Abstract
Rickettsia is a genus of intracellular bacteria that causes a variety of diseases in humans and other mammals and associates with a diverse group of arthropods. Although Rickettsia appears to be common in ticks, most Rickettsia-tick relationships remain generally uncharacterized. The most intimate of these associations is Rickettsia species phylotype G021, a maternally and transstadially transmitted endosymbiont that resides in 100% of I. pacificus in California. We investigated the effects of this Rickettsia phylotype on I. pacificus reproductive fitness using selective antibiotic treatment. Ciprofloxacin was 10-fold more effective than tetracycline in eliminating Rickettsia from I. pacificus, and quantitative PCR results showed that eggs from the ciprofloxacin-treated ticks contained an average of 0.02 Rickettsia per egg cell as opposed to the average of 0.2 in the tetracycline-treated ticks. Ampicillin did not significantly affect the number of Rickettsia per tick cell in adults or eggs compared to the water-injected control ticks. We found no relationship between tick embryogenesis and rickettsial density in engorged I. pacificus females. Tetracycline treatment significantly delayed oviposition of I. pacificus ticks, but the antibiotic’s effect was unlikely related to Rickettsia. We also demonstrated that Rickettsia-free eggs could successfully develop into larvae without any significant decrease in hatching compared to eggs containing Rickettsia. No significant differences in the incubation period, egg hatching rate, and the number of larvae were found between any of the antibiotic-treated groups and the water-injected tick control. We concluded that Rickettsia species phylotype G021 does not have an apparent effect on embryogenesis, oviposition, and egg hatching of I. pacificus.
Highlights
Bacterial endosymbiosis is ubiquitous in arthropods and ranges from mutualism to parasitism [1,2,3]
We have concluded that (1) ciprofloxacin is a considerably more effective anti-rickettsial antibiotic than tetracycline when applied to I. pacificus in vivo
Our findings indicate that the phylotype does not appear to have an effect on embryogenesis, oviposition and egg hatching of I. pacificus
Summary
Bacterial endosymbiosis is ubiquitous in arthropods and ranges from mutualism to parasitism [1,2,3]. Bacterial symbionts may exhibit multiple effects on their hosts [3] – for example, the most well studied arthropod symbiont Wolbachia is a reproductive manipulator that increases fitness of the mosquito Aedes albopictus [4]. The most intimate association between bacteria and arthropods is heritable obligate mutualism, where the host cannot survive and/or produce viable offspring without the symbiont [5]. Reproductive manipulation that increases the female:male ratio of arthropod offspring is a common strategy among bacterial endosymbionts in arthropods, as endosymbionts’ heritability in the host lineage is usually strictly maternal [1]. Classification of pathogenic rickettsiae is largely coincident with the diseases the bacteria cause in humans: spotted fever group (SFG) rickettsiae are known to cause spotted fevers while the typhus group is responsible for endemic typhus [11,12]. SFG Rickettsia species are primarily vectored by the ixodid (‘‘hard’’) ticks and have been found on all continents but Antarctica [13]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
