Interpopulation variation in early growth of threespine sticklebacks (Gasterosteus aculeatus) under laboratory conditions

Logistical difficulties associated with accurately measuring juvenile stages have contributed to a lack of detailed information on population-level variation in the early growth of fish. In this study, we used computerised image analysis to determine the trajectories of early growth, from hatching to 126 days posthatch, of replicated, laboratory-bred, full-sibling groups of threespine stickleback (Gasterosteus aculeatus) from five resident freshwater populations. Sibling groups were held under controlled "common garden" conditions and fed ad libitum, to excess, and standard lengths (SL) of all individuals in each sibling group were recorded at regular intervals over four separate time periods (0-6, 6-38, 38-70, and 70-126 days). Although there was no significant population-level variation in SL at hatching, we detected significant population-level differences in growth trajectory after 38 days and population differences in mean SL of up to 6.8 mm (16.6%) by 126 days. Our results suggest that population-level variation in the intrinsic growth rates of juvenile sticklebacks has a strong genetic component.