TDK conference 2017

Contaminants that get into natural water bodies in agricultural and urban areas can cause lethal and sublethal effects in wild animals. They can decrease the fertility of the individuals and they can induce changes that make the offspring more resistant to the harmful effects of the contaminants. We captured common toads at the beginning of the mating season from natural, urban, and agricultural areas to investigate these effects. Examination of eggs laid in the laboratory showed that the mass of the clutch and the fertilisation and hatching success did not differ significantly among the pairs collected from the three habitat types. Females from the contaminated areas, however, produced large clutch mass even when the eggs’ mass was smaller. This implies that these females produce larger jelly coat around the eggs, which can provide protection against contaminants. However, this protection might be costly, since the pairs originating from contaminated areas produced smaller tadpoles than did pairs originating from natural habitats. In order to examine resistance, we raised one part of each clutch in clear water, the other part in contaminated water. Urban contamination was simulated by an artificial oestrogen derivative; agricultural contamination by a glyphosate based pesticide. We found that the hormone derivative slightly decreased hatching success in the case of offspring coming from natural habitats, but it increased hatching success in the case of offspring from urban habitats. The pesticide significantly decreased hatching success in families from natural habitats and slightly in families from urban habitats, and had no effect on families from agricultural habitats. These effects were relatively small. The growth and survival of the hatched tadpoles was significantly decreased by the pesticide, regardless of the habitat type of the parents. These results are in accord with the hypothesis that populations living in contaminated habitats can become more resistant to the harmful effects of contaminants if these effects are not too strong.