Abstract
BackgroundA host infected with multiple parasitic species provides a unique system to test evolutionary and ecological hypotheses. Different parasitic species associated with a single host are expected to occupy different niches. This niche specialization can evolve from intraguild competition among parasites. However, niche specialization can also be structured directly by the host when its defence strategy depends on the parasite’s potential impact. Then it can be expected that species with low or no tendency to prey on host brood will elicit less aggression than severe brood parasitic species and will be able to integrate better in the host system.We examined this hypothesis in a large community of symbionts associated with European red wood ants (Formica rufa group) by testing the association between 1) level of symbiont integration (i.e. presence in dense brood chambers vs. less populated chambers without brood) 2) level of ant aggression towards the symbiont 3) brood predation tendency of the symbiont.ResultsSymbionts differed vastly in integration level and we demonstrated for the first time that relatively unspecialized ant symbionts or myrmecophiles occur preferentially in brood chambers. Based on their integration level, we categorize the tested myrmecophiles into three categories: 1) species attracted to the dense brood chambers 2) species rarely or never present in the brood chambers 3) species randomly distributed throughout the nest. The associates varied greatly in brood predation tendency and in aggression elicited. However, we did not find a correlation for the whole myrmecophile community between a) brood predation tendency and host’s aggression b) integration level and host’s aggression c) integration level and brood predation tendency.ConclusionsOur results indicate that red wood ants did not act more hostile towards species that have a high tendency to prey on brood compared to species that are less likely or do not prey on brood. We show that potentially harmful parasites can penetrate into the deepest parts of a social insect fortress. We discuss these seemingly paradoxical findings in relation to models on coevolution and evolutionary arms races and list factors which can make the presence of potentially harmful parasites within the brood chambers evolutionary stable.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0583-6) contains supplementary material, which is available to authorized users.
Highlights
A host infected with multiple parasitic species provides a unique system to test evolutionary and ecological hypotheses
Such plastic defence has been demonstrated in studies with a small number of parasites associated with mammals, pine weevils and social insects [7,8,9,10], where hosts maximize the investment of costly defense strategies towards potential more harmful parasites, while potential less detrimental symbionts are tolerated
Myrmecophiles could be classified into three categories based on their association with the brood chambers: 1) attraction to the dense brood chambers 2) avoidance of the brood chambers and 3) random distribution (Fig. 2, Table 1)
Summary
A host infected with multiple parasitic species provides a unique system to test evolutionary and ecological hypotheses. Different parasitic species associated with a single host are expected to occupy different niches. This niche specialization can evolve from intraguild competition among parasites. The parasite's potential impact can vary substantially Parasites in such systems tend to specialize in different temporal and spatial niches associated with their host. As an adequate defence response against parasites involves costs [6], it could be beneficial for the host if its level of aggression is hierarchically adjusted to the harmfulness of the symbiont. Such plastic defence has been demonstrated in studies with a small number of parasites associated with mammals, pine weevils and social insects [7,8,9,10], where hosts maximize the investment of costly defense strategies towards potential more harmful parasites, while potential less detrimental symbionts are tolerated
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