Babineau, Marielle , Bruneau, Anne .
Systematics of three closely related and endangered Legume genera (Delonix, Colvillea and Lemuropisum): implications for Malagasy-African dispersion during the Tertiary.
The genus Delonix comprises eleven species: nine are endemic to Madagascar and the two others occur in East Africa. Delonix is considered to be paraphyletic with regards to its closest relatives, two monospecific genera endemic to Madagascar: Colvillea and Lemuropisum. All of the above species are endangered despite being important ecological trees of local and worldwide economic interest. However, to argue for their protection it is essential to account for the genetic uniqueness of each and to establish their past and present evolutionary relationships. This study aims to clarify phylogenetic relationships within this trigeneric clade and to estimate divergence times, geographical origin and dispersal patterns. Parsimony and Bayesian analyses, based on four chloroplast (matK, trnL-F, trnD-T, rps16) and three nuclear (ITS, Leafy, tRALs) markers, strongly refute the monophyly of Delonix with Lemuropisum occurring as nested within it. Colvillea is a unique lineage sister to Delonix. Our analyses suggest rapid speciation of Delonix, with species showing numerous morphological, ecological and pollination differences, but low genomic variation. Seven clades are found which are congruent with morphological classifications, except that the two African species generally do not group together. A biogeographical analysis, together with a penalized likelihood fossil-calibrated method, shows at least one clear event of dispersal from Madagascar to East Africa around 30 Ma. This could have been facilitated by the presence of a land bridge from 25-40Ma in the Mozambique canal. Our analyses support recent studies indicating that the flora of Madagascar is not necessarily derived from African ancestors. The geographical pattern also indicates a spatial tendency where southern xerophytic woodland lineages are derived relative to northern deciduous forest species. Based on our studies, conservation efforts and classification should1) consider Colvillea as an evolutionary and morphologically unique genus, 2) treat Lemuropisum as a specialised species within Delonix, and 3) emphasise protection of the three diversity centers observed for Delonix, which presently are poorly covered by national parks.
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1 - Centre sur la Biodiversité, Institut de Recherche en biologie vegetale, 4101 rue Sherbrooke est, Montreal, Qc, H1X 2B2, Canada
2 - Université de Montréal, Institut de Recherche en Biologie Végétale , 4101 Sherbrooke Est, Montreal, Qc, H1X 2B2, Canada
Presentation Type: Oral Paper:Papers for Sections
Location: Lindell C/Chase Park Plaza
Date: Tuesday, July 12th, 2011
Time: 10:45 AM