![]() ![]() ![]() For example, natural populations experience temporal fluctuations in density as a result of variation in resource or stress levels ( Grant, 1986 Smith et al., 1999 Grant & Grant, 2002 Persson et al., 2003), influencing the diet and habitat choices of individuals ( Norén & Angerbjörn, 2013). In contrast, phenotypic plasticity can be a successful strategy in an environment where selection pressures vary over time, conditions that are not favourable for a genotype with fixed traits ( Siepielski, DiBattista & Carlson, 2009). This process leads to resource polymorphism and eventually to speciation ( Day, 2000, 2001 Bolnick, 2004 Rueffler et al., 2006). In environments where selection pressures remain relatively stable over time, it is predicted that disruptive selection will act on genetic variation, favouring alternative specialized genotypes. There are two processes by which diversification can occur: genetic variation, and phenotypic plasticity ( Ackerley, 2003). Indeed, both intra- and interspecific competition may be important for diversification of populations ( Rosenzweig, 1991). Interspecific interactions can also affect species diversification, and there are many examples in which competition and predation have resulted in a change in the morphological traits of a species ( Doebeli & Dieckmann, 2000 Schluter, 2000 Kekalainen et al., 2010), known as character displacement ( Brown & Wilson, 1956). If intraspecific competition is high, then resource polymorphism, where individuals become specialized on particular resources, thereby relaxing competition, is likely ( Skúlason & Smith, 1995 Svanbäck et al., 2008). On both ecological and evolutionary timescales, processes act to reduce this competition and promote the gain of fitness advantages via diversification ( Hutchison, 1959 Macarthur & Levins, 1967 Alley, 1982). Individuals are constantly in competition with one another, vying for the best mate, the most productive resources, or the greatest territory. The behavioural mechanisms facilitating associative mating need to be investigated to explore the interaction between phenotypic plasticity and adaptive genetic divergence and their roles in diversification.Īdaptation, AFLP, diversification, phenotypic plasticity, postglacial lakes, resource polymorphism Introduction These results suggest that assortative mating, which can lead to genetically determined adaptive divergence, does occur in these species, particularly perch, but not according to genetically fixed morphological traits. Instead, there was evidence that the extent of resource polymorphism may be largely caused by phenotypic plasticity. Although there was evidence of assortative mating (elevated kinship values) in both species, we could not find any significant coupling of morphology and genetic divergence. We found a large degree of variation in the genetic and morphological divergence between littoral and pelagic perch and roach across Swedish lakes. Here we have investigated the genetic (AFLP) and morphological (geometric morphometrics) aspects of the littoral–pelagic axis, a commonly observed resource polymorphism in freshwater fishes of postglacial lakes. Individuals are constantly in competition with one another and, on both ecological and evolutionary timescales, processes act to reduce this competition and promote the gain of fitness advantages via diversification.
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