Fig. 1.

Head lengths (in mm) of successfully mated partners (mothers and fathers of the seahorse broods). The regression is significant (n = 22, r = 0.56, P = 0.007), indicating positive size-assortative mating. Head length is reported here because its measurement is precise and repeatable. Nonetheless, head length is highly correlated with total body length (regression: n = 44, r = 0.90, P < 0.001), which also yielded similar evidence of assortative mating (regression: n = 22, r = 0.47, P = 0.03).