Conservation Genetics

, Volume 15, Issue 6, pp 1403–1415

Active sexual reproduction but no sign of genetic diversity in range-edge populations of Vanilla roscheri Rchb. f. (Orchidaceae) in South Africa

Authors

  • Rodolphe L. Gigant
    • CiradUnité Mixte de Recherche C53 Peuplements Végétaux et Bioagresseurs en Milieu Tropical Université de la Réunion (UMR C53 PVBMT)
    • Université de la RéunionUMR C53 PVBMT
  • Alexandre De Bruyn
    • CiradUnité Mixte de Recherche C53 Peuplements Végétaux et Bioagresseurs en Milieu Tropical Université de la Réunion (UMR C53 PVBMT)
    • Université de la RéunionUMR C53 PVBMT
  • Brigitte Church
    • Threatened Plant Conservation UnitBiodiversity Research
  • Laurence Humeau
    • Université de la RéunionUMR C53 PVBMT
  • Anne Gauvin-Bialecki
    • Université de la RéunionLaboratoire de Chimie des Substances Naturelles et des Sciences des Aliments
  • Thierry Pailler
    • Université de la RéunionUMR C53 PVBMT
  • Michel Grisoni
    • CiradUnité Mixte de Recherche C53 Peuplements Végétaux et Bioagresseurs en Milieu Tropical Université de la Réunion (UMR C53 PVBMT)
    • Université de la RéunionUMR C53 PVBMT
Research Article

DOI: 10.1007/s10592-014-0626-8

Cite this article as:
Gigant, R.L., De Bruyn, A., Church, B. et al. Conserv Genet (2014) 15: 1403. doi:10.1007/s10592-014-0626-8

Abstract

In South Africa, the wild leafless Vanilla roscheri Rchb. f. (Orchidaceae) is distributed only on the banks of the Lake Sibaya in KwaZulu-Natal Coastal Forest in the iSimangaliso Wetland Park. It is the southernmost vanilloid orchid on the African continent and a species of high conservation priority with little understanding of its reproductive biology and levels of genetic diversity. Mating systems and pollination ecology of the species were assessed by in situ experiments, in addition to genotyping plants at 16 microsatellite markers. Allogamous but self-compatible, V. roscheri depends on pollinators to achieve sexual reproduction. Its natural fruit set (26.3 %) is the highest reported for a non-spontaneously self-pollinating Vanilla species. It was associated with numerous flower visitors including two female allodapine bees (Allodapula variegata and Allodape rufogastra, Xylocopinae), captured with pollinia stored on the hind legs, and one female anthophorine bee. On the other hand, we report an absence of genetic diversity and homozygosity of the South-African populations of V. roscheri for all the genetic markers. Given the preferential outbreeding, the high natural fruit set and the pollinator/visitor richness of V. roscheri in Sibaya, a high level of genetic diversity was expected, but this was not the case. We detected a counterintuitive situation between the results of reproductive biology and genetics, making sense once the population situation on the margins of the species distribution is included. The null diversity expressed through the homozygous monomorphic markers is a consequence of the range-edge localization of the populations, which may have been subjected to severe bottlenecks (due to long distance colonization or fragmentation) along with inbreeding, in the past. The analysis highlights the complementarity of the approaches for which the implications in terms of conservation of the species in South Africa are discussed.

Keywords

Conservation Genetic diversity Mating systems Range-edge populations South Africa Vanilla roscheri

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Copyright information

© Springer Science+Business Media Dordrecht 2014