nucleation

LIT-1568: The Black Queen Hypothesis: Evolution of Dependencies through Adaptive Gene Loss

2 min read

Properties5
StatusActive — read in full 2026-10-27 (NOTE-1212) from the PubMed Central copy of the version of record (PMC3315703, CC BY-NC-SA); worth reading as the selection route to microbial dependency, in which losing a costly, leaky function is favoured until helpers just supply the community (THEORY-1048). Read it knowing that it is an opinion piece with one worked case (katG in Prochlorococcus) whose benefit is computed, not measured; that it is stated for free-living microbes and credits drift for endosymbiont reduction; that its equations assume linear responses; and that its other examples and the "shooting the moon" acceleration are suggestions.
Version3
Tagsendosymbiosis, ecology, natural-sciences
Cited as “paper” byNOTE-1212 — Morris, Lenski & Zinser — The Black Queen Hypothesis
Cited as “source” byTHEORY-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, THEORY-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

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Morris, J. J., Lenski, R. E. & Zinser, E. R. (2012). The Black Queen Hypothesis: Evolution of Dependencies through Adaptive Gene Loss. mBio 3(2): e00036-12. doi:10.1128/mBio.00036-12.

Key takeaways

From the reading, NOTE-1212.

  • Leaky and costly. A function whose product leaks to neighbours is dispensable to any one cell while others perform it. Losing it saves a fraction B = (Q_A − Q_M)/Q_A of a limiting resource.
  • Self-limiting loss. The cost of loss rises as producers thin out, so loss stops where B = C, leaving rare “helpers” and many dependent “beneficiaries” (THEORY-1048).
  • Not kin selection, not necessarily cheating. No relatedness is needed. Beneficiaries harm helpers only when they share a limiting resource.
  • One case. Prochlorococcus lacks katG and depends on its community to remove peroxide. The 0.2% iron saving is computed, and the other functions named are suggestions.
  • Scope. It is stated for free-living microbes, and endosymbiont reduction is credited to drift.

Why this is here

A1 and A2 cite it as the case where dependency arises from selection for individual gene loss, not from selection for the collective; A2 rates it “Critical”. One correction from the abstract: the hypothesis is stated for free-living community members, and it attributes the reduction common in endosymbionts to drift. The exchange applies it to symbiosis generally. A reading should say whether the paper extends it to endosymbionts.

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