Data from: Strong and consistent natural selection associated with armour reduction in sticklebacks

Measuring the strength of natural selection is tremendously important in evolutionary biology, but remains a challenging task. In this work, we analyse the characteristics of selection for a morphological change (lateral-plate reduction) in the threespine stickleback Gasterosteus aculeatus. Adaptation to freshwater, leading to the reduction or loss of the bony lateral armor, has indeed occurred in parallel on numerous occasions in this species. Completely-plated and low-plated sticklebacks were introduced into a pond, and the phenotypic changes were tracked for twenty years. Fish from the last generation were genotyped for the Ectodysplasin-A (Eda) locus, the major gene involved in armor development. We found a strong fitness advantage for the freshwater-type fish (in average, 20% for the freshwater morph, and 92% for the freshwater genotype). The trend is best explained by assuming that this fitness advantage is maximum at the beginning of the invasion and decreases with time. Such fitness differences provide a quantifiable example of rapid selection-driven phenotypic evolution associated to environmental change in a natural population.

量化自然选择的强度在进化生物学中具有极为重要的学术价值，但同时也是一项颇具挑战性的研究课题。本研究以三刺鱼（Gasterosteus aculeatus）为研究对象，针对其形态变化——侧骨板退化（lateral-plate reduction）相关的选择特征展开分析。该物种为适应淡水环境而发生骨质侧甲退化或丢失的演化事件，已在自然历史中多次平行独立出现。研究人员将完全骨板型与低骨板型三刺鱼引入一处池塘，并对其表型变化开展了长达20年的跟踪观测。随后，研究人员对最后一代实验个体的外胚层发育蛋白A（Ectodysplasin-A, Eda）位点进行了基因分型，该位点是调控骨甲发育的关键基因。本研究结果显示，淡水型三刺鱼具有显著的适合度优势：淡水形态个体的适合度平均提升20%，淡水基因型个体的适合度提升幅度更是高达92%。该变化趋势可通过如下假设得到最优解释：这类适合度优势在种群定植初期达到峰值，并随时间推移逐步衰减。此类适合度差异为自然种群中伴随环境变化、由选择驱动的快速表型演化提供了一个可量化的实证案例。