Contrasting patterns in trophic niche evolution of polymorphic Arctic charr populations in two subarctic Norwegian lakes

Abstract

Parallelism in trophic niches of polymorphic populations of Arctic charr was investigated in two similar subarctic lakes, Ta ˚rnvatn and Skøvatn, in northern Norway. Analysis of eleven microsatellite loci confirmed, respectively, the existence of three and two genetically differentiated morphs. Three methods were used to describe their trophic niches: habitat choice and stomach contents for the recent feeding behaviour, and trophically transmitted parasites and stable isotopes (d 13 C and d 15 N) as proxies for the longer term trophic niche differences. The results showed a distinct segregation in trophic resource utilization of the different morphs. Ta ˚rnvatn has three morphs: a littoral omnivorous (LO), a small-sized profundal benthivorous (PB), and a large-sized profundal piscivorous (PP). In contrast, a novel Arctic charr morph was discovered in Skøvatn: a small-sized profundal zooplanktivorous-morph (PZ), which when compared to the sympatric LO-morph, had distinct stable isotope values and a contrasting parasite community. A parallelism in habitat choice and external morphology was found among the smallsized, deep-water morphs and between the upperwater, omnivorous LO-morphs in both lakes. There was a no parallel pattern in diet choice between the PB-and the PZ-morphs. These findings show how evolution can produce diverse outcomes, even among

“And if you gaze long into an abyss, the abyss gazes also into thee”: four morphs of Arctic charr adapting to a depth-gradient in Lake Tinnsjøen

“…Several studies have compared Arctic charr among lakes with regard to their genetic differentiation (where there may be lakes holding more than one morph of Arctic charr) revealing a F ST range of 0.003-0.627 when contrasted in Holarctic lakes [119–127]. Presence of two morphs associated (or not) with genetic clusters have been found in a number of Arctic charr lakes revealing a F ST range of 0.001-0.381 in Holarctic lakes [55, 60, 62, 66, 123–125, 128–133]. When considering Arctic charr lakes with support for three morphs and/or genetic clusters, much fewer systems are reported.…”

“…When considering Arctic charr lakes with support for three morphs and/or genetic clusters, much fewer systems are reported. Moccetti et al [62] report three morphs (littoral omnivorous, small-sized profundal benthivorous, and large-sized profundal piscivorous) in Lake Tårnvatn in Norway with a range in F ST 0.042-0.134. Gíslason et al [128] compared three morphs (planktivore, piscivore and benthivore) in Iceland in Lake Svinavatn with F ST of 0-0.059.…”

“…A set of 11 microsatellites were amplified and analyzed after procedures in Moccetti et al [62] (Additional file: Table S2b,c). 3-6% negative controls per plate and 4% replicate samples were included in the analysis to control cross-contamination and consistency of genotypes.…”

“…However, there are often lake-specific differences in morph variance regarding e.g. niche occupation, phenotype, and life history [15, 19, 61, 62]. This large-scale parallel evolution in Holarctic lakes, with similar morphs appearing apparently due to similar selection pressures exerted in same niches, is a unique feature when studying natural selection and early steps in the speciation continuum, making the Arctic charr species complex an excellent model system in evolutionary biology and eco-evo-devo studies.…”

Marine trophic niche use and life history diversity among Arctic charrSalvelinus alpinusin southwestern Greenland

“…The combination of growth trajectories, age and size at maturity and variable δ 13 C and δ 15 N values suggests several freshwater resident life history patterns in each system, that is, the often reported presence of normal and dwarf morphotypes (e.g., Hindar & Jonsson, 1993;Johnson, 1980;Svedäng, 1990). Such patterns can occur if reproductively separated morphotypes with distinctly different trophic niches exists in sympatry, such as small-sized benthivorous or zooplanktivorous or large-growing piscivorous populations (e.g., Moccetti et al, 2019;Power et al, 2009).…”