Origins of learned reciprocity in solitary ciliates searching grouped ‘courting’ assurances at quantum efficiencies

Learning to reciprocate socially valued actions, such as cheating and cooperation, marks evolutionary advances in animal intelligence thought unequalled by even colonial microbes known to secure respective individual or group fitness tradeoffs through genetic and epigenetic processes. However, solitary ciliates, unique among microbes for their emulation of simple Hebbian-like learning contingent upon feedback between behavioral output and vibration-activated mechanosensitive Ca²⁺ channels, might be the best candidates to learn to reciprocate necessary preconjugant touches perceived during complex ‘courtship rituals’. Testing this hypothesis here with mock social trials involving an ambiguous vibration source, the large heterotrich ciliate Spirostomum ambiguum showed it can indeed learn to modify emitted signals about mating fitness to encourage paired reproduction. Ciliates, improving their signaling expertise with each felt vibration, grouped serial escape strategies gesturing opposite ‘courting’ assurances of playing ‘harder to get’ or ‘easier to get’ into separate, topologically invariant computational networks. Stored strategies formed patterns of action or heuristics with which ciliates performed fast, quantum-like distributed modular searches to guide future replies of specific fitness content. Heuristic-guided searches helped initial inferior repliers, ciliates with high initial reproductive costs, learn to sensitize their behavioral output and opportunistically compete with presumptive mating ‘rivals’ advertising higher quality fitness. Whereas, initial superior repliers, ciliates with low initial reproductive costs, learned with the aid of heuristics to habituate their behavioral output and sacrifice net reproductive payoffs to cooperate with presumptive ‘suitors’, a kind of learned altruism only before attributed to animal social intelligences. The present findings confirm that ciliates are highly competent decision makers capable of achieving paired fitness goals through learning.