Abstract
Maternally inherited bacterial endosymbionts are common in many arthropod species. Some endosymbionts cause female-biased sex ratio distortion in their hosts that can result in profound changes to a host’s mating behaviour and reproductive biology. Dance flies (Diptera: Empidinae) are well known for their unusual reproductive biology, including species with female-specific ornamentation and female-biased lek-like swarming behaviour. The cause of the repeated evolution of female ornaments in these flies remains unknown, but is probably associated with female-biased sex ratios in individual species. In this study we assessed whether dance flies harbour sex ratio distorting endosymbionts that might have driven these mating system evolutionary changes. We measured the incidence and prevalence of infection by three endosymbionts that are known to cause female-biased sex ratios in other insect hosts (Wolbachia, Rickettsia and Spiroplasma) across 20 species of dance flies. We found evidence of widespread infection by all three symbionts and variation in sex-specific prevalence across the taxa sampled. However, there was no relationship between infection prevalence and adult sex ratio measures and no evidence that female ornaments are associated with high prevalences of sex-biased symbiont infections. We conclude that the current distribution of endosymbiont infections is unlikely to explain the diversity in mating systems among dance fly species.
Highlights
Transmitted symbiotic bacteria that are inherited from mother to offspring are common infections of arthropods [1,2,3]
For adult population sex ratio (ASR) estimates from sweeping vegetation, most species did not differ from a 1:1 sex ratio except for E. tessellata and R. longipes, which both had female-biased sex ratios
We found eight species that were infected with two symbionts, and one, E. nigripes, where PCR indicated the presence of Wolbachia, Rickettsia and Spiroplasma bacteria
Summary
Transmitted symbiotic bacteria that are inherited from mother to offspring are common infections of arthropods [1,2,3]. These bacteria persist in host populations either as mutualists, by elevating aspects of host fitness, or as reproductive parasites, by manipulating host reproduction [2]. Whilst some reproductive parasites induce cytoplasmic incompatibility, which leaves host sex ratios unaltered, others are sex ratio distorters that increase the proportion of female offspring in the progeny of symbiont-infected females (reviewed in [2]). Most sex ratio distorting symbionts of insects have modest impacts [4,5]), some cause very strongly female-biased host population sex ratios Most sex ratio distorting symbionts of insects have modest impacts (e.g. [4,5]), some cause very strongly female-biased host population sex ratios (e.g. [6]).
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