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 fit...

量化自然选择的强度在进化生物学领域具有极为重要的研究价值，但至今仍是一项颇具挑战性的课题。本研究以三棘刺鱼（Gasterosteus aculeatus）为研究对象，分析其侧骨板退化这一形态变化所受的选择作用特征。该物种在适应淡水环境的过程中，骨质侧甲退化甚至完全丢失的现象已在多个独立类群中平行演化出现。研究人员将全侧板式与低侧板式三棘刺鱼引入一处池塘，对其表型变化开展了长达20年的跟踪监测。随后对最后一代个体进行外异蛋白A（Ectodysplasin-A, Eda）位点的基因分型——该位点是调控护甲发育的关键主效基因。本研究发现，淡水型个体具有显著的适合度优势：淡水形态个体平均适合度提升20%，淡水基因型个体的适合度提升幅度更是高达92%。该趋势可通过如下假设得到最佳解释：此类适合度优势在种群入侵初期达到峰值，随后随时间推移逐渐衰减。此类适合度优势……