Institute of Genetics, University of Nottingham, Queen's Medical Centre, Nottingham NG72UH, UK.
BMC Evol Biol. 2010 Feb 11;10:37. doi: 10.1186/1471-2148-10-37.
Endosymbionts that manipulate the reproduction of their hosts have been reported widely in invertebrates. One such group of endosymbionts is the male-killers. To date all male-killers reported are bacterial in nature, but comprise a diverse group. 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. 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. 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. 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. 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. 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.
A male-killer was detected in the Japanese coccinellid, Propylea japonica (Thunberg) a species not previously known to harbour male-killers. Families produced by female P. japonica showed significantly female-biased sex ratios. One female produced only daughters. This male-killer trait was maternally inherited and antibiotic treatment produced a full, heritable cure. Molecular analysis identified Rickettsia to be associated with the trait in this species of ladybird.
We conclude that P. japonica is host to a bacterial male-killer that is vertically inherited with variable transmission efficiency. 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. 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.
已广泛报道在无脊椎动物中存在操纵宿主繁殖的共生菌。其中一类共生菌是雄性杀手。迄今为止，所有报道的雄性杀手都是细菌，但它们构成了一个多样化的群体。瓢虫已被描述为研究雄性杀手的模式系统，在广泛的地理区域的多个物种中都有报道。虽然低卵孵化率和雌性偏向的后代性别比例标准已被用于鉴定雄性杀手的雌性宿主，但垂直传播效率和宿主遗传因素的变化可能导致这些雄性杀手存在的表型指标发生变化。细菌的分子鉴定和细菌存在的筛查为我们提供了一种比繁殖数据更准确的方法，将细菌的存在与雄性杀手表型联系起来。此外，通过鉴定负责的细菌，我们可能会发现共生宿主之间水平转移的证据，并深入了解雄性杀手的进化起源。雄性杀手细菌的系统发育定位将使我们能够解决雄性杀手是否只是某些或所有母系遗传细菌的潜在策略的问题。雄性杀手的表型和分子特征的综合分析将使我们能够更深入地了解宿主和共生体之间的相互作用，这最终可能导致我们了解雄性杀手如何识别和杀死雄性宿主。
在日本瓢虫，Propylea japonica（Thunberg）中检测到一种雄性杀手，该物种以前不被认为具有雄性杀手。由雌性 P. japonica 产生的家族表现出明显的雌性偏向性别比例。一只雌性只产雌性后代。这种雄性杀手特征是母系遗传的，抗生素处理产生了完全的、可遗传的治愈效果。分子分析表明，在这种瓢虫中，与该特征相关的是立克次体。
我们得出结论，P. japonica 是一种细菌雄性杀手的宿主，这种雄性杀手是垂直遗传的，具有可变的传播效率。立克次氏体的存在与雄性杀手特征相关，但由于与宿主因素的相互作用，该特征的表型表达存在一些差异。使用 16S rRNA 和 17 kDa 抗原基因进行的系统发育分析表明，立克次氏体雄性杀手可能在不同的瓢虫宿主之间发生了水平转移。
