Biometry, isotopic composition and diet of Arctic charr (Salvelinus alpinus) from Lake Aigneau, Northern Quebec

Two modal size groups of sexually mature Arctic charr (Salvelinus alpinus) differing in shape and found at different depths in Lake Aigneau in the Canadian sub-Arctic are described and tested for genetic and ecological differentiation. Forms consisted of a small littoral resident, mean size 21.7 cm, and a large profundal resident, mean size 53.9 cm. Mitochondrial DNA analysis indicated that seven of eight haplotypes were diagnostic for either the littoral or profundal fish, with 66.6% of the variation being found within form groupings. Pairwise tests of microsatellite data indicated significant differences in nine of 12 loci and a significant difference between the forms across all tested loci. Molecular variation was partitioned to 84.1% within and 15.9% between forms and suggestive of either restricted interbreeding over time or different allopatric origins. Stable isotope signatures were also significantly different, with the profundal fish having higher d13C and d15N values than the littoral fish. Overlap and separation, respectively, in the range of form d13C and d15N signatures indicated that carbon was obtained from similar sources, but that forms fed at different trophic levels. Littoral fish relied on aquatic insects, predominantly chironomids. Profundal fish were largely piscivorous, including cannibalism. Predominantly empty stomachs and low per cent nitrogen muscle-tissue composition among profundal fish further indicated that the feeding activity was limited to the winter when ice-cover increases the density of available prey at depth. Results provide evidence of significant differences between the modal groups, with origins in both genetics and ecology.

本研究对加拿大亚北极地区的艾诺湖（Lake Aigneau）中栖息于不同深度、形态存在差异的两类性成熟北极红点鲑（Salvelinus alpinus）体型模态组开展了形态描述，并对其遗传与生态分化进行了检测。两类群分别为小型沿岸定居型（平均体长21.7 cm）与大型深底栖定居型（平均体长53.9 cm）。线粒体DNA（mitochondrial DNA）分析显示，8个单倍型中有7个可作为沿岸型或深底栖型红点鲑的诊断性单倍型，且66.6%的遗传变异分布于类群组内。对12个微卫星（microsatellite）位点的成对检测结果显示，其中9个位点存在显著差异，且两类群在所有检测位点上均呈现显著分化。分子变异组分分析表明，84.1%的变异存在于类群内部，15.9%的变异存在于类群之间，这提示二者可能存在长期的有限基因交流，或具有不同的异域起源。稳定同位素特征同样存在显著差异，深底栖型个体的δ13C与δ15N值显著高于沿岸型个体。两类群的δ13C和δ15N特征值范围分别呈现重叠与分离，表明二者获取的碳源相似，但所处营养级存在差异。沿岸型个体主要以水生昆虫为食，优势猎物为摇蚊（chironomids）。深底栖型个体主要以鱼类为食，其中包含同类相食行为。深底栖型个体的胃部大多为空，且肌肉组织的氮百分比含量较低，这进一步表明其摄食活动仅局限于冬季——此时冰盖会提升深水区可获取猎物的种群密度。本研究结果为两类体型模态组之间存在显著差异提供了实证支持，且这种差异同时受到遗传与生态因素的共同塑造。