Data for: Immigration counter-acts local micro-evolution of a major fitness component: migration-selection balance in free-living song sparrows

AbstractOngoing adaptive evolution, and resulting ‘evolutionary rescue’ of declining populations, requires additive genetic variation in fitness. Such variation can be increased by gene flow resulting from immigration, potentially facilitating evolution. But, gene flow could in fact constrain rather than facilitate local adaptive evolution if immigrants have low additive genetic values for local fitness. Local migration-selection balance and micro-evolutionary stasis could then result. However, key quantitative genetic effects of natural immigration, comprising the degrees to which gene flow increases the total local additive genetic variance yet counter-acts local adaptive evolutionary change, have not been explicitly quantified in wild populations. Key implications of gene flow for population and evolutionary dynamics consequently remain unclear. Our quantitative genetic analyses of long-term data from free-living song sparrows (Melospiza melodia) show that mean breeding value for local juvenile survival to adulthood, a major component of fitness, increased across cohorts more than expected solely due to drift. Such micro-evolutionary change should be expected given non-zero additive genetic variance and consistent directional selection. However, this evolutionary increase was counter-acted by negative additive genetic effects of recent immigrants, which increased total additive genetic variance but prevented a net directional evolutionary increase in total additive genetic value. These analyses imply an approximate quantitative genetic migration-selection balance in a major fitness component, and hence demonstrate a key mechanism by which substantial additive genetic variation can be maintained yet decoupled from local adaptive evolutionary change., MethodsPlease refer to: Immigration counter-acts local micro-evolution of a major fitness component: migration-selection balance in free-living song sparrows Jane M. Reid et al. Evolution Letters, 2021

摘要 持续的适应性进化以及由此实现的衰退种群“进化拯救”，需要在适合度（fitness）性状上存在加性遗传变异（additive genetic variation）。迁入所引发的基因流（gene flow）可提升此类变异水平，从而潜在地促进进化过程。但倘若迁入个体针对本地适合度的加性遗传值较低，基因流反而可能抑制而非推动本地适应性进化，进而可能形成本地的迁移-选择平衡（migration-selection balance）与微进化停滞（micro-evolutionary stasis）。然而，自然迁入所带来的关键数量遗传效应——即基因流在多大程度上提升了本地总加性遗传方差，同时又抵消本地适应性进化变化——尚未在野生种群（wild populations）中得到明确量化。因此，基因流对种群动态与进化动态的核心影响仍未明晰。
我们对自由生活的歌带鹀（Melospiza melodia）长期监测数据开展的数量遗传分析显示：作为适合度核心组分的本地幼体至成体存活率的平均育种值（mean breeding value），在不同世代间的增幅超过了仅由遗传漂变所预期的水平。在存在非零加性遗传变异且存在持续定向选择（directional selection）的前提下，此类微进化变化本应出现。但该进化增幅被近期迁入个体的负向加性遗传效应所抵消：这些迁入个体提升了总加性遗传方差，却阻止了总加性遗传值出现净的定向进化增长。
上述分析表明，在适合度的核心组分中存在近似的数量遗传迁移-选择平衡，从而证实了一种关键机制：该机制可维持可观的加性遗传变异，却使其与本地适应性进化变化脱钩。
方法 请参阅：《迁入抵消核心适合度组分的本地微进化：野生歌带鹀的迁移-选择平衡》（Immigration counter-acts local micro-evolution of a major fitness component: migration-selection balance in free-living song sparrows），Jane M. Reid 等，《Evolution Letters》，2021年