Reproductive tactics and fertilization success of mature male Miyabe charr,Salvelinus malma miyabei

Synopsis Spawning behaviour, fertilization success and reproductive ecology of stream-resident and lake-run male Miyabe charr, Salvelinus malma miyabei, were studied under natural and artificial conditions. In Shikaribetsu Lake, Japan, the ratio of the two types of males is approximately 1:1, estimated by weir data. The majority of stream-resident males mature sexually at 2⁺ years of age, while the lake-run males begin to mature at 4⁺. In contrast to the large-bodied lake-run males, which paired with females, the smaller stream-resident males attempted to fertilize eggs by ‘streaking’ into the nest. We demonstrated through electrophoretic techniques that stream-resident males were able to fertilize eggs by streaking. Under artificial conditions, the estimated maximum proportion of eggs fertilized by a single stream-resident male was about 16.8. The evolutionary stability of the charr's dual mating system may be explained by Gross's theory for alternative life-history evolution, although further testing is necessary.