The symbiosis between termites and their hindgut protists is mutually obligate and vertically inherited. It was established by the late Jurassic in the cockroach ancestors of termites as they transitioned to wood feeding. Since then, protist symbionts have been transmitted from host generation to host generation by proctodeal trophallaxis (anal feeding). The protists belong to multiple lineages within the eukaryotic superphylum Metamonada. Most of these lineages have evolved large cells with complex morphology, unlike the non-termite-associated Metamonada. The species richness and taxonomic composition of symbiotic protist communities varies widely across termite lineages, especially within the deep-branching clade Teletisoptera. In general, closely related termites tend to harbour closely related protists, and deep-branching termites tend to harbour deep-branching protists, reflecting their broad-scale co-diversification. A closer view, however, reveals a complex distribution of protist lineages across hosts. Some protist taxa are common, some are rare, some are widespread, and some are restricted to a single host family or genus. Some protist taxa can be found in only a few, distantly related, host species. Thus, the long history of co-diversification in this symbiosis has been complicated by lineage-specific loss of symbionts, transfer of symbionts from one host lineage to another, and by independent diversification of the symbionts relative to their hosts. This review aims to introduce the biology of this important symbiosis and serve as a gateway to the diversity and systematics literature for both termites and protists. A searchable database with all termite-protist occurrence records and taxonomic references is provided as a supplementary file to encourage and facilitate new research in this field.

中文翻译：

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白蚁的原生共生体：多样性、分布和共同进化

白蚁与其后肠原生生物之间的共生是相互必然且垂直遗传的。它是在侏罗纪晚期白蚁的蟑螂祖先中建立起来的，当时它们过渡到以木材为食。从那时起，原生生物共生体通过直肠营养轴（肛门进食）从宿主世代传播到宿主世代。原生生物属于真核超门 Metamonada 内的多个谱系。与非白蚁相关的后单胞菌不同，这些谱系中的大多数已经进化出具有复杂形态的大细胞。不同白蚁谱系中，共生原生生物群落的物种丰富度和分类组成差异很大，尤其是在远翅目深层分支分支中。一般来说，密切相关的白蚁往往含有密切相关的原生生物，而深分支白蚁往往含有深分支原生生物，反映了它们广泛的共同多样化。然而，更仔细的观察揭示了原生生物谱系在宿主之间的复杂分布。有些原生生物类群很常见，有些很罕见，有些广泛分布，有些仅限于单一宿主科或属。一些原生生物类群仅存在于少数亲缘关系较远的宿主物种中。因此，这种共生体的共同多样化的悠久历史因共生体谱系特异性丧失、共生体从一个宿主谱系转移到另一个宿主谱系以及共生体相对于宿主的独立多样化而变得复杂。本综述旨在介绍这种重要共生关系的生物学原理，并作为了解白蚁和原生生物多样性和系统学文献的门户。包含所有白蚁原生生物发生记录和分类学参考的可搜索数据库作为补充文件提供，以鼓励和促进该领域的新研究。