Despite stories of "wasps getting drunk" and "beetles consuming beer," it has been thought that alcohol consumption in the non-human animal world has not been particularly widespread, deliberate or sought out for a physiological benefit. Now, ecologists challenge this theory, saying it's far more commonplace and strategic than scientists believed.
A team of international ecologists has made the case based on the fact that ethanol is a naturally occurring compound in nearly every ecosystem on the planet, and is consumed frequently by animals that have a diet of fruit and nectar.
“We're moving away from this anthropocentric view that ethanol is just something that humans use,” says behavioral ecologist and senior author Kimberley Hockings, of the University of Exeter. “It's much more abundant in the natural world than we previously thought, and most animals that eat sugary fruits are going to be exposed to some level of ethanol.”
Alcohol, of course, has been traced back to ancient human history – from beer made from rice 9,000 years ago, to evidence of beer consumed in China 5,000 years in the past. But despite anecdotal reports of non-human animals appearing drunk after consuming ripe fruit or sugary substances, there's been very little research into its actual prevalence in the broader kingdom of life.
In the study, the researchers cite reported instances of intoxicated animals, including: "Elephants (Loxodonta africana), baboons (Papio ursinus), and other wildlife apparently get ‘drunk’ on marula (Sclerocarya birrea) fruit in Botswana, and a moose (Alces alces) found stuck in a tree in Sweden was reportedly drunk on fermented apples. In none of these cases was ethanol measured in the fruit nor was ethanol (or its metabolites) confirmed in the animals. However, mammals will take alcoholic drinks from humans. For example, wild green monkeys (Chlorocebus aethiops) introduced to the Caribbean during the 1600s take alcoholic fruit cocktails from tourists on St. Kitts."
Ethanol, the key alcoholic compound that's produced when yeast ferments the sugars in fruit, as well as grains and vegetables, has been readily available for around 100 million years. Around this time, the evolution of flowering plants to produce sweet nectar and fruits made it possible for ethanol to be naturally produced and consumed by animals that subsist on certain diets.
While, the researchers add, the amount of ethanol in naturally fermented foods on average is only about 1-2% alcohol by volume (ABV), some ripe fruit in tropical regions – such as in extremely ripe Astrocaryum standleyanum palm fruit in Panama – has reached ABV levels of 10.3%. However, it's not indicative of all tropical areas, with fruits in Singapore having been identified as containing between 0.006% to 0.61% ABV.
To put it into context, a regular can of beer, hard seltzer or hard cider has around 5% ABV.
While animals have been genetically adept at being able to process and break down ethanol before yeast fermentation takes place, the researchers believe there may be some evolutionary switches that have driven certain species to seek out fruit and nectar with a higher concentration of sugars.
“On the cognitive side, ideas have been put forward that ethanol can trigger the endorphin and dopamine system, which leads to feelings of relaxation that could have benefits in terms of sociality,” says behavioral ecologist and first author Anna Bowland of the University of Exeter. “To test that, we'd really need to know if ethanol is producing a physiological response in the wild.”
More research is needed to observe whether species are being more impacted by ethanol consumption than previously thought, or whether overly ripe fermenting fruits provide other kind of triggers – such as their strong odor, which allows animals to find them more easily, or that the higher sugar content means they're an advantageous source of energy. After all, the non-animal kingdom is a finely tuned energy gain-cost machine, and more sugar content means more fuel for an individual.
“From an ecological perspective, it is not advantageous to be inebriated as you're climbing around in the trees or surrounded by predators at night – that's a recipe for not having your genes passed on,” says molecular ecologist and senior author Matthew Carrigan of the College of Central Florida. “It’s the opposite of humans who want to get intoxicated but don’t really want the calories– from the non-human perspective, the animals want the calories but not the inebriation.”
However, there still may be more to how animals are using alcohol to their biological benefit. Fruit flies deliberately lay eggs in ethanol-rich products, which is thought to ward off parasites. The larvae of these flies (Drosophila melanogaster) will also up their ethanol intake when targeted by parasitic wasps.
Previous studies have looked into alcohol consumption and behavior in the animal kingdom – such as whether hummingbirds are getting intoxicated at mealtimes, the beneficial social changes in buzzed flies and how zebrafish become bolder when 'drunk.'
The researchers call for more studies into the use of ethanol in nature, as anecdotes of "drunk" animals suggest we may not fully understand what is behind species that seek out potentially boozy foods. The team will now look into how ethanol consumption in primates – and the enzymes responsible for breaking down the alcohol in their diets – relates to their social interactions and behaviors.
"A broad eco-evolutionary view of alcohol usage suggests that ethanol is neither rare nor simply avoided," the researchers concluded. "It can be toxic but also protective against ‘competing’ organisms, and metabolic adaptations to ethanol can expand the resources that provide calories to an animal. This leads us to reconsider ethanol’s ecological role and evolutionary impact in nature.
The study was published in the journal Trends in Ecology & Evolution.
Source: University of Exeter
