Exposure to 17α-ethinyl estradiol impairs courtship and aggressive behaviour of male sand gobies (Pomatoschistus minutus)

Endocrine disrupting chemicals (EDCs), natural or manmade, are known to interfere with the endocrinology of organisms and also cause behavioural changes. The aim of this study was to test how 1-4 weeks exposure to 17 alpha-ethinyl estradiol (EE2, 11 ng L-1) affects nest building, courtship and aggressive behaviour of male fish. Our study species, the sand goby (Pomatoschistus minutus) exhibits a polygynous mating system, in which males compete for females and defend their nest against intruders. Nest takeovers are common in their nest-constrained habitat. In our experiment, control and EE2-exposed males were first allowed to build a nest and mate with non-exposed females. When the males had received eggs in their nest, three rival males were introduced into the test aquarium, and the males were left to compete for the nest site overnight. Courtship and aggressive defence behaviour were recorded using a video camera. In addition to behavioural endpoints we measured the expression of hepatic vitellogenin (Vtg) and zona radiata protein (Zrp) mRNA, and several common somatic indices. Our study showed that exposure to EE2 delays nest building and decreases male courtship and leading behaviour. Additionally, EE2-exposed males were significantly less aggressive than control males. Nest takeover rate was not affected by EE2 exposure: an equal percent of males in both treatments lost their nest to competitors. EE2 exposure also induced Vtg and Zrp mRNA expression in males and decreased the hepatosomatic index. The observed changes in nest building, courtship and aggressive behaviour of EE2-exposed males are likely to have negative implications for male reproductive success.