Island Ecology and Evolution Research Group, IPNA-CSIC, La Laguna, Tenerife, Canary Islands, Spain.
PLoS One. 2011;6(11):e27697. doi: 10.1371/journal.pone.0027697. Epub 2011 Nov 16.
A central aim of island biogeography is to understand the colonization history of insular species using current distributions, fossil records and genetic diversity. Here, we analyze five plastid DNA regions of the endangered Juniperus brevifolia, which is endemic to the Azores archipelago.
METHODOLOGY/PRINCIPAL FINDINGS: The phylogeny of the section Juniperus and the phylogeographic analyses of J. brevifolia based on the coalescence theory of allele (plastid) diversity suggest that: (1) a single introduction event likely occurred from Europe; (2) genetic diversification and inter-island dispersal postdated the emergence of the oldest island (Santa Maria, 8.12 Ma); (3) the genetic differentiation found in populations on the islands with higher age and smaller distance to the continent is significantly higher than that on the younger, more remote ones; (4) the high number of haplotypes observed (16), and the widespread distribution of the most frequent and ancestral ones across the archipelago, are indicating early diversification, demographic expansion, and recurrent dispersal. In contrast, restriction of six of the seven derived haplotypes to single islands is construed as reflecting significant isolation time prior to colonization.
CONCLUSIONS/SIGNIFICANCE: Our phylogeographic reconstruction points to the sequence of island emergence as the key factor to explain the distribution of plastid DNA variation. The reproductive traits of this juniper species (anemophily, ornithochory, multi-seeded cones), together with its broad ecological range, appear to be largely responsible for recurrent inter-island colonization of ancestral haplotypes. In contrast, certain delay in colonization of new haplotypes may reflect intraspecific habitat competition on islands where this juniper was already present.
岛屿生物地理学的一个主要目标是通过当前的分布、化石记录和遗传多样性来理解岛屿物种的殖民历史。在这里，我们分析了濒危物种短叶松（Juniperus brevifolia）的五个质体 DNA 区域，该物种是亚速尔群岛的特有种。
方法/主要发现：根据等位基因（质体）多样性的融合理论，对 Juniperus 组的系统发育和 J. brevifolia 的系统地理分析表明：（1）很可能发生了一次从欧洲的单一传入事件；（2）遗传多样化和岛间扩散发生在最古老的岛屿（圣玛丽亚岛，8.12 万年前）出现之后；（3）在年龄较大、与大陆距离较小的岛屿上发现的种群的遗传分化明显高于年龄较小、距离较远的岛屿；（4）观察到的单倍型数量很多（16 个），最常见和最原始的单倍型广泛分布在整个群岛，这表明早期的多样化、种群扩张和反复的扩散。相比之下，将七个衍生单倍型中的六个限制在单个岛屿上，则表明在殖民之前存在显著的隔离时间。
结论/意义：我们的系统地理重建表明，岛屿出现的顺序是解释质体 DNA 变异分布的关键因素。这种 Juniperus 物种（风媒传粉、鸟类传播、多种子的球果）的繁殖特征，以及其广泛的生态范围，似乎在很大程度上导致了祖先单倍型的反复岛间殖民。相比之下，某些新单倍型的殖民延迟可能反映了该 Juniperus 已经存在的岛屿上种内栖息地竞争。
