Reproductive-timing-dependent alternation of offspring life histories in female threespine sticklebacks

Abstract

Relationships between reproductive timing of spawners and timing of hatch and age at maturity of their offspring were examined in fluvial threespine sticklebacks, Gasterosteus aculeatus. Some age 2 and all age 3 females matured in this age-structured population, with only a few females reproducing over two successive breeding seasons. Age 2 females spawned over the relatively long breeding season (March-August), whereas age 3 females spawned mainly early in the season (March-June). Although the standard length of mature age 3 females was greater than that of age 2 females, the back-calculated standard lengths of the former were always shorter than those of the latter at an equivalent age, the most distinct differences being apparent in young of the year. Analysis of daily otolith increments showed that the earlier the young of the year were born, the larger they were at the end of the growing season. As a result of these findings, age 3 females can be expected to produce offspring that will mature at age 2, whereas the offspring of late-spawning age 2 females are more likely to mature at age 3. Therefore, a partial alternation of life histories between generations is thought to occur.