Variation in male courtship effort, with males ( N = 39) ordered according to their body size. The two vertically attached symbols represent courtship effort towards the two stimulus females within a single focal male's 'experimental unit'. The larger of the two females is indicated with a larger symbol and the smaller female with a smaller symbol. The two males within each unit (i.e. the two males that courted the same pair of females) are identified by a shared combination of symbol colour and type.