Abstract
This is a post-peer-review, pre-copyedit version of an article published in Hydrobiologia. The final authenticated version is available online at https://doi.org/10.1007/s10750-019-3969-9 .
Highlights
A resource polymorphism is defined as the occurrence of distinct morphs specialized in different resource use within a single species (Skúlason & Smith, 1995)
A novel Arctic charr morph was discovered in Skøvatn: a small-sized profundal zooplanktivorous-morph (PZ), which when compared to the sympatric littoral omnivorous (LO)-morph, had distinct stable isotope values and a contrasting parasite community
There was a no parallel pattern in diet choice between the profundal benthivorous (PB)- and the PZ-morphs. These findings show how evolution can produce diverse outcomes, even among systems with apparently similar environmental and ecological conditions. 45 46 Key-words: Salvelinus alpinus, polymorphism, genetic differences, trophic niche divergence, stomach contents, stable isotope analyses, trophically transmitted parasites. 49 Acknowledgments: 50 We thank Rachel Patterson and Helge Jakobsen for assistance during the fieldwork, André
Summary
A resource polymorphism is defined as the occurrence of distinct morphs specialized in different resource use within a single species (Skúlason & Smith, 1995). Polymorphic populations of several fish species have repeatedly been found in postglacial lakes, especially within the genera Salvelinus, Gasterosteus, and Coregonus (Skúlason & Smith, 1995; Skúlason et al, 1999; Amundsen et al, 2008; Klemetsen, 2013). Similar ecological niches and environments in many isolated postglacial lakes have resulted in parallel adaptations in the morphology, behaviour, physiology, and life-history traits of several fish species (Endler, 1986; Schluter, 2000), including Arctic charr, Salvelinus alpinus (L.) (Skúlason & Smith, 1995; Klemetsen, 2010), which is the target species of the present study. The initial step in the evolutionary divergence of northern fishes has been suggested to be competition for discrete habitats and food resources, which allow fish to specialize and segregate in distinctive niches (Wimberger, 1994; Skúlason & Smith, 1995; Jonsson & Jonsson, 2001; Adams et al, 2003; Garduño-Paz & Adams, 2010). The frequent incidents of parallel evolution observed in several fish taxa such as e.g. Arctic charr and three-spined stickleback (Gasterosteus aculeatus L.), are considered strong evidence of ecologically induced divergence, as they are unlikely to arise solely by genetic drift or other nonecological mechanisms (Schluter & Nagel, 1995; Schluter, 1996, 2001; Nosil & Rundle, 2009; Kaeuffer et al, 2012; Saltykova et al, 2017)
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