Evolutionary patterns in the assembly of fern diversity on the oceanic Mascarene Islands

Authors

  • Sabine Hennequin,

    Corresponding author
    1. UMR 7205 CNRS MNHN UPMC EPHE Institut de Systématique, Evolution, Biodiversité, Université Pierre et Marie Curie, Paris, France
    2. UMR 7207 CNRS MNHN UPMC ‘Centre de recherche sur la Paléobiodiversité et les Paléoenvironnements’, Paris, France
    • Correspondence: Sabine Hennequin, UMR 7205 Institut de Systématique, Evolution, Biodiversité, 43 rue de Buffon, CC48, 75005 Paris, France.

      E-mail: shennequ@snv.jussieu.fr

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  • Michael Kessler,

    1. Institute of Systematic Botany, University of Zurich, Zurich, Switzerland
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  • Stuart Lindsay,

    1. Royal Botanic Garden Edinburgh, Edinburgh, UK
    2. Gardens by the Bay, Singapore
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  • Harald Schneider

    1. Department of Life Sciences, Natural History Museum, London, UK
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Abstract

Aim

To provide insights into the assembly and structure of biotic communities by exploring several processes of island biodiversity assembly: in situ speciation, immigration and ecological processes.

Location

The Mascarene Islands.

Methods

The phylogenetic relationships of 211 out of 232 Mascarene leptosporangiate fern species were reconstructed in relation to a global phylogeny of 400 leptosporangiate fern species to assess the importance of immigration versus in situ speciation and any deviation from randomness. Correlations between speciation and habit (terrestrial or epiphytic/lithophytic) were tested.

Results

We inferred at least 197 colonization events onto the islands, accounting for > 80% of their leptosporangiate fern diversity. The phylogenetic structure of the assemblage of colonists was mostly overdispersed but aggregated at the tips of the phylogeny. Several families were more diverse on the islands than expected by their global richness. Among the 46 endemic species, up to 65% were inferred to have originated by cladogenesis, which in turn was found to be significantly related to a terrestrial habit.

Main conclusions

Immigration has played a major role in the assembly of the fern flora on the Mascarene Islands. The overdispersion pattern supports the hypothesis of a dominant role of competitive interactions in the flora assembly, and we propose that most available niches were filled by species arriving via long-distance dispersal, preventing further immigration of closely related taxa. The over-representation of some families may reflect better colonization capacities, preadaptation to the Mascarene ecological niches, or ecological differentiation. Frequent colonization by long-distance dispersal has probably hampered in situ speciation in some habitats such as the epiphytic realm. Conversely, cladogenetic speciation appears to occur more frequently in terrestrial habitats.

Ancillary