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Alpine Botany

, Volume 126, Issue 1, pp 59–71 | Cite as

Vicariance, dispersal, and hybridization in a naturally fragmented system: the afro-alpine endemics Carex monostachya and C. runssoroensis (Cyperaceae)

  • Abel Gizaw
  • Tigist Wondimu
  • Tusiime Felly Mugizi
  • Catherine Aloyce Masao
  • Ahmed Abdikadir Abdi
  • Magnus Popp
  • Dorothee Ehrich
  • Sileshi Nemomissa
  • Christian Brochmann
Original Article

Abstract

The naturally fragmented habitat on the tallest African mountains provides a good model system to study vicariance, dispersal, and hybridization. Many mountains are separated by lowland that likely was unsuitable for high-alpine plants even during cold climatic periods. We explore the relative importance of these processes using two endemic sister species: the widespread Ethiopian/eastern East African Carex monostachya and the mainly western East African C. runssoroensis. These bog-forming sedges co-occur in some mountains and are hypothesized to hybridize. The two species were distinctly differentiated for genome-wide amplified fragment length polymorphisms (AFLPs), also in one mountain where they co-occur. However, the plants from another mountain showed strong signals of admixture. The results suggest initial divergence into one western and one northern/eastern lineage, followed by long-distance dispersal resulting in secondary contact zones. In addition within species genetic diversity was clearly structured with distinct genetic groups on some, but not all mountains. Differentiation levels varied considerably and did not always correspond to the extent of lowland habitat between mountains. The narrow Rift Valley in the otherwise nearly contiguous highlands in Ethiopia appears to present a much stronger barrier to dispersal than the extensive lowlands separating Ethiopia from East Africa. This may be a general pattern since it has been documented also for other afro-alpine species.

Keywords

Afro-alpine Carex Hybridization Long-distance dispersal Vicariance 

Notes

Acknowledgments

This study was funded by The Norwegian Programme for Development, Research and Higher Education (NUFU) Project No 2007/1058 (AFROALP-II-Afroalpine ‘sky islands’: genetic versus taxonomic biodiversity, climate change, and conservation) to S. Nemomissa and C. Brochmann. We thank Kåre Lye for verifying the identifications of the herbarium material and Berit Gehrke for helpful comments and discussions. We are grateful to the other members of AFROALP-II team, in particular Geoffrey Mwachala (Kenya), Pantaleo Munishi (Tanzania), and Gerald Eilu (Uganda) for facilitating collection permits and for helping to organize the field work in their respective countries. We also thank two anonymous reviewers for helpful comments and corrections.

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Copyright information

© Swiss Botanical Society 2016

Authors and Affiliations

  • Abel Gizaw
    • 1
    • 2
  • Tigist Wondimu
    • 1
    • 2
  • Tusiime Felly Mugizi
    • 1
    • 3
  • Catherine Aloyce Masao
    • 1
    • 4
  • Ahmed Abdikadir Abdi
    • 1
    • 5
  • Magnus Popp
    • 1
  • Dorothee Ehrich
    • 6
  • Sileshi Nemomissa
    • 2
  • Christian Brochmann
    • 1
  1. 1.Natural History MuseumUniversity of OsloOsloNorway
  2. 2.Department of Plant Biology and Biodiversity ManagementAddis Ababa UniversityAddis AbabaEthiopia
  3. 3.Department of Forestry, Biodiversity and Tourism, School of Forestry, Environmental and Geographical SciencesMakerere UniversityKampalaUganda
  4. 4.Department of Forest BiologySokoine University of AgricultureMorogoroTanzania
  5. 5.Botany DepartmentNational Museums of KenyaNairobiKenya
  6. 6.Institute for Arctic and Marine BiologyUniversity of TromsøTromsøNorway

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