Investigating Secondary Endosymbiotic Bacterial Infections in Harvestman: Diversity and Evolutionary Dynamics

The diversity of secondary endosymbiotic bacteria plays an important role in host biology. Our recent findings revealed multiple secondary endosymbiotic infections in harvestmen, particularly involving Wolbachia and Rickettsiella , which have been rarely reported in this group. In this study, we found that Sinonychia martensi populations from six of the seven caves sampled were positive for Wolbachia , and one cave population was infected with Rickettsiella . Additionally, 12 of the 14 surface‐dwelling harvestmen populations showed varying levels of infection with Wolbachia and Rickettsiella , while Cardinium was detected in only one population. Both cave and surface‐dwelling harvestmen exhibited variable levels of secondary endosymbiotic infection, and multiple infections were common. Comparative phylogenetic analyses, population structure analyses of cave‐dwelling harvestmen, and recombination analyses suggested that the acquisition of secondary endosymbionts did not result from host‐symbiont co‐divergence. Instead, horizontal transmission and genetic recombination appear to have played significant roles in their evolutionary history.