[en] 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, which 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 non-admixed 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.
Disciplines :
Genetics & genetic processes
Author, co-author :
Daïnou, Kasso ; Université de Liège - ULiège > Forêts, Nature et Paysage > Laboratoire de Foresterie des régions trop. et subtropicales
Mahy, Grégory ; Université de Liège - ULiège > Forêts, Nature et Paysage > Biodiversité et Paysage
Duminil, Jérôme
Dick, Christopher
Doucet, Jean-Louis ; Université de Liège - ULiège > Forêts, Nature et Paysage > Laboratoire de Foresterie des régions trop. et subtropicales
Donkpegan, Seggbedji ; Université de Liège - ULiège > Forêts, Nature et Paysage > Laboratoire de Foresterie des régions trop. et subtropicales
Pluijgers, Michaël
Sinsin, Brice
Lejeune, Philippe ; Université de Liège - ULiège > Forêts, Nature et Paysage > Gestion des ressources forestières et des milieux naturels
Hardy, Olivier
Language :
English
Title :
Species delimitation and diversification in the widespread tree genus Milicia (Moraceae)
Alternative titles :
[en] Délimitation des espèces et diversification du genre Milicia (Moraceae)
Publication date :
June 2013
Number of pages :
19
Event name :
ATBC - OTS. New Frontiers in Tropical Biology: The Next 50 years