Abstract

Bacterial endosymbionts are very common in terrestrial arthropods, but infection levels vary widely among populations. Experiments and within-species comparisons suggest that environmental temperature might be important in explaining this variation. To investigate the importance of temperature, at broad geographical and taxonomic scales, we extended a global database of terrestrial arthropods screened for Wolbachia and Cardinium. Our final dataset contained data from more than 117 000 arthropods (over 2500 species) screened for Wolbachia and more than 18 000 arthropods (over 800 species) screened for Cardinium, including samples from 137 different countries, with mean temperatures varying from −6.5 to 29.2°C. In insects and relatives, Cardinium infection showed a clear and consistent tendency to increase with temperature. For Wolbachia, a tendency to increase with temperature in temperate climates is counteracted by reduced prevalence in the tropics, resulting in a weak negative trend overall. We discuss the implications of these results for natural and introduced symbionts in regions affected by climate change.

Highlights

  • Bacterial endosymbionts can exert profound effects on their hosts, for example, by manipulating host reproductive biology to maximize their own vertical transmission [1,2,3]

  • Positive temperature clines have been observed for Cardinium infection in Culicoides midges in Israel [11], for the global prevalence of Wolbachia infection in Lepidoptera, and across tropical/temperate gradients in Australian Diptera [12,13,14]

  • We extended the database of Weinert et al [3] to yield 135 876 arthropods screened for Wolbachia and Cardinium, drawn from a total of 320 publications

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Summary

Introduction

Bacterial endosymbionts can exert profound effects on their hosts, for example, by manipulating host reproductive biology to maximize their own vertical transmission [1,2,3]. Several factors may shape variation in prevalence, including costs of reproductive parasitism [4], benefits of protection against viral pathogens [5] or host dispersal patterns [6] Another putative influence on endosymbiont prevalence is environmental temperature [7]. Positive temperature clines have been observed for Cardinium infection in Culicoides midges in Israel [11], for the global prevalence of Wolbachia infection in Lepidoptera, and across tropical/temperate gradients in Australian Diptera [12,13,14] These are isolated results, and the prevalence of Wolbachia in insect populations, for example, remains remarkably constant across broad continental scales [15]

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