Mechanisms of speciation in Crematogaster spp. subgenus Decacrema associated with Macaranga

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Mutualistic ant-plant associations are common and important elements of the tropical ecosystems. In these speciose habitats biotic interactions could be a crucial factor driving diversification. The most prominent ant-plant system in the palaeotropics consists of the pioneer tree genus Macaranga and its manifold associations with Crematogaster-ants. The various types of interaction in this complex and its considerable degree of radiation concerning all partners offer an exceptional model system for studying the processes of speciation and radiation in mutualistic systems in general. Our aim is to analyse the proximate factors that can lead to divergent or disruptive selection in our system (ecological, genetical or behavioural mechanisms). We will test whether competition, changes in colony structure or the evolution of specific interactions between species lead to a genetic substructuring of ant symbiont populations and can therefore provide the raw material for speciation in our system. Since phylogenetic analyses of both groups are on their way or already finished we can also ask questions about the evolution of traits correlated with speciation and determine the key innovations that started the radiation in the plant-associated ants. We want to test whether these traits are adaptive, i.e. provide a fitness advantage and evolved through natural selection, or show just phylogenetic persistence. These questions will be addressed with a combination of field observations and experiments, and population genetic analyses.