González-Astorga Jorge, Vovides Andrew P, Cruz-Angon Andrea, Octavio-Aguilar Pablo, Iglesias Carlos
Laboratorio de Genética de Poblaciones, Departamento de Biología Evolutiva, Instituto de Ecología, A. C. Km. 2.5 Antigua Carretera a Coatepec No. 351, Xalapa 91070, Veracruz, Mexico.
Ann Bot. 2005 May;95(6):999-1007. doi: 10.1093/aob/mci106. Epub 2005 Mar 10.
Dioon angustifolium was considered within D. edule. Recent morphometric and allozyme studies on D. edule have shown that D. angustifolium has originated from geographic isolation and is therefore considered to be a separate species. This cycad is endemic to north-eastern Mexico and is known only from three populations in the Sierra Madre Oriental mountain chain. Its populations are small when compared with its southern relative D. edule. In this study, genetic variation was determined within and between populations of D. angustifolium and the genetic consequences of habitat fragmentation and isolation of populations of this species were assessed.
Allozyme electrophoresis of 14 presumptive loci was used. The data were analysed with statistical approximations for estimating genetic diversity, structure, gene flow and recent genetic bottlenecks.
Means and standard deviations of genetic diversity estimators were: number of alleles per locus (A = 1.67 +/- 0.23), percentage of polymorphic loci (P = 52.4 +/- 23 %) and expected heterozygosity (H(E) = 0.218 +/- 0.093). The genetic variation attributable to differences among populations was 16.7 %. Mean gene flow between paired populations was Nm = 1.55 +/- 0.67, which is similar to that reported for endemic plant species of narrow geographical distribution and species with gravity-dispersed seed. A recent bottleneck is detected in the populations studied.
Dioon angustifolium presents high levels of genetic diversity compared with other cycad species, in spite of small population sizes. The recent bottleneck effect did not effectively reduce the genetic variation to the extent of eliminating these populations. The distribution of D. angustifolium appears to be the result of historical biogeographical effects related to the Pleistocene glaciations. It is recommended that this species be catalogued in the IUCN Red List of Threatened Species and conservation efforts be made to preserve it.
狭叶铁树曾被视为泽米铁的一种。近期对泽米铁的形态测量和等位酶研究表明，狭叶铁树源自地理隔离，因此被视为一个独立的物种。这种苏铁是墨西哥东北部特有的，仅在东马德雷山脉的三个种群中被发现。与它在南部的近缘种泽米铁相比，其种群数量较少。在本研究中，测定了狭叶铁树种群内部和种群之间的遗传变异，并评估了该物种栖息地破碎化和种群隔离的遗传后果。
采用对14个假定基因座进行等位酶电泳分析。运用统计近似方法对数据进行分析，以估计遗传多样性、结构、基因流和近期的遗传瓶颈。
遗传多样性估计值的均值和标准差分别为：每个基因座的等位基因数（A = 1.67 ± 0.23）、多态性基因座的百分比（P = 52.4 ± 23%）和预期杂合度（H(E) = 0.218 ± 0.093）。种群间差异导致的遗传变异为16.7%。成对种群间的平均基因流为Nm = 1.55 ± 0.67，这与报道的地理分布狭窄的特有植物物种以及种子靠重力传播的物种的情况相似。在所研究的种群中检测到近期存在瓶颈效应。
尽管狭叶铁树种群规模较小，但与其他苏铁物种相比，仍呈现出较高水平的遗传多样性。近期的瓶颈效应并未有效降低遗传变异，以至于消除这些种群。狭叶铁树的分布似乎是与更新世冰川作用相关的历史生物地理效应的结果。建议将该物种列入世界自然保护联盟濒危物种红色名录，并采取保护措施对其加以保护。
