Population- and sex-specific divergence in growth patterns between two ninespine stickleback (Pungitius pungitius L) populations Nurul Izza Ab Ghani 1 , Anna Kuparinen 2 , Tuomas Leinonen 1 and Juha Merilä 1 1 Ecological Genetics Research Unit, Department of Biosciences, University of Helsinki, Helsinki, Finland and 2 Fisheries and Environmental Management Group, Department of Environmental Sciences, University of Helsinki, Helsinki, Finland ABSTRACT Background: Growth rate is an important life-history trait that often shows sex- and population-specific differentiation in many organisms. Yet the relative contributions of additive genetic, non-additive genetic, environmental, and maternal effects underlying these differences remain largely unknown, especially in wild animal populations. Goal: To determine the relative contributions of additive genetic, non-additive genetic, and environmental effects underlying population differences in growth rate between two stickleback populations differing markedly in their body size. Organism: Ninespine stickleback (Pungitius pungitius). Methods: We crossed two phenotypically and genetically distinct populations to produce ‘pure’ marine (Hel-Hel; small sized), ‘pure’ pond (Pyö-Pyö; large sized), and ‘hybrid’ (Hel-Pyö and Pyö-Hel) offspring. We reared them in standardized common garden settings until maturation. Results: Analyses of Von Bertalanffy growth curve parameters revealed that sexes and cross- types differed in their intrinsic growth rates (k) and asymptotic sizes (L ∞ ). In general, males and marine fish (Hel-Hel) had higher k and smaller L ∞ than females and fish from the pond (Pyö-Pyö). Fish from ‘hybrid’ crosses exhibited k and L ∞ intermediate to the ‘pure’ crosses, but were more similar in both respects to the pure marine than to the pure pond fish. Thus population differentiation in k and L ∞ has a genetic basis, but additive genetic effects do not explain all the observed differences. k and L ∞ were negatively correlated within three cross-types (both ‘hybrids’ and Pyö-Pyö): low intrinsic growth rates were associated with increased asymptotic size. k and L ∞ were not correlated within the Hel-Hel cross: high intrinsic growth rate was not directly associated with reduced asymptotic size. Neither k nor L ∞ predicted the age at maturation in Hel-Hel fish, and only poorly so in Pyö-Pyö fish. Conclusion: We discovered genetically based population differentiation in key growth-related life-history traits, but little or no evidence for a role of intrinsic growth rate or asymptotic size in determining the timing of maturation in ninespine stickleback. Keywords: asymptotic length, common garden, growth rate, maturation, Pungitius pungitius, von Bertalanffy. Correspondence: J. Merilä, Ecological Genetics Research Unit, Department of Biosciences, PO Box 65, University of Helsinki, FI-00014 Helsinki, Finland. e-mail: juha.merila@helsinki.fi Consult the copyright statement on the inside front cover for non-commercial copying policies. Evolutionary Ecology Research, 2013, 15: 793–808 © 2013 Nurul Izza Ab Ghani