How similar are endosymbiont strains within the community?
If an ecological community is the primary site of horizontal transfer of endosymbionts then the same (or very similar) bacterial strains would be found in multiple host taxa. This would result in a lower estimate of pairwise divergence among the endosymbionts present. Using the model from Baldo et al. (2008), we tested whether there is a significant reduction in the expected pairwise divergence of the endosymbionts found from the soil arthropod community. Mean pairwise distance was computed from three different sources: 1) endosymbionts within the community, 2) their expected value obtained from the equivalent number of pairwise distances randomly selected from the database, 3) all unique endosymbiont sequences obtained from PubMLST and NCBI database. These were computed separately for Wolbachia supergroup A, supergroup B, Cardinium and Arsenophonus . Results indicate that mean pairwise distance of Wolbachia supergroup A within the community (2.67%) was significantly less (Wilcox rank-sum test, p<0.05) than expected mean (3.54%; Table S4) and mean of all supergroup A strains in the PubMLST database (3.69%; Figure S6). In contrast, the mean pairwise distance of Wolbachia supergroup B strains within the community (4.17%) was significantly more (Wilcox rank-sum test, p<0.05) than expected mean (3.38%) and mean of B supergroup strains in the PubMLST database (3.43%). This higher than expected values for Wolbachia B supergroup strains can indicate presence of more divergent strains as compared to Wolbachia A supergroup within this community. However, when all the Wolbachia supergroup infections were taken together and their mean pairwise distance (8.68%) was compared with all such strains in the PubMLST database (8.66%), no significant difference was found (Wilcox rank-sum test, p>0.05). This perhaps indicates that although the soil arthropod community yielded several unique Wolbachia infections (Table 1), on average this still represents a subset of Wolbachiadiversity reported till now. Similar to Wolbachia supergroup A,Cardinium strains also showed similar trend where community pairwise distance (1.41%) was significantly less (Wilcox rank-sum test, p<0.05) than expected mean (2.48%) and mean of strains obtained from the database (2.01%). Whereas mean pairwise distance ofArsenophonus strains within the community (1.19%) was not significantly different (p>0.05) from the expected mean (1.38%) as well as from mean of strains obtained from the database (1.55%). Thus, Wolbachia supergroup A as well asCardinium strains within the community are more closely related among themselves (Table S4) but not Wolbachia supergroup B andArsenophonus .