Table 1 Definition of key terms used in this study:Â As many of the terms below are used inconsistently in the literature, we explain here how we interpret them.
From: Fidelity varies in the symbiosis between a gutless marine worm and its microbial consortium
Term | Definition |
|---|---|
Vertical transmission | The direct transmission of a symbiont from a parent to its offspring. In most symbioses, the transmission is from mother to offspring (maternal), but there are cases of paternal transmission [6, 7]. |
Horizontal transmission | The transmission of a symbiont to a host from the environment or a co-occurring host [6]. |
Mixed-mode transmission | The transmission of a symbiont by vertical transmission mixed with occasional or frequent events of horizontal transmission over evolutionary time [5]. Note that the transmission of a symbiont community from one generation to the next in which some members are transmitted vertically and others horizontally is not meant here when using this term. |
Partner fidelity | The stability of the association between host and symbiont genotypes over multiple host generations [8]. Partner fidelity is generated by vertical symbiont transmission or genotype-dependent partner choice in horizontal symbiont transmission [4]. Note that studies on mechanism of how microbiomes are transmitted across 1–2 generations in host individuals (e.g. parents to offspring) are not the same as partner fidelity studies, which examine fidelity across many generations in multiple individuals. In this study, we used congruent phylogenies of host mitochondrial genomes and symbiont genomes at microevolutionary scales as an indicator of partner fidelity. |
Partner choice | The ability of hosts, symbionts or both to preferentially choose their partner. Partner choice describes interactions between individual partners within their lifetime and is distinct from partner fidelity requiring repeated interactions over evolutionary time [8, 9]. |
Partner specificity | The taxonomic range of partners in an association [10]. Symbiont specificity is defined as the range of symbionts with which a host associates, while host specificity is defined as the range of hosts with which a symbiont associates. In this study, we distinguish partner specificity from partner fidelity, as the former measures the possible diversity of host-symbiont associations, but not the stability of each association. |
Coinheritance | The transmission of two or more traits from a host parent to its offspring. Traits can include any combination of phenotypes, genes, alleles, organelles and symbionts. In this study, we use the term to describe the coinheritance of mitochondria and symbionts from parents to their offspring. |
Phylosymbiosis | Microbial community relationships that recapitulate the phylogeny of their hosts [11]. Phylosymbiosis tests how similar the composition of microbial communities is to the phylogeny of host species and can arise through ecological or evolutionary forces. Phylosymbiosis differs from partner fidelity in that the structure of the microbial community is analysed, not the phylogeny of each symbiont taxon. |
Microevolution | Evolutionary change in a population over short time scales and generally applied to evolution within a species or conspecific populations. |
Macroevolution | Evolutionary change over longer time scales and generally applied to evolution across species and higher taxonomic groups. |