Abstract
BackgroundTermites of the subfamily Macrotermitinae live in a mutualistic symbiosis with basidiomycete fungi of the genus Termitomyces. Here, we explored interaction specificity in fungus-growing termites using samples from 101 colonies in South-Africa and Senegal, belonging to eight species divided over three genera. Knowledge of interaction specificity is important to test the hypothesis that inhabitants (symbionts) are taxonomically less diverse than 'exhabitants' (hosts) and to test the hypothesis that transmission mode is an important determinant for interaction specificity.ResultsAnalysis of Molecular Variance among symbiont ITS sequences across termite hosts at three hierarchical levels showed that 47 % of the variation occurred between genera, 18 % between species, and the remaining 35 % between colonies within species. Different patterns of specificity were evident. High mutual specificity was found for the single Macrotermes species studied, as M. natalensis was associated with a single unique fungal haplotype. The three species of the genus Odontotermes showed low symbiont specificity: they were all associated with a genetically diverse set of fungal symbionts, but their fungal symbionts showed some host specificity, as none of the fungal haplotypes were shared between the studied Odontotermes species. Finally, bilaterally low specificity was found for the four tentatively recognized species of the genus Microtermes, which shared and apparently freely exchanged a common pool of divergent fungal symbionts.ConclusionInteraction specificity was high at the genus level and generally much lower at the species level. A comparison of the observed diversity among fungal symbionts with the diversity among termite hosts, indicated that the fungal symbiont does not follow the general pattern of an endosymbiont, as we found either similar diversity at both sides or higher diversity in the symbiont. Our results further challenge the hypothesis that transmission-mode is a general key-determinant of interaction specificity in fungus-growing termites.
Highlights
Termites of the subfamily Macrotermitinae live in a mutualistic symbiosis with basidiomycete fungi of the genus Termitomyces
We investigated how specific the interactions between termites and fungal symbionts in South Africa are at the genus, species and population level and how the different levels of specificity might relate to inferred co-evolutionary dynamics and known modes of transmission
Sequence analyses Complete ITS sequences were obtained for 101 strains (Table 1; Table 1 in Additional file 1) and sequence length ranged from 597 to 690 nucleotides
Summary
Termites of the subfamily Macrotermitinae live in a mutualistic symbiosis with basidiomycete fungi of the genus Termitomyces. We explored interaction specificity in fungus-growing termites using samples from 101 colonies in South-Africa and Senegal, belonging to eight species divided over three genera. Mutualistic interactions between species are common and have played a central role in the diversification of life [1]. Interactions range from temporal, facultative encounters to obligate permanent symbioses. Mutualistic symbioses often represent major and ecologically highly successful transitions in evolution [2]. Co-evolution of mutualistic taxa involves reciprocal evolutionary change through natural selection [3]. If co-evolutionary interactions persist through speciation events, whole clades of different species can co-speciate [4]. When symbionts regularly switch between different host species, they may still be specific to a particular host genus
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