Context-specific behavioural changes induced by exposure to an androgenic endocrine disruptor

Pharmaceutical contaminants arc being detected with increased frequency in organisms and ecosystems worldwide. This represents a major environmental concern given that various pharmaceuticals act on drug targets that arc evolutionarily conserved across diverse taxa, arc often persistent in the environment, and can bioconcentrate in organisms and bioaccumulate in food chains. Despite this, relatively little is known about the potential for pharmaceutical contaminants to affect animal behaviour, especially across multiple fitness-related contexts. Here, we investigated impacts of 21-day exposure of wild-caught male eastern mosquitofish (Gambusia holbrooki) to a field-realistic level of the veterinary pharmaceutical 17 beta-trenbolone-a growth-promoting steroid used extensively in beef production worldwide and a potent androgenic endocrine disruptor repeatedly detected in surface waters affected by livestock effluent run-off First, we examined male boldness, activity, and exploratory behaviour in a novel environment (maze arena) and found no significant effect of 17 beta-trenbolone exposure. Second, the same males were tested in a reproductive assay for their tendency to associate with a stimulus (unexposed) female behind a partition. Exposed males exhibited reduced association behaviour, taking longer to first associate with, and spending less time within close proximity to, a female. Third, all males were assayed fur sperm function (computer-assisted sperm analysis, sperm viability) or quantity (total sperm count) and, although no significant main effects of 17 beta-trenbolone were seen on sperm trails, exposure altered the relationship between male morphology and sperm function. Lastly, morphological traits were assessed and exposed males were found to have, on average, increased mass relative to length. In combination, these results demonstrate that exposure to a field-realistic level of 17 beta-trenbolone can produce subtle but important trait alterations in male fish including context-specific behavioural changes, disruption of key sperm function trade-offs, and altered morphology with potential impacts on exposed wildlife.