Choosing a healthy mate: listen, do you smell something? (#217)
Choosing a sick partner can lead to infection, or reduced benefits provided by the partner due to its inferior health. In sexually reproducing species honest signaling of health is important for female choice of a mating partner, and avoidance of parasitized or sick conspecifics has been described. Animals use different channels of communication to gain information about potential partners and this is especially critical for mate choice. Not all signals, however, may be honest since males from a number of different species are able to overcome behavioural symptoms of infection when mating opportunities are available. Here, we studied the consequences of experimental manipulation of sickness on two signals that function in female mate choice and attraction in house mice (M. musculus domesticus): ultrasonic vocalization (USV) and a urinary protein (Darcin). We manipulated sickness status by administering lipopolysaccharide (LPS) injections, and recorded the behaviours and vocalizations of brother pairs receiving opposite injections (Control or LPS) when simultaneously exposed to a female overnight. We assessed Darcin and testosterone levels of these males, as well as female visits to each male. Males decreased the number of ultrasonic syllables and the expression of Darcin after injection of LPS. We conclude that male mice cannot maintain the production of sexually attractive signals while responding to an infection and thus are not able to conceal symptoms of sickness when presented with an opportunity to mate. Females in estrus might use these cues when making mating decisions, since they prefer to spend more time near Control-injected males. Testosterone was reduced in LPS-injected males and could be a unifying mechanism down-regulating both of the traits quantified, since it is known that both traits are under androgenic influence. Darcin and USVs produced in the context of courtship may function as an honest signal of health.