Frequently defecting participants did not experience much cooperation by cooperator partners and might not realize that these partners are cooperators, reflected by the large variability of cooperativeness evaluations of cooperator partners (Figure 4).
Assortment was calculated by subtracting the average frequency with which cooperators interact with other cooperators and the frequency with which defectors interact with cooperators, which is consistent with the regression definition of relatedness in inclusive fitness models [ 31].
However, the feature that we are focusing on, i.e., more association of cooperators compared to cheaters with the partner, is consistent in all cases.
Moreover, the mean cooperativeness evaluation of cooperator partners increased.
First, rather than cooperating unconditionally, our cooperator partners played Tit-For-Tat and, therefore, were not as easily identifiable as cooperators.
Consistent with this, dispersal morphs among cooperators would be capable of much longer range dispersal than non-cooperative individuals in T. thermophila since longer shaped cells are capable of longer distance dispersal [ 31].
Consistent with theory [ 8], we found that only when cooperation and punishment traits were in tight linkage were cooperators able to invade (in three out of six populations); in all other populations, cooperators were driven to extinction (one-tailed Fisher's exact test, p = 0.037).
If one player defected and the other cooperated, the defector earned $3 and the cooperator nothing.
To be consistent with other online public observation databases developed by the USGS and its cooperators such as "Did you feel it?, Earthquake reporting database (2005)" for reporting felt earthquakes, and "Did you see it?, Landslide reporting database (2014)" for reporting landslides, we named the ash reporting database, "Is Ash Falling?".
The assignment of types allows individuals to ignore occasional defections of cooperator partners, for example, as long as the cooperator partners, in general, cooperate.
If the environment allows co-infection, virus φ6 cheaters can displace the wild type ancestor, consistent with cheating behavior as an evolutionary stable strategy (ESS) in game theory contexts pitting evolved cheaters against the ancestral cooperator [ 42].
