<it>Wolbachia </it>transmission dynamics in <it>Formica </it>wood ants

• Main Authors: Reuter Max, Viljakainen Lumi, Pamilo Pekka
• Format: Article
• Language: English
• Published: BMC 2008-02-01
• Series: BMC Evolutionary Biology
• Online Access: http://www.biomedcentral.com/1471-2148/8/55

<p>Abstract</p> <p>Background</p> <p>The role of <it>Wolbachia </it>endosymbionts in shaping the mitochondrial diversity of their arthropod host depends on the effects they have on host reproduction and on the mode of transmission of the bacteria. We have compared the sequence diversity of <it>wsp </it>(<it>Wolbachia </it>surface protein gene) and the host mtDNA in a group of <it>Formica </it>ant species that have diverged approximately 0.5 million years ago (MYA). The aim was to study the relationship of <it>Wolbachia </it>and its ant hosts in terms of vertical and horizontal transmission of the bacteria.</p> <p>Results</p> <p>All studied ant species were doubly infected with two <it>Wolbachia </it>strains (wFex1 and wFex4) all over their geographical distribution area in Eurasia. The most common haplotypes of these strains were identical with strains previously described from a more distantly related <it>Formica </it>ant, with an estimated divergence time of 3.5 – 4 MYA. Some strain haplotypes were associated to the same or closely related mtDNA haplotypes as expected under vertical transmission. However, in several cases the <it>wsp </it>haplotypes coexisted with distant mtDNA haplotypes, a pattern which is more compatible with horizontal transmission of the bacteria.</p> <p>Conclusion</p> <p>Two lines of evidence suggest that the sharing of <it>Wolbachia </it>strains by all <it>F. rufa </it>species is rather due to horizontal than vertical transmission. First, the fact that endosymbiont strains identical to those of <it>F. rufa </it>ants have been found in another species that diverged 3.5–4 MYA strongly suggests that horizontal transfer can and does occur between <it>Formica </it>ants. Second, the frequent sharing of identical <it>Wolbachia </it>strains by distant mitochondrial lineages within the <it>F. rufa </it>group further shows that horizontal transmission has occurred repeatedly. Nevertheless, our dataset also provides some evidence for longer-term persistence of infection, indicating that <it>Wolbachia </it>infection within this host clade has been shaped by both horizontal and vertical transmission of symbionts. The fact that all the ants were infected irrespective of the family structure of their societies gives no support to the proposed hypotheses that the spreading of <it>Wolbachia </it>in ants might be associated to the types of their societies.</p>