Phenotypic variation of walleye, Sander vitreus , in Canadian Shield lakes: New insights on percid polymorphism
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Springer 2005
Phenotypic variation of walleye, Sander vitreus, in Canadian Shield lakes: New insights on percid polymorphism Yves Paradis & Pierre Magnan Groupe de recherche sur les e´cosyste`mes aquatiques, Universite´ du Que´bec a` Trois-Rivie`res, C.P. 500, Trois-Rivie`res, Que´bec, G9A 5H7, Canada (e-mail: [email protected]) Received 15 March 2004
Accepted 11 October 2004
Key words: colour polymorphism, blue pike, blue walleye, morphology, Stizostedion vitreum glaucum, Stizostedion vitreum Synopsis Literature on colour dimorphism in walleye has concerned only the blue form, Sander vitreus glaucum (formerly Stizostedion vitreum glaucum), historically found in lakes Erie and Ontario (Canada) and considered to be extinct from the fish fauna since the 1960s. In this paper, we report unusual observations of a blue form of walleye living in sympatry with the yellow form, Sander vitreus (formerly Stizostedion vitreum), in five lakes of the Canadian Shield, northern Que´bec. We compared head morphology, diet, and growth of the two forms to determine if there are any variations in characteristics other than colour and to examine the potential adaptive value of the two phenotypes. The blue form has a significantly longer head than the yellow form but does not differ in diet; the blue form also exhibits slower growth. The existence of a blue form of walleye in lakes of the Canadian Shield provides new insights into percid polymorphism and gives important information about their occurrence outside the Great Lakes area. Introduction Phenotypic variation between populations of the same species is common in fishes, particularly in freshwater forms (Robinson & Wilson 1994). These variations are often interpreted as a result of selective pressures and are frequently associated with the initial stage of sympatric speciation (Sku´lason & Smith 1995). Such phenotypic variations are well documented in Salmonid (Adams et al. 1998, Dynes et al. 1999), Gasterosteid (Schluter 1995), and Centrarchid (Robinson et al. 2000) species but are uncommon in percid fishes (Svanba¨ck & Eklo¨v 2002). In walleye, Sander vitreus (formerly Stizostedion vitreum), the only case of phenotypic polymorphism reported in North America is in the Great Lakes, where walleye with an uncommon blue colouration were observed in the 1900s. The blue form of walleye, S. vitreus glaucum, com-
monly referred to as blue pike, are distinct from the usual yellow form in colour, size, growth rate, morphological features, and other biological characteristics such as a preference for deeper, cooler waters (Campbell 1987). At the beginning of the century, populations of the blue form of walleye were abundant in lakes Erie and Ontario (Canada). Due to overexploitation and environmental stress, they began to fluctuate greatly by 1915 and became extinct, with the last specimen being reported in 1965 (Campbell 1987, Wing & Glazier 1991). However, catches of this morphotype continued to be reported from this area (Morrison & King 20031). Although the evolutionary status of the li
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