By Isabel Rowbotham, Co-Editor in Chief

Published March 29th, 2023

Researchers from Sweden, the United States and Austria have collaborated to understand the impacts of chemical pollutants on wildlife. Here are their perspectives on how animal behavioural ecology is influenced by pharmaceuticals.

Synthetic chemical pollutants such as pharmaceuticals have made their way into the environment, the animals that inhabit them and their food web. This under-researched form of pollution has been previously studied in the context of how it impacts the way social animals establish groups. However, until now, there has been little research into how pharmaceutical pollutants may impact collective behaviour of highly social animals over their lifetime.

The big question is: how are our pharmaceuticals reaching animals in their natural environments? Many drugs are designed to resist becoming inactive. Therefore, when drug residues are excreted by our bodies, they can persist for a long time in wastewater sewage and reach water systems.

So, how do these drugs affect animals when they were intended to treat humans? The answer to this is linked to how certain drugs reach their target receptors in human tissue in the first place. Most of these receptors in human cells are evolutionarily conserved, meaning that our receptors share very similar structures with those across the animal kingdom.

How do chemical pollutants impact individuals?

Previous research on this topic has focused on chemical pollution, with impacts ranging from psychological stress, to physical impairment, to death. Studies on agile frogs (Rana dalmatina) and common toads (Bufo bufo) found that the drug carbamazepine, which is used to treat epilepsy, can reduce their average adult body size. However, the ecological implications of these changes are not well understood.

Another study found that exposure to trace metals can affect feral pigeons’ (Columba livia) feather coloration by reducing the iridescence brightness, which could in turn have implications for sexual selection.

Chemicals can also disturb animal behaviour neurologically, through the alteration of hormones and neurotransmitters. Male zebra finches (Taeniopygia guttata) exposed to lead during development had shrunken key neural circuits and song nuclei, affecting song learning ability that is crucial to attract females.

The window of opportunity for a male zebra finch to learn song chirping is sensitive for development. As a result, song, as well as colouration, is vulnerable to adverse environmental conditions—consequently influencing the species reproductive success.

A further study found evidence that fluoxetine antidepressants in the environment may interfere with the neurotransmission or endocrine systems of some aquatic species, such as by inducing tentacle contraction and reducing swimming ability. Thus, these unintentional impairments can affect reproductive behaviour and therefore indirectly limit an individual’s ability to join and form groups.

Formation of animal groups

In order to increase their survival, social animals gravitate towards forming, joining and maintaining a group. For example, hierarchical macaque social groups can comprise 50 or more individuals of all ages and both sexes. Other animals form fission–fusion societies, which are highly dynamic groups such as swarms of insects, schools of fish or flocks of birds.

In these social groups, members can split (fission) or merge (fusion) as needed. Chemical pollution can interfere with these group formation processes by altering individual phenotypes or removing phenotypes from a population, affecting population densities over time.

In another instance, fish rely on group formation to find food, potential mates, and minimise risk from predators. A study investigated the effects of the psychoactive drug Prozac on guppy populations (Poecilia reticulata) from Alligator Creek, in Bowling Green Bay National Park, Australia.

They found evidence that this pharmaceutical chemical pollution was associated with a decline in individual behavioural variation, such as repeatability and reduced risk-taking, which lead to reduced predator-avoidance and reproduction. The population consequently also suffered from reduced genetic variation.

‘Chemical pollution can also interfere with these group formation processes.’

Antidepressants have also been known to alter social behaviour, even impacting the individual’s decision to join a group. Turquoise killifish (Nothobranchius furzeri) that are exposed to fluoxetine, an SSRI that is often found in surface waters worldwide, are more prone to join a group and reproduce.

On the other hand, Siamese fighting fish (Betta splendens) exposed to a sunscreen filter known as benzophenone-3 (BP3) had the opposite effect; the individual’s preference to join a group was attenuated. This is because the chemical decreased the fish's courtship behaviours, which impeded successful mating.

Either way chemical exposure comes at a cost; pharmaceuticals trigger diverse biochemical pathways influencing the body’s physiological demands. An animal having a decreased propensity to join a group will lead to a higher overall energetic cost without the assistance of additional group members and will need more resources to meet this increased demand.

Chemicals can influence entire groups of animals, such as those that depend on collective behaviours that arise due to feedback and social interactions. Schools of fish or flocks of birds can travel in synchrony by individuals collectively matching each other's speeds and movements.

The chronic exposure to pharmaceuticals is affecting animal behaviour in ways we do not yet fully understand. More worrying, is the fact that these effects can be transgenerational, with phenotypic changes being passed down through generations.

Coupled with non-pharmaceutical pollution, such as metal from mining, oil and carbon emissions from the fossil fuel industry and transportation, and pesticides from agriculture, it is clear both animals and humans are at risk.

Featured Image: Olivier GRYSON | Flickr / Insung Yoon | Unsplash

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