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SOCIAL POPULATIONS. "The presence of programmed cell death systems in the great majority of prokaryotes strongly suggests that structured populations are the rule in microbial ecosystems. Indeed, some kind of social interaction, such as biofilm formation, is found on almost every bacterial group, and more advanced forms of sociality, such as quorum sensing, are often present in Proteobacteria and Firmicutes." https://lnkd.in/d9zsv9R View in LinkedIn

CONSTRAINTS. "In real biological communities, the efficacy of innate and adaptive immune systems is constrained by ecological factors such as population size, structure and diversity. The never-stopping arms race between hosts and pathogens sets a limit on the performance of defense strategies, which is determined by the ability of the host to keep the pace with pathogen escape mutations." https://lnkd.in/d9zsv9R View in LinkedIn

PRE-REQUISITES. "Population structure is required for the evolution of suicide. This pre-requisite had been previously proposed on the basis of experimental studies with a genetically engineered, suicidal strain of E. coli grown on agar plates and is theoretically extended here to a broader spectrum of population structures, suicide efficacies and co-occurring immune mechanisms." https://lnkd.in/d9zsv9R View in LinkedIn

LOW-COST SUICIDE. "Altogether, our findings demonstrate that low-cost suicide can evolve with ease, represents an effective host-defence strategy, and seems to be widespread among microbes. Moreover, low-cost suicide might also occur in higher organisms as exemplified by infected social insect workers leaving the colony to die in isolation." https://lnkd.in/d53-z28 View in LinkedIn

RANGE OF MEASURES. "Different defense mechanisms are geared to fight different threats. Immunity systems might be highly effective against certain threats but less proficient against others. Suicide can serve as a defense mechanism that acts on those threats against which the immunity systems are less effective." https://lnkd.in/d9zsv9R View in LinkedIn

LOW COST. "Recent experiments with suicide-prone E. coli have shown that at least when defense against highly virulent phages is involved, the cost of suicide could be quite low because the infected bacteria are moribund in any case and have virtually no chance to propagate. Conceivably, these experiments reflect the regime with failing immunity and subsequent low-cost suicide." https://lnkd.in/d9zsv9R View in LinkedIn

LAST RESORT. "Host suicide can potentially evolve either as an immediate response to infection or as a means of last resort after immunity mechanisms fail to stop pathogen reproduction. Intuitively, the second strategy would appear advantageous, and indeed in our model, when the two strategies evolve independently and then are allowed to compete, “suicide after immunity failure wins”." https://lnkd.in/d9zsv9R View in LinkedIn

COMPETING STRATEGIES. "Similarly, hosts with large suicide efficacy overtake those with adaptive immunity provided that the suicide propensity is greater than a threshold that grows with the efficacy of adaptive immunity. Notwithstanding this general trend, innate and adaptive immunity systems appear to coexist in other regions of the phase space." https://lnkd.in/d9zsv9R View in LinkedIn

TRAIT FIXATION. "High suicide efficacies prevent fixation of adaptive immunity not only in those regions where the cost-benefit balance for adaptive immunity is slightly unfavorable (even if fixation would occur in the absence of suicide by virtue of population structure), but also in some regions where this balance is favorable to adaptive immunity." https://lnkd.in/d9zsv9R View in LinkedIn

COEXISTING GROUPS. "On the other hand, if the immune efficacy is too high, hosts with and without adaptive immunity tend to coexist as the former generate environments with low pathogen pressure. This result resembles those obtained by previous theoretical studies on well-mixed populations, which predict lack of fixation for highly effective immunity systems and possible polymorphisms on the degree of immunity evolved by hosts." https://lnkd.in/d9zsv9R View in LinkedIn