Rare colonisation events may strongly affect evolution of biotas, especially from large continuous biomes into smaller isolated ones. Colonisation is often difficult, particularly for bilateral mutualists: successful dispersal requires partners either to be permanently associated or to find one another after dispersing separately. Vertical transmission of symbionts should facilitate colonization, as partners disperse together. I will study this hypothesis using fungus-growing termites and their obligate fungal symbionts (genus Termitomyces). This system allows strong tests of these ideas, as fungus-growing termites show horizontal and vertical transmission and the transmission mode is particular to species groups. It is thus ideal for examining rare colonisations and their evolutionary and ecological consequences. Madagascar, isolated from Gondwanaland 165 mya, has a well-characterised termite fauna, with only three fungus-growing termite genera described. Recent data show that Microtermes is ubiquitous and that the other putative genera appear to phylogenetically nest within Microtermes. Microtermes (with presumably, uniquely, vertical transmission) may thus have found free niche space in Madagascar and diversified there in analogous ways to relatives in African tropics, and thereby show extraordinary morphological convergence. Phylogenetic reconstructions will determine i) the origin and age of Malagasy fungus-growing termites and their symbiotic Termitomyces, ii) the relevance of transmission mode for colonization and iii) the extent to which hosts and symbionts have co-speciated. Furthermore, symbiont transmission mode of Malagasy termites will be studied and advanced DNA techniques will be applied to trace Termitomyces spores in soil to test whether the availability of the right spores limits fungus-growing termite colonisation. Finally, combined spatial and phylogenetic analysis will elucidate how Malagasy fungus-growing termites evolved and diversified.