Data from: Fitness dynamics within a poplar hybrid zone: I. Prezygotic and postzygotic barriers impacting a native poplar hybrid stand.

Hybridization and introgression are pervasive evolutionary phenomena that provide insight to the selective forces that maintain species boundaries, permit gene flow and control the direction of evolutionary change. Poplar trees (Populus L.) are well known for their ability to form viable hybrids and maintain their distinct species boundaries despite this interspecific gene flow. We sought to quantify the hybridization dynamics and postzygotic fitness within a hybrid stand of balsam poplar (Populus balsamifera L.), eastern cottonwood (P. deltoides Marsh.) and their natural hybrids to gain insight to the barriers maintaining this stable hybrid zone. We observed asymmetrical hybrid formation with P. deltoides acting as the seed parent, but with subsequent introgression biased towards P. balsamifera. Native hybrids expressed fitness traits intermediate to the parental species and were not universally unfit. That said, native hybrid seedlings were absent from the seedling population, which may indicate additional selective pressures controlling their recruitment. It is imperative that we understand the selective forces maintaining this native hybrid zone in order to quantify the impact of exotic poplar hybrids on this native system.

杂交与基因渐渗是广泛存在的进化现象，可为解析维持物种界限、介导基因流并调控进化方向的选择压力提供重要见解。杨树（杨属 *Populus* L.）因其可形成可育杂种，且即便存在种间基因流仍能维持自身独特物种边界的特性而广为人知。本研究旨在对香脂杨（*Populus balsamifera* L.）、美洲黑杨（*P. deltoides* Marsh.）及其天然杂种构成的杂种林分中的杂交动态与合子后适合度进行量化分析，以解析维持该稳定杂交带的隔离障碍机制。研究观察到不对称的杂种形成模式：以美洲黑杨作为种子亲本，而后续的渐渗过程则偏向于香脂杨。天然杂种的适合度性状表现为双亲的中间型，并非普遍适应性低下。尽管如此，幼苗种群中并未发现天然杂种实生苗，这或许表明存在额外的选择压力调控其种群补充过程。为量化外来杨树杂种对该本土生态系统的影响，解析维持该本土杂交带的选择压力机制至关重要。