Animal Resilience To Air Pollution: Strategies And Adaptations

Animals are rapidly adapting to the increasingly polluted world caused by humans. From pigeons and rats thriving in urban environments to coral reefs and giant pandas facing extinction, animals are doing their best to weather the hurricane that is human-induced climate change. As animals come to grips with this new reality, evolution marches on.

Animals may adapt by altering their behaviour, as seen with raccoons and their ability to open bins

Animals are vulnerable to harm from air pollution, which can affect the quality of their environment and food supply. While some species are evolving to cope with pollutants, others are dangerously close to extinction.

Raccoons are one example of animals that have adapted to urban life. In cities like Chicago and Toronto, raccoons have become adept at opening bins and garbage cans to access food scraps. This behaviour has been driven by the smell of food coming from human garbage, which is irresistible to raccoons. While this adaptation allows raccoons to find food, it can also be harmful. Raccoons can get their heads or paws stuck in cans, jars, and bottles, causing injury or even death.

The ability to open bins is a learned behaviour for raccoons, as they do not have opposable thumbs. They use their nimble paws to turn handles and latches, and sometimes hang from the side of bins to reach bags at the bottom. This behaviour has been observed by biologists, who note that raccoons have been adapting to city life since humans started building cities thousands of years ago.

To prevent raccoons from getting into garbage, people can take various measures such as keeping garbage inside until pickup day, storing bins in closed sheds or garages, or using bungee cords to keep lids closed. These measures can help reduce human-wildlife conflicts and protect raccoons from potential harm caused by consuming human food waste.

Genetic changes can occur, such as in fish in New York's Hudson River

Genetic changes are an important way for animals to adapt to air pollution. One example of this is seen in the fish of New York's Hudson River, where the Atlantic tomcod has developed a genetic resistance to PCBs (polychlorinated biphenyls).

PCBs are toxic chemicals that were released into the Hudson River by two General Electric plants from 1947 to 1976, amounting to nearly 600,000 kilograms (about 1.3 million pounds). These chemicals are extremely harmful to fish, causing severe deformities and even death. Despite this, the Atlantic tomcod has not only survived but appears to be thriving in the Hudson River environment.

Researchers from the Woods Hole Oceanographic Institution (WHOI), New York University (NYU), and NOAA investigated this phenomenon and found that the tomcod in the Hudson River had undergone a rapid evolutionary change, developing a genetic resistance to PCBs. This change occurred in the AHR2 receptor gene, which is important in mediating toxicity in early life stages and controlling sensitivity to PCBs. The Hudson River tomcod's AHR2 proteins are missing two of the 1,104 amino acids normally found in this protein, making it harder for PCBs to bind to the receptor. This reduces the toxicity of PCBs in this population of fish.

This genetic change is an example of natural selection, where mutation generates random genetic variation that allows some individuals to better survive and reproduce in challenging environments. Over time, these advantageous genes become more common in the population. While this evolutionary change has benefited the tomcod, there may be trade-offs, such as increased sensitivity to other chemicals or negative impacts on their health. Additionally, the accumulation of PCBs in the tomcod's bodies can lead to bioaccumulation in their predators, potentially affecting the entire food web.

The case of the Hudson River tomcod demonstrates how animals can adapt to polluted environments through genetic changes. While these changes can provide short-term survival benefits, there may also be long-term consequences that are difficult to predict.

Animals may adapt by changing their diet to include less commonly consumed foods

Animals are vulnerable to harm from air pollution, which can affect their habitats and food supply. While some animals are able to adapt to polluted environments, the changes required to do so can have long-term evolutionary consequences, such as reduced reproductive success.

One way that animals may adapt to air pollution is by changing their diet to include less commonly consumed foods. This could involve reducing their consumption of animal-based foods, which are a major source of air pollutants such as methane and ammonia. These pollutants contribute to the formation of particulate matter and ground-level ozone, which have negative impacts on human and animal health.

Research suggests that dietary changes towards more plant-based diets can lead to significant reductions in air pollution and associated health risks. For example, a study published in *Nature Communications* estimated that a shift towards vegan, vegetarian, or flexitarian diets could reduce premature mortality by tens of thousands of deaths globally each year. Similarly, a study by Nina G. G. Domingo et al. found that about 12,700 premature deaths in the United States were attributed to the production of animal-based foods.

By consuming less animal products, animals can reduce their exposure to toxic substances and improve their chances of survival. This strategy may be particularly effective for top-level predators, such as bears and eagles, which are highly susceptible to the bioaccumulation of air pollutants.

Some animals may be able to adapt to polluted environments by desensitising their aryl-hydrocarbon receptor pathway

The aryl hydrocarbon receptor (AhR) is a protein that plays a role in mediating toxicity. It is a ligand-activated transcription factor from the Per-Arnt-Sim (PAS) superfamily of proteins. The PAS domain of the AhR mediates heterodimerization with a structurally related protein known as the aryl hydrocarbon receptor nuclear translocator (ARNT). The AhR:ARNT heterodimer directs transcription of genes from dioxin-responsive enhancer elements (DREs) within the genome.

The AhR pathway is a regulatory pathway for cell adhesion and matrix metabolism. It is involved in the expression of genes encoding proteins involved in growth control, such as transforming growth factor-α, transforming growth factor-β2, Bax, and p27kip1. The AhR pathway also controls the expression of a variety of genes unrelated to xenobiotic metabolism, including genes encoding cytokines interleukin-1β and interleukin-2, and nuclear transcription factors such as c-fos, Jun-B, c-Jun, and Jun-D.

The AhR pathway has been found to be responsive to changes in matrix composition as well as cell-cell and cell-matrix interactions. Activation of the AhR pathway alters cellular adhesion in a variety of model systems. For example, AhR activation results in decreased expression of T-cadherin, an atypical cadherin expressed in diverse organs and cell types during development and in adult tissues.

Some animals may be able to adapt to polluted environments by desensitizing their AhR pathway. This is supported by evidence that animals can adapt to polluted environments and persist even in environments that are inhospitable to most living things. However, these changes in the AhR pathway may cause evolutionary trade-offs, leading to long-term consequences that are difficult to predict and could ultimately lead to the decline of a species.

Animals may adapt by evolving to have lower energy demands

Animals are evolving to adapt to the pollutants introduced into the environment by human activity. While some species, such as pigeons and rats, seem to be thriving in new urban environments, others, like coral reefs and giant pandas, seem to be dangerously close to extinction.

Animals that are best able to cope with human-caused climate shifts tend to be the ones to pass on their genes to the next generation. This is an example of selective pressures influencing the building blocks (genes) of evolution in a species.

One example of this is the Poecilia mexicana species complex, which is composed of multiple independent lineages of fish that have colonized toxic, hydrogen sulfide-rich springs occurring naturally in river drainages in southern Mexico. Hydrogen sulfide is a respiratory toxicant that slows down energy production by interfering with the mitochondria in cells. It also takes a lot of energy—in the form of dedicated proteins and metabolic processes—to detoxify.

Given the energy shortage at multiple levels of biology, researchers hypothesized that populations from hydrogen sulfide-contaminated springs adapted to have lower energetic demands than fish from uncontaminated waters. They found that fish from sulfurous springs showed evidence of adaptation for lower energetic demands—they were smaller, and had lower oxygen consumption rates than fish from uncontaminated sites, even when reared in the lab.

This is an example of convergent evolution, where multiple, distantly related, independent lineages appear to find the same solution to the problem of life in a toxic environment.

Frequently asked questions