Animal hosts have initiated myriad symbiotic associations with microorganisms and often have maintained these symbioses for millions of years, spanning drastic changes in ecological conditions and lifestyles. The establishment and persistence of these relationships require genetic innovations on the parts of both symbionts and hosts. The nature of symbiont innovations depends on their genetic population structure, categorized here as open, closed or mixed. These categories reflect modes of inter-host transmission that result in distinct genomic features, or genomic syndromes, in symbionts. Although less studied, hosts also innovate in order to preserve and control symbiotic partnerships. New capabilities to sequence host-associated microbial communities and to experimentally manipulate both hosts and symbionts are providing unprecedented insights into how genetic innovations arise under different symbiont population structures and how these innovations function to support symbiotic relationships.

动物宿主已经与微生物建立了无数的共生关系，并且经常维持这些共生关系数百万年，跨越生态条件和生活方式的巨大变化。这些关系的建立和持续需要共生体和宿主的基因创新。共生创新的性质取决于它们的遗传种群结构，这里分为开放、封闭或混合。这些类别反映了在共生体中导致不同基因组特征或基因组综合征的宿主间传播模式。尽管研究较少，但宿主也进行创新以维护和控制共生伙伴关系。