Intracellular symbionts drive sex ratio in the whitefly by facilitating fertilization and provisioning of B vitamins

Abstract

Symbionts can regulate animal reproduction in multiple ways, but the underlying physiological and biochemical mechanisms remain largely unknown. The presence of multiple lineages of maternally inherited, intracellular symbionts (the primary and secondary symbionts) in terrestrial arthropods is widespread in nature. However, the biological, metabolic, and evolutionary role of co-resident secondary symbionts for hosts is poorly understood. The bacterial symbionts Hamiltonella and Arsenophonus have very high prevalence in two globally important pests, the whiteflies Bemisia tabaci and Trialeurodes vaporariorum, respectively. Both symbionts coexist with the primary symbiont Portiera in the same host cell (bacteriocyte) and are maternally transmitted. We found that elimination of both Hamiltonella and Arsenophonous by antibiotic treatment reduced the percentage of female offspring in whiteflies. Microsatellite genotyping and cytogenetic analysis revealed that symbiont deficiency inhibited fertilization in whiteflies, leading to more haploid males with one maternal allele, which is consistent with distorted sex ratio in whiteflies. Quantification of essential amino acids and B vitamins in whiteflies indicated that symbiont deficiency reduced B vitamin levels, and dietary B vitamin supplementation rescued fitness of whiteflies. This study, for the first time, conclusively demonstrates that these two intracellular symbionts affect sex ratios in their whitefly hosts by regulating fertilization and supplying B vitamins. Our results reveal that both symbionts have the convergent function of regulating reproduction in phylogenetically-distant whitefly species. The 100% frequency, the inability of whiteflies to develop normally without their symbiont, and rescue with B vitamins suggests that both symbionts may be better considered co-primary symbionts.

Host Plant Affects Symbiont Abundance in Bemisia tabaci (Hemiptera: Aleyrodidae)

“…With regard to the S-symbionts, both Hamiltonella and Rickettsia genomes keep most of genes involved in synthesis of two EAAs: phenylalanine (Phe) and lysine (Lys), which are missing in the genome of Portiera [ 4 , 17 , 18 , 19 , 20 , 21 ]. In the present study, lower quantities of Hamiltonella and higher quantities of Rickettsia were found in the whitefly populations on eggplants, a more-nitrogen diet ( Figure 2 and Figure 5 ); the former showed similar changes with Portiera amounts in response to different host plants.…”

“…Recent research indicated that Hamiltonella can synthesize biotin; biotin provisioned by whitefly horizontally transferred genes (HTGs) affects the survival and fecundity of adult whiteflies [ 22 ]. A Hamiltonella deficiency reduced the level of B vitamin but not EAAs and affected the sex ratio, so this symbiont affects sex ratios in B. tabaci MEAM1 by regulating the fertilization and supplying B vitamins [ 21 ]. Except for the nutritional functions, S-symbionts may confer ecologically important traits, e.g., a resistance to parasitoids, thermotolerance, viral transmission, and hosts’ susceptibility to insecticides [ 15 ].…”

“…The genomes of Hamiltonella and Rickettsia retain some genes involved in the biosynthesis of several EAAs, cofactors, and vitamins [ 4 , 17 , 18 , 19 , 20 ]. While the presence of these genes hints at metabolic cooperation between the S-symbionts and whiteflies [ 18 , 21 , 22 ], there have been a few studies focusing on the relationship between the amount of S-symbionts and EAAs synthesis.…”

Benefits and costs of hosting facultative symbionts in plant‐sucking insects: A meta‐analysis

“…After more than two decades of research, experimental work directly measuring the costs and benefits of hosting symbionts in aphids is being replaced by work aiming to understand the ecological and evolutionary consequences of these interactions, and the mechanisms behind specific effects (Oliver & Higashi, 2019; Tian et al, 2019). For whitefly, most of the work is on a single species and its symbionts, with more recent focus on understanding mechanisms underlying these interactions (Santos‐Garcia et al, 2020; Wang, Ren, et al, 2020; Zchori‐Fein et al, 2014). For other plant‐sucking insects, work to identify a symbiotic microbiome is just starting, particularly for many Heteropterans that rely on diverse gut bacteria for digestion, nutrient synthesis or toxin degradation (Moran et al, 2019).…”

The Costs and Benefits of Two Secondary Symbionts in a Whitefly Host Shape Their Differential Prevalence in the Field

“…The secondary symbionts have diverse effects on their hosts. For example, the Rickettsia confers general benefits to host fitness ( Himler et al, 2011 ) and assists its host in resistance to entomopathogen Pseudomonas syringae in MEAM1 whitefly ( Hendry et al, 2014 ); the Hamiltonella influences host sex ratio via provisioning of nutrients in MEAM1 whitefly ( Shan et al, 2019 ; Wang Y. B. et al, 2020 ), and some Cardnium and Rickettsia strains confer lower host fitness in B. tabaci MED and SSA1-SG3 species, respectively ( Fang et al, 2014 ; Ghosh et al, 2018 ; Zhao et al, 2018 ).…”