SummaryIt is generally accepted that the permanent arrest of cell division known as cellular senescence contributes to aging by an antagonistic pleiotropy mechanism: cellular senescence would act beneficially early in life by suppressing cancer, but detrimentally later on by causing frailty and, paradoxically, cancer. In this review, we show that there is room to rethink this common view. We propose a critical appraisal of the arguments commonly brought in support of it, and we qualitatively analyse published results that are of relevance to understand whether or not cellular senescence-associated genes really act in an antagonistic-pleiotropic manner in humans.
Resource polyphenisms, where single genotypes produce alternative feeding strategies in response to changing environments, are thought to be facilitators of evolutionary novelty. However, understanding the interplay between environment, morphology, and behavior and its significance is complex. We explore a radiation of Pristionchus nematodes with discrete polyphenic mouth forms and associated microbivorous versus cannibalistic traits. Notably, comparing 29 Pristionchus species reveals that reproductive mode strongly correlates with mouth-form plasticity. Male-female species exhibit the microbivorous morph and avoid parent-offspring conflict as indicated by genetic hybrids. In contrast, hermaphroditic species display cannibalistic morphs encouraging competition. Testing predation between 36 co-occurring strains of the hermaphrodite P. pacificus showed that killing inversely correlates with genomic relatedness. These empirical data together with theory reveal that polyphenism (plasticity), kin recognition, and relatedness are three major factors that shape cannibalistic behaviors. Thus, developmental plasticity influences cooperative versus competitive social action strategies in diverse animals.
According to the classic theory of life history evolution, ageing evolves because selection on traits necessarily weakens throughout reproductive life. But this inexorable decline of the selection force with adult age was shown to crucially depend on specific assumptions that are not necessarily fulfilled. Whether ageing still evolves upon their relaxation remains an open problem. Here, we propose a fully dynamical model of life history evolution that does not presuppose any specific pattern the force of selection should follow. The model shows: (i) ageing can stably evolve, but negative ageing cannot; (ii) when ageing is a stable equilibrium, the associated selection force decreases with reproductive age; (iii) non-decreasing selection is either a transient or an unstable phenomenon. Thus, we generalize the classic theory of the evolution of ageing while overturning its logic: the decline of selection with age evolves dynamically, and is not an implicit consequence of certain assumptions.
Social behavior in human and animal populations can be studied as an evolutionary process. Individuals often make decisions between different strategies, and those strategies that yield a fitness advantage tend to spread. Traditionally, much work in evolutionary game theory considers symmetric games: Individuals are assumed to have access to the same set of strategies, and they experience the same payoff consequences. As a result, they can learn more profitable strategies by imitation. However, interactions are oftentimes asymmetric. In that case, imitation may be infeasible (because individuals differ in the strategies they are able to use), or it may be undesirable (because individuals differ in their incentives to use a strategy). Here, we consider an alternative learning process which applies to arbitrary asymmetric games, \textit{introspection dynamics}. According to this dynamics, individuals regularly compare their present strategy to a randomly chosen alternative strategy. If the alternative strategy yields a payoff advantage, it is more likely adopted. In this work, we formalize introspection dynamics for pairwise games. We derive simple and explicit formulas for the abundance of each strategy over time and apply these results to several well-known social dilemmas. In particular, for the volunteer's timing dilemma, we show that the player with the lowest cooperation cost learns to cooperate without delay.
Population structure can strongly affect evolutionary dynamics. The most general way to describe population structures are graphs. An important observable on evolutionary graphs is the probability that a novel mutation spreads through the entire population. But what drives this spread of a mutation towards fixation? Here, we propose a novel way to understand the forces driving fixation by borrowing techniques from evolutionary demography to quantify the invasion fitness and the effective population size for different graphs. Our method is very general and even applies to weighted graphs with node dependent fitness. However, we focus on analytical results for undirected graphs with node independent fitness. The method will allow to conceptually integrate evolutionary graph theory with theoretical genetics of structured populations.
Correct decision making is fundamental for all living organisms to thrive under environmental changes. The patterns of environmental variation and the quality of available information define the most favourable strategy among multiple options, from randomly adopting a phenotypic state to sensing and reacting to environmental cues. Cellular memory—the ability to track and condition the time to switch to a different phenotypic state—can help withstand environmental fluctuations. How does memory manifest itself in unicellular organisms? We describe the population-wide consequences of phenotypic memory in microbes through a combination of deterministic modelling and stochastic simulations. Moving beyond binary switching models, our work highlights the need to consider a broader range of switching behaviours when describing microbial adaptive strategies. We show that memory in individual cells generates patterns at the population level coherent with overshoots and non-exponential lag times distributions experimentally observed in phenotypically heterogeneous populations. We emphasise the implications of our work in understanding antibiotic tolerance and, in general, bacterial survival under fluctuating environments.
Survival and fertility are the two most basic components of fitness, and they drive the evolution of a life cycle. A trade-off between them is usually present: when survival increases, fertility decreases-and vice versa. Here we show that at an evolutionary optimum, the generation time is a measure of the strength of the tradeoff between overall survival and overall fertility in a life cycle. Our result both helps to explain the known fact that the generation time describes the speed of living in the slow-fast continuum of life cycles and may have implications for the extrapolation from model organisms of longevity to humans.
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