Arthropods Shopping for Wolbachia

Within the large group of arthropod-associated bacteria, one genus of the α-Proteobacteria, Wolbachia, has attracted particular attention by serving as a microbial model system for deciphering the complexities of arthropod symbiosis, ranging from manipulation of host reproduction to interactions in nutritional and metabolic pathways, interferences in development and life span, and protection from pathogens and parasites (reviewed in Moran et al. 2008; Brownlie and Johnson 2009; Gross et al. 2009; Cook and McGraw 2010). Wolbachia were first described as intracellular Rickettsia-like organisms (RLOs) in the gonad cells of the mosquito Culex pipiens (Hertig and Wolbach 1924) and named Wolbachia pipientis (Hertig 1936). Since their first description in the early twentieth century, Wolbachia have been found in a uniquely wide range of host species mostly belonging to the arthropod phylum. Wolbachia infect up to two-thirds of all insect species (Jeyaprakash and Hoy 2000; Hilgenboecker et al. 2008), as well as a variety of mites, spiders, scorpions, and terrestrial crustaceans (Rowley et al. 2004; Bordenstein and Rosengaus 2005; Baldo et al. 2007, 2008; Wiwatanaratanabutr et al. 2009). In addition to arthropods, Wolbachia are also present in filarial nematodes (see Taylor et al. 2010 for review), and have been detected in a plant-associated nematode (Haegeman et al. 2009). Over the last two decades Wolbachia have attracted major foci within arthropod research and evince the largest growth in publications compared to any other bacterial arthropod symbiont. The reasons for this are multiple: Wolbachia are extremely common, have a wide host range, and have manifold ways of influencing host fitness and behavior. Host species appear to experience recurring Wolbachia epidemics, or occasionally accumulate Wolbachia strains, perhaps as a strategy to extend their metabolic pathways with gene networks that they could otherwise not as quickly exploit. This “shopping for Wolbachia” could be seen as an analogy to the stepwise acquisition of different types of plastids by photosynthetic organisms, previously introduced as “shopping for plastids” (Larkum et al. 2007) in the light of the endosymbiotic theory (Sagan 1967).