Negligible Long-Term Impact of Nonlinear Growth Dynamics on Heterogeneity in Models of Cancer Cell Populations.

Linear compartmental models are often employed to capture the change in cell type composition of cancer cell populations. Yet, these populations usually grow in a nonlinear fashion. This begs the question of how linear compartmental models can successfully describe the dynamics of cell types.

Grace period of human mortality has declined for over a century.

Objectives: Human mortality is U-shaped and, therefore, defines an age separating lives with an overall negative net change in mortality from lives with an overall positive net change in mortality. How has age changed, also relatively to life expectancy, over recent human history? And how does compare between humans and other primates, the mortality of which is also U-shaped?

Methods: Modeling data from the Human Mortality Database, the historical change of in advanced economies is reported and compared with that of primates in wild and captive conditions the demography of which was already modeled in the literature.

Results: In humans, a marked decline in for both sexes, also relatively to their life expectancy, is associated with medical and economic progress.

Understanding and leveraging phenotypic plasticity during metastasis formation.

Cancer metastasis is the process of detrimental systemic spread and the primary cause of cancer-related fatalities. Successful metastasis formation requires tumor cells to be proliferative and invasive; however, cells cannot be effective at both tasks simultaneously. Tumor cells compensate for this trade-off by changing their phenotype during metastasis formation through phenotypic plasticity.

Generation Time in Stage-Structured Populations under Fluctuating Environments.

AbstractA common measure of generation time is the average distance between two recruitment events along a genetic lineage. In populations with stage structure that live in a constant environment, this generation time can be computed from the elasticities of stable population growth to fecundities, and it is equivalent to another common measure of generation time: the average parental age of reproductive-value-weighted offspring. Here, we show three things.

On Citing Dobzhansky about the Significance of Evolution to Biology.

Evolutionary thinking illuminates biology. Dobzhansky advocated this view in two distinct papers. The earliest paper (1964) is a discussion of the relationship between distinct biological disciplines, and one of the key ideas is that evolution is an integrative principle of biology.

Age-specific sensitivity analysis of stable, stochastic and transient growth for stage-classified populations.

Sensitivity analysis in ecology and evolution is a valuable guide to rank demographic parameters depending on their relevance to population growth. Here, we propose a method to make the sensitivity analysis of population growth for matrix models solely classified by stage more fine-grained by considering the effect of age-specific parameters. The method applies to stable population growth, the stochastic growth rate, and transient growth.

Selection on age-specific survival: Constant versus fluctuating environment.

According to a classic result in evolutionary biodemography, selection on age-specific survival invariably declines with reproductive age. The result assumes proportional changes in survival and a constant environment. Here, we look at selection on age-specific survival when changes are still proportional but the environment fluctuates.

The selection force weakens with age because ageing evolves and not vice versa.

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.

Medawar and Hamilton on the selective forces in the evolution of ageing.

Both Medawar and Hamilton contributed key ideas to the modern evolutionary theory of ageing. In particular, they both suggested that, in populations with overlapping generations, the force with which selection acts on traits declines with the age at which traits are expressed. This decline would eventually cause ageing to evolve.

Memory shapes microbial 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.

Sex or cannibalism: Polyphenism and kin recognition control social action strategies in nematodes.

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 nematodes with discrete polyphenic mouth forms and associated microbivorous versus cannibalistic traits.

Generation Time Measures the Trade-Off between Survival and Reproduction in a Life Cycle.

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 trade-off between overall survival and overall fertility in a life cycle.

Invasion and effective size of graph-structured populations.

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.

How Life History Can Sway the Fixation Probability of Mutants.

In this work, we study the effects of demographic structure on evolutionary dynamics when selection acts on reproduction, survival, or both. In contrast to the previously discovered pattern that the fixation probability of a neutral mutant decreases while the population becomes younger, we show that a mutant with a constant selective advantage may have a maximum or a minimum of the fixation probability in populations with an intermediate fraction of young individuals. This highlights the importance of life history and demographic structure in studying evolutionary dynamics.

The Effect of Post-Reproductive Lifespan on the Fixation Probability of Beneficial Mutations.

Post-reproductive lifespan is a common trait among mammals and is usually considered to be neutral; i.e. with no influence on population dynamics.

Modeling evolutionary games in populations with demographic structure.

Classic life history models are often based on optimization algorithms, focusing on the adaptation of survival and reproduction to the environment, while neglecting frequency dependent interactions in the population. Evolutionary game theory, on the other hand, studies frequency dependent strategy interactions, but usually omits life history and the demographic structure of the population. Here we show how an integration of both aspects can substantially alter the underlying evolutionary dynamics.

Evolution of aging through reduced demographic stochasticity - an extension of the pleiotropy theory to finite populations.

In finite populations, there is selection against demographic stochasticity. In this study, it is shown that an increase in the rate of aging, here defined as an increase in early-life survival at the expense of later survival, may reduce this form of stochasticity. In particular, a trade-off between juvenile and adult survival is highly efficient in reducing demographic stochasticity.

Are some conventional measures of the rate of ageing consistent with antagonistic pleiotropy?

Several measures of the rate of ageing have been proposed in the literature. But are they all equally good? In this work, three of these measures are considered: ωG and the parameter b for the Gompertz model, and ωW for the Weibull model. It is shown that ωG and ωW may fail to detect genuine changes in the rate of ageing when this rate varies in response to the fixation of antagonistic-pleiotropic mutations with effects on survival, while the parameter b never fails to detect such changes.

Is cellular senescence an example of antagonistic pleiotropy?

It 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.