Department of Aquaculture and Fish Biology, Hólar University, Sauðárkrókur, Iceland.
Department of Biology and Environmental Science, University of Jyväskylä, Jyväskylä, Finland.
BMC Ecol Evol. 2024 Apr 15;24(1):45. doi: 10.1186/s12862-024-02232-3.
A major goal in evolutionary biology is to understand the processes underlying phenotypic variation in nature. Commonly, studies have focused on large interconnected populations or populations found along strong environmental gradients. However, studies on small fragmented populations can give strong insight into evolutionary processes in relation to discrete ecological factors. Evolution in small populations is believed to be dominated by stochastic processes, but recent work shows that small populations can also display adaptive phenotypic variation, through for example plasticity and rapid adaptive evolution. Such evolution takes place even though there are strong signs of historical bottlenecks and genetic drift. Here we studied 24 small populations of the freshwater fish Arctic charr (Salvelinus alpinus) found in groundwater filled lava caves. Those populations were found within a few km2-area with no apparent water connections between them. We studied the relative contribution of neutral versus non-neutral evolutionary processes in shaping phenotypic divergence, by contrasting patterns of phenotypic and neutral genetic divergence across populations in relation to environmental measurements. This allowed us to model the proportion of phenotypic variance explained by the environment, taking in to account the observed neutral genetic structure.
These populations originated from the nearby Lake Mývatn, and showed small population sizes with low genetic diversity. Phenotypic variation was mostly correlated with neutral genetic diversity with only a small environmental effect.
Phenotypic diversity in these cave populations appears to be largely the product of neutral processes, fitting the classical evolutionary expectations. However, the fact that neutral processes did not explain fully the phenotypic patterns suggests that further studies can increase our understanding on how neutral evolutionary processes can interact with other forces of selection at early stages of divergence. The accessibility of these populations has provided the opportunity for long-term monitoring of individual fish, allowing tracking how the environment can influence phenotypic and genetic divergence for shaping and maintaining diversity in small populations. Such studies are important, especially in freshwater, as habitat alteration is commonly breaking populations into smaller units, which may or may not be viable.
进化生物学的一个主要目标是理解自然界中表型变异的背后过程。通常，研究集中在大型相互关联的种群或沿着强烈环境梯度发现的种群上。然而，对小而破碎的种群的研究可以深入了解与离散生态因素有关的进化过程。小种群中的进化被认为主要由随机过程主导，但最近的研究表明，小种群也可以通过可塑性和快速适应性进化等方式表现出适应性表型变异。即使存在明显的历史瓶颈和遗传漂变的迹象，这种进化也会发生。在这里，我们研究了在充满地下水的熔岩洞穴中发现的 24 个小的淡水鱼北极红点鲑种群（Salvelinus alpinus）。这些种群位于几平方公里的区域内，彼此之间没有明显的水联系。我们通过对比种群之间表型和中性遗传分歧与环境测量的关系，研究了中性和非中性进化过程对塑造表型分歧的相对贡献。这使我们能够在考虑到观察到的中性遗传结构的情况下，通过模型来解释环境对表型方差的解释比例。
这些种群起源于附近的米湖（Lake Mývatn），种群规模较小，遗传多样性较低。表型变异主要与中性遗传多样性相关，只有很小的环境影响。
这些洞穴种群的表型多样性似乎主要是中性过程的产物，符合经典的进化预期。然而，中性过程没有完全解释表型模式的事实表明，进一步的研究可以增加我们对中性进化过程如何在分化的早期与其他选择力量相互作用的理解。这些种群的可及性为长期监测个体鱼类提供了机会，使我们能够跟踪环境如何影响表型和遗传分歧，从而塑造和维持小种群的多样性。这些研究很重要，特别是在淡水环境中，因为栖息地的改变通常会将种群分割成更小的单元，这些单元可能具有生存能力，也可能没有。
