Many vertebrate males display androgen-regulated mating signals that are intensified by increased testosterone. Males displaying better signals are preferred by females, have greater mating opportunities, are dominant over other males, and have better fertilization success. This study has focused on the effects of anthropogenic contaminants on male ornaments and courtship behaviors. Sex hormones are important for the maintenance of mating signals. Several endocrine disrupting contaminants (EDCs) alter sex hormone levels. Atrazine, a widely used herbicide EDC, increases estrogen and decreases testosterone in exposed individuals. Effects of atrazine on mating behaviors and signals in vertebrates are less well established.
Guppies were used as a model organism to test the effects of atrazine exposure on ornaments (orange color spots) and mating behaviors. Adult male guppies were exposed to two levels of atrazine (1 μg/L and 10 μg/L) for six weeks. Estradiol and flutamide were used as estrogenic and anti-androgenic controls. Area and intensity of orange color spots were measured before and after atrazine exposure. Reproductive behaviors – persistence for mating, display rates, aggression towards competing males – were measured, by pairing males with non-experimental males and scoring their behavior towards females as well as each other.
Atrazine exposure reduced intensity and area of orange color spots, as did estradiol and flutamide. Atrazine exposed males were less persistent for matings than control males, displayed less and were less aggressive to the paired male. Estradiol-exposed males responded similarly to atrazine-exposed males, indicating that atrazine behaves as a xenoestrogen. The levels of atrazine used in the study were less than those deemed safe by the EPA, and about ten-fold less than those found in water bodies in and around agricultural areas. Because atrazine, like many EDCs, can persist in sediments and soil for years and enter water bodies through runoff periodically, many aquatic species can be exposed to atrazine across generations. Bioccumulation can expose non-aquatic species as well. Disruption of mating signals and behaviors can alter population dynamics catastrophically by altering reproduction. This study contributes to our understanding of sub-lethal effects of EDC-exposure on reproductive health and wildlife populations.