Data from: Temporal population genetic structure in the pollen pool for flowering time: a field experiment with Brassica rapa (Brassicaceae)

Premise of the study: Assortative mating by flowering time can cause temporal genetic structure in species with heritable flowering times. A strong temporal structure, when coupled with a seasonal shift in selection, may lead to adaptive temporal clines. We implemented a
prospective and retrospective method to estimate the temporal genetic structure in the pollen pool of Brassica rapa.
Methods: The prospective method uses flowering schedules to estimate the seasonal shift in the pollen donors’ phenotype. By examining the offspring generation, we can get a direct estimate of temporal genetic structure, i.e., a retrospective estimate. However, this estimate is problematic because of the phenotypic correlation of the trait of interest, flowering time, between dam and sire. We developed a novel retrospective method that isolates flowering time by holding the maternal contribution constant and sampled the pollen pool in eight open-pollinated field plots throughout the flowering season.
Key results: We found temporal genetic structure for flowering time in seven of the eight field plots. Interestingly, the direct (retrospective) temporal structure estimate was 35% larger than the prospective estimate based on flowering schedules. Spatial clumping of pollen donors did not affect temporal structure, but structure intensified when heritability was experimentally enhanced.
Conclusions: Temporal genetic structure, especially for flowering time, likely occurs in many plant populations and may be underestimated using a prospective method. We discuss the genome-wide consequences of temporal genetic structure and the potential for adaptive temporal clines in plant populations.

研究背景：开花时间介导的选型交配可在开花时间可遗传的物种中引发时间遗传结构。较强的时间遗传结构若与选择的季节偏移共同作用，可能会形成适应性时间梯度。为此，本研究针对白菜型油菜（Brassica rapa）的花粉库，采用前瞻性与回顾性方法对其时间遗传结构进行估算。
方法：前瞻性方法通过开花物候来估算花粉供体表型的季节偏移。通过对子代世代进行检测，可直接估算时间遗传结构，即回顾性估算。但由于目标性状——开花时间在母本与父本间存在表型相关性，该估算方法存在一定局限。本研究开发了一种新型回顾性方法：通过固定母本贡献来分离开花时间性状，并在整个开花季的8个开放式授粉田间样地中对花粉库进行采样。
主要结果：我们在8个田间样地中的7个里检测到了开花时间相关的时间遗传结构。尤为值得关注的是，直接（回顾性）时间遗传结构估计值比基于开花物候的前瞻性估计值高出35%。花粉供体的空间聚集并未对时间遗传结构产生影响，但当遗传力经实验提升后，该结构会显著增强。
结论：时间遗传结构，尤其是开花时间相关的结构，大概率广泛存在于各类植物种群中，且采用前瞻性方法可能会低估该结构的存在。本文还探讨了时间遗传结构的全基因组层面影响，以及植物种群形成适应性时间梯度的潜在可能。