Maternal control of sex ratio in Rana rugosa: evidence from DNA sexing

Parental control of primary sex ratio has been reported in a mammal (red de er), some birds, and a snake. However, it remains uncertain whether other v ertebrates including Amphibia can control sex ratio. In this paper, we exam ined the possibility in a wild population of the Japanese frog Rana rugosa which has female heterogamety. Sex ratios of their eggs were determined usi ng DNA markers. The eggs were sampled in the field from May to August in 19 98. Each egg was then sexed by polymerase chain reaction-restriction fragme nt length polymorphism (PCR-RFLP) using a sex-specific DNA marker. The resu lt showed a male bias early in the season which changed to a female bias la ter suggesting that females of R, rugosa can control the primary sex ratio.