Personality, sperm traits and a test for their combined dependence on male condition in guppies

There is evidence that animal personality traits can have spill-over effects for sexual selection, with studies reporting that male behavioural types are associated with success during pre- and post-copulatory sexual selection. Given these links between personality and sexual traits, and the evidence that their expression can depend on an individual's nutritional status (i.e. condition), a novel prediction is that changes in a male's diet should alter both the average expression of personality and sexual traits, and their covariance. We tested these predictions using the guppy Poecilia reticulata, a species previously shown to exhibit strong condition dependence in ejaculate traits and a positive correlation between sperm production and individual variation in boldness. Contrary to expectation, we found that dietary restriction – when administered in mature adult males – did not affect the expression of either behavioural (boldness and activity) or ejaculate traits, although we did find that males subjected to dietary stress exhibited a positive association between sperm velocity and boldness that was not apparent in the unrestricted diet group. This latter finding points to possible context-dependent patterns of covariance between sexually selected and personality traits, which may have implications for patterns of selection and evolutionary processes under fluctuating environmental conditions.