Female life-history traits of a species pair of threespine stickleback in Mud Lake, Alaska

Aim: Compare several female life-history traits in a stickleback species pair (i.e. size and age at reproduction, clutch size, egg mass, and reproductive effort) to determine whether time during the reproductive season (early or late) or breeding habitat (vegetation, open sites) significantly affect trait values. Organisms: Sympatric ecotypes of anadromous and resident freshwater threespine stickleback (Gasterosteus aculeatus). Time and place: Mud Lake, Cook Inlet region, Alaska, May-July 2003. Results: Both resident and anadromous fish in Mud Lake bred primarily at age 2. Anadromous breeders were larger than resident breeders. Size of reproductive females declined from early to late in the breeding season for both anadromous and resident freshwater populations, but time and breeding habitat were not significant sources of variation in most life-history traits. Clutch mass showed a similar, positive correlation with female body mass in both populations, but clutch size (fecundity) rose more slowly with female size in resident fish. Both ecotypes made eggs of similar size overall, with egg size in resident females increasing modestly with female body size. Both ecotypes showed a trade-off between clutch size and egg mass after adjustment for the level of reproductive effort. The egg mass and clutch mass of both ecotypes were small compared with other Cook Inlet resident and anadromous populations.