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

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