Alcoholized animal?

How well do elephants tolerate alcohol? (Image: az_garret / iStock)

At some point, as is well known, the measure is exceeded – but in principle people can tolerate alcohol quite well. But what about animals? Which types can also metabolize alcohol well and to what extent are the reports of alcoholized behavior in elephants and the like credible? A study now provides insights into these questions. Accordingly, species with nectar or fruit-rich food tend to be well adapted to alcohol degradation – pure leaf or carnivores, on the other hand, are bad. Regarding animal drunkenness, the researchers come to the conclusion, in contrast to previous estimates, that such behavior could certainly occur in wild animals.

Humans seem to be extremely well adapted to the consumption of alcohol, the researchers led by Mareike Janiak from the University of Calgary report in the introduction to their study. Because we and the other great apes have a special form of an enzyme that ensures a particularly efficient breakdown of the potentially harmful substance in the body. This high-performance version of alcohol dehydrogenase IV (ADH IV) is believed to have arisen because the common ancestors of humans and great apes occasionally ate fruit that contained considerable amounts of alcohol through fermentation.

On the trail of an alcohol-degrading enzyme

However, little is known about the characteristics of alcohol dehydrogenase IV in other mammalian groups, the scientists write. That is why they have now devoted a study to this interesting enzyme. Her focus was on the question of whether a connection between certain diets of animal species and the properties of the alcohol-degrading enzyme can be determined. There are also other alcohol dehydrogenases in mammals that may have a role in the breakdown of alcohol. But according to the researchers, ADH IV is suitable as an indicator of the metabolic abilities with regard to alcohol or the question of whether animals can get drunk. As part of their study, Janiak and her colleagues examined the gene responsible for the production of ADH IV in 85 mammal species. As they explain, the sequence of the genetic makeup allows conclusions to be drawn about the functionality of the enzyme.

As they report, they found a striking range of variation in the characteristics of the ADH IV gene in the animal kingdom. The genetic makeup is present in some species, but has become functionless through mutations, the scientists report. This decommissioning of hereditary systems typically occurs when the product in question no longer has an important meaning for the living being and can therefore be saved. In other species, on the other hand, genetic peculiarities emerged, which lead to a similar effect to that of the ADH IV gene of the great apes: it makes the enzyme particularly powerful in breaking down alcohol.

Connection with the diet

The researchers report that the comparisons with the animal species’ diets partially confirmed the assumption that they are linked to the respective alcohol degradability. There is a tendency to show that specializing in fruits or nectars – which make it possible to produce alcohol – has led to the maintenance or expansion of the ADH IV enzyme. For example, certain types of fruit-eating fruit bats have special variants with presumably increased performance. In contrast, the loss of gene function is typical of species that feed only on meat, fish or grass or foliage. Examples include dogs, marine mammals, and some ungulates. A prominent example of an animal without a functional ADH IV gene is the elephant.

As Janiak and her colleagues explain, the study results show that there are apparently large differences in the ability to metabolize alcohol in the animal kingdom. It also becomes clear that the human abilities to break down cannot be transferred to other animal species. According to the researchers, this point is important when considering the extent to which the stories about allegedly alcoholized wild animals are true. In this context reports of elephants, which are said to have behaved “drunk” after eating fermented fruit, are particularly well known.

Drunk animals may not be just a myth

In a previous report, scientists came to the conclusion that this does not seem plausible and is more likely to be attributed to an excessive humanization of animal behavior. According to this assessment, the uptake potential via the fruits measured by the enormous body mass of the elephants is not sufficient to achieve a “relevant” alcohol level in the blood.

But Janiak and her colleagues are now questioning this judgment. As you explain, this assessment was based on human tolerance to alcohol. However, as her study now shows, the elephant does not have a functional ADH IV gene. Accordingly, he may be very sensitive to alcohol intake. However, it cannot be ruled out that these animals have other mechanisms of alcohol degradation, the researchers concede. So far, it cannot be said what effects the consumption of high-percentage fruit can have.

“Humans may have a tendency to humanize animals and thereby misjudge their behavior. But it is also wrong to project human metabolic abilities onto other animals, ”the researchers write. To what extent it seems plausible that elephants show alcoholized behavior could ultimately only provide measurements that show the blood values ​​to which certain alcohol intakes through food lead.

Source: Biology Letters, doi: 10.1098 / rsbl.2020.0070

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