Fruit flies like banana? Yes, but they might like alcohol more

Specific behaviors have been evolved to protect us from pathogens. An interesting study shows that flies drink for medication benefit.

        Sometimes when stimulated, our bodies give rise to mysterious unconscious response the occurance of which we don’t understand at all. For example, when watching horror movies we may show gooseflesh that push us to avoid those disgusting scenes. As a result, we feel relaxed and comfortable. These natural responses like gooseflesh are protective measures our bodies acquired during evolution. Similar behaviors include our unconscious fear of snakes, spiders, and other animals. These protective behaviors are reminiscent of our immune system that is evolved to use cells and molecules in our bodies to prevent invading parasites. For such a resemblance, behavioral immune system was coined to describe our behavioral response against outside hazards.

        In general, any biological behaviors protecting an organism from infection can be called behavioral immune. Medication, the use of substance or procedures by humans to fight infection, belongs to behavioral immune response.

        Behavioral immune system can explain some of our unconscious behaviors. For example, we sometimes dislike strangers for no reason. It is not for no reason. It is only a reason you don’t realize. Your behavioral system automatically discriminate different persons according to their faces, their poses, their age, their figure or their smell. Thus, behavioral immune may lead to prejudices against obese, elderly, short or disabled individuals. Moreover, behavioral immune system even contributes to xenophobia and ethnocentrism.   

        Flies are much smarter than we thought. They can use behavioral changes to adapt to environments. Flies often face the threat from wasps under natural environments. Alcohol is useful for flies to prevent infection from wasps. Although flies are not alcoholic, they do use alcohol to combat infection from wasps. A paper in this volume of Science¹ unveiled an interesting discovery about how flies tackle this threat from wasps by utilizing alcohol, showing us an example of self-medication of flies.

        Researchers placed 300 flies in cages containing two food dishes one of which was added with 6% alcohol by volume. In addition, flies were also housed with or without female wasps as a threat. Fly eggs were collected for counting from different dishes in each situation (with or without wasps). Interestingly, researchers found in the cages no wasps were provided, flies preferred laying eggs in dishes without alcohol. On the contrary, in dishes with wasps, flies laid more eggs in dishes with alcohol.

        This is not the whole astonishing story. Flies can even tell the gender of wasps. Female wasps are more dangerous. When flies were housed with male wasps, flies would just ignore them and did not show preference on alcohol containing dishes.

        Under the situation when wasps don’t exist, flies have some tendency toward alcohol. They prefer laying eggs in 3% alcohol. This means flies like a little bit alcohol. However, when realizing deadly wasps are nearby, they would like to try even 12—15% alcohol, the highest level of alcohol found in nature.

        How can flies tell wasps, especially more deadly female wasps are nearby? They may do this by olfactory or visual cues. To answer this question, flies harboring mutations that result in defects in olfactory or visual system were used to observe their alcohol preference. Researchers found flies with mutations in response to olfactory stimuli can still display alcohol preference whereas vision mutants of flies failed to show their fancy on alcohol. Thus, flies must use sight to sense the existence of wasps. A small protein called neuropeptide F has been shown to increase of alcohol tolerance of flies. In this study, researchers also found neuropeptide F played a role in transmitting visual signal from wasps to guide the alcohol preference behavior of flies.

        Flies can have a short time memory of the existence of wasps. When flies were first housed with female wasps and then wasps were removed, flies still displayed an alcohol preference at most 4 days after wasps were devoid.

        Flies’s behavioral immune system showed an vivid example how organisms have obtained ability to adapt to nature.

[1] Fruit Flies Medicate Offspring After Seeing Parasites. SCIENCE VOL 339 22 FEBRUARY 2013 947-950.

Note: the attached picture is from website: http://en.paperblog.com/mental-health-fruit-flies-turn-to-alcohol-when-sexually-frustrated-163917/