Early survival and growth in populations of grayling with recent common ancestors—field experiments

Among eight populations of grayling Thymallus thymallus that shared common ancestors 8-28 generations earlier, mean egg mortality ranged between 1DT2 and 59DT8%; mortality during yolk sac absorption was low (0DT0-8DT0%) and mean survival to swim-up was high (90-97%), with two exceptions (20% and 50%). Survival probabilities differed significantly among populations, even after statistically adjusting for size at swim-up and water depth, water velocity, gravel size and temperature. Development time from fertilization to first observed swim-up was significantly different among populations, ranging between 27 to 40 days, or 264 to 280 degree-days. Mean specific growth rates during the first external feeding period varied between 1DT2 and 2DT0% day-1among populations. Population-specific growth rates were independent of temperature. Rates of divergence were of the same order as in other salmonid studies showing rapid evolution. The phenotypic differences may be due partly to genetic differentiation among the populations. Copyright 2000 The Fisheries Society of the British Isles