Historical biogeography of the coffee family (Rubiaceae, Gentianales) in Madagascar: case studies from the tribes Knoxieae, Naucleeae, Paederieae and Vanguerieae


  • This paper is an additional contribution to the Special Issue that arose from the symposium Evolutionary islands: 150 years after Darwin (http://science.naturalis.nl/darwin2009), held from 11 to 13 February 2009 at the Museum Naturalis, Leiden, The Netherlands. The theme of the symposium was to explore the contribution of islands to our understanding of evolutionary biology and to analyse the role of island biological processes in a world in which the insularity of island and mainland ecosystems is being drastically altered.

N. Wikström, Bergius Foundation, Royal Swedish Academy of Sciences and Department of Botany, Stockholm University, SE-10691 Stockholm, Sweden.
E-mail: niklas.wikstrom@bergianska.se


Aim  In Madagascar the family Rubiaceae includes an estimated 650 species representing 95 genera. As many as 98% of the species and 30% of the genera are endemic. Several factors make the Rubiaceae a model system for developing an understanding of the origins of the Malagasy flora. Ancestral area distributions are explicitly reconstructed for four tribes (Knoxieae, Naucleeae, Paederieae and Vanguerieae) with the aim of understanding how many times, and from where, these groups have originated in Madagascar.

Location  Indian Ocean Basin, with a focus on Madagascar.

Methods  Bayesian phylogenetic analyses are conducted on the four tribes. The results are used for reconstructing ancestral areas using dispersal–vicariance analyses. Phylogenetic uncertainties in the reconstructions are accounted for by conducting all analyses on the posterior distribution from the analyses.

Results  Altogether, 11 arrivals in Madagascar (one in Paederieae, five in Knoxieae, three in Vanguerieae, and two in Naucleeae) are reconstructed. The most common pattern is a dispersal event (followed by vicariance) from Eastern Tropical Africa. The Naucleeae and Paederieae in Madagascar differ and originate from Asia. Numerous out-of-Madagascar dispersals, mainly in the dioecious Vanguerieae, are reconstructed.

Main conclusions  The four tribes arrived several times in Madagascar via dispersal events from Eastern Tropical Africa, Southern Africa and Tropical Asia. The presence of monophyletic groups that include a number of species only found in Madagascar indicates that much endemism in the tribes results from speciation events occurring well after their arrival in Madagascar. Madagascar is the source of origin for almost all Rubiaceae found on the neighbouring islands of the Comoros, Mascarenes and Seychelles.