Department of Forest Sciences, University of British Columbia, Vancouver, British Columbia, Canada.
PLoS One. 2012;7(5):e36769. doi: 10.1371/journal.pone.0036769. Epub 2012 May 10.
With predicted decreases in genetic diversity and greater genetic differentiation at range peripheries relative to their cores, it can be difficult to distinguish between the roles of current disturbance versus historic processes in shaping contemporary genetic patterns. To address this problem, we test for differences in historic demography and landscape genetic structure of coastal giant salamanders (Dicamptodon tenebrosus) in two core regions (Washington State, United States) versus the species' northern peripheral region (British Columbia, Canada) where the species is listed as threatened. Coalescent-based demographic simulations were consistent with a pattern of post-glacial range expansion, with both ancestral and current estimates of effective population size being much larger within the core region relative to the periphery. However, contrary to predictions of recent human-induced population decline in the less genetically diverse peripheral region, there was no genetic signature of population size change. Effects of current demographic processes on genetic structure were evident using a resistance-based landscape genetics approach. Among core populations, genetic structure was best explained by length of the growing season and isolation by resistance (i.e. a 'flat' landscape), but at the periphery, topography (slope and elevation) had the greatest influence on genetic structure. Although reduced genetic variation at the range periphery of D. tenebrosus appears to be largely the result of biogeographical history rather than recent impacts, our analyses suggest that inherent landscape features act to alter dispersal pathways uniquely in different parts of the species' geographic range, with implications for habitat management.
与核心区域相比，预测边缘区域的遗传多样性减少，遗传分化更大，因此很难区分当前干扰与历史过程在塑造当代遗传模式中的作用。为了解决这个问题，我们测试了沿海巨型蝾螈（Dicamptodon tenebrosus）在两个核心区域（美国华盛顿州）与该物种被列为受威胁的北部边缘区域（加拿大不列颠哥伦比亚省）之间的历史人口动态和景观遗传结构的差异。基于合并的人口动态模拟与冰河期后范围扩张的模式一致，核心区域内的祖先和当前有效种群大小估计都远远大于边缘区域。然而，与最近人类导致的边缘地区遗传多样性较低的种群减少的预测相反，没有种群大小变化的遗传特征。使用基于阻力的景观遗传学方法，当前人口动态过程对遗传结构的影响是明显的。在核心种群中，遗传结构最好由生长季节的长度和阻力隔离（即“平坦”景观）来解释，但在边缘地区，地形（坡度和海拔）对遗传结构的影响最大。尽管 D. tenebrosus 分布范围边缘的遗传变异减少似乎在很大程度上是生物地理历史的结果，而不是最近的影响，但我们的分析表明，内在的景观特征独特地改变了物种地理分布范围内不同部分的扩散途径，对生境管理具有影响。
