Evolution of Social Insect Polyphenism Facilitated by the Sex Differentiation Cascade.
Evolution of Social Insect Polyphenism Facilitated by the Sex Differentiation Cascade.
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DOI：
10.1371/journal.pgen.1005952
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发表时间：
2016-03
期刊：
影响因子：
4.5
通讯作者：
Oettler J
中科院分区：
文献类型：
--
作者：
Klein A;Schultner E;Lowak H;Schrader L;Heinze J;Holman L;Oettler J
向真社会性的重大转变需要一个开关的进化，以将发展引导到生殖或助手，其性质目前尚不清楚。根据“易变理论”的预测，我们确定性别分化途径作为有前途的候选人，因为它们的预适应调节复杂表型的发展。我们发现，保守的核心基因，包括青少年的敏感性主性别分化基因doublex（dsx）和Krüppel同源物2（kr-h2）与假定的调节功能，表现出性别和形态特异性表达的蚂蚁condyla obscurior在整个生命阶段。我们假设性别分化级联中的基因进化了对种姓分化（即环境或遗传线索）的替代输入信号的感知，并且它们固有的开关样和上位性行为促进了信号向下游目标的转移，从而使它们能够控制形态种姓的差异发育。在蚂蚁、蜜蜂和黄蜂的社会中，劳动分工成生殖女王和辅助工人是通过表型可塑性实现的，表型可塑性允许个体根据可变信号走上离散的发展轨迹。这些信号可以是遗传的、表观遗传的或环境的，从而类似于多细胞动物性别决定信号的极端变化。我们发现，这些输入信号的下游，包括保守的性别分化基因doublyex，调节性别和种姓特异性表型分化的蚂蚁物种obscurior的共同发展途径。许多不同的基因调控机制都与控制社会性昆虫的种姓特异性发育有关，但这些都依赖于更高水平的遗传开关。我们提出，高度保守的枢纽基因，如dsx，它可以翻译可变的输入信号到大的转录差异，使用中间水平的监管机构，是紧密联系在一起的重复进化过渡到真社会性和种姓多态性。
The major transition to eusociality required the evolution of a switch to canalize development into either a reproductive or a helper, the nature of which is currently unknown. Following predictions from the ‘theory of facilitated variation’, we identify sex differentiation pathways as promising candidates because of their pre-adaptation to regulating development of complex phenotypes. We show that conserved core genes, including the juvenile hormone-sensitive master sex differentiation gene doublesex (dsx) and a krüppel homolog 2 (kr-h2) with putative regulatory function, exhibit both sex and morph-specific expression across life stages in the ant Cardiocondyla obscurior. We hypothesize that genes in the sex differentiation cascade evolved perception of alternative input signals for caste differentiation (i.e. environmental or genetic cues), and that their inherent switch-like and epistatic behavior facilitated signal transfer to downstream targets, thus allowing them to control differential development into morphological castes. Division of labor into reproductive queens and helper workers in the societies of ants, bees and wasps is achieved by phenotypic plasticity, which allows individuals to embark on discrete developmental trajectories in response to variable signals. These signals can be genetic, epigenetic or environmental, thereby resembling the extreme variation in signals for sex determination across multicellular animals. We show that common developmental pathways downstream of these input signals, including the conserved sex differentiation gene doublesex, regulate sex and caste-specific phenotypic differentiation in the ant species Cardiocondyla obscurior. Many different mechanisms of gene regulation have been implicated in controlling caste-specific development in social insects but these all depend on a higher-level genetic switch. We propose that highly conserved hub genes such as dsx, which can translate variable input signals into large transcription differences using intermediate-level regulators, are tightly linked with the repeated evolutionary transition to eusociality and caste polyphenism.