U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, Corvallis, Oregon, United States of America.
U.S. Department of Agriculture Forest Service, Pacific Northwest Region, Corvallis, Oregon, United States of America.
PLoS One. 2018 Aug 2;13(8):e0201720. doi: 10.1371/journal.pone.0201720. eCollection 2018.
Landscape genetics investigations examine how the availability and configuration of habitat influence genetic structure of plants and animals. We used landscape genetics to evaluate the role that forest connectivity plays in determining genetic structure of the federally-threatened Northern Spotted Owl (Strix occidentalis caurina) using genotypes of 339 Northern Spotted Owls obtained for 10 microsatellite loci. Spatial clustering analyses identified a distinct genetic cluster at the southern extent of the region examined. This cluster could not be linked to landscape connectivity patterns and suggested that post-Pleistocene processes were involved with its development rather than contemporary landscape configuration. We also compared matrices of pairwise inter-individual genetic distances with resistance distances derived from a circuit-theory based framework. Resistance distances were obtained for an idealized raster map that reflected continuous unimpeded dispersal habitat across the landscape along with five empirically-derived raster maps reflecting the 1870's, 1940's, 1986, 1994, and 2012. Resistance distances from the idealized map served as surrogates for linear geographic distances. Relative to idealized conditions, resistance distances were ~250% higher in the 1940's and ~200% higher from 1986 onward. Resistance distances from the 1870's were ~40% higher than idealized conditions. Inter-individual genetic distances were most highly correlated with resistance distances from the idealized map rather than any of the empirical maps. Two hypotheses explain our results. First, our results may reflect temporal lags between the onset of large-scale habitat alterations and their novel effects on genetic structure in long-lived species such as Northern Spotted Owls. Second, because Northern Spotted Owls disperse over long distances, our results may indicate that forest habitat has never been sufficiently fragmented to the point where connectivity was disrupted. The second hypothesis could indicate that forest management practices mandated by the Northwest Forest Plan succeeded with one of its primary goals. However, our results do not represent a complete portrayal of the status of Northern Spotted Owls given detection of significant population declines and bottlenecks in other studies. Future investigations based on computer simulations may help distinguish between hypotheses.
景观遗传学研究考察了栖息地的可及性和配置如何影响植物和动物的遗传结构。我们使用景观遗传学来评估森林连通性在确定受联邦威胁的北方斑点猫头鹰（Strix occidentalis caurina）遗传结构中的作用，方法是使用在 10 个微卫星基因座上获得的 339 只北方斑点猫头鹰的基因型。空间聚类分析在研究区域的南部边缘确定了一个独特的遗传聚类。该聚类与景观连通性模式无关，表明后更新世过程与其发展有关，而不是与当代景观配置有关。我们还将个体间遗传距离的矩阵与基于电路理论框架得出的抗阻距离进行了比较。抗阻距离是从反映景观中连续无障碍扩散栖息地的理想化栅格地图以及反映 1870 年代、1940 年代、1986 年、1994 年和 2012 年的五个经验栅格地图中获得的。理想地图的抗阻距离可作为线性地理距离的替代物。与理想条件相比，1940 年代的抗阻距离高约 250%，1986 年以来的抗阻距离高约 200%。1870 年代的抗阻距离比理想条件高约 40%。个体间遗传距离与理想地图的抗阻距离相关性最高，而与任何经验地图的相关性都不高。有两个假设可以解释我们的结果。首先，我们的结果可能反映了大规模栖息地改变的开始与它们对像北方斑点猫头鹰这样的长寿命物种遗传结构的新影响之间的时间滞后。其次，由于北方斑点猫头鹰长距离扩散，我们的结果可能表明森林栖息地从未被分割到足以破坏连通性的程度。第二个假设可能表明，西北森林计划规定的森林管理实践成功地实现了其主要目标之一。然而，鉴于其他研究中发现了北方斑点猫头鹰数量显著下降和瓶颈的情况，我们的结果并不能完全代表北方斑点猫头鹰的现状。基于计算机模拟的未来研究可能有助于在假设之间做出区分。
