Drosophila melanogaster, The ‘Fruit’ Fly

Margaret C. Bloch Qazi
Department of Biology
Gustavus Adolphus College

The small fly Drosophila melanogaster is frequently around kitchen fruit bowls and trash during the summer months. Despite the common appellation ‘fruit fly’, this insects’ scientific name (translated from the Greek) means black belly (melanogaster) dew-lover (Drosophila). This is attributed to their affiliation with moist habitats and the black abdomen exhibited by males. These harmless insects do not cause fruit and vegetables to rot, but feed upon the bacteria and fungi growing on vegetable matter that has already begun to decay (Powell 1997).
Figure 1: A Male Drosophila melanogaster

Taxonomy:

            Phylum                      Arthropoda

                 Class                         Insecta

                     Order                         Diptera (fly)

                           Family                        Drosophilidae

                                    Genus species        Drosophila melanogaster

Drosophila melanogaster’s assignment within the hierarchical Linnean taxonomic system is based upon particular anatomical characteristics. D. melanogaster is an arthropod, the most species-rich phylum in the animal kingdom. Like all arthropods, they secrete an exoskeleton called a cuticle. The cuticle is hardened, segmented and jointed. Furthermore, they lack moving cilia (Pechenik 2005). Within the arthropods, D. melanogaster is classified as an insect, and distinguished from other classes of arthropods, by the absence of abdominal appendages among adults and the presence of a type of lower lip (called the labium). Insects are also frequently identified by the presence of wings and three pairs of legs in the adult form. Finally, D. melanogaster have structures called halteres which are a modified second pair of wings that help flies balance during flight, as do all members of the Order Diptera (flies).  Within the genus Drosophila, there are as many as 2,000 species. All Drosophilids have red eyes and plumose arista (feather-like antennal structures). Anatomically, D. melanogaster is distinguished from most other Drosophilids by the location and elaboration of a patch of bristles on the male foreleg called the sex comb. However, it is the male genitalia (and unique sequences for particular genes) that distinguishes this species from the 2,000,000 or more animal species that roam the earth, swim in the ocean, and sail through the sky (O’Grady 2003).
Figure 2: Male D. melanogaster a) lateral view of the body with identifying characteristics indicated, and b) anterior view of a fly head with the arista and red eyes indicated.

Ecological & Laboratory Roles:

While in its natural habitat Drosophila participates in the processes of decomposition and pollination (Powell 1997) it is perhaps best known and has made the greatest contribution to human welfare through its use as a model laboratory organism. In biological research, scientists often focus their attentions on a small number of organisms for intense study, called model organisms, with the idea of applying the findings to other organisms. Drosophila’s use as a model organism began in the first decade of the 20th century by W.E. Castle and soon after by T.H. Morgan (Weiner 1999). Both of these biologists used this fly in the study of genetics. D. melanogaster has continued to be a key player in the study of genetics, but has also become very useful in our understanding of development, evolution, physiology and behavior at the cellular and molecular levels. The widespread use of D. melanogaster as a model organism is illustrated by a search of PubMed (a search engine for basic and biomedical research papers at:  http://www.pubmed.gov). When directed to search for papers on the subject of “Drosophila melanogaster” over the last 5 years (from July 2006), more than 6400 research papers are identified. On average, that is ~107 papers published every month! These unassuming insects have clearly had a large impact on our understanding of basic biological questions.

D. melanogaster is a model laboratory organism par excellence. There are several reasons why D. melanogaster is appropriate to use for studies.

1. It is easy and relatively inexpensive to maintain large numbers of flies within a laboratory. They are small, develop rapidly, highly fertile and have relatively simple dietary requirements. A single inseminated female can produce more than 300 offspring within two weeks. In an additional two weeks all of these offspring will have developed into mature adults producing offspring of their own!






2. There are literally thousands of different genetic lines (i.e. strains) available that serve as 'tools' to examine developmental, behavioral, and physiological processes. Several stock centers exist around the world to catalogue, culture, and distribute these lines to scientists who study a variety of experimental questions. Furthermore, D. melanogaster's genome has been sequenced (see Adams et al. 2000) facilitating the identification of genes involved in behavioral, physiological and anatomical traits.





3. The behavior and ecology of these flies is well-studied permitting the physiological, cellular and molecular basis of these phenomena to be examined (see references below).

Therefore, this animal serves as a tractable system to understand the molecular and genetic basis of many characteristics while still allowing one to relate that understanding to the whole animal.
Figure 3: a) Normal (i.e. wild type) flies in a vial. All developmental stages are present in the culture. b) The number of flies present in a culture bottle after 60 days (2 months) assuming that the food remained fresh and that each female produced 50 offspring every two weeks. c) A female with several mutations including white eyes, short and thick thoracic bristles, and curled wings. Compare this fly's appearance with that of the male in figure 2b. These flies are particularly useful for mapping (locating) novel mutations to specific regions of the chromosome.

Want to learn more?

The following references and links are excellent resources related to Drosophila behavior, evolution, development and genetics.

References Cited: