Systematics and Biogeography of Western Indian Ocean Region Rubiaceae : examples from Danaideae, Hymenodictyeae, and Naucleeae
Sammanfattning: This thesis focuses on the systematics and biogeography of the tribes Danaideae, Hymenodictyeae, and Naucleeae in the angiosperm family Rubiaceae (coffee family), with a special interest in the Western Indian Ocean region (WIOR). The levels of endemism in the WIOR are remarkably high and Madagascar is the largest island surrounded by three main archipelagos with islands of various age and size. Rubiaceae is one of the species-rich families in the region, rendering it a suitable group for addressing evolutionary and biogeographic questions.Danaideae consists of the two Malagasy endemic genera Payera and Schismatoclada, and the WIOR-centered Danais. The monophyly and generic delimitations of the tribe were tested with molecular data. The tribe was strongly supported as monophyletic, and resolved in two well-supported clades: the Danais and Payera-Schismatoclada clade. The ancestor of Danaideae was inferred to have dispersed from continental Africa to Madagascar, where the major diversification of the tribe took place in the Late Miocene to Pliocene. Danais colonized the neighbouring archipelagos between 6.54 and 2.98 Mya, and recolonized continental Africa once.The predominantly Paleotropical sister tribes Hymenodictyeae and Naucleeae belong to the mainly Neotropical subfamily Cinchonoideae. The monophyly of the Hymenodictyeae genera, Hymenodictyon and Paracorynanthe, received strong support. Naucleeae consists of 26 genera divided in seven subtribes. All subtribes were resolved as monophyletic, while seven genera are paraphyletic; as a result, we recognize 17 genera. Both our results and the fossil record support the hypothesis of a boreotropical distribution for the ancestor of the Hymenodictyeae-Naucleeae clade. All dispersal events in the WIOR took place in the Miocene or later. The Malagasy species were the result of separate dispersal events from Africa and Gyrostipula comorensis endemic to the Comoros is the result of a single dispersal event from Madagascar.
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