Abstract
The early stages of intraspecific diversity are important for the evolution of diversification and speciation. Early stages of diversification can be seen in individual specialization, where individuals consume only a portion of the diet of the population as a whole, and how such specialization is related to phenotypic diversity within populations. Here, we study the strength of the relationship between morphological and dietary distances among individuals in eighteen populations of Icelandic small benthic charr. We furthermore studied if the strength of the relationship could be related to variation in local ecological factors these populations inhabit. In all the populations studied, there was a clear relationship between morphological and dietary distances, indicating that fish that had similar morphology were at the same time‐consuming similar food items. Our findings show a systematic variation in the relationship between morphology and diet at early stages of diversification in a highly specialized small benthic charr morph. The results show the importance of fine scale comparisons within populations and furthermore the value that systematic comparisons among populations under parallel evolution can contribute toward our increased understanding of evolutionary and ecological processes.
Highlights
The understanding of intraspecific diversity, both among and within populations, is a key focus of evolutionary studies
Studies have focused on population divergence, leading to morph formation and/or sympatric speciation (Grant & Grant, 2002; Schluter, 2000), with the majority of studies focusing on the later stages of divergence, for example, ecological speciation (Schluter, 2000) and/or adaptive radiation within species (Bolnick, 2006)
Small benthic charr in Iceland have evolved phenotypes that are quite different from the common ancestor, an anadromous charr that colonized Icelandic freshwater systems about 10,000 ya (Kristjánsson et al, 2012)
Summary
The understanding of intraspecific diversity, both among and within populations, is a key focus of evolutionary studies. Such comparison takes its roots in the modeling of niche evolution theory which predicts that among individual competition should drive individuals that differ in morphology further apart in resource use and reduce competition among them (Bolnick et al 2003; Dieckmann & Doebeli, 2004; Rouchgarden, 1972; Slatkin, 1979) It is, unknown whether ecological variables play an important role in the first steps of population divergence. Ecological variables may influence the strength of the relationships between morphology and died by acting upon both morphological variation, for example, through phenotypic plasticity (West-Eberhard, 2003), and upon the variation in diet, for example, through changes in invertebrate composition (e.g., Govoni, Kristjánsson & Ólafsson 2017) and available prey and/or diet selection (Svanbäck & Persson, 2004) It is unclear how the relationships between morphology and diet are shaped in populations showing strong local adaptations to their habitat, such as the small benthic charr. This prediction is based on the different nature of these two spring types, where limnocrene springs have more diverse invertebrate composition (Govoni, Kristjánsson & Ólafsson 2017) reflected in more diverse diet of small benthic charr (Kristjánsson et al, 2012)
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