Ageing might have evolutionary advantages

Mauro Santos, evolutionary biologist at the Autonomous University of Barcelona, spent some months at the ELKH Centre for Ecological Research (MTA Excellence Research Site) as a participant in the Distinguished Guest Scientist Fellowship Programme of MTA, on the request of director Eörs Szathmáry, academician. Santos dedicated his time here to some major unsolved problems in evolutionary biology, from the formation of chromosomes to the evolutionary effects of ageing. Our interview with him reveals that the pandemic might lead to new possibilities for theoretical scientists.

2021. március 8.
Mauro Santos

Mauro Santos arrived in Hungary at the very beginning of the coronavirus pandemic, in March 2020, in order to begin his research at the Institute of Evolution, Centre for Ecological Research. When asked how the circumstances hindered his work, Santos gave us a surprising answer. “In a sense, the pandemic was beneficial for us. There was nothing else to do, so we worked. I conducted research both in Tihany and Budapest. We met once or twice a week to discuss how to proceed. I spent most of my time at my accommodation, and I constantly communicated with the colleagues at the Institute. I must say the lockdown helped us progress so fast and write so many studies. Fortunately, the researchers’ lodge in Tihany is surrounded by vast open spaces, which was very good during the lockdown.”

Concerning the research conducted at the Centre for Ecological Research, the evolutionary biologist said that several questions were touched upon, including both theoretical and practical problems. A good example of the latter is the question of how global warming affects animal communities, which is closely related to the heat tolerance of a given species.

“Very often, it is useful to determine the heat tolerance of a given species, that is, to find out the maximum temperature these species are able to tolerate. Several methods are used by scientists to determine this value. We unified the predictions of these various methods in a complex model and

showed that the critical thermal maximum variable, which is widely used, is not reliable. Much more reliable results can be arrived at if simulations are carried out.”

This result was published in Science.

Origin of chromosomes

“As my host in Hungary, Eörs Szathmáry, has proven, one of the major transitions of evolution was when genes formed chromosomes. However, the exact mechanism of this process is not clear to us in detail. We have identified the factors that were necessary for the formation of chromosomes”, Santos added.

“We have shown that during the evolution of chromosomes, gene multiplication also took place.

Consequently, multigene families appeared on chromosomes, which facilitated their evolution and enhanced their effectiveness.”

According to Santos, it is extremely difficult to estimate when chromosomes first formed. The birth of a species existing today is defined as the time when their evolutionary line broke off from that of their relatives. That is, a determination of when the species last common ancestor existed is needed. However, it is much more difficult to explore what happened before the existence of the common ancestor and when these things happened – and if we want to research the emergence of life, this common ancestor examined should be the ancestor of all known living organisms. According to the researcher, this can mean a step forward toward the solution if we come to understand the conditions which were required for the formation of the precursors of life, that is, protocells, including the genes and chromosomes formed from them.

“We think that vesicles called protocells were packages of individual genes at the very beginning of life. However, this setup was problematic. One of the main problems is the confirmation of the fact that descendants were able to inherit all essential genes in the required proportions”, continued Santos. “If genes form chromosomes, this can guarantee that each gene is inherited at the same rate. Thus, the probability of having descendants from which one or more essential genes are missing decreases.”

The regulated transmission of genes was thus one of the most important advantages of chromosome formation. This is why evolutionary biologists think that

the formation of chromosomes was one of the prerequisites for the increase in the complexity of organisms.

Otherwise, it is impossible to ensure that all the genes necessary for the functioning of a complex organism are passed on to the descendants.

The research on chromosome formation is slowly moving into the experimental sciences as, owing to the advancement of microfluidics, the process can be modelled in experiments. Various RNA molecules are placed in some microlitre droplets (which serve as replicators of this experiment), and probable circumstances are simulated.

Genetically-programmed ageing

Ageing is at least as much a mystery of evolution as the emergence of the first cells or the formation of chromosomes. Why do we age? Is it possible to eliminate ageing? Does ageing have advantages? These are problems that humanity had been preoccupied with for millennia before the discovery of evolution. In the past decades, science has come closer to answering some of these questions.

“According to the most widely held view, ageing is a side-effect, and thus selection has no influence on it. However, the latest results suggest that

ageing might be genetically encoded, which is almost unbelievable for those thinking within the standard evolutionary framework”

, argues Santos. “This also means that ageing might have advantages. One of the most important of these is that if a given species lives in a changing environment, then the generations made up of ageing and dying individuals can adapt to changes faster.”

“To be able to understand this, let us imagine two groups of living organisms. One group does not age, while in the other group all individuals age, and after some generations, they also die. Those individuals that do not age can adapt to the environmental effects at the given moment, but are unable to adapt to future changes. Conversely, in the other group, the individuals have a limited lifespan. In a given period of time, several generations grow up, and each generation has the possibility to adapt evolutionarily. In such a setup, the ageing organisms might be favoured by selection. Although ageing organisms have a demographic disadvantage, owing to adaption, they might have a fitness advantage”, said Santos.

Papers published by Mauro Santos and the researchers at the Research Centre for Ecology

Rezende, E. L., Bozinovic, F., Szilágyi, A., Santos, M., 2020. Predicting temperature mortality and selection in natural Drosophila populations. Science, 369, 1242–1245.

Szilágyi, A., Szabó, P., Santos M., Szathmáry, E., 2020. Phenotypes to remember: Evolutionary developmental memory capacity and robustness. PLoS Computational Biology, 16(11).

Szilágyi, A., Kovács, V. P., Szathmáry E., Santos, M., 2020. Evolution of linkage and genome expansion in protocells: The origin of chromosomes. PLoS Genetics, 16(10).

Mauro Santos’ interview with Eörs Szathmáry Eörs is available in the journal of the Spanish Society for Evolutionary Biology.