Janni Dolby Clement:
Exploitation strategies in social parasites of fungus growing ants

One of the most remarkable and complex parasitic interactions is social parasitism, where a parasite exploits a complete society, rather than an individual organism. By integrating into a society the parasite gains protection against predators and diseases, and can redirect resources from the host to increase its own fitness. The host will use a sophisticated recognition system in order to accept nestmates and expel intruders from their societies. However this defence barrier can be overcome by parasites. Among the most specialized social parasites are the inquilines that exploit social insect colonies. Inquilines are usually close relatives of their host and so share ancestral characteristics (Emery’s rule). They are dependent on being fully integrated into their host’s colony throughout their lives in order to reproduce. Most inquiline ants have completely lost their sterile worker caste. Exceptions to this are Acromyrmex insinuator and Acromyrmex ameliae, parasites of fungus-growing ants. By still producing a worker caste both species offers a rare opportunity to study adaptive features in parasite worker behaviour. Furthermore can closely related inquiline-host combinations give us an insight in the trade-offs occurring in natural selection.

This thesis is based on research conducted on these two fascinating and rare inquilines species. I focus on elucidating aspects in parasite behaviour, recognition and queen competition.

We describe the distribution and location of parasites inside the fungus garden of the host colony. The parasite distribute itself where it is most advantageous and where manipulation and host control could be archived most efficiently. We conduct experiments showing that parasite gynes (female reproductive individuals), unlike the host, would not perform worker related behaviours to help the survival of the host colony, when prevented from dispersing. We show that parasite queens will prefer to integrate into host colonies already infested with parasites and that they are more easily accepted into these colonies. We perform a morphological comparison of the olfactory sensory system between the three distinctive castes of host workers and minor parasites workers and study the recognition abilities of the parasite.

We elucidate infiltration strategies and chemical profile of parasite queens, gynes and workers as well as host queens and host workers in parasitized and non-parasitized colonies. Finally we investigate the reproductive competition between polygynous parasite queens and discuss the potential for hyperparasitism.