Symbiont‐conferred reproduction and fitness benefits can favour their host occurrence

Abstract

Double infections of Wolbachia and Spiroplasma are frequent in natural populations of Tetranychus truncatus, a polyphagous mite species that has been a dominant species in China since 2009. However, little is known about the causes and ecological importance of such coexistences. In this study, we established T. truncatus strains with different infection types and then inferred the impact of the two endosymbionts on host reproduction and fitness. Double infection induced cytoplasmic incompatibility, which was demonstrated by reduction in egg hatchability of incompatible crosses. However, doubly infected females produced more eggs relative to other strains. Wolbachia and Spiroplasma did not affect host survival, whereas doubly infected females and males developed faster than other strains. Such reproduction and fitness benefits provided by double infections may be associated with the lower densities of each symbiont, and the quantitative results also confirmed competition between Wolbachia and Spiroplasma in doubly infected females. These symbiont‐conferred beneficial effects maintain stable prevalence of the symbionts and also help drive T. truncatus outbreaks in combination with other environmental factors.

Wolbachia dominate Spiroplasma in the co‐infected spider mite Tetranychus truncatus

“…In our previous study (Zhang et al ., ), we found that the spider mites doubly infected with Wolbachia and Spiroplasma have reproductive and fitness advantages, like higher egg deposition and faster developmental rate, compared with singly infected and uninfected spider mite strains. Doubly infected mites could induce incomplete CI, whereas Wolbachia singly infected mites could not induce CI.…”

“…). These results were similar to those found in our former study (Zhang et al ., ). There was no direct association between CI and Wolbachia density, with Wolbachia density significantly higher in 1‐day‐old male adults from the co‐infected strain (Fig.…”

“…A, D). These results contrast with the previous study (Zhang et al ., ), where co‐infection was considered to confer host benefits and the symbiont infections did not have fitness costs. Similar results have been obtained in Nasonia vitripennis , when wasps infected with two Wolbachia strains ( w Av and w Bv) appeared to produce more offspring when in different genetic backgrounds to the strains used for comparison, whereas no positive fitness effects were found once host genetic background was controlled (Bordenstein and Werren, ).…”

“…In the spider mite T. truncatus , Spiroplasma and Wolbachia can co‐infect the same individual. To investigate phenotypic effects associated with co‐infections, we previously established four strains in this species, which involved a co‐infected strain, two singly infected strains and one uninfected strain (Zhang et al ., ). We found mites doubly infected with Wolbachia and Spiroplasma gained benefits over singly infected and uninfected T. truncatus .…”

Combined effects of elevated CO2 concentration and Wolbachia on Hylyphantes graminicola (Araneae: Linyphiidae)

“…Yun et al (2013) and Zhang, Yang, Zhu, and Hong (2018) assessed Wolbachia as endosymbiotic bacteria that induce beneficial effect in spiders' growth and development process; this beneficial association was helpful in regulation of biological traits in spiders. Furthermore, a nonsignificant relationship was found between the total survival rate and Wolbachia infection in H. graminicola.…”