Pesticide makes frogman female

Weed killers cause chemical castration and endanger wild amphibians

Clawed Frog Xenopus laevis © Peter Halasz / GFDL
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Atrazine, one of the world's most common herbicides, completely turns the endocrine system of male frogs on its head. Three quarters became infertile, and every tenth male became female. These frightening results, now published in "Proceedings of the National Academy of Sciences" (PNAS), confirm previous studies and suggest that atrazine plays a disreputable role in the decline of amphibians worldwide.

The herbicide Atrazine has been one of the standard remedies for many years, especially in maize or potato crops. Today, more than 36 million kilograms of the photosynthesis blocker are used in the US alone every year. In the EU, however, the pesticide has been banned since the early 1990s. Already at that time there were increasing indications that even the smallest amounts of atrazine confused the hormonal balance of many animals, including fish, amphibians, but also birds and mammals. Recent studies also found associations with birth defects in human infants.

However, despite this, the pesticide is still used in many countries, and even where it is now banned, large amounts of it are still found in groundwater and soil in the environment. Now researchers at the University of California at Berkeley have once again carried out experiments with frogs, which for the first time provide quantitative data on the sex-altering effect of atrazine. So far, the sex determination of frogs was relatively difficult and the statements therefore only qualitatively possible.

Chemical castration by atrazine

The researchers led by Roger Liu and Tyrone B. Hayes, a professor of biology at the University of California at Berkeley, developed a strain of pure male African Clawed Frogs (Xenopus laevis) for their experiments. These were soaked in water that added with the minute amount of atrazine of 2.5 parts per billion - particles per billion of water particles. Then they watched the further development of the frogs for three years.

It turned out that three quarters of the frogs did not develop normal masculine behaviors and were physiologically more hybrids than clearly male. "These male frogs lack testosterone and everything that is controlled by testosterone, including sperm, " explains Hayes. "Their fertility is correspondingly low, only ten percent in some cases - and only if we isolate these animals and put them together with females. In an environment where they compete with healthy animals, their chance of reproduction is zero

Ten percent "pseudo kiddie"

One-tenth of the animals even completely change their gender and become female: They behave in almost every way like females: They have estrogen, lay eggs and mate with other males. The atrazine has caused a hormonal imbalance that allows them to develop into the wrong sex in terms of their genetic constitution

These ten percent "pseudo-calves" can even mate successfully with male nibbles. However, because they are genetically male, the offspring consists only of males. "If we let those guys grow up, we'll get 10 to even 50 percent more pseudo-boobs, " Hayes says. In the course of time, this does not immediately lead to the extinction of the population, because even more offspring is produced. In the long run, however, such a drastic shift in the gender ratio will endanger the survival of the species.

Although the experiments on claw research have been carried out, field studies indicate that atrazine also affects similarly native Fries in temperate latitudes. According to Hayes and his colleagues, the pesticide could therefore be one of the contributing factors to the species extinction of amphibians around the globe.

These issues, such as sex reversal and thus shifted gender relationships, are more dangerous than any chemical that immediately kills a population of frogs, "says Hayes. "In affected populations, it looks at first sight as if the frogs are reproducing normally, but in fact the population is gradually degrading by the multiplication of these altered animals."

The pesticide manufacturing company Syngenta has already responded to the study and denies the results. Hayes replies: "If you have studies from around the world that show problems with atrazine in any vertebrate studied fish, frogs, reptiles, birds and suckers then k Not all of them can be wrong. We have to realize that, as with many medications, we have to decide whether the effects justify the side effects

(University of California Berkeley, 02.03.2010 - NPO)