Female swordtail fish use chemical cues to select well-fed mates

Selection favours females that attend to reliable information about male health or genetic quality. Male nutritional state can be an important indicator of mate quality since poor nutrition can be related to reduced sperm quality, low sperm quantity and sexually transmitted diseases. Here we show that female swordtail fish, Xiphophorus birchmanni, preferred the chemical cues of males that were well fed over those that had been food deprived. However, focal females did not discriminate among the odour of other females with respect to nutritional state, suggesting that they were responding to a sex-specific chemical cue, not simply to food excretions. It is therefore likely that nutritional condition is related to the production of sexual pheromones in males. Our results suggest that chemical cues convey information about male nutritional state, and that females attend to these cues during mate choice. By doing so, females are able to discriminate among males that may differ in important aspects of quality.