Drunken Butterflies and Drunken Elephants: Animals Drink Alcohol Too | Science

The Bicyclus anynana Native to East Africa, the butterfly gets part of its diet from fermented palm nectar, which is known for producing high levels of alcohol. Around the world, in North America, American waxwings have been observed flying erratically and colliding with objects. Autopsies of some of these birds revealed atrophied livers, likely due to consumption of overripe, fermented berries. In laboratory studies, male and female flies from different fruit fly species showed a shift toward more solitary or promiscuous behavior when exposed to ethanol.

A review of current scientific knowledge highlights that alcohol consumption in the animal world is more widespread than previously thought. Dozens of species, including mammals, birds and insects, prefer fruit or nectar containing some level of alcohol. Reasons for using this potentially toxic and dangerous substance range from seeking a source of calories to demonstrating disinhibited behavior, similar to what is observed in humans.

Until the beginning of this century, even the scientific community believed that the use of such an objectively harmful substance as alcohol is an exclusively human phenomenon. This was considered a universal behavior; Archaeological sites from various cultures have revealed evidence of beer, wine, and other beverages made by fermenting the sugars in fruit to produce ethanol.

However, the drunken monkey hypothesis appeared, suggesting that other primate species also consume alcohol. Ten years ago, such behavior was associated with the fact that the ancestors of orangutans, chimpanzees and humans came down from the trees about 10 million years ago. Notably, the only large primate that has not been observed feasting on fermented fruit is the orangutan, the only species that remains primarily in the treetops. The rationale is that the soil contains the ripest fruits colonized by such yeasts Saccharomyces cerevisiaereal agents for converting sugar into alcohol.

This hypothesis, however, does not account for many other animals. In the article published in Trends in ecology and evolution, the authors collect numerous cases of consumption of various types of fermented fruits. While the researchers note that many of these observations lack certain criteria for full scientific confirmation — such as confirming the presence of ethanol, measuring its content in the fruit, or detecting metabolites indicative of poisoning — they say there is enough evidence to support the widespread nature of this behavior

Among mammals, at least 85 species have genetic adaptations for alcohol metabolism. These adaptations include variations in genes encoding enzymes such as aldehyde dehydrogenase (ALDH), which plays a role in the metabolism of certain alcohols. Such genetic modifications are found not only in primates, but also in other frugivores, such as the great flying fox, one of the largest bat species. Ethanol metabolites have even been found in the fur of some shrews and tricolor squirrels.

“We’re moving away from this anthropocentric view that ethanol is just something people use,” senior author Kimberly Hawkings of the University of Exeter said in a press release. “It’s much more abundant in nature than we previously thought, and most animals that eat sugary fruit will be exposed to some amount of ethanol.”

Of the more than 325,000 species of flowering plants (angiosperms), many fruits are raw materials — sugars — for the production of natural spirits. Although the oldest flowering plant in the fossil record dates back to only 130 million years ago, molecular clocks suggest that their origins go back even further. During their evolution, angiosperms developed defense mechanisms, including compounds such as geraniol, methanol, ethanol, and isopropanol, which have fungicidal properties. It is believed that the first yeast appeared about 200 million years ago. Biologist Laura Kamon wrote in an article that “yeasts have developed a strategy to eliminate competition: by fermentation, they convert sugar into ethanol, which is harmful to bacteria.”

From the cold forests of Finland to the jungles of Uganda, fruits, nectars, and alcoholic juices can be found in all ecosystems. In most cases, the alcohol content in them does not exceed 1%, as in non-alcoholic beer. However, this study highlights dozens of plant species that exceed this concentration. An exceptional case is makara (Astrocarium standlianum), a palm tree native to Costa Rica, Panama and large areas of Ecuador and Colombia, whose ripe fruit can reach 10.3% alcohol, comparable to white wine. Of the 61 plant species included in the study, only 10 exceed the 1% threshold. But the researchers note that the effects on the body are different, and the effects of long-term consumption should also be considered.

Although not all animals have the ALDH enzyme, many have another enzyme specific to ethanol metabolism: alcohol dehydrogenase (ADH). The degree of ethanol consumption varies greatly. Apart from primates, both human and non-human, one of the most notable examples is the fruit fly, also known as the vinegar fly. Female flies lay their eggs in fermented fruit with an alcohol content of up to 15%, comparable to red wine. Widely used as a model organism in laboratories, Drosophila melanogaster well studied; for example, ADH is known to convert alcohol into lipid deposits. However, systematic studies of ethanol consumption are rare. That’s what one study found worker honey bees Nectar gatherers have this enzyme, but those who take care of the larvae and stay in the hive do not. Both enzymes are present in the tongues, esophagus, and stomachs of primates and other mammals, including several species of fruit bats.

In a series of experiments, several species of bats, slow loris (a type of primate), and Campbell’s dwarf hamsters were shown to prefer fruits with higher ethanol content when given a choice. Metabolites found in the hair of shrews confirm their absorption of relatively large amounts of alcohol. There were even cases of drunken elephants. What motivates animals to consume a substance that may be harmful, dangerous, or reduce their ability to cope with predators? The authors of the study admit that they are not entirely sure, but reject the idea of ​​accidental ingestion as the main cause. Instead, the widespread presence of yeast and ethanol, combined with genetic adaptations for metabolism, suggests a more conscious consumption.

Indeed, researchers suggest that ethanol consumption may have several benefits for wildlife. First, it is a source of calories. In addition, volatiles from fermentation can help insects, birds, and mammals to food sources. Ethanol may also have medicinal properties, as seen in fruit flies, which lay their eggs in alcohol-containing substances to protect them from parasites.

“On the cognitive side, it has been suggested that ethanol may trigger the endorphin and dopamine system, leading to a feeling of relaxation that may have benefits in terms of sociality,” said Anna Bowland, first author of the study.

For example, research shows that Drosophila simulansflies, closely related to fruit flies, are more likely to mate after contact with alcohol. Meanwhile, the male D. melanogaster They have been known to seek out alcohol after failed mating attempts. However, to confirm the link between ethanol and behavioral changes, Bowland notes, it is necessary to determine “whether ethanol causes a physiological response in nature.”

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