Navigation Links
Pesticide atrazine can turn male frogs into females
Date:3/1/2010

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.

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 they 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. Last week, Hayes and colleagues published a review of pesticide's effects on amphibians in the Journal of Experimental Biology, concluding that atrazine is a likely contributor to worldwide amphibian declines.

"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 presticide. 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?"


'/>"/>

Contact: Robert Sanders
rsanders@berkeley.edu
510-643-6998
University of California - Berkeley
Source:Eurekalert

Related biology news :

1. Storm runoff and sewage treatment outflow contaminated with household pesticides
2. A deadly scorpion provides a safe pesticide
3. Even at sublethal levels, pesticides may slow the recovery of wild salmon populations
4. Getting plants to rid themselves of pesticide residues
5. Pesticides -- easier detection of pollution and impact in rivers
6. Pitt research suggests EPA pesticide exposure test too short, overlooks long term effects
7. Natural seed treatment could drastically cut pesticide use
8. Parasite-resistant peppers green alternatives to chemical pesticides
9. Pitt research finds that low concentrations of pesticides can become toxic mixture
10. Pesticide concentrations decreasing
11. Pesticide build-up could lead to poor honey bee health
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:3/23/2016)... March 23, 2016 ... Sicherheit Gesichts- und Stimmerkennung mit Passwörtern ... (NASDAQ: MESG ), ein führender Anbieter ... Unternehmen mit SpeechPro zusammenarbeitet, um erstmals dessen ... wird die Möglichkeit angeboten, im Rahmen mobiler ...
(Date:3/18/2016)... March 18, 2016 --> ... Biometrics, ICT, Manned & Unmanned Vehicles, Physical infrastructure and Perimeter ... companies in the border security market and the continuing migration ... Europe has led visiongain to publish ... success. --> defence & security companies in ...
(Date:3/14/2016)... NXTD ) ("NXT-ID" or the "Company"), ... the airing of a new series of commercials on Time ... 21 st .  The commercials will air on Bloomberg TV, ... the Street show. --> NXTD ) ("NXT-ID" or ... market, announces the airing of a new series of commercials ...
Breaking Biology News(10 mins):
(Date:5/24/2016)... AVIV, Israel , May 24, 2016   MedyMatch ... providing physicians with artificial intelligence, real-time decision support tools in ... to present at the 2016 Israeli Advanced Technology Industries (IATI) ... of Israel,s 15th National Life Sciences ... 26th at the David Intercontinental Hotel in Tel ...
(Date:5/24/2016)... ... May 24, 2016 , ... Media ... The new Media Cybernetics corporate branding reflects a results-driven revitalization for a company ... analysis. The re-branding components include a crisp, refreshed logo and a new web ...
(Date:5/23/2016)... Ohio (PRWEB) , ... May 23, 2016 , ... ... Trends That Will Drive Precision Farming in 2017 and Beyond. The paper outlines ... practitioners in the precision ag industry. , “We’ve witnessed a lot of highs ...
(Date:5/23/2016)... OXFORD, England , May 23, 2016 ... Wednesday, May 25 th at 10:15 a.m. ET before ... about the role genetically engineered mosquitos can play in controlling ... known carrier of the Zika virus.      (Logo: ... genetically engineered male mosquito with a self-limiting gene. Trials in ...
Breaking Biology Technology: