Most everyone knows that fruit flies gravitate toward bananas and most overripe fruit and almost magically appear in kitchens around the world. Less well known is that this insect species has been used by thousands of scientists around the world for more than 100 years to study genetics and developmental biology.

The reasons are that fruit flies are easily cultured in the laboratory, are low cost, have a short life cycle, a simple genome (all the inheritable traits of an organism), and produce many offspring. Fruit flies have been used in studies as diverse as alcoholism, learning and behavior, ecology and evolution, human disease and the development of new pharmaceuticals. It is fair to say that fruit flies have revolutionized biological science.

Fruit flies, or Drosophila melanogaster, live in almost all temperate regions of the world. The only aspects limiting the habitats are temperature and availability of water, as the scientific name actually means “lover of dew,” implying that the species requires a moist environment.

The common fruit fly is normally tan, and 3 mm in length and 2 mm in width. It has a rounded head with large, red compound eyes; three smaller simple eyes; and a short antenna. The female is slightly larger than the male, with black stripes on the dorsal surface of the abdomen used to determine the sex of an individual. Males have a greater amount of pigmentation concentrated at the posterior end of the abdomen. Reproduction is rapid: A single pair of flies can produce litters numbering in the hundreds within a few weeks, and the offspring become sexually mature with one week.

As the name implies, fruit flies live primarily on plant material. Adults thrive on rotting plants and fruits, where eggs are laid.



History

The Drosophila research story begins in the early years of the 20th century. However, the first wave of fruit fly immigrants had arrived years before at ports in the Caribbean, carried across the Atlantic in slave ships from Africa and southern Europe. In the 1870s, in the immediate aftermath of the Civil War, the burgeoning trade in rum, sugar, bananas and other fresh fruits delivered them north to Boston, New York, Philadelphia and other flourishing cities on the east coast.

In the early 1900s, fruit flies were one among many animals used in the laboratory. Those early years were also witness to an explosion in experimental biology. In 1907, Thomas H. Morgan, a zoologist at Columbia University, began using the insect to substantiate the chromosomal theory of inheritance. (That chromosomes are the carriers of genetic information.) In early May 1910, while routinely examining his fly collection, Morgan spotted a fly with two white eyes instead of the usual red variety. The white-eyed fly was a new mutant. In subsequent breeding the white-eyed characteristic had disappeared, as Mendel would have predicted. Later generations began to appear, some with white eyes, in the ratio conforming to previously determined expectations. From this and subsequent work, Morgan conjured up a compelling amalgam of hereditary ideas.

Life, for both Morgan and the fly, would never be the same. His accomplishments led to his winning the Nobel Prize in 1933. In 1913, Alfred Sturtevant, a student of Morgan, created the first genetic maps using D. melanogaster.

As mentioned above, fruit flies have proven themselves as pioneers in genetic research. They also produce immense quantities of saliva, and the chromosomes inside the salivary glands are huge, a thousand times thicker than normal. Each chromosome is made up of many parallel strands of DNA that have failed to separate. Chemical staining of these supersized chromosomes reveals dark horizontal bands along their length, distinct landmarks corresponding to the positions of specific genes. These supersized chromosomes are similar to biological barcodes that gave biologists the first glimpse of genetic differences between individuals and populations.

Inebriated fruit flies have been used to help scientists find potential drug targets for alcoholism. This finding provides a crucial explanation of why some people seem to tolerate alcohol better than others. The discovery also sheds new light on many of the negative aspects of drinking, such as liver damage.

Fruit flies may seem to be unlikely heroes in the battle against drug abuse, but new research suggests that these insects could claim that role. Scientists have found that fruit flies can be used as a simpler and more convenient animal model for studying the effects of cocaine and drugs like amphetamine and methylphenidate on the brain.

Fortunately, the relationship between fruit fly and human genes is so close that sequences of newly discovered human genes, including those implicated in disease, can often be matched against their fly counterparts. This provides a lead toward the function of the human gene and could help in the development of new and effective drugs or other forms of treatment. Such research has been responsible for a host of biological discoveries that began with the humble fruit fly more than a century ago. One wonders what the remainder of this century will unveil.

Max Sherman is a medical writer and pharmacist retired from the medical device industry. He has taught college courses on regulatory and compliance issues at Ivy Tech, Grace College and Butler University. Sherman has an unquenchable thirst for knowledge on all levels. Eclectic Science, the title of his column, will touch on famed doctors and scientists, human senses, aging, various diseases, and little-known facts about many species, including their contributions to scientific research. He can be reached by email at maxsherman339@gmail.com.