Effect of the Genotypic Variation of an Aphid Host on the Endosymbiont Associations in Natural Host Populations.

Francisca Zepeda-Paulo,Blas Lavandero

doi:10.3390/insects12030217

Abstract

Simple SummaryThe host–endosymbiont complex could be a key determinant in spread and maintenance of the infection polymorphism of endosymbionts. Variation among host–endosymbiont complexes can contribute to genetic variation of a host species and then provide the necessary material for the operating coevolutionary dynamics. We studied the seasonal dynamic of facultative endosymbiont infections among different host clones of the grain aphid Sitobion avenae and whether their presence affects the total hymenopteran parasitism of aphid hosts at the field level. We observed that aphid infections in the field with endosymbionts increase over time, by favoring particular aphid clones closely associated with endosymbionts, but without an effect of endosymbionts on parasitism rate in the host populations. Our results highlight the importance of host–endosymbiont couples in shaping the prevalence and distributions of symbionts throughout nature and the success of their hosts as pests.Understanding the role of facultative endosymbionts on the host’s ecology has been the main aim of the research in symbiont–host systems. However, current research on host–endosymbiont dynamics has failed to examine the genetic background of the hosts and its effect on host–endosymbiont associations in real populations. We have addressed the seasonal dynamic of facultative endosymbiont infections among different host clones of the grain aphid Sitobion avenae, on two cereal crops (wheat and oat) and whether their presence affects the total hymenopteran parasitism of aphid hosts at the field level. We present evidence of rapid seasonal shifts in the endosymbiont frequency, suggesting a positive selection of endosymbionts at the host-level (aphids) through an agricultural growing season, by two mechanisms; (1) an increase of aphid infections with endosymbionts over time, and (2) the seasonal replacement of host clones within natural populations by increasing the prevalence of aphid clones closely associated to endosymbionts. Our results highlight how genotypic variation of hosts can affect the endosymbiont prevalence in the field, being an important factor for understanding the magnitude and direction of the adaptive and/or maladaptive responses of hosts to the environment.

Highlights

Four aphid clones were found at a high prevalence in the crop fields (G1, G2, G3 and G4), accounting for about 84% of the whole sample analyzed from host plants across the growing season (Table S2)
The aphid clone G1 was significantly more prevalent than the aphid clones G2 (0.27 ± 0.01 SE), prevalence in the crop fields (G1, G2, G3 and G4), accounting for about 84% of the wh sample analyzed from host plants across the growing season (Table S2)
Our results showed major differences found in the percentages of infected aphids when compared to uninfected aphids for the studied common aphid clones, suggesting that the host genotype determines the endosymbiont associations found at the field level

Summary

Introduction

Facultative bacterial endosymbionts are ubiquitous in many insects as they may produce ecologically important effects in their insect hosts, contributing to the host’s adaptation to their environment [1]. A well-studied adaptative trait mediated by facultative endosymbionts is the defense again parasitoid wasps (especially hymenopteran parasitoids), which have been reported in two groups of insect hosts including Drosophila flies [11,12,13] and aphids [2]. Some facultative endosymbionts can directly improve host survival by negatively affecting the development and survival of immature stages of parasitoid wasps through toxin-based protection [14]

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Conclusion