Radiation in socially parasitic formicoxenine ants

The ecological and physiological relationships between parasites and their hosts constitute some of the most impressive examples of biological adaptation known. Contrary to parasites that exploit the physiology of another individual, social parasites exploit entire societies. A social parasite coexists with another social insect species in the same nest and is the dependent beneficiary. Social parasites are quite common in bees, wasps, and in ants. In the Formicidae, several hundred species are known to be social parasites. Because of their peculiar life style they represent unique model systems to study a number of fundamental problems in evolutionary biology. The more advanced types of social parasitism, slavery or dulosis and inquilinism, are mainly known in the subfamilies Formicinae and Myrmicinae, and they are concentrated in certain genera. The myrmicine tribe Formicoxenini for example is extremely rich in social parasites. Within the Formicoxenini, different degrees of diversification exist. This work is aimed at investigating the causes of variation in species diversity among the six slave-making taxa Protomognathus (1 species), Temnothorax duloticus and an undescribed Temnothorax species, Harpagoxenus (3 species), Chalepoxenus (8 species) and Myrmoxenus (12 species). For this purpose, there is a focus on the age and distribution patterns of the parasitic lineages, as well as on the chemical basis of colony odour and its role in imprinting and host race formation. First, phylogenetic analyses based on mitochondrial DNA sequences confirmed six convergent origins of slavery within the Formicoxenini, which is one more than previously known. The phylogenetic trees document different degrees of genetic divergence between the slave-making monophyla, suggesting that they evolved from their non-parasitic ancestors at different times. By comparing the genetic data of the socially parasitic lineages, it can be concluded that the differences in species-richness among the parasitic Formicoxenini are not only due to their different age. Furthermore, sequence analyses of the Mediterranean representatives of the genus Chalepoxenus and its hosts indicate two lineages, one comprising C. muellerianus and C. tauricus, and a sister group containing C. kutteri and C. brunneus. The grouping of the Chalepoxenus samples points to the possibility of speciation by host race formation in this genus, as demonstrated especially in C. muellerianus. In the genus Myrmoxenus, phylogenetic data suggest that a shift from slavery to workerless parasitism took place several times independently. It is known that both Chalepoxenus and Myrmoxenus species strongly prefer certain hosts and rarely keep mixed slave stocks, in contrast to Harpagoxenus or Protomognathus. Therefore, it is likely that parasite diversity reflects at least in part the diversity and distribution patterns of their ancestor or host species. Cuticular extracts of C. muellerianus analysed by gas chromatography and mass spectrometry mainly contained linear and methyl-branched hydrocarbons with chain lengths ranging from C25 to C31. Statistical analyses of chromatograms of C. muellerianus sexuals reared with two different suitable host species indicated that the host species present in the nest clearly influenced the slavemakers� chemical profile. Simultaneously, a distinct correlation existed between the modifications of the sexuals� odour components and their mate choice. Especially Chalepoxenus males reared by the main host species were much more interested in females that were reared with the same host. Several years ago, imprinting was demonstrated in C. muellerianus queens and workers. It seems likely that a preference for mating partners reared by the same host promotes the formation of host races and eventually speciation in Chalepoxenus. Finally, the mutual influences of C. muellerianus and their slaves on each others� cuticular hydrocarbon pattern were examined. The results suggest that the chemical profiles of both slavemakers and slaves appear to adjust without totally losing their own characteristics. Additional studies are recommended to ensure the protection of these rare and threatened parasitic ant species