Organismal and Evolutionary Biology Research Program, Faculty of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland.
Department of Biology, University of Turku, Turku, Finland.
Mol Ecol. 2020 Mar;29(6):1173-1184. doi: 10.1111/mec.15390. Epub 2020 Mar 9.
In species with complex life cycles, life history theory predicts that fitness is affected by conditions encountered in previous life history stages. Here, we use a 4-year pedigree to investigate if time spent in two distinct life history stages has sex-specific reproductive fitness consequences in anadromous Atlantic salmon (Salmo salar). We determined the amount of years spent in fresh water as juveniles (freshwater age, FW, measured in years), and years spent in the marine environment as adults (sea age, SW, measured in sea winters) on 264 sexually mature adults collected on a river spawning ground. We then estimated reproductive fitness as the number of offspring (reproductive success) and the number of mates (mating success) using genetic parentage analysis (>5,000 offspring). Sea age is significantly and positively correlated with reproductive and mating success of both sexes whereby older and larger individuals gained the highest reproductive fitness benefits (females: 62.2% increase in offspring/SW and 34.8% increase in mate number/SW; males: 201.9% offspring/SW and 60.3% mates/SW). Younger freshwater age was significantly related to older sea age and thus increased reproductive fitness, but only among females (females: -33.9% offspring/FW and -32.4% mates/FW). This result implies that females can obtain higher reproductive fitness by transitioning to the marine environment earlier. In contrast, male mating and reproductive success was unaffected by freshwater age and more males returned at a younger age than females despite the reproductive fitness advantage of later sea age maturation. Our results show that the timing of transitions between juvenile and adult phases has a sex-specific consequence on female reproductive fitness, demonstrating a life history trade-off between maturation and reproduction in wild Atlantic salmon.
在具有复杂生命周期的物种中，生活史理论预测，适应度会受到之前生命史阶段所遇到的条件的影响。在这里，我们使用一个 4 年的谱系来研究在溯河洄游的大西洋鲑鱼（Salmo salar）中，两个不同的生命史阶段所花费的时间是否会对雄性和雌性的生殖适应性产生影响。我们确定了个体在淡水环境中作为幼鱼（淡水年龄，FW，以年为单位）所花费的时间，以及在海洋环境中作为成鱼（海龄，SW，以海冬为单位）所花费的时间，共对 264 个在河流产卵场采集的性成熟个体进行了测量。然后，我们使用遗传亲子分析（>5000 个后代）来估计生殖适应性，即后代数量（生殖成功）和配偶数量（交配成功）。海龄与两性的生殖和交配成功率呈显著正相关，年龄较大和体型较大的个体获得了最高的生殖适应性优势（雌性：后代/SW 增加 62.2%，配偶/SW 增加 34.8%；雄性：后代/SW 增加 201.9%，配偶/SW 增加 60.3%）。较年轻的淡水年龄与较老的海龄显著相关，从而提高了生殖适应性，但仅限于雌性（雌性：后代/FW 减少 33.9%，配偶/FW 减少 32.4%）。这一结果表明，雌性可以通过更早地进入海洋环境来获得更高的生殖适应性。相比之下，淡水年龄对雄性的交配和生殖成功率没有影响，而且尽管海龄较晚成熟具有生殖适应性优势，但更多的雄性比雌性更早返回。我们的研究结果表明，幼鱼和成鱼阶段之间的转变时间对雌性生殖适应性具有性别特异性影响，这表明野生大西洋鲑鱼的成熟和繁殖之间存在生活史权衡。
