nucleation

LIT-1570: The Evolution of Dependence and Cohesion in Incipient Endosymbioses

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Properties5
StatusActive — read in full 2026-10-27 (NOTE-1211) from the bioRxiv preprint, version 2 of 2025-05-31 (CC BY-NC 4.0), not the version of record, which was not reached; worth reading as the first model to separate mutual dependence from reproductive cohesion in an incipient endosymbiosis, with logistic growth for host, symbiont and collective, and for its results that the faster-evolving partner becomes obligate first and that the other's fate turns on births and deaths inside the collective (THEORY-1051). Read it knowing that its headline result, dependence evolving ahead of cohesion, is fixed by the authors' choice of how traits enter free growth and dissociation and reverses under the opposite choice in their own appendix (THEORY-1050); that nothing is tested against data, as the authors say; and that obligacy is a phenomenological trade-off, not gene loss.
Version3
Tagsendosymbiosis, ecology, individuation
Cited as “paper” byNOTE-1211 — Athreya, Czuppon & Gokhale — The evolution of dependence and cohesion in incipient endosymbioses
Cited as “source” byTHEORY-1050 — In Athreya, Czuppon and Gokhale's adaptive-dynamics model of an incipient endosymbiosis, mutual dependence (the product of the partners' obligacies) evolves ahead of reproductive cohesion (the product of their adhesions) early on, but only under the mapping in which each partner's free-living growth depends on its own obligacy alone while dissociation depends on both partners' adhesions; the authors' own appendix shows the bias vanishing under matched mappings and reversing under the opposite one, and their survey of real symbioses cannot test it, THEORY-1051 — In Athreya, Czuppon and Gokhale's model of an incipient endosymbiosis, the partner with the larger and faster-growing population evolves faster and becomes fully obligate first, which the authors read as a Red King effect in which the collective's shared fate aligns interests; with equal within-collective rates for both partners, the other partner's dependence then stays where it was, rises to full dependence, or falls to none, according to whether partners are born or die inside the collective; and in its simulations dependence rose from zero at the higher collective carrying capacities tried and not at the lowest, under a condition the authors show sufficient and not necessary, so a full transition to a mutually dependent, co-reproducing pair is a parameter-dependent outcome and not the default, THEORY-1243 — In incipient endosymbioses in nature, mutual dependence evolves ahead of reproductive cohesion, so that endosymbioses are more likely to be mutually dependent than cohesive

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Athreya, G. S., Czuppon, P. & Gokhale, C. S. (2025). The Evolution of Dependence and Cohesion in Incipient Endosymbioses. The American Naturalist 206(5): 435–451. doi:10.1086/737588.

Key takeaways

From the reading, NOTE-1211.

  • Two axes. Dependence comes from each partner’s “obligacy”, its investment in collective over free growth. Cohesion comes from its “adhesion”, its investment in synchronized reproduction. A transition is both axes at their maximum.
  • The faster partner goes first. The symbiont, with a larger and faster population, becomes fully obligate first, a Red King effect aligned by shared fate. The host’s obligacy is then neutral. It rises to full dependence if partners die inside the collective, and falls to none if they reproduce there (THEORY-1051).
  • Carrying capacity, not growth rate. Traits leave zero only if the collective’s carrying capacity exceeds about aK_HK_S/d.
  • Dependence before cohesion, conditionally. This holds when free growth depends on a partner’s own obligacy and dissociation on both adhesions. The appendix (Table S1) shows it vanishing or reversing under other mappings (THEORY-1050).
  • Untested. The authors’ table of ten real symbioses “does not allow us to confirm/refute” the bias.

Why this is here

A2’s highest priority: it “addresses almost exactly the conceptual gap”, separating two properties the record discusses together. A2 crossed them into a two-by-two of regimes, which it called a conceptual classification, not stable endpoints. QUESTION-277 rests its first two dimensions on it. A2 proposed connecting it to THEORY-141 and THEORY-418.

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