![]() ![]() bipunctata) to less than 72% for Rickettsia in some samples of A. axyridis and one strain of Wolbachia in A. In addition, the vertical transmission efficiency of different male-killing bacteria varies from almost perfect (> 99% for Spiroplasmas in A. To address this question, more bacteria associated with the male-killing phenotype need to be characterised and placed phylogenetically. The diversity of male-killers identified to date raises the question as to whether male-killing is a potential property of a few, many or almost all maternally inherited bacteria. bipunctata, several species of Acraea butterfly, first reported in Acraea encedon, another butterfly, Hypolimnas bolina and two Drosophila species, D. bipunctata, Harmonia axyridis, Danaus chrysippus and Anisosticta novemdecimpunctata γ-Proteobacteria, from Nasonia vitripennis and Cheilomenes sexmaculatus Rickettsia from Adalia bipunctata and Adalia decempunctata a Flavobacterium from Colemegilla maculatus, Adonia variegata and Coccinula sinensis and Wolbachia from A. However, a fourth manipulation, the biasing of secondary host sex ratios in favour of females by killing males, has been shown to have evolved in six different clades of bacteria: Group II Spiroplasma from Drosophila species, first identified in Drosophila willistoni Group VI Spiroplasma from A. In insects, three forms of manipulation, cytoplasmic incompatibility, feminisation of genetic males, and induction of parthenogenesis, are largely the province of a single genus of bacteria, the Wolbachia. Invertebrate reproductive systems are frequently manipulated by inherited symbionts. Phylogenetic analysis using the 16S rRNA and 17 kDa antigen genes suggests there may have been horizontal transfer of Rickettsial male-killers between different ladybird hosts. Rickettsia presence correlates with the male-killing trait, but there is some variation in the phenotypic expression of the trait due to interaction with host factors. ![]() japonica is host to a bacterial male-killer that is vertically inherited with variable transmission efficiency. Molecular analysis identified Rickettsia to be associated with the trait in this species of ladybird. This male-killer trait was maternally inherited and antibiotic treatment produced a full, heritable cure. japonica showed significantly female-biased sex ratios. ![]() ResultsĪ male-killer was detected in the Japanese coccinellid, Propylea japonica (Thunberg) a species not previously known to harbour male-killers. Together, phenotypic and molecular characterisation of male-killers will allow a deeper insight into the interactions between host and endosymbiont, which ultimately may lead to an understanding of how male-killers identify and kill male-hosts. Phylogenetic placement of male-killing bacteria will allow us to address the question of whether male-killing is a potential strategy for only some, or all, maternally inherited bacteria. In addition, by identifying the bacteria responsible we may find evidence for horizontal transfer between endosymbiont hosts and can gain insight into the evolutionary origins of male-killing. Molecular identification of bacteria and screening for bacterial presence provide us with a more accurate method than breeding data alone to link the presence of the bacteria to the male-killing phenotype. Whilst criteria of low egg hatch-rate and female-biased progenic sex ratio have been used to identify female hosts of male-killers, variation in vertical transmission efficiency and host genetic factors may result in variation in these phenotypic indicators of male-killer presence. Ladybirds have been described as a model system for the study of male-killing, which has been reported in multiple species from widespread geographic locations. To date all male-killers reported are bacterial in nature, but comprise a diverse group. One such group of endosymbionts is the male-killers. Endosymbionts that manipulate the reproduction of their hosts have been reported widely in invertebrates. ![]()
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