Endosymbiotic bacteria are prevalent and diverse in agricultural spiders

Abstract

Acknowledgements:We thank J. Harwood and J. Dryer for providing and collecting 22 specimens.Abstract 31 Maternally inherited bacterial endosymbionts are common in arthropods, but their distribution 32 and prevalence is poorly characterized in many host taxa. For example, spiders (Araneae) have 33 received little attention, but initial surveys suggest that vertically transmitted symbionts may be 34 common. Here, we characterized endosymbiont infection in a community of agricultural spiders. 35Using a combination of diagnostic PCR and high-throughput sequencing of the bacterial 36 microbiome, we evaluated symbiont infection in 267 individual spiders representing 14 species 37 in 3 families. We found 27 Operational Taxonomic Units (OTUs) that are likely endosymbiotic, 38 including several strains of Wolbachia, Rickettsia and Cardinium, all of which are vertically 39 transmitted and frequently associated with reproductive manipulation of arthropod hosts. 40Seventy percent of spider species had individuals that tested positive for one or more 41 endosymbiotic OTUs, and specimens frequently contained multiple symbiotic strain types. The 42 most symbiont-rich species, Idionella rugosa, had eight endosymbiotic OTUs, with as many as 43 five present in the same specimen. Individual specimens within infected spider species had a 44 variety of symbiotypes, differing from one another in the presence or absence of symbiotic 45 strains. Our sample included both starved and unstarved specimens, and dominant bacterial 46OTUs were consistent per host species, regardless of feeding status. We conclude that spiders 47 contain a remarkably diverse symbiotic microbiota. Spiders would be an informative group for 48 investigating endosymbiont population dynamics in time and space, and unstarved specimens 49 collected for other purposes (e.g., food web studies) could be used, with caution, for such 50 investigations. 51 52 53The majority of terrestrial arthropod species are infected by inherited bacterial symbionts. 54The most common of such bacteria, Wolbachia, is estimated to infect approximately half of 55 arthropod species, albeit often at a low frequency of infected individuals within a given species 56 [1-3]. These bacteria are primarily transmitted vertically, but horizontal transfers among host 57 taxa occasionally occur through a variety of ecological mechanisms such as shared host 58 substrates or shared enemies [4-8]. Following successful establishment in a new host lineage, the 59 endosymbiont then promotes the continued existence of that infected lineage, either by providing 60 some sort of fitness benefit to the host [9,10], or by manipulating host reproduction such that 61 infected mothers produce more daughters than uninfected mothers [11]. Over generations, the 62 result is an infection that can spread through the host population via selection, rather than 63 contagion. 64 It is inevitable that this process of infection and spread sometimes occurs in the context 65 of other vertically-transmitted endosymbionts, ...

Endosymbiotic Rickettsiella causes cytoplasmic incompatibility in a spider host

“…Rickettsiella were rescreened at least two more times, and additionally tested for extraction 111 quality via diagnostic PCR of a segment of the arthropod COI gene [4]. 112…”

“…Spiderlings originating from seven infected matrilines were 124 treated with a combination of tetracycline (0.1%) and ampicillin (0.1%) by a fine mist spray 125 daily until sub-adulthood [20,26]. Upon maturity, treated spiders were mated to one another, and 126 a subset of those offspring were diagnostically tested for endosymbionts (Wolbachia,Rickettsia,127 Rickettsiella) [4,20]. Sibships that were negative for all endosymbionts were used to initiate the 128 uninfected (cured) population for experimental assays.…”

“…for Wolbachia, Rickettsia, and Rickettsiella [4,19,20]. Final classification of all matings was 147 based on these diagnostic results; in several instances spiders from "cured" matrilines were 148 found to be symbiont infected, presumably due to cryptic low titer infections that rebounded in 149 subsequent generations.…”

“…Maternally transmitted endosymbiotic bacteria are common in arthropods, and are 35 estimated to infect nearly half of all arthropod species [1][2][3][4]. These inherited endosymbionts 36 frequently manipulate host reproduction to promote symbiont transmission and spread in the host 37 population [5].…”

“…to Rickettsiella, although both co-infecting symbionts may have contributed to the CI phenotype 210 [29]. Focus on taxa that are well-established as reproductive manipulators, such as Wolbachia, 211 may lead researchers to overlook co-infecting bacteria that cause or contribute to manipulated 212 host reproductive phenotypes, as co-infections are common in arthropods [1,4]. 213…”