Male calling song provides a reliable signal of immune function in a cricket

A critical prediction of the immunocompetence handicap hypothesis is that t he expression of secondary sexual traits should be positively correlated wi th pathogen resistance ability. This correlation is necessary if females ar e to be able to use a particular sexual trait as an indicator of a male's r esistance ability. In this study we document a positive correlation between a sexually selected component of the calling song of male house crickets ( the number of syllables per chirp) and haemocyte load, an important determi nant of the ability to encapsulate pathogens in insects. The results indica te that, by favouring males which produce more syllables per chirp, females may also select males with higher pathogen resistance ability, potentially generating either direct or indirect selection on female mating preference s.