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THEORY-1048: On the Black Queen Hypothesis of Morris, Lenski and Zinser, losing a costly function whose product leaks to neighbours is favoured by ordinary individual selection in large free-living microbial populations, and the loss proceeds until the remaining producers just supply the community, so that most cells come to depend on a rare few with no relatedness, cooperation or collective required

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StatusActive
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Tagsendosymbiosis, ecology
SourceLIT-1568 — The Black Queen Hypothesis: Evolution of Dependencies through Adaptive Gene Loss
Bears onQUESTION-277 — When formerly autonomous partners come to depend on one another, which of mutual dependence, reproductive cohesion, the distribution of essential functions across genomes, the host's regulatory control and the alignment of selection does each route to dependence bring about, and which of them, alone or together, make the partnership a new evolutionary individual?
Cited as “extends” byTHEORY-1235 — Losing a costly function whose product leaks to neighbours is favoured by ordinary individual selection in large free-living microbial populations, and the loss proceeds until the remaining producers just supply the community, so that most cells come to depend on a rare few with no relatedness, cooperation or collective required
Cited as “grounds” byCLAIM-546 — Negative frequency dependence that keeps two types in coexistence does not make their interaction cooperative: in Hawk–Dove with cost C above value V each type increases when rare and they coexist at the interior equilibrium of V/C Hawks, with Hawks still taking the whole resource from Doves, and on the Black Queen account producers of a leaked good and the cells that use it without paying coexist at a frequency set by the community's need; so whether types persist together and whether they cooperate are separate questions, and a coexistence criterion answers only the first

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Morris, Lenski & Zinser (2012), mBio 3(2): e00036-12, LIT-1568, read in full in NOTE-1212 from the PubMed Central copy. The sections “The Black Queen Hypothesis” (equations 1–3), “Are beneficiaries ‘cheaters’?”, and the katG case with Figure 1.

What was actually shown

  • A cost–benefit condition.

    • The benefit of loss is the fractional saving in a limiting resource, B = (Q_A − Q_M)/Q_A.
    • The cost is the shortfall in a function’s effective rate, k = k₀ + Σ NᵢLᵢkᵢ, which includes the leaky contribution of every other cell. With growth linear in k, C = (k_M − k)(μ_M − μ₀)/(μ_M k_M).
    • A mutant invades when B > C. As it spreads, the producers thin out, k falls and C rises, so the spread stops where B = C.

    This follows from the definitions, and was re-derived in the reading.

  • Outcomes.

    • Against its ancestor alone, the mutant and the ancestor coexist on one limiting resource.
    • Where unrelated species supply the good, the ancestor goes extinct.
    • In a mixed community, loss proceeds “in every species … until B is less than or equal to C for all individuals”.

  • The case.

    • No Prochlorococcus genome has katG. The Synechococcus KatG proteins are monophyletic, so the gene was lost.
    • Axenic Prochlorococcus dies in sunlit seawater, and co-occurring cells remove peroxide. These are cited results, not shown in the paper.
    • The benefit is an iron-quota saving of about 0.2%, computed, not measured as fitness.

  • Distinct from kin selection. It needs no relatedness between producer and user: leakiness and density dependence do the work.

What could have failed: the formal condition cannot, given its premises. The case could have failed if katG absence were ancestral, or Prochlorococcus were peroxide-tolerant.

What this does not say

  • Not that endosymbiont reduction is Black Queen. The paper credits drift for endosymbionts and states the hypothesis for free-living organisms. Others extend it to symbionts (LIT-1570’s “environment-induced redundancy”).
  • Not that the outcome benefits all. The conclusion says the division of labour “is often to the advantage of all”. The paper’s own analysis allows beneficiaries to harm helpers when they share a limiting resource.
  • Not a collective or a transition. Nothing is co-transmitted or reproduces as a unit. The dependence is a community pattern, not a higher-level individual.
  • Not tested beyond one function. Nitrogen fixation, siderophores, sulfur assimilation and biofilm matrix are matched to criteria, not analysed. The “shooting the moon” acceleration is speculation.
  • Not shown for nonlinear responses. The linearity of equation 3 is assumed, and robustness to nonlinearity is asserted.

Connections

  • QUESTION-277. This bears on the question’s first route. Dependence arises by individual selection. It is directional (D, one way), and function is distributed across genomes (G). Cohesion, host control and collective-level selection are all absent. It is the record’s clearest case of interdependence that is not individuality.
  • THEORY-141. That account’s stability condition presupposes a collective. This one produces dependence without any, so the two do not compete. They describe different outcomes.
  • LIT-1225. Cooper & West (unread) model extreme specialization favoured within a group, where helpers are selected as helpers. Here helpers are what remains after others defect.

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