Species delimitation in the genus Greenwayodendron based on morphological and genetic markers reveal
by Brandet-Junior Lissambou, Thomas L.P. Couvreur, Christiane Atteke, Tariq Stévart, Rosalia Piñeiro, Gilles Dauby, Franck K. Monthe, Davy U. Ikabanga, Bonaventure Sonké, Bertrand M’batchi, Olivier J. Hardy
Combining genetic and morphological markers is a powerful approach for species delimitation, much needed in tropical species complexes. Greenwayodendron (Annonaceae) is a widespread genus of tree species distributed from West to East African rainforests. Two species and four infra-specific taxa are currently recognized. However, preliminary genetic studies suggested the occurrence of several cryptic species, undescribed to date. We tested species delimitation within Greenwayodendron by combining morphological and population genetics data. First, a visual inspection of about a thousand specimens suggested the existence of seven morpho-groups: four of them occur in Central Africa and overlap in Gabon while three other ones are allopatric, occurring respectively in West Africa, East Africa, and the islands of São Tomé and Prìncipe. The difference between morphological groups was confirmed by measuring 26 morphological characters on 233 herbarium specimens. Second, after genotyping 800 samples at eight nuclear microsatellites, Bayesian clustering analyses identified four genetic clusters corresponding to the well-sampled morpho-groups, whereas a factorial correspondence analysis (FCA) and pairwise FST and RST measures confirmed the genetic differentiation of the three remaining morpho-groups represented by few samples. We considered that a clear genetic differentiation occurring between sympatric populations advocate for recognizing distinct species following the Biological Species Concept. Our analyses highlight that the current taxonomic treatment of Greenwayodendron underestimates the total number of species. We identified two new species ('Glabrum' and 'Littorale') and support the elevation to the rank of species of two varieties (G. suaveolens subsp suaveolens var. gabonica and G. suaveolens subsp suaveolens var. suaveolens) and one subspecies (G. suaveolens subsp usambaricum). The taxonomic status of specimens collected in São Tomé and Prìncipe remains inconclusive, partly due to the limited fertile material available. Our study highlights the strength of combining morphological and population genetics data to discover new taxa.