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.

在进化生物学研究中，测定自然选择的强度具有极为重要的意义，但该任务始终颇具挑战。本研究针对三刺鱼（Gasterosteus aculeatus）的侧骨板退化这一形态变化，分析其相关选择作用的特征。该物种在适应淡水环境的过程中，其骨质侧甲出现退化或完全消失的现象，且该适应性演化事件在该物种中已多次平行发生。研究人员将全骨板型与低骨板型三刺鱼投放至一处人工池塘中，并对其表型变化展开了长达20年的跟踪观测。随后，研究人员对最后一代实验鱼的外异蛋白A（Ectodysplasin-A, Eda）位点进行基因分型，该位点是调控骨质甲发育的关键基因。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%。该变化趋势可通过以下假设得到最佳解释：该适合度优势在入侵初期达到峰值，并随时间推移逐渐减弱。这类适合度差异为自然种群中伴随环境变化、由选择作用驱动的快速表型演化提供了一个可量化的研究范例。