes, the struggle to pass on advantageous genetic material.

On Thursday 4th March 2010, Karachi, Dr Sheh Shah, President of the Pakistan Medical Association, Dr Habib-ur-Rehman Soomro, Secretary General PMA and Dr Huma Qureshi, Executive Director Pakistan Medical Research Council launched the world’s first comprehensive snakebite protocol called ‘A2 Snakebite Management in Asia and Africa’ for use by doctors to treat snakebite in the key areas of Africa and Asia.

Snakebite has been described as a ‘neglected disease’ and yet little practical work has been done by experts to attempt to reduce the suffering caused by snakebite. The need for better guidelines has been frequently discussed but action has been conspicuously lacking. Pakistan published a National Snakebite Protocol in 2008, based on a comprehensive analysis of the conditions and infrastructure present in front line hospitals that deal with snakebite.

Above: The Malyan Pitviper (Calloselasma rhodostoma) is responsible for may envenomations in Southeast Asia. Photo: John C. Murphy.

Dr Qureshi said, “Following the success of the local protocol we decided to set ourselves the challenge of assisting with comprehensive guidelines for our African and Asian neighbours in a bid to contribute a major reduction in mortality. The use of western medical textbooks has led to sub optimal anti snake venom (ASV) dosages, ASV being given to patients who are not envenomed and too much ASV being given due to the lack of clear clinical endpoints for ASV therapy and many other problems in treatment”.

Over 95% of the world’s mortality from snakebite originates in Africa and Asia and Pakistan is ideally situated in geographical terms and in terms of it’s position in the top five countries for mortality, to provide guidance on the most effective way to approach snakebite.

The guidelines contain excellent photographs of the major medically significant snakes in Africa and Asia and recommendations for the use and dosage of anti snake venom. In addition, it includes chapters on first aid, prevention and some of the key support areas such as dealing with neurotoxic species and adverse reactions to anti venom.  There is also a unique chapter on the practical aspects of managing airway in snakebite, which has great applicability across other medical conditions.

Dr Shah stated, “The PMA has a long and distinguished history of supporting and endorsing practical solutions to medical conditions that affect the rural poor. Developed world snakebite experts do not understand the priority of snakebite in developing countries or the nature of local conditions. Many recommendations such as the routine use of mechanical ventilators are just not possible in developing country set-ups”.

There are useful guidelines on how to equip a basic medical facility to treat snakebite and methods to treat and effectively refer patients from a basic facility to a better-equipped hospital, which is crucial if significant reductions in mortality are to be secured.

Ian Simpson, the author stated, “The guidelines are specifically targeted at rural doctors in Africa and Asia who are based at basic health facilities and contain chapters of specific interest to health officials and administrators. It is vital that health officials ensure the right drugs and simple equipment are available in the correct quantities and that they can determine if their doctors are treating snakebite using the most effective methods”.

In order for doctors to be able to freely download the guidelines locally, the guidelines are available online at:

http://www.pmrc.org.pk/index_2.htm

This enables doctors to print out those sections specific to their area.

Dr Qureshi said, “These guidelines will also help to more efficiently use currently produced anti snake venom and enable useful epidemiology data to be gathered with consistent and rational processes. Recent snakebite mortality assessments for Pakistan have been heavily overstated and effective protocols such as this will enable more accurate reporting”.

Giant plankton-eating fishes roamed the prehistoric seas for over 100 million years before they were wiped out in the same event that killed off the dinosaurs, new fossil evidence has shown.

An international team describe how new fossils from Asia, Europe and the US reveal a previously unknown dynasty of giant plankton-eating bony fishes that filled the seas of the Jurassic and Cretaceous periods, between 66-172 million years ago.
The team report their findings in this week’s Science.

Illustration of Bonnericthys by Robert Nicholls

‘Today’s giant plankton-feeders – such as baleen whales, basking sharks and manta rays – include the largest living vertebrate animals, so the fact that creatures of this kind were missing from the fossil record for hundreds of millions of years was always a mystery,’ said Dr Matt Friedman of Oxford University’s Department of Earth Sciences, an author of the report.

‘We used to think that the seas were free of big filter feeders during the age of dinosaurs, but our discoveries reveal that a dynasty of giant fishes filled this ecological role in the ancient oceans for more than 100 million years.’

Diagram showing reconstruction of Bonnericthys and position of bones Several of the most important new fossils came from deposits in Kansas in the USA, with other remains from as far afield as Dorset and Kent in the UK, and Japan. Some members of this filter-feeding fish group are estimated to have been up to 9 metres long, a similar size to modern plankton-eating giants such as the basking shark.

‘One of the reasons these big fishes were overlooked or misidentified lies in their anatomy,’ said Dr Friedman. ‘Over their evolutionary history, these fishes reduced the amount of bone in their skeletons, probably to save weight, with the consequence that most of their hard parts were easily scattered after death. As it turns out, the only parts you routinely find in the fossil record are their well-developed forefins.’

With few clues to go on, palaeontologists had argued that the owner of these isolated fins looked something like the modern-day swordfish. This changed when some of Dr Friedman’s colleagues began cleaning a fossil that preserved skull bones along with the fins.

Dr Friedman said: ‘Instead of finding a head with a long sword-like snout and jaws lined with predatory fangs, they found something completely different: long, toothless jaws supporting a gaping mouth, and long, rod-like bones that contributed to the huge gill arches needed to filter out enormous quantities of tiny plankton.’ The team named this fish Bonnerichthys, honouring the Kansas family who discovered the fossil.

Remains of similar giant plankton-eating fishes had been known from much older rocks, but they were thought to be a short-lived and unsuccessful evolutionary experiment. ‘As soon as we recognised that these animals had a longer history than anyone thought, I started examining museum collections and found more examples that had been overlooked or misidentified,’ explained Dr Friedman. Revisiting previously collected fossils netted the team evidence that these fishes thrived for millions of years and colonised many parts of the globe.

Intriguingly the ancestors of large modern filter-feeders such as baleen whales and whale sharks only appeared after the extinction of Bonnerichthys and its relatives, suggesting that today’s filter-feeders evolved to fill the ecological niche left behind by these plankton-eating contemporaries of the dinosaurs.

he research team consisted of scientists from Oxford University (UK), DePaul University, Chicago (US), Fort Hays State University, Kansas (US), University of Kansas (US), University of Glasgow (UK), and Triebold Paleontology Inc & Rocky Mountain Dinosaur Resource Centre, Colorado (US).

A report of the research, entitled ‘100-Million-Year Dynasty of Giant Planktivorous Bony Fishes in the Mesozoic Seas’, is published in this week’s Science.

By Robert Sanders | 1 March 2010

BERKELEY —Atrazine, one of the world’s most widely used pesticides, wreaks havoc with the sex lives of adult male frogs, emasculating three-quarters of them and turning one in 10 into females, according to a new study by University of California, Berkeley, biologists.

Above: An atrazine-induced female frog (a genetic male) is shown (bottom) copulating with an unexposed male sibling. This union produced viable eggs and larvae that survived to metamorphosis and adulthood. Yet, because both animals were genetic males, the offspring were all males. (Tyrone Hayes photo)

The 75 percent that are chemically castrated are essentially “dead” because of their inability to reproduce in the wild, reports UC Berkeley’s Tyrone B. Hayes, professor of integrative biology.

“These male frogs are missing testosterone and all the things that testosterone controls, including sperm. So their fertility is as low as 10 percent in some cases, and that is only if we isolate those animals and pair them with females,” he said. “In an environment where they are competing with unexposed animals, they have zero chance of reproducing.”

The 10 percent or more that turn from males into females – something not known to occur under natural conditions in amphibians – can successfully mate with male frogs but, because these females are genetically male, all their offspring are male.

“When we grow these guys up, depending on the family, we will get anywhere from 10 to 50 percent females,” Hayes said. “In a population, the genetically male females can decrease or wipe out a population just because they skew sex ratios so badly.”

Though the experiments were performed on a common laboratory frog, the African clawed frog (Xenopus laevis), field studies indicate that atrazine, a potent endocrine disruptor, similarly affects frogs in the wild, and could possibly be one of the causes of amphibian declines around the globe, Hayes said.

Hayes and his UC Berkeley colleagues report their results in this week’s online early edition of the journal Proceedings of the National Academy of Sciences. In last week’s issue of the Journal of Experimental Biology, Hayes and colleagues published a review of the possible causes of a worldwide decline in amphibian populations, concluding that atrazine and other hormone-disrupting pollutants are a likely contributor because they affect recruitment of new individuals and make amphibians more susceptible to disease.

“These kinds of problems, like sex-reversing animals skewing sex ratios, are much more dangerous than any chemical that would kill off a population of frogs,” he said. “In exposed populations, it looks like there are frogs breeding but, in fact, the population is being very slowly degraded by the introduction of these altered animals.”

Some 80 million pounds of the herbicide atrazine are applied annually in the United States on corn and sorghum to control weeds and increase crop yield, but such widespread use also makes atrazine the most common pesticide contaminant of ground and surface water, according to various studies.

More and more research, however, is showing that atrazine interferes with endocrine hormones, such as estrogen and testosterone – in fish, amphibians, birds, reptiles, laboratory rodents and even human cell lines at levels of parts per billion. Recent studies also found a possible link between human birth defects and low birth weight and atrazine exposure in the womb.

As a result of these studies, the Environmental Protection Agency (EPA) is reviewing its regulations on use of the pesticide. Several states are considering banning atrazine, and six class action lawsuits have been filed seeking to eliminate its use. The European Union already bars the use of atrazine.

Hayes’s studies in the early 2000s were the first to show that the hormonal effects of atrazine disrupt sexual development in amphibians. Working with the African clawed frog, Hayes and his colleagues showed in 2002 that tadpoles raised in atrazine-contaminated water become hermaphrodites – they develop both female (ovaries) and male (testes) gonads. This occurred at atrazine levels as low as 0.1 parts per billion (ppb), 30 times lower than levels allowed in drinking water by the EPA (3 ppb).

Subsequent studies showed that native leopard frogs (Rana pipiens) collected from atrazine-contaminated streams in the Midwest, including from areas up to 1,000 miles from where atrazine is applied, often had eggs in their testes. And many males had lower testosterone levels than normal females and smaller than normal voice boxes, presumably limiting their ability to call mates.

Hayes’ research also established that many frogs in Midwestern streams contaminated by atrazine and other pesticides have compromised immune systems, leading to increased mortality from bacterial disease.

Those early studies were hampered by the inability to easily distinguish genetically male from genetically female frogs. Male frogs have two identical sex chromosomes (ZZ) while females have both a Z and a W – the opposite of XX female and XY male humans. But because all frog chromosomes look the same under a light microscope, it’s not simple to distinguish male from female.

To overcome this, Hayes’ colleague Roger Liu developed a line of all-male frogs so that the genetics would be unequivocal.

“Before, we knew we got fewer males than we should have, and we got hermaphrodites. Now, we have clearly shown that many of these animals are sex-reversed males,” Hayes said. “We have animals that are females, in the sense that they behave like females: They have estrogen, lay eggs, they mate with other males. Atrazine has caused a hormonal imbalance that has made them develop into the wrong sex, in terms of their genetic constitution.”

Coincidentally, another lab in 2008 discovered a sex-linked genetic marker in Xenopus, which has allowed Hayes to confirm the genetic sex of his frogs.

In Hayes’ study, where 40 frogs lived for about three years after hatching in water with 2.5 ppb atrazine, about 10 percent of the frogs appeared to be resistant to the effects of the pesticide. In ongoing studies, Hayes is investigating whether this apparent resistance is inherited, as well as whether the sex-reversed males have more susceptible offspring.

Syngenta, which manufactures atrazine, disputes many of these studies, including Hayes’, that show adverse effects of the pesticide. But Hayes said that “when you have studies all over the world showing problems with atrazine in every vertebrate that has been looked at – fish, frogs, reptiles, birds, mammals – all of them can’t be wrong.”

“What people have to realize is that, just as with taking pharmaceuticals, they have to decide whether the benefits outweigh the costs,” he said. “Not every frog or every human will be affected by atrazine, but do you want to take a chance, what with all the other things that we know atrazine does, not just to humans but to rodents and frogs and fish?”

Hayes’ long-term studies of the effects of atrazine on frogs have been assisted by many UC Berkeley students, including co-authors on the current paper: undergraduates Vicky Khoury, Anne Narayan, Mariam Nazir, Andrew Park, Lillian Adame and Elton Chan; and graduate students Travis Brown, Daniel Buchholz, Sherrie Gallipeau and Theresa Stueve.

The work was funded by the Park Water Co., Mitch Kapor, Freada Klein, the Mitch Kapor Foundation, the David Foundation, the Cornell-Douglas Foundation, the Wallace Foundation, the UC Berkeley Class of ‘43 endowed chair and the Howard Hughes Biology Fellows Program.