Direct selection for a single preference; two preference, two trait model. This figure shows the strength of direct selection against a single female preference (ap1,0) as male trait frequency increases. Each line represents selection against P1 for a different combination of preference frequencies (P1 and P2) and cost (γ) as male trait frequencies (T1 and T2) increase. The solid black line indicates P1=.95, P2=.01, γ=.01; solid gray indicates P1=.95, P2=.01, γ=.1; dashed black indicates P1=.01, P2=.01, γ=.01; dashed grey indicates P1=.01, P2=.01, γ=.1; dot-dashed black indicates P1=.95, P2=.95, γ=.01; and dot-dashed grey indicates P1=.95, P2=.95, γ=.1. For all simulations, α=5; changing preference strength did not change the shape of the cost curve, but only scaled up the strength of selection against preference. Regardless of the parameters, direct selection on P1 is always negative, except when male traits are absent. All the cost curves turn downwards as male trait frequency increases—this is due to selection for multiple preferences (P1P2 together) when male trait frequencies are sufficiently high; the curves displayed are for a single preference (P1).