Gonzales E, Hamrick J L
Department of Ecology, Evolution and Natural Resources, Rutgers University, New Brunswick, NJ 08901-8551, USA.
Heredity (Edinb). 2005 Oct;95(4):306-14. doi: 10.1038/sj.hdy.6800719.
We assessed genetic diversity and its distribution in the rare southeastern US forest understory species, Trillium reliquum. In all, 21 loci were polymorphic (PS=95.5%) and the mean number of alleles per polymorphic locus was 3.05. However, genetic diversity was relatively low (Hes=0.120) considering the level of polymorphism observed for this outcrossing species. A relatively high portion of the genetic diversity (29.7%) was distributed among populations. There was no relationship between population size and genetic diversity, and we did not detect significant inbreeding. These results are best explained by the apparent self-incompatibility of this species, its longevity and clonal reproduction. To address questions regarding the history of T. reliquum's rarity, we compared results for T. reliquum with that of its more common and partially sympatric congener, T. cuneatum. Despite shared life history traits and history of land use, we observed significant genetic differences between the two species. Although T. cuneatum contains slightly lower polymorphism (Ps=85%), we detected significantly higher genetic diversity (Hes=0.217); most of its genetic diversity is contained within its populations (GST=0.092). Our results suggest that not only is there little gene flow among extant T. reliquum populations, but that rarity and population isolation in this species is of ancient origins, rather than due to more recent anthropogenic fragmentation following European colonization. The Chattahoochee River was identified as a major barrier to gene exchange.
我们评估了美国东南部稀有林下物种延龄草（Trillium reliquum）的遗传多样性及其分布情况。总共21个位点具有多态性（PS = 95.5%），每个多态性位点的平均等位基因数为3.05。然而，考虑到该异交物种所观察到的多态性水平，其遗传多样性相对较低（Hes = 0.120）。遗传多样性中有相对较高的比例（29.7%）分布在种群之间。种群大小与遗传多样性之间没有关系，并且我们未检测到显著的近亲繁殖现象。这些结果最好用该物种明显的自交不亲和性、长寿和克隆繁殖来解释。为了解决有关延龄草稀有性历史的问题，我们将延龄草的结果与其更常见且部分同域分布的近缘种楔叶延龄草（Trillium cuneatum）的结果进行了比较。尽管它们具有共同的生活史特征和土地利用历史，但我们观察到这两个物种之间存在显著的遗传差异。尽管楔叶延龄草的多态性略低（Ps = 85%），但我们检测到其遗传多样性显著更高（Hes = 0.217）；其大部分遗传多样性存在于种群内部（GST = 0.092）。我们的结果表明，现存的延龄草种群之间不仅几乎没有基因流动，而且该物种的稀有性和种群隔离起源古老，而非由于欧洲殖民后最近的人为碎片化。查塔胡奇河被确定为基因交流的主要障碍。
