Evolutionary rescue: what is it and how does it affect species preservation?

The theory of evolutionary rescue shows us that sometimes biological evolution can be rapid.

Climate change and anthropization take their toll on ecosystems and, as a result, experts estimate that 150 to 200 species of living beings become extinct every 24 hours. Habitats are not going through their best times either, as it is also estimated that a total of 13.7 million hectares of forest are cut down every year worldwide, the equivalent of the area occupied by Greece.

All these data show us a harsh reality: the Earth is approaching a point of no return. Will nature be able to keep up with the pace of human-induced change? Do living beings have sufficient evolutionary strategies to cope with the dizzying pace of environmental change? This question and many others seek to be answered by the theory of the theory of evolutionary rescue. We explain it to you below.

What is the theory of evolutionary rescue?

The human being is in the sixth mass extinction (Holocene extinction), since the extinction rate of species today is 100 to 1,000 times the natural average in evolution. Unfortunately, this data has been backed up with scientific evidence on multiple occasions.

According to the International Union for the Conservation of Nature (IUCN) more than 32,000 taxa of living beings are endangered, i.e. one in eight taxa in the world are threatened.One in eight bird species, one in four mammals, almost half of all amphibians and 70 % of all plants are endangered. In short, 27 % of all species assessed by humans are in some category of threat.

This raises the following question for conservation professionals: Do living things have tools to cope with the growing threat that is human action? How have some species survived other extinction events? Evolutionary rescue theory attempts to partially cover these answers, at least on paper.

Theoretical basis of the evolutionary rescue theory

In the face of climatic variation, populations of living beings have three tools to survive over time:

• Phenotypic plasticity: this refers to the genetic properties of the individual to adapt to an environmental change. The genotype encodes more than one phenotype.
• Dispersal: any population movement that has the potential to lead to gene flow between individuals of a species.
• Adaptive evolution: rapid speciation of one or more species to fill many new ecological niches.

Although in the short term dispersal phenomena may be the solution, physical space is finite and the new territories explored are often already occupied by other living beings.. For this reason, the persistence of species in a changing environment depends largely on their ability to evolve adaptively, i.e. to specialize in new environmental variants before disappearing.

The theory of evolutionary rescue is based on this last point. In other words, it proposes that living things can recover from environmental pressures through advantageous genetic modification, rather than by placing all their "genetic "resources" at the disposal of the environment.instead of placing all their "hope" in gene flow, migration of individuals or dispersal.

Typical evolution" proposes that living things evolve slowly, but we are no longer in a typical situation. Thus, a new concept of "contemporary evolution" is explored, or what is the same, that living things can evolve more rapidly in a short time to survive in the environment despite rapid changes in it. despite rapid changes in the environment.

Factors to take into account

Several factors play a key role in the theory of evolutionary rescue. We present them briefly in the following lines.

Demographic factors

Theoretical postulations stipulate that the size of the population being evaluated is an essential factor in determining whether or not evolutionary rescue can occur. In populations there is a value called "minimum viable population" (MVP), the lower limit that allows a species to survive in nature.. When taxa are below this value, extinction becomes much more plausible by stochastic or random processes, such as genetic drift.

Thus, the longer a population is below the MVP, the less likely it is that an evolutionary rescue will occur. Moreover, the faster the population declines, the more the viability of this theory is reduced: the species has to be given "time" to generate a viable adaptation before it is evoked to extinction..

Genetic factors

The genetic variability of a species, its mutation rate and its dispersal rate are also key to the occurrence of an evolutionary rescue phenomenon.

Of course, the greater the genetic variability of a species, the greater the genetic variability of the species, the greater the genetic variability of a population, the more likely it is to be rescued, since natural selection can act on the genetic variability of a population.natural selection can act on a greater number of traits. Thus, the most suitable for that moment will be favored and, ideally, the less prepared will disappear and the population will fluctuate to the most effective change: adaptive evolution will take place.

The mutation rate should also promote evolutionary rescues, since non-deleterious or beneficial mutations are another way of acquiring genetic variability in species. Unfortunately, in animals this phenomenon is usually quite slow.

3. Extrinsic factors

Clearly, the probability of a successful evolutionary rescue also depends on the environment.. If the rate of change in the environment is faster than the rate of generational turnover of the population, things become very complicated. In the same way, interactions with other living things play an essential role: both intra- and interspecific competitions can increase or decrease the probability of evolutionary rescue.

A practical approach

So far we have told you part of the theory, but ideally any postulation should be based, at least in part, on practical observations. Unfortunately, proving the theory of evolutionary rescue is tremendously complex, even more so when we take into account that genetic tests and population monitoring that must be maintained for decades are required..

A very clear example (although not entirely valid due to its anthropogenic nature) is the resistance to Antibiotics by various groups of bacteria. Bacteria mutate at a much faster rate than is evolutionarily expected, as drugs unintentionally select the most resistant and viable individuals on a continuous basis. The same is true for some insect species and the application of insecticides on crops.

Another ideal case could be that of rabbits, as viral myxomatosis reduced their populations in some areas of Europe and Australia by up to 99% during the 20th century.. This caused the selection, in the long term, of those individuals with mutations resistant to infection (up to 3 effective genetic variations have been identified). This fact has prevented, at least in part, the complete disappearance of the species, since immunoresistant individuals are those that have offspring and survive over time.

Unresolved questions

Although the data previously presented seem promising, we must emphasize that, for every striking case, there are many others in which the species have disappeared due to viruses and pandemics without being able to do anything about it. This is the example of the chytrid fungus in amphibians, which has caused the decline of 500 amphibian species and the complete extinction of almost 100 of them in just 50 years. Of course, in no case is this a miraculous adaptive mechanism.

Another question to be resolved is to make the real distinction between evolutionary rescue and normal adaptation rates.. Differentiating between the two terms is complex to say the least, as it requires a great deal of empirical evidence and factors to be taken into account for each species analyzed.

Summary

Perhaps these terms may sound a bit confusing to the reader, but if we want to leave you with one idea before we finish, it is the following: evolutionary rescue is not an act performed by humans nor a measure of conservation, but rather a hypothetical situation in which living things can cope with environmental pressures through rapid adaptive evolution..

To empirically test this concept presents a titanic logistical complexity, as it requires very long-term population monitoring, genetic analysis and many other parameters. In any case, we cannot rely on nature itself to fix the disaster we have created: if anyone can reverse this situation, at least in part, it is man.

Bibliographic references:

• Data on extinctions: International Union for Conservation of Nature (IUCN).
• Carlson, S. M., Cunningham, C. J., & Westley, P. A. (2014). Evolutionary rescue in a changing world. Trends in Ecology & Evolution, 29(9), 521-530.
• Bell, G., & Gonzalez, A. (2009). Evolutionary rescue can prevent extinction following environmental change. Ecology letters, 12(9), 942-948.
• Bell, G. (2017). Evolutionary rescue. Annual Review of Ecology, Evolution, and Systematics, 48, 605-627.
• Bell, G. (2013). Evolutionary rescue and the limits of adaptation. Philosophical Transactions of the Royal Society B: Biological Sciences, 368(1610), 20120080.