Reproductive compensation favours male-killing <I>Wolbachia</I> in a live-bearing host

Abstract

are maternally inherited, cellular endosymbionts that can enhance their fitness by biasing host sex ratio in favour of females. Male killing (MK) is an extreme form of sex-ratio manipulation that is selectively advantageous if the self-sacrifice of in males increases transmission through females. In live-bearing hosts, females typically produce more embryos than can be carried to term, and reproductive compensation through maternal resource reallocation from dead males to female embryos could increase the number of daughters born to infected females. Here, we report a new strain of MK (Csc2) in the pseudoscorpion, , and present the first empirical evidence that reproductive compensation favours the killing of males in a viviparous host. Females infected with the Csc2 strain produced 26 per cent more and significantly larger daughters than tetracycline-cured females. In contrast to the previously described Csc1 MK strain in , Csc2 infection was not accompanied by an increase in the rate of spontaneous brood abortion. Characterization of the Csc1 and Csc2 strains by multi-locus sequence typing and by surface protein () gene sequencing indicates that the marked divergence between these two MK strains in their impact on host reproductive success, and hence in their potential to spread, has occurred in association with homologous recombination in the gene.