MIGRATION AND LIFE HISTORIES OF THE THREESPINE STICKLEBACK - EVIDENCE FOR ADAPTIVE VARIATION IN GROWTH-RATE BETWEEN POPULATIONS

Migratory fishes should exhibit higher growth rates and larger body size than nonmigrants. To test this hypothesis, laboratory reared threespine sticklebacks, Gasterosteus aculeatus, representing three populations from a single drainage in northern California, U.S.A. were compared. These populations differ in their migratory patterns, ranging from highly migratory anadromous forms to nonmigratory freshwater residents. The nonmigratory 'inland' population was significantly smaller in standard length at most ages, with correspondingly reduced growth rates compared to the more migratory 'upstream' and 'estuary' populations. Von Bertalanffy growth functions described the growth trajectories of these fish well, accounting for approximately 99% of the variance in body size exhibited by these populations. Broad sense heritability estimates for body size were significant for all three populations at age 60 days but were significant only for the inland population at later ages. The results of this study provide evidence of genetically-based variation in growth rate and body size among these stickleback populations, and these differences are consistent with the hypothesis that adaptation to different migratory lifestyles has occurred.