title: Speciation slowing down in widespread and long-living tree taxa: insights from the tropical timber tree genus Milicia (Moraceae).
abstract: 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.
authors.affiliation: 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.
authors.forename: K
authors.initials: K
authors.lastname: Daïnou
authors.affiliation: Biodiversity and Landscape Unit, Gembloux Agro-Bio Tech, University of Liege, Gembloux, Belgium.
authors.forename: G
authors.initials: G
authors.lastname: Mahy
authors.affiliation: 1] Evolutionary Biology and Ecology, Faculté des Sciences, Université Libre de Bruxelles, Brussels, Belgium [2] Bioversity International, Forest Genetic Resources Programme, Sub-Regional Office for Central Africa, Yaoundé, Cameroon.
authors.forename: J
authors.initials: J
authors.lastname: Duminil
authors.affiliation: 1] Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA [2] Smithsonian Tropical Research Institute, Gamboa, Republic of Panama.
authors.forename: C W
authors.initials: CW
authors.lastname: Dick
authors.affiliation: Laboratory of Tropical and Subtropical Forestry, Unit of Forest and Nature Management, Gembloux Agro-Bio Tech, University of Liege, Gembloux, Belgium.
authors.forename: J-L
authors.initials: JL
authors.lastname: Doucet
authors.affiliation: Laboratory of Tropical and Subtropical Forestry, Unit of Forest and Nature Management, Gembloux Agro-Bio Tech, University of Liege, Gembloux, Belgium.
authors.forename: A S L
authors.initials: AS
authors.lastname: Donkpégan
authors.affiliation: Laboratory of Tropical and Subtropical Forestry, Unit of Forest and Nature Management, Gembloux Agro-Bio Tech, University of Liege, Gembloux, Belgium.
authors.forename: M
authors.initials: M
authors.lastname: Pluijgers
authors.affiliation: Laboratory of Applied Ecology, Faculty of Agronomic Science, University of Abomey-Calavi, Cotonou, Benin.
authors.forename: B
authors.initials: B
authors.lastname: Sinsin
authors.affiliation: Unit of Forest and Nature Management, Gembloux Agro-Bio Tech, University of Liege, Gembloux, Belgium.
authors.forename: P
authors.initials: P
authors.lastname: Lejeune
authors.affiliation: Evolutionary Biology and Ecology, Faculté des Sciences, Université Libre de Bruxelles, Brussels, Belgium.
authors.forename: O J
authors.initials: OJ
authors.lastname: Hardy
mesh_terms: D000349:Africa; D001483:Base Sequence; D001499:Bayes Theorem; D005075:Biological Evolution; D017931:DNA Primers / Q000235:genetics; D019143:Evolution, Molecular; D049810:Genetic Speciation; D006239:Haplotypes / Q000235:genetics; D018895:Microsatellite Repeats / Q000235:genetics; D008957:Models, Genetic; D008969:Molecular Sequence Data; D029586:Moraceae / Q000033:anatomy & histology* / Q000235:genetics*; D005810:Multigene Family / Q000235:genetics; D010802:Phylogeny; D058974:Phylogeography; D017422:Sequence Analysis, DNA
chemical_list: D017931:DNA Primers