Divergent growth patterns between juveniles of two sympatric Arctic charr morphs with contrasting depth gradient niche preferences

Abstract

Seasonal growth patterns have been investigated in juveniles of two reproductively isolated Arctic charr [Salvelinus alpinus (L.)] morphs, which coexist in distinct ecological niches (upper-water and deep-water environments) in a subarctic lake. Offspring (F1-generation) of each of the littoral spawning charr (LO) and the profundal spawning charr (PB) were reared individually over a period of 12 months under simulated natural photoperiod (at 69°N) and two different temperature regimes to mimic the profundal zone conditions with constantly low temperature (*4°C) and the littoral zone conditions with seasonally cycling temperatures. All charr increased in weight during the experimental period. The LO-morph performed generally best at naturally fluctuating temperature, whereas the PB-morph grew best at a constantly low temperature (4°C). The LO-morph showed a typical seasonal growth pattern found earlier for anadromous Arctic charr, with elevated specific growth rates (SGR) during June-October and profoundly reduced or negative SGR-values during November-February suggesting that the fish ceased feeding during this period. In contrast, the PB-morph maintained a steady growth rate, regardless of temperature regime, and showed less signs of reduced appetite during the polar night period and exhibited significantly higher SGR-values during late autumn and early winter compared to the LO-morph. This study suggests different heritable adaptations in somatic growth trajectories where the deep-water PB-morph do not show a down-regulation of appetite and voluntary fasting during winter conditions with typically low light intensity and low temperatures, and up-regulation of appetite with hyperphagia during summer, as characteristically found for the upperwater LO-morph and anadromous Arctic charr.

Introduction of Mysis relicta (Mysida) reduces niche segregation between deep-water Arctic charr morphs

“…Based on recent ecological and genetic studies, deep-water morphs of Arctic charr and whitefish are replicated in several locations and appear to originate locally (Østbye et al, 2006;Knudsen et al, 2006;Klemetsen 2010;Praebel et al, 2013Praebel et al, , 2016. Profundal morphs of Arctic charr have evidently inherited traits selected for surviving in cold, dark and nutrient-poor deep-water environments, including specific adaptations in trophic morphology, behavior and growth (Klemetsen et al, 2002(Klemetsen et al, , 2006Knudsen et al, 2015). Other traits seem to a lesser degree to be under strong natural selection, such as temperature preference and vision capabilities (Siikavuopio et al, 2014;Kahilainen et al, 2016).…”

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

“…The anadromous individuals from the three watercourses appear to grow well, reaching sizes of >400 mm by age 6 years as seen in other northern populations (Dempson & Green, ; Johnson, ; Klemetsen et al ., ; Rikardsen et al ., ; Rubin, ). Arctic charr are able to sustain positive growth even at very low water temperatures (Knudsen et al ., ), which is clearly supported by the growth pattern of anadromous individuals from the Greenland watercourses studied here. Further, the anadromous individuals ( i.e ., high δ 34 S values) seem to mature at a larger size, which is typically seen elsewhere (Dempson & Green, ; Rikardsen et al ., ).…”

Growth Disparity in Sympatric Kokanee Breeding Groups

“…The offspring of two sympatric Arctic Char Salvelinus alpinus morphs exhibited incongruent growth patterns in Lake Fjellfrøsvatn, Norway (Knudeson et al. ). Knudeson et al.…”

“…Knudeson et al. () suggested that the divergent growth patterns were due to differences in habitat use whereby one morph occupied the profundal zone and exhibited consistent growth rates and the other morph occurred in the littoral zone and exhibited seasonal fluctuations in growth. Early‐ and late‐run hatchery kokanee are stocked in the same locations in LPO and are thought to occupy the same habitat type (limnetic zone) based on standard midwater trawl surveys.…”