PHYSIOLOGICAL ADAPTATION: WHAT IT IS AND EXAMPLES - BIOLOGY - 2025

A physiological adaptation is a trait or characteristic at the level of the physiology of an organism - call it a cell, tissue or organ - that increases its biological efficacy or fitness.

In physiology, there are three terms that should not be confused: adaptation, setting, and acclimatization. Charles Darwin's natural selection is the only known mechanism that leads to adaptations. This process is generally slow and gradual.

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It is common for adaptation to be confused with setting or acclimatization. The first term is related to variations at the physiological level, although it can also occur in anatomy or biochemistry, as a result of the body's exposure to a new environmental condition, such as extreme cold or heat.

Acclimatization involves the same changes described in the term environment, only that the environmental variations are induced by a researcher in the laboratory or in the field. Both acclimatization and setting are reversible phenomena.

What does it consist of?

Physiological adaptations are characteristics of cells, organs and tissues that increase the efficiency of the individuals who possess it, with respect to those who do not.

When we speak of "efficacy" we mean the term widely used in evolutionary biology (also called Darwinian efficacy or fitness) related to the ability of organisms to survive and reproduce. This parameter can be broken down into two components: the probability of survival and the average number of offspring.

That is, when we have certain physiological characteristics that increase the fitness of individuals, we can intuit that it is an adaptive trait.

We must be careful when identifying adaptations, since all the characteristics that we see in an animal are not adaptive. For example, we all know that our blood has a vibrant red color.

This characteristic has no adaptive value and is only a chemical consequence. Blood is red because it has a molecule called hemoglobin, responsible for the transport of oxygen.

How can we conclude that a trait is a physiological adaptation?

When we observe a specific characteristic of an organism we can make several hypotheses about its adaptive meaning.

For example, there is no doubt that the eyes of animals are structures that allow the capture of light. If we apply the order of ideas set out above, we can conclude that individuals with structures that perceive light have some advantage over their peers, such as easily escaping from predators or finding food more easily.

However, according to the famous evolutionary biologist and paleontologist Stephen Jay Gould "no explanation of the adaptive value of a character should be accepted just because it is plausible and charming."

In fact, the demonstration that characters are adaptations is one of the most prominent tasks of evolutionary biologists, since the time of Charles Darwin.

Examples

Digestive systems in flying vertebrates

Flying vertebrates, birds and bats, face a fundamental challenge: to overcome the force of gravity to be able to move.

Thus, these organisms have unique characteristics that we do not find in another group of vertebrates whose way of moving is clearly terrestrial, such as a mouse, for example.

Modifications of these peculiar vertebrates range from lightweight bones with internal holes to a considerable reduction in brain size.

According to the literature, one of the most important selective pressures that has shaped this animal group is the need to decrease its mass to increase flight efficiency.

It is presumed that the digestive system has been shaped by these forces, favoring individuals with shorter intestines, which would imply less mass during flight.

However, when reducing the intestines comes an additional complication: the assimilation of nutrients. As there is a smaller absorption surface, we can intuit that the intake of nutrients is affected. Recent research has shown that this does not happen.

According to Caviedes – Vidal (2008), there is a paracellular absorption pathway that compensates for the decrease in intestinal tissue. To reach these conclusions, the authors investigated the absorption pathways in the intestines of the fruit bat Artibeus lituratus.

Plant adaptations to arid environments

When plants are exposed to adverse environmental conditions, they cannot move to other locations with better circumstances, as a bird that migrates to warm areas to escape the heat stress of winter might.

For this reason, different plant species have adaptations, including physiological ones, that allow them to face unfavorable conditions, such as drought in deserts.

There are trees with particularly extensive root systems (roots) that allow them to take water from deep reservoirs.

They also present alternative metabolic pathways that help reduce water loss. Among these pathways we have C4 plants that reduce the phenomenon of photorespiration, thanks to the spatial separation of the Calvin cycle and the fixation of carbon dioxide.

Photorespiration is an alternative pathway that does not provide any gain and occurs when the enzyme RuBisCO (ribulose-1,5-bisphosphate carboxylase / oxygenase) uses oxygen and not carbon dioxide.

CAM plants (crassulaceae acid metabolism) slow down the photorespiration process and allow the plant to reduce water loss, thanks to a temporary separation.

Antifreeze proteins in teleost fish

Several species of marine teleost fish (belonging to the Teleostei infraclass) have achieved a series of magnificent adaptations to be able to develop in environments with low temperatures.

These physiological adaptations include the production of antifreeze proteins and glycoproteins. These molecules are produced in the liver of fish and are exported to the bloodstream to fulfill their function.

According to the biochemical composition of the proteins, four groups are distinguished. Furthermore, not all species have the same mechanism: some synthesize proteins before being exposed to low temperatures, others do so in response to thermal stimuli, while another group synthesizes them throughout the year.

Thanks to the colligative effects of the solutions, when adding more solutes to the plasma, the temperature at which it freezes significantly decreases. In contrast, the tissues of a fish that does not have this type of protection would begin to freeze after the temperature reaches 0 ° C.

References

1. Caviedes – Vidal, E., Karasov, WH, Chediack, JG, Fasulo, V., Cruz – Neto, AP, & Otani, L. (2008). Paracellular absorption: a bat breaks the mammal paradigm. PLoS One, 3 (1), e1425.
2. Davies, PL, Hew, CL, & Fletcher, GL (1988). Fish antifreeze proteins: physiology and evolutionary biology. Canadian Journal of Zoology, 66 (12), 2611–2617.
3. Freeman, S., & Herron, JC (2002). Evolutionary analysis. Prentice Hall.
4. Price, ER, Brun, A., Caviedes – Vidal, E., & Karasov, WH (2015). Digestive adaptations of aerial lifestyles. Physiology, 30 (1), 69–78.
5. Villagra, PE, Giordano, C., Alvarez, JA, Bruno Cavagnaro, J., Guevara, A., Sartor, C.,… & Greco, S. (2011). Being a plant in the desert: strategies for water use and resistance to water stress in the Central Mountain of Argentina. Austral Ecology, 21 (1), 29–42.