Department of Biological Sciences, University of Calgary, Calgary, AB, Canada.
Earth to Ocean Research Group, Simon Fraser University, Burnaby, BC, Canada.
J Anim Ecol. 2019 May;88(5):717-733. doi: 10.1111/1365-2656.12965. Epub 2019 Mar 14.
Plasticity, local adaptation and evolutionary trade-offs drive clinal variation in traits associated with lifetime growth. Disentangling the processes and determinants that cause these traits to vary helps to understand species' responses to changing environments. This is particularly urgent for exploited populations, where size-selective harvest can induce life-history evolution. Lake trout (Salvelinus namaycush) are an exploited fish with a life history adapted to low-productivity freshwaters of northern North America, which makes them highly vulnerable to ecosystem changes and overfishing. We characterized life-history variation across a broad and diverse landscape for this iconic northern freshwater fish and evaluated whether clinal variation was consistent with hypotheses for local adaptation or growth plasticity. We estimated growth-associated traits for 90 populations exposed to a diversity of environments using a Bayesian multivariate hierarchical model. We tested for clinal variation in their somatic growth, size at maturity and reproductive allocation along environmental gradients of lake productivity, climate, prey and exploitation clines under competing hypotheses of plasticity and local adaptation. Clinal life-history variation was consistent with growth plasticity and local adaptations but not harvest-induced evolution. Variation in somatic growth was explained by exploitation, climate and prey fish occurrence. Increased exploitation, from pristine to fully exploited conditions, led to increased somatic growth (from 32 to 45 mm/year) and adult life spans, and reduced age at maturity (from 11 to 8 years). Variation in size at maturity was explained by climate and, less certainly, prey fish occurrence, while reproductive allocation was explained by evolutionary trade-offs with mortality and other traits, but not environment. Lake trout life-history variation within this range was as wide as that observed across dozens of other freshwater species. Lake trout life histories resulted from evolutionary trade-offs, growth plasticity and local adaptations along several environmental clines. Presuming a plastic response, we documented ~1.4-fold growth compensation to exploitation-lower growth compensation than observed in many freshwater fishes. These results suggest that harvested species exposed to spatially structured and diverse environments may have substantial clinal variation on different traits, but due to different processes, and this has implications for their resilience and successful management.
可塑性、局部适应和进化权衡驱动与终生生长相关的性状的渐变变异。 厘清导致这些性状发生变化的过程和决定因素有助于了解物种对不断变化的环境的反应。 对于受捕捞影响的种群来说，这一点尤为紧迫，因为大小选择性捕捞会诱导生活史进化。 湖鳟（Salvelinus namaycush）是一种受捕捞影响的鱼类，其生活史适应于北美的低生产力淡水，这使得它们极易受到生态系统变化和过度捕捞的影响。 我们描述了这种标志性的北方淡水鱼在广泛而多样的景观中的生活史变异，并评估了渐变变异是否与局部适应或生长可塑性的假说一致。 我们使用贝叶斯多变量层次模型，使用暴露于各种环境中的 90 个种群来估计与生长相关的性状。 我们在竞争的可塑性和局部适应假说下，测试了其在湖生产力、气候、猎物和捕捞渐变的环境梯度上的躯体生长、成熟大小和生殖分配的渐变变异。 渐变的生活史变异与生长可塑性和局部适应一致，但与捕捞诱导的进化不一致。 躯体生长的变异由捕捞、气候和猎物鱼类的出现来解释。 从原始状态到完全捕捞状态的增加的捕捞导致了躯体生长（从 32 毫米/年增加到 45 毫米/年）和成年寿命的增加，以及成熟年龄（从 11 年减少到 8 年）的减少。 成熟大小的变异由气候解释，而不太确定的是猎物鱼类的出现，而生殖分配则由与死亡率和其他性状的进化权衡来解释，但与环境无关。 在这个范围内，湖鳟的生活史变异与观察到的其他数十种淡水物种一样广泛。 湖鳟的生活史是由几个环境渐变的进化权衡、生长可塑性和局部适应形成的。 假定存在一种可塑性反应，我们记录到与捕捞相关的生长补偿约为 1.4 倍——比许多淡水鱼类观察到的生长补偿要低。 这些结果表明，暴露于空间结构和多样化环境中的受捕捞影响的物种可能在不同性状上具有相当大的渐变变异，但由于不同的过程，这对它们的恢复力和成功管理具有影响。
