Showing posts with label frogs. Show all posts
Showing posts with label frogs. Show all posts

Monday, November 28, 2011

Atrazine, Gender & Frogs

Above: Both of these African clawed frogs are genetically male, but lifelong exposure to the herbicide atrazine transformed the frog on the bottom to female. The frog reproduced with normal males twice. Photo Credit: Tyrone B. Hayes.

The following is a press release from the University of Illinois at Champaign.

CHAMPAIGN, lll. — An international team of researchers has reviewed the evidence linking exposure to atrazine – an herbicide widely used in the U.S. and more than 60 other nations – to reproductive problems in animals. The team found consistent patterns of reproductive dysfunction in amphibians, fish, reptiles and mammals exposed to the chemical.

Atrazine is the second-most widely used herbicide in the U.S. More than 75 million pounds of it are applied to corn and other crops, and it is the most commonly detected pesticide contaminant of groundwater, surface water and rain in the U.S.

The new review, compiled by 22 scientists studying atrazine in North and South America, Europe and Japan, appears in the Journal of Steroid Biochemistry and Molecular Biology.

The researchers looked at studies linking atrazine exposure to abnormal androgen (male hormone) levels in fish, amphibians, reptiles and mammals and studies that found a common association between exposure to the herbicide and the “feminization” of male gonads in many animals.

The most robust findings are in amphibians, said University of Illinois comparative biosciences professor Val Beasley, a co-author of the review. At least 10 studies found that exposure to atrazine feminizes male frogs, sometimes to the point of sex reversal, he said.

Beasley’s lab was one of the first to find that male frogs exposed to atrazine in the wild were more likely to have both male and female gonadal tissue than frogs living in an atrazine-free environment. And in a 2010 study, Tyrone Hayes, a professor of integrative biology at the University of California at Berkeley and lead author of the review, reported in the Proceedings of the National Academy of Sciences that atrazine exposure in frogs was associated with “genetic males becoming females and functioning as females,” Beasley said.

“And this is not at extremely high concentrations,” he said. “These are at concentrations that are found in the environment.”

The new review describes the disruptions of hormone function and sexual development reported in studies of mammals, frogs, fish, reptiles and human cells exposed to the herbicide. The studies found that atrazine exposure can change the expression of genes involved in hormone signaling, interfere with metamorphosis, inhibit key enzymes that control estrogen and androgen production, skew the sex ratio of wild and laboratory animals (toward female) and otherwise disrupt the normal reproductive development and functioning of males and females.

“One of the things that became clear in writing this paper is that atrazine works through a number of different mechanisms,” Hayes said. “It’s been shown that it increases production of (the stress hormone) cortisol. It’s been shown that it inhibits key enzymes in steroid hormone production while increasing others. It’s been shown that it somehow prevents androgen from binding to its receptor.”

The review also consolidates the evidence that atrazine undermines immune function in a variety of animals, in part by increasing cortisol.

“Cortisol is a nonspecific response to chronic stress,” Beasley said. “But guess what? Wildlife in many of today’s habitats are stressed a great deal of the time. They’re stressed because they’re crowded into little remnant habitats. They’re stressed because there’s not enough oxygen in the water because there are not enough plants in the water (another consequence of herbicide use). They’re stressed because of other contaminants in the water. And the long-term release of cortisol causes them to be immuno-suppressed.”

There also are studies that show no effects – or different effects – in animals exposed to atrazine, Beasley said. “But the studies are not all the same. There are different species, different times of exposure, different stages of development and different strains within a species.” All in all, he said, the evidence that atrazine harms animals, particularly amphibians and other creatures that encounter it in the water, is compelling.

“I hope this will stimulate policymakers to look at the totality of the data and ask very broad questions,” Hayes said. “Do we want this stuff in our environment? Do we want – knowing what we know – our children to drink this stuff? I would think the answer would be no.”

Citation
Tyrone B. Hayes, Lloyd L. Anderson, Val R. Beasley, Shane R. de Solla, Taisen Iguchi, Holly Ingraham, Patrick Kestemont, Jasna Kniewald, Zlatko Kniewald, Valerie S. Langlois, Enrique H. Luque, Krista A. McCoy, Mónica Muñoz-de-Toro, Tomohiro Oka, Cleida A. Oliveira, Frances Orton, Sylvia Ruby, Miyuki Suzawa, Luz E. Tavera-Mendoza, Vance L. Trudeau, Anna Bolivar Victor-Costa, Emily Willingham. Demasculinization and feminization of male gonads by atrazine: Consistent effects across vertebrate classes. The Journal of Steroid Biochemistry and Molecular Biology, 2011; 127 (1-2): 64 DOI: 10.1016/j.jsbmb.2011.03.015

Wednesday, August 31, 2011

Okinawa Montane Viper Feeds During the Winter

Ovophis okinavensis. Photo Credit: 
Al Coritez.
The Okinawa Montane Viper, Ovophis okinavensis is a short, stout-bodied snake that inhabits forested areas, especially near streams, ponds, and marshes, in the subtropical Okinawa and Amami island groups in the Ryukyu Archipelago of Japan. The species is primarily terrestrial and nocturnal and is considered a typical ambush predator. Its diet consists of frogs, lizards, snakes, birds, and small mammals. Although this viper exhibits a generalized diet; however, the diet of some local populations is almost exclusively frogs. Previous ecological studies of O. okinavensis in the northern mountains of Okinawa Island suggested the species is most active from winter to early spring (December to March). And, those studies suggest that the activity pattern of the snake is closely associated with the breeding activities of frogs. Most snakes are active during the warmer parts of the year because they are ectotherms and rely on external heat  to maintain their body temperatures. Ovophis okinavensis is apparently an exception to this pattern. This unusual activity pattern may reflect the availability of prey, which obliges the snake to engage in feeding activities during periods of low temperatures. To test this hypothesis Kadota (2011) examined seasonal activity patterns of both O. okinavensis and the frogs in the study area. He found snake emergence corresponded with the emergence of frogs. The daily emergence of snakes was strongly correlated with that of frogs. These results suggest that O. okinavensis exhibits a foraging strategy that is adjusted to spatial and temporal fluctuations of the emergence of frogs. It would also be interesting to examine the impact of climate change on the behavior of this snake.

Citation: Kadota, Y. 2011. Is Ovophis okinavensis Active Only in the Cool Season? Temporal Foraging Pattern of a Subtropical Pit Viper in Okinawa, Japan.  Zoological Studies 50:269-275.

Monday, August 29, 2011

Daphnia Feed on Bd: Can this Save Frog Species From Extinction?

Researchers have confirmed that this
zooplankton, Daphni magna, will eat
a deadly fungus that is devastating
amphibian populations around the world.
 It may provide a new biocontrol agent
to help address this crisis. (Photo
Credit:Oregon State University)
Zoologists at Oregon State University have discovered that a freshwater species of zooplankton will eat a fungal pathogen which is devastating amphibian populations around the world.

This tiny zooplankton, called Daphnia magna, could provide a desperately needed tool for biological control of this deadly fungus, the scientists said, if field studies confirm its efficacy in a natural setting.

The fungus, B. dendrobatidis, is referred to as a "chytrid" fungus, and when it reaches high levels can disrupt electrolyte balance and lead to death from cardiac arrest in its amphibian hosts. One researcher has called its impact on amphibians "the most spectacular loss of vertebrate biodiversity due to disease in recorded history."

The research, reported August 26 in the journal Biodiversity and Conservation, was supported by the National Science Foundation.

"There was evidence that zooplankton would eat some other types of fungi, so we wanted to find out if Daphnia would consume the chytrid fungus," said Julia Buck, an OSU doctoral student in zoology and lead author on the study. "Our laboratory experiments and DNA analysis confirmed that it would eat the zoospore, the free-swimming stage of the fungus."

"We feel that biological control offers the best chance to control this fungal disease, and now we have a good candidate for that," she said. "Efforts to eradicate this disease have been unsuccessful, but so far no one has attempted biocontrol of the chytrid fungus. That may be the way to go."

The chytrid fungus, which was only identified in 1998, is not always deadly at low levels of infestation, Buck said. It may not be necessary to completely eliminate it, but rather just reduce its density in order to prevent mortality. Biological controls can work well in that type of situation.

Amphibians have been one of the great survival stories in Earth's history, evolving about 400 million years ago and surviving to the present while many other life forms came and went, including the dinosaurs. But in recent decades the global decline of amphibians has reached crisis proportions, almost certainly from multiple causes that include habitat destruction, pollution, increases in ultraviolet light due to ozone depletion, invasive species and other issues.

High on the list, however, is the chytrid fungus that has been documented to be destroying amphibians around the world, through a disease called chytridiomycosis.

Its impact has been severe and defied various attempts to control it, even including use of fungicides on individual amphibians. Chytridiomycosis has been responsible for "unprecedented population declines and extinctions globally," the researchers said in their report.

"About one third of the amphibians in the world are now threatened and many have gone extinct," said Andrew Blaustein, a professor of zoology, co-author on this study and an international leader in the study of amphibian decline.

"It's clear there are multiple threats to amphibians, but disease seems to be a dominant cause," he said.

Although they have survived for hundreds of millions of years, amphibians may be especially vulnerable to rapid environmental changes and new challenges that are both natural and human-caused. They have a permeable skin, and exposure to both terrestrial and aquatic environments.

Because of this, OSU researchers said, other animals such as mammals, birds and fish have so far not experienced such dramatic population declines

Original Citation
Julia C. Buck, Lisa Truong, Andrew R. Blaustein. Predation by zooplankton on Batrachochytrium dendrobatidis: biological control of the deadly amphibian chytrid fungus? Biodiversity and Conservation, 2011; DOI: 10.1007/s10531-011-0147-4