Realistic nitrate concentration alters the expression of sexual traits and olfactory male attractiveness in newts

Abstract

The occurrence of endocrine disruption is increasing and may now affect most, if not all, ecosystems. Owing to its impact on survival and reproduction, it is increasingly important to consider this factor in ecological studies. The study of secondary sexual traits is of particular interest because they are under strong hormonal control and play a crucial role in mating. A neglected sub-lethal effect of endocrine disruption is the reduction of male attractiveness, and the distortion of the sexual selection process.2. Nitrate is one of the most widespread endocrine disruptors because of its extensive use in agriculture. Studies, especially in amphibians, have mostly focused on early developmental stages, probably because these were considered critical for population dynamics. However, negative effects on adult survival or reproductive success may also affect population demography.3. We surveyed nitrate concentration in a large sample of ponds. We then exposed male palmate newts, Triturus helveticus, to high (75 mg L-1) but realistic concentration of sodium nitrate to investigate the effect of nitrate on the expression of secondary sexual traits and male attractiveness.4. Exposure to nitrate for 3 weeks was found to limit the expression of sexual traits and to reduce body growth; exposure for 10 days reduced male attractiveness. Female preferred males unexposed to nitrate in olfactory tests but not in visual tests.5. The expression of secondary sexual characteristics and body size is reduced in males exposed to realistic nitrate concentration. However, a drop in male attractiveness may first be caused by disruption of the production of olfactory cues. Depending on the frequency of contaminated breeding sites, the disruption of male ability to express sexual signals might affect the sexual selection process in palmate newts and eventually reduce population reproductive output. We discuss the ecological and evolutionary implications of this result. © 2009 British Ecological Society.