ADR-055: endosymbiosis joins the topics

Context

The exchange of 2026-10-27, “Repository coverage assessment”, found that the record had no treatment of reductive genome evolution or of the endosymbiont-to-organelle transition. Eighteen works it cited were registered the same day (PR #337, curation entry of 2026-10-27). They were tagged with the nearest words the list had:

• ecology for the symbioses, under ADR-028’s “symbiosis and host–microbe partnerships”;
• natural-sciences for everything else: genome reduction, organelle import and loss, eukaryogenesis.

The exchange had warned that ecology and individuation “would otherwise obscure their shared mechanism”. The mechanism is how a partner loses autonomy, by gene loss, drift, gene transfer or host control, and the filing showed the problem. The Black Queen paper and Monocercomonoides landed under different words, though both are about what losing functions does to an organization. The eukaryogenesis papers sat under natural-sciences with physics and astronomy. ADR-028 had anticipated this: “Split it when the holdings warrant it.” On 2026-10-27 the owner asked for the topic, and a further seventeen works came with it.

Decision

Add endosymbiosis (label: Endosymbiosis and reductive evolution). It covers how one organism comes to live inside another and depend on it, and how that ends:

• reductive genome evolution and its causes, whether drift, deletional bias or adaptive loss. This includes free-living microbes that come to depend on a community (the Black Queen Hypothesis);
• complementary gene loss across partners, nested symbioses, and symbiont lineage splitting and replacement;
• endosymbiotic gene transfer, protein import and the host’s control of symbiont division and transmission;
• organellogenesis, including organelles in the making, and organelle loss;
• eukaryogenesis as the founding case.

Tags:

• Works whose subject this is take endosymbiosis first. That covers the thirty-five works of 2026-10-27, apart from the four adjacent ones on cooperation, branching processes and transmission conflict, which take it second or not at all.
• QUESTION-277 and the six CASEs filed with this decision take it.
• Other documents are retagged as they are next touched, as ADR-028 arranged. NOTE-114, NOTE-159, LIT-210 and LIT-528 mention endosymbiosis in passing and are not retagged.

ecology’s blurb now points here, so it is clear which word a work goes under. The ecology of a partnership is ecology, and its evolution into dependence is endosymbiosis.

Alternatives considered

• Keep ecology plus natural-sciences. This is what the first filing did, and it split one mechanism across two words.
• reductive-evolution and organelle-evolution as two words. The exchange offered both names. Its thesis, though, is that reduction and integration are one subject whose dimensions come apart, so two words would file one argument twice. Split it when the holdings warrant it.
• symbiosis. This is broader. Ecological mutualisms and holobionts are already ecology, and the new word is for the intimate, dependency-forming end.