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Open Access Research article

Should sex-ratio distorting parasites abandon horizontal transmission?

Joseph E Ironside1*, Judith E Smith2, Melanie J Hatcher3 and Alison M Dunn4

Author Affiliations

1 Institute of Biological, Environmental and Rural Sciences, Aberystwyth University, Aberystwyth, Ceredigion SY23 3DA, UK

2 University of Salford, Salford, Greater Manchester M5 4WT, UK

3 School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK

4 Institute of Integrative and Comparative Biology, Faculty of Biological Science, University of Leeds, Leeds LS2 9JT, UK

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BMC Evolutionary Biology 2011, 11:370  doi:10.1186/1471-2148-11-370

Published: 21 December 2011

Abstract

Background

Sex-ratio distorting parasites are of interest due to their effects upon host population dynamics and their potential to influence the evolution of host sex determination systems. In theory, the ability to distort host sex-ratios allows a parasite with efficient vertical (hereditary) transmission to dispense completely with horizontal (infectious) transmission. However, recent empirical studies indicate that some sex-ratio distorting parasites have retained the capability for horizontal transmission.

Results

Numerical simulations using biologically realistic parameters suggest that a feminising parasite is only likely to lose the capability for horizontal transmission if its host occurs at low density and/or has a male-biased primary sex ratio. It is also demonstrated that even a small amount of horizontal transmission can allow multiple feminising parasites to coexist within a single host population. Finally it is shown that, by boosting its host's rate of population growth, a feminising parasite can increase its own horizontal transmission and allow the invasion of other, more virulent parasites.

Conclusions

The prediction that sex-ratio distorting parasites are likely to retain a degree of horizontal transmission has important implications for the epidemiology and host-parasite interactions of these organisms. It may also explain the frequent co-occurrence of several sex-ratio distorting parasite species in nature.