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Beeren, Christoph von (2012): Social integration of macroparasites in ant societies: ultimate and proximate mechanisms. Dissertation, LMU München: Faculty of Biology
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Abstract

Ant colonies are commonly parasitized simultaneously by several species. While some parasites are recognized and attacked by their ant hosts, others have apparently cracked the ants’ recognition code and interact mainly peacefully with their hosts. Although such apparent differences in social integration among ant parasites have been described, the underlying mechanisms resulting in differential integration remain mostly unknown. Using Leptogenys army ants and their parasites, I studied ultimate mechanisms that might be responsible for differing integration levels by comparing the strength of host defence with the negative impact of parasites. In addition, I investigated proximate mechanisms of differing integration levels by evaluating the role of chemical deception by mimicry. The interactions of several parasitic beetle species with their Leptogenys hosts revealed that particular species fed on host larvae, while others did not. The hosts’ aggressiveness was enhanced towards brood-killing species, while non-predatory species received almost no aggression, resulting in social integration. Accordingly, the fitness costs of parasites likely influence the evolution of host defences against them in a multi-parasite situation. The role of chemical mimicry has been investigated in detail for two kleptoparasites, namely the silverfish Malayatelura ponerophila and the spider Gamasomorpha maschwitzi. By analyzing the transfer of a chemical label from the host ants to the parasites, I empirically demonstrated for the first time that ant parasites are able to acquire mimetic compounds from their host. Additional biosynthesis of mimetic compounds seems unlikely in both parasites, since the concentration of each cuticular hydrocarbon decreased in individuals that were isolated from the host. In addition, a high accuracy in chemical host resemblance was shown to be beneficial for the social integration of both parasites. Reduced accuracy in chemical host resemblance resulted either in aggressive host responses towards the silverfish or elevated host inspection behaviour towards the spider. The degree of dependency on chemical mimicry to achieve social integration differed considerably between the two parasites, however. Accordingly, the parasites’ level of social integration is affected by ultimate mechanisms such as the negative impact on the host as well as by proximate mechanisms such as the degree of accuracy in chemical host resemblance.