Sex role reversal in a pipefish: female ornaments as amplifying handicaps

The reasons for sex role reversal in the pipefish Syngnathus typhle are rev iewed. In this species, females compete for males, which are choosier than females. Before mating, females display a sexual ornament, a cross-wise str iped pattern along their body sides. This ornament is here shown to be an a mplifier that facilitates for males to tell females of different sizes apar t (males prefer larger females). When students were asked to compare bar si zes, where bars differed in "ornamentation", accuracy in estimating size wa s highest with "heavy ornamented" as compared with "intermediate" or "not o rnamented" bars. Moreover, bar size was more accurately judged with crosswi se than with lengthwise striped bars, explaining why stripes run cross- rat her than lengthwise in females. The ornament is probably costly tit reduces crypsis and may be socially provocative), and it is also attractive to mal es. Thus, the ornament is best described as an amplifying handicap.