Differential effect of polyandry on male sexual selection. (A) Opportunity for pre- (IM) and postcopulatory (IP) sexual selection in relation to average group polyandry. IM significantly decreased with polyandry (slope = −1.16 ± 0.26, t = −4.40, R2 = 0.60, df = 11, P = 0.001) but not IP (slope = −0.53 ± 0.39, t = −1.32, R2 = 0.06, df = 10, P = 0.218). A qualitatively similar pattern was obtained using alternative measures of IM and IP (38): IM (t = −4.40, R2 = 0.60, df = 11, P = 0.001); IP (t = −0.14, R2 = −0.09, df = 11, P = 0.892). (B) Multivariate gradients of pre- (βM) and postcopulatory (βP) sexual selection in relation to average group polyandry. βM significantly decreased with polyandry (slope = −1.32 ± 0.56, t = −2.42, R2 = 0.31, df = 10, P = 0.036), but this trend was much weaker for βP (slope = −0.66 ± 0.35, t = −1.90, R2 = −0.25, df = 7, P = 0.099). A qualitatively similar pattern was obtained using univariate measures of βM and βP based on ref. 38: βM (t = −6.30, R2 = 0.78, df = 10, P < 0.001); βP (t = −3.16, R2 = 0.45, df = 10, P = 0.010). (C) The opportunity for total sexual selection (IT) significantly decreased with group polyandry (−1.35 ± 0.26, t = −5.19, R2 = 0.68, df = 11, P < 0.001). (D) In more polyandrous groups, the proportion of the variance in total male reproductive success explained by male mating success tended to decline (solid line, t = −2.06, df = 11, P = 0.064), and simultaneously the proportion of male reproductive success explained by paternity share increased (shaded line, t = 1.50, df = 10, P = 0.019). Data points represent individual replicate groups.