Data from: Human impacted landscapes facilitate hybridization between a native and an introduced tree

Spatial and temporal dynamics of hybridization, in particular the influence of local environmental conditions, are well studied for sympatric species but less is known for native-introduced systems, especially for long-lived species. We used microsatellite and chloroplast DNA markers to characterize the influence of anthropogenic landscapes on the extent, direction, and spatial distribution of hybridization between a native North American tree Juglans cinerea (butternut) and an introduced tree Juglans ailantifolia (Japanese walnut) for 1363 trees at 48 locations across the native range of butternut. Remarkably, admixture in anthropogenic sites reached nearly 70%, while fragmented and continuous forests showed minimal admixture (7.5% and 2.5%, respectively). Furthermore, more hybrids in anthropogenic sites had J. ailantifolia seed parents (95%) than hybrids in fragmented and continuous forests (69% and 59%, respectively). Our results show a strong influence of landscape on rate and direction of realized gene flow. While hybridization is clearly rampant in anthropogenic landscapes, our results suggest that even small forested landscapes serve as substantial barriers to hybridization, a key consideration for conservation planning for butternut, a species already exhibiting severe decline, and for other North American forest trees that hybridize with introduced congeners.

杂交的时空动态，尤其是局域环境条件的影响，在同域共存物种中已得到充分研究，但对于本土-外来物种种间系统，尤其是长寿物种，相关认知仍较为匮乏。本研究以灰胡桃（Juglans cinerea，butternut）的自然分布区内48个采样点的1363株个体为研究对象，利用微卫星（microsatellite）与叶绿体DNA标记（chloroplast DNA marker），解析人为景观对北美本土树种灰胡桃与外来树种日本胡桃（Juglans ailantifolia，Japanese walnut）之间杂交的程度、方向及空间分布的影响。值得注意的是，人为干扰生境中的基因混合比例接近70%，而片段化生境与连续森林生境中的基因混合比例极低，分别仅为7.5%与2.5%。此外，人为干扰生境中以日本胡桃为母本的杂交个体占比（95%）显著高于片段化生境与连续森林生境中的对应比例（分别为69%与59%）。本研究结果表明，景观格局对实际发生的基因流速率与方向具有显著影响。尽管人为景观中杂交现象极为普遍，但本研究结果显示，即便小型林地也可成为杂交发生的显著障碍——这一点对于已面临严重种群衰退的灰胡桃，以及其他与外来同属树种发生杂交的北美林木的保护规划而言，均为关键考量因素。