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Species delimitation in the African tree genus Lophira (Ochnaceae) reveals cryptic genetic variation

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Abstract

Species delimitation remains a crucial issue for widespread plants occurring across forest-savanna ecotone such as Lophira (Ochnaceae). Most taxonomists recognize two parapatric African tree species, widely distributed and morphologically similar but occurring in contrasted habitats: L. lanceolata in the Sudanian dry forests and savannahs and L. alata in the dense Guineo-Congolian forests. Both species co-occur along a ca. 3000 km long forest-savanna mosaic belt, constituting ideal models for investigating hybridization patterns and the impact of past glacial periods on the genetic structures in two types of ecosystems. We genotyped 10 nuclear microsatellites for 803 individuals sampled across the distribution range of Lophira. Both species exhibit similar levels of genetic diversity [He = 0.52 (L. alata); 0.44 (L. lanceolata)] and are well differentiated, consistent with taxonomic delimitation (FST = 0.36; RST = 0.49), refuting the hypothesis that they might constitute ecotypes rather than distinct species. Furthermore, L. alata displayed two deeply differentiated clusters (FST = 0.37; RST = 0.53) distributed in parapatry, one endemic to Western Gabon while another cluster extended over the remaining species range, suggests that L. alata is made of two cryptic species. We showed that rare hybrids occur in some contact zones between these three species, leaving a weak signal of introgression between L. lanceolata and the northern cluster of L. alata. At the intra-specific level, the latter species also show weak genetic structuring between Upper and Lower Guinea and the intensity did not differ strikingly between rainforest and savanna ecosystems. The discovery of a new species of Lophira with a narrow distribution in West Gabon where it is intensively exploited for its timber requires to evaluate its conservation status.

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Acknowledgements

Financial support was provided by the Belgian Federal Science Policy Office (Belspo) through a postdoctoral grant (EEBK) within the project AFRIFORD, and by the F.R.S.-FNRS (Grant No. J.0292.17). Furthermore, this project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 801505. We would like to thank Dakis-Yaoba Ouedraogo for providing herbarium data for L. alata individuals from Gabon including phenological traits, and Marc Sosef for having compared the few herbarium vouchers from western Gabon and eastern/northern Gabon available at the Meise Botanic Garden (BR). We thank CENAREST (Gabon) for the sampling permission (AR0012/18). Moreover, we thank the three anonymous reviewers whose comments have greatly improved this manuscript.

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  1. Eben-Ezer Baba Kayode Ewédjè and Simon Jansen have contributed equally to this work.

Authors and Affiliations

  1. Evolutionary Biology and Ecology Unit, Faculté des Sciences, Université Libre de Bruxelles, Avenue F. D. Roosevelt 50, CP 160/12, Brussels, 1050, Belgium

    Eben-Ezer Baba Kayode Ewédjè, Simon Jansen, Guillaume Kouame Koffi, Adrien Staquet, Rosalia Piñeiro, Rodolphe Abessole Essaba & Olivier J. Hardy

  2. Gembloux Agro-bio Tech, Université de Liège, Passage des Déportés 2, Gembloux, 5030, Belgium

    Kasso Daïnou, Achille Bernand Biwolé & Jean-Louis Doucet

  3. Laboratoire de Génomique Fonctionnelle et Amélioration Génétique, Université Nangui Abrogoua, BP 801, Abidjan 02, Côte d’Ivoire

    Guillaume Kouame Koffi

  4. Institut de Recherche Ecologie Tropicale (IRET), BP 13 354, Libreville, Gabon

    Nestor Laurier Engone Obiang

  5. Laboratoire de Biologie, Ecologie végétale appliquée et de génétique forestière, Faculté des Sciences et Techniques de Dassa Zoumè, Université Nationale des Sciences, Technologies, Ingénierie et Mathématiques (UNSTIM-Abomey), Abomey, Benin

    Eben-Ezer Baba Kayode Ewédjè

  6. Herbier National du Gabon, BP 1156, Libreville, Gabon

    Nestor Laurier Engone Obiang

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  1. Eben-Ezer Baba Kayode Ewédjè
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Ewédjè, EE.B.K., Jansen, S., Koffi, G.K. et al. Species delimitation in the African tree genus Lophira (Ochnaceae) reveals cryptic genetic variation. Conserv Genet 21, 501–514 (2020). https://doi.org/10.1007/s10592-020-01265-7

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