Effect of parental phenotype on dispersal, growth and maturation of offspring in wild masu salmon ( Oncorhynchus masou )

Offspring traits are influenced by complex interactions among parent genotypes and phenotypes. However, ecological studies of these effects have tended to focus on one of either maternal or paternal influences. In this study, we investigated the effects of both parental phenotypes on offspring dispersal, growth and early sexual maturity in masu salmon. We used wild-caught parental fish in a half-sib mating design that allowed comparison of offspring from males of two different life-history types (precocious males that had lived only in fresh water and anadromous males that had migrated to the sea). These males were mated with anadromous females and the eggs planted in natural streams in three different years. Natal dispersal distance depended on offspring sex, body size and paternal life history: female offspring moved further downstream than males, whilst daughters of precocious fathers tended to move further downstream than those of anadromous sires. There was a maternal effect on offspring growth, with larger eggs resulting in larger offspring at least until these became precociously mature at the end of the first summer. However, while faster growing male offspring were more likely to become precociously mature, there was no evidence that the probability of precocious maturation was influenced by parental life history. We conclude that, although body size of young salmon was significantly influenced by egg size and there were sex differences in dispersal, their growth rate and divergence in life history types were mainly environmentally driven.