Abstract
BackgroundMany insects, including ants, are infected by maternally inherited Wolbachia endosymbiotic bacteria though other secondary endosymbionts have not been reported in ants. It has been suggested that the ability of Wolbachia to invade and remain in an ant population depends on the number of coexisting queens in a colony. We study the genetic and social structure of populations in the ant Formica cinerea which is known to have populations with either monogynous or polygynous colonies. We screen populations for several endosymbiotic bacteria to evaluate the presence of different endosymbionts, possible association between their prevalence and the social structure, and the association between endosymbiont prevalence and genetic differentiation of ant populations.ResultsWe found three endosymbiotic bacteria; 19% of the nests were infected by Wolbachia, 3.8% by Cardinium and 33% by Serratia. There was significant variation among the populations regarding the proportion of nests infected by Serratia, Wolbachia and the pooled set of all the endosymbionts. Some individuals and colonies carried two of the bacteria, the frequency of double infections agreeing with the random expectation. The proportion of infected ants (individuals or colonies) did not correlate significantly with the population level relatedness values. The difference in the prevalence of Wolbachia between population pairs correlated significantly with the genetic distance (microsatellites) of the populations.ConclusionsThe discovery of several endosymbionts and co-infections by Wolbachia and Cardinium demonstrate the importance of screening several endosymbionts when evaluating their possible effects on social life and queen-worker conflicts over sex allocation. The low prevalence of Wolbachia in F. cinerea departs from the pattern observed in many other Formica ants in which all workers have been infected. It is likely that the strain of Wolbachia in F. cinerea differs from those in other Formica species. The correlation between the difference in Wolbachia prevalence and the pair-wise genetic distance of populations suggests that spreading of the bacteria is restricted by the isolation of the host populations.
Highlights
Many insects, including ants, are infected by maternally inherited Wolbachia endosymbiotic bacteria though other secondary endosymbionts have not been reported in ants
We found three endosymbiotic bacteria (Candidatus Cardinium, Candidatus Serratia symbiotica and Wolbachia) infecting F. cinerea
We found that the F. cinerea ants were infected by multiple endosymbiotic bacterial species Wolbachia, Cardinium and Serratia
Summary
Many insects, including ants, are infected by maternally inherited Wolbachia endosymbiotic bacteria though other secondary endosymbionts have not been reported in ants. Primary (or obligate) endosymbionts are usually mutualistic, host-specific and are restricted to vertical transmission in the maternal line and have long-term coevolution with their host These include Buchnera in aphids, Blochmannia in Camponotus carpenter ants, Wigglesworthia glossinidium in tsetse flies and Baumannia cicadellinicola in leafhoppers [2]. Secondary (or facultative) endosymbionts can be either some of the secondary endosymbionts can give direct benefits to the host by delivering nutrients, by giving defence against natural enemies, by improving thermal tolerance, by enhancing fecundity and by inducing variation in breeding behaviour of the host [2,5] Such features have raised questions about the role of endosymbiotic bacteria in inducing and controlling various phenotypic features of their arthropod hosts. Mutualistic endosymbionts can enhance the evolution of social behaviour and group living by forcing individuals to interact in order to obtain or receive benefits delivered by beneficial bacteria [see [8]]
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