Effects of population, family, and diet on craniofacial morphology of Icelandic Arctic charr (Salvelinus alpinus) EVA KÜTTNER 1 *, KEVIN J. PARSONS 1 †, BEREN W. ROBINSON 1 , SKÚLI SKÚLASON 2 , ROY G. DANZMANN 1 and MOIRA M. FERGUSON 1 1 Department of Integrative Biology, University of Guelph, 50 Stone Road West, Guelph, ON, Canada N1G 2W1 2 Hólar University College, Hólar, Hjaltadalur, 551 SauËarkrókur, Iceland Received 30 August 2012; revised 20 September 2012; accepted for publication 20 September 2012 We evaluated hypotheses of intralacustrine diversification and plastic responses to two diet environments in Icelandic Arctic charr (Salvelinus alpinus). Full-sib families of progeny of wild polymorphic charr from two lakes where morphs vary in their degree of phenotypic and ecological divergence were split, with half of the offspring reared on a benthic and half on a limnetic type of diet to estimate family norms of reaction. We focused on variation in craniofacial traits because they are probably functionally related to diet and complement a previous study of body shape in these charr. A hierarchical analysis of phenotypic variation between lakes, pairs of morphs within each lake, and two families within each morph found that phenotypic variation partitioned between families relative to morphs was reduced in the more ecologically diversified population, which is consistent with adaptive diversification. The effect size of plastic responses between lake populations was similar, suggesting little difference in the degree of canalization in contrast to a previous analysis of body form plasticity. Thus, the role that plastic morphological responses play in the adaptive diversification of morphs and different lake populations of Arctic charr may depend on the trait. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 108, 702–714. ADDITIONAL KEYWORDS: phenotypic plasticity – polymorphism – adaptive diversification – specialization – QTL – salmonid. INTRODUCTION Considerable intraspecific diversity exists as discrete or continuous polymorphisms in populations facing low species-diversity but heterogeneous environments (Skulason & Smith, 1995; Robinson & Schluter, 2000). The coexistence of divergent phenotypes ecologically specialized for alternate niches can reflect the devel- opmental divergence of individuals through adaptive phenotypic plasticity (West-Eberhard, 1989; Adams & Huntingford, 2004; Schlichting, 2004; Crispo, 2007) or the adaptive genetic divergence of populations (Pigliucci, Murren & Schlichting, 2006; Crispo, 2007). Phenotypic plasticity may also contribute to adaptive divergence (Ghalambor et al., 2007; Pigliucci, 2010; Thibert-Plante & Hendry, 2011) because it can evolve in polymorphic populations (Adams & Huntingford, 2004; Pigliucci, 2005; Parsons & Robinson, 2006; Svanback & Eklov, 2006; Chevin & Lande, 2011; Michimae & Emura, 2012). In the present study, we evaluated hypotheses about the intralacustrine diversification of polymorphic Icelandic Arctic charr (Salvelinus alpinus) using a hierarchical analysis of phenotypic variation between two lakes, pairs of morphs within each lake, and families within each morph, split and reared under different diet treatments. Adaptive divergence arises as selection sorts genetic variation that underlies functionally useful phenotypic variation into alternate niches. The *Corresponding author. E-mail: e.kuettner@gmx.de †Current address: College of Medical, Veterinary, and Life Sciences, Institute of Biodiversity, Animal Health, and Comparative Medicine, University of Glasgow, Glasgow G12 8QQ, UK. Biological Journal of the Linnean Society, 2013, 108, 702–714. With 3 figures © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 108, 702–714 702 Downloaded from https://academic.oup.com/biolinnean/article-abstract/108/3/702/2415610 by guest on 21 May 2020