Plant Ecology and Evolution, Department of Ecology and Genetics, EBC, Uppsala University, SE-752 36 Uppsala, Sweden.
UMR 8198 -Evo-Eco-Paleo, University of Lille, Lille, France.
Am J Bot. 2024 Feb;111(2):e16273. doi: 10.1002/ajb2.16273. Epub 2024 Jan 30.
Density-dependent pollinator visitation can lead to density-dependent mating patterns and within-population genetic structure. In Gymnadenia conopsea, individuals in low-density patches receive more self pollen than individuals in high-density patches, suggesting higher relatedness at low density. Ongoing fragmentation is also expected to cause more local matings, potentially leading to biparental inbreeding depression.
To evaluate whether relatedness decreases with local density, we analyzed 1315 SNP loci in 113 individuals within two large populations. We quantified within-population genetic structure in one of the populations, recorded potential habitat barriers, and visualized gene flow using estimated effective migration surfaces (EEMS). We further estimated the magnitude of biparental inbreeding depression that would result from matings restricted to within 5 m.
There was no significant relationship between local density and relatedness in any population. We detected significant fine-scale genetic structure consistent with isolation by distance, with positive kinship coefficients at distances below 10 m. Kinship coefficients were low, and predicted biparental inbreeding depression resulting from matings within the closest 5 m was a modest 1-3%. The EEMS suggested that rocks and bushes may act as barriers to gene flow within a population.
The results suggest that increased self-pollen deposition in sparse patches does not necessarily cause higher selfing rates or that inbreeding depression results in low establishment success of inbred individuals. The modest relatedness suggests that biparental inbreeding depression is unlikely to be an immediate problem following fragmentation of large populations. The results further indicate that habitat structure may contribute to governing fine-scale genetic structure in G. conopsea.
密度依赖型传粉者访问可以导致密度依赖型交配模式和种群内遗传结构。在 Gymnadenia conopsea 中，低密度斑块中的个体比高密度斑块中的个体接收更多的自花粉，表明低密度下的亲缘关系更高。正在进行的片段化也预计会导致更多的本地交配，可能导致双亲近亲交配的衰退。
为了评估亲缘关系是否随局部密度降低，我们分析了两个大种群中 113 个个体的 1315 个 SNP 位点。我们在其中一个种群中量化了种群内遗传结构，记录了潜在的栖息地障碍，并使用估计的有效迁移面（EEMS）可视化基因流。我们进一步估计了由于限制在 5 米内的交配而导致的双亲近亲交配衰退的幅度。
在任何种群中，局部密度与亲缘关系之间都没有显著的关系。我们检测到与距离隔离一致的显著细尺度遗传结构，在 10 米以下的距离上存在正亲缘系数。亲缘系数较低，预测由于在最近的 5 米内的交配而导致的双亲近亲交配衰退幅度适中为 1-3%。EEMS 表明岩石和灌木可能成为种群内基因流动的障碍。
结果表明，稀疏斑块中自花粉沉积的增加不一定会导致更高的自交率或近亲交配衰退导致近交个体的建立成功率降低。适度的亲缘关系表明，在大种群分裂后，双亲近亲交配的衰退不太可能成为一个立即的问题。结果进一步表明，栖息地结构可能有助于控制 G. conopsea 的细尺度遗传结构。
