The effects of the endocrine disruptor linuron on frogs are not limited to those exposed, but are passed on to their offspring and grand-offspring as well, shows a new study by researchers at the Department of Environmental Science and their colleagues from Uppsala University. First generation offspring had reduced body weight and decreased fertility, while second generation offspring had increased body weight and disrupted metabolism. The study was published in the journal Science of the Total Environment.
“This is the first time anyone has been able to demonstrate that pesticides can cause effects that are passed on to several generations of frogs. This knowledge is important for understanding the environmental impact of endocrine disrupting chemicals, which is, in turn, necessary for maintaining biodiversity,” says Oskar Karlsson, Associate Professor at the Department of Department of Environmental Science who studies epigenetic changes over generations, with a special focus on paternal contribution.
Almost half of all species of amphibians, of which frogs make up a significant part, are threatened by extinction, with environmental toxins being a contributory factor. For example, it has been shown that endocrine disrupting pesticides such as linuron, which is often used to control the growth of grass and weeds in crops such as soybeans, causes damage to the reproductive capacity of amphibians. The extent of this damage and whether it can be passed down to subsequent generations is, as yet, not fully understood.
Multigenerational effects of linuron on frogs
The study compared the offspring of males of the western clawed frog (Xenopus tropicalis) that had been exposed to linuron as tadpoles to the offspring of a control group that had not been exposed to linuron. The team found that the first generation offspring had reduced body weight, decreased fertility and signs of endocrine system disruption when compared to the control group. Moreover, the second generation – i.e. the grand-offspring of the exposed frogs – had increased body weight and disruption of fat- and carbohydrate metabolism when compared to the control group.
“The likely explanation is that the pesticide inhibits the function of testosterone and thyroid hormones in the body and that these changes are then passed on to future generations via sperm and epigenetic mechanisms. This leads to hereditary changes in gene regulation in the offspring,” explains Cecilia Berg, Associate Professor at Uppsala University and co-author of the study. By using the western clawed frog as a model organism, Berg’s research group has developed a test system for studying how chemicals affect the reproductive system.
“The results show that animals exposed to the effects of environmental contaminants may pass on these effects to future generations, which implies their complex role in species extinction, especially frogs,” says Oskar Karlsson.