Daïnou K, Mahy G, Duminil J, Dick C W, Doucet J-L, Donkpégan A S L, Pluijgers M, Sinsin B, Lejeune P, Hardy O J
1] Laboratory of Tropical and Subtropical Forestry, Unit of Forest and Nature Management, Gembloux Agro-Bio Tech, University of Liege, Gembloux, Belgium [2] Laboratory of Applied Ecology, Faculty of Agronomic Science, University of Abomey-Calavi, Cotonou, Benin.
Biodiversity and Landscape Unit, Gembloux Agro-Bio Tech, University of Liege, Gembloux, Belgium.
Heredity (Edinb). 2014 Jul;113(1):74-85. doi: 10.1038/hdy.2014.5. Epub 2014 Feb 19.
The long generation time and large effective size of widespread forest tree species can result in slow evolutionary rate and incomplete lineage sorting, complicating species delimitation. We addressed this issue with the African timber tree genus Milicia that comprises two morphologically similar and often confounded species: M. excelsa, widespread from West to East Africa, and M. regia, endemic to West Africa. We combined information from nuclear microsatellites (nSSRs), nuclear and plastid DNA sequences, and morphological systematics to identify significant evolutionary units and infer their evolutionary and biogeographical history. We detected five geographically coherent genetic clusters using nSSRs and three levels of genetic differentiation. First, one West African cluster matched perfectly with the morphospecies M. regia that formed a monophyletic clade at both DNA sequences. Second, a West African M. excelsa cluster formed a monophyletic group at plastid DNA and was more related to M. regia than to Central African M. excelsa, but shared many haplotypes with the latter at nuclear DNA. Third, three Central African clusters appeared little differentiated and shared most of their haplotypes. Although gene tree paraphyly could suggest a single species in Milicia following the phylogenetic species concept, the existence of mutual haplotypic exclusivity and nonadmixed genetic clusters in the contact area of the two taxa indicate strong reproductive isolation and, thus, two species following the biological species concept. Molecular dating of the first divergence events showed that speciation in Milicia is ancient (Tertiary), indicating that long-living tree taxa exhibiting genetic speciation may remain similar morphologically.
广泛分布的森林树种世代时间长且有效种群规模大，可能导致进化速度缓慢和不完全谱系分选，使物种界定变得复杂。我们以非洲用材树种米利西亚属（Milicia）来解决这个问题，该属包含两个形态相似且常被混淆的物种：分布于西非至东非的M. excelsa，以及西非特有的M. regia。我们整合了核微卫星（nSSRs）、核DNA和质体DNA序列信息以及形态系统学信息，以识别重要的进化单元，并推断它们的进化和生物地理历史。我们利用nSSRs检测到五个地理上连贯的遗传簇以及三个遗传分化水平。第一，一个西非簇与形态物种M. regia完全匹配，该形态物种在两个DNA序列上均形成单系分支。第二，一个西非M. excelsa簇在质体DNA上形成单系类群，与M. regia的亲缘关系比与中非M. excelsa的更近，但在核DNA上与后者共享许多单倍型。第三，三个中非簇几乎没有分化，共享大部分单倍型。尽管根据系统发育物种概念，基因树并系可能表明米利西亚属为单一物种，但在两个分类单元的接触区域存在相互单倍型排他性和非混合遗传簇，这表明存在强烈的生殖隔离，因此，根据生物物种概念，为两个物种。首次分歧事件的分子定年表明，米利西亚属的物种形成很古老（第三纪），这表明表现出遗传物种形成的长寿树木类群在形态上可能仍然相似。
