Drosophila (fruit fly)
external image fruit_fly_research03_6801.JPG&sa=X&ei=eJXKUOqeKIyq0AG9moDgDg&ved=0CAoQ8wc&usg=AFQjCNGgIPEaQY1vI5882_L31eu5L4gBBw

Classification/Diagnostic characteristics
Drosophila is of the kingdom Animalia, the phylum Arthropoda, the class Insecta, the order Diptera, and family Drosophilidae. It is a flying insect that is hatched in fruit and has a life span of about two weeks. [1]
Three defining characteristics of drosophilia and insecta as a whole are the exoskeleton, three body segments, and the six legs.

Relationship to humans
Drosophila has been studied by humans in order to determine the presence of Hox and segmentation genes in the genome of organisms. [1]
ABout 75% of the genes that cause disease in humans are genes that are present in the fruit fly. Fruit flies are studied in labs across the world in an effort to help treat certain human diseases.
Fruit fly are incredibly destructive to fruit and vegetable crops, particularly the Mediterranean Fruit Fly, lay its larvae on such produce, which then eat the pulp and destroy the fruit and damage economies. (GC)

Drosophila are most commonly found in close association with human habitation, and are often found inside houses, especially in the fall where they are attracted by fruit and wine.
The ecological versatility required to associate with human habitations, from the coasts of New Guinea to Manhattan, has predisposed Drosophila to be a very robust laboratory organism. The world-wide distribution of this fly is relatively recent, however. Its ancestral home is thought to be tropical West Africa. From there it spread to Europe and Asia, perhaps 6,000-10,000 years ago. It spread to the Americas only 500 or so years ago, probably on trans-Atlantic slave ships.

Over the last century, Drosophila have been a favorite organism for biological research, initially in the field of genetics, but latter for the investigation of fundamental problems in biology from the fields of ecology to neurobiology. Thomas Hunt Morgan was the preeminent biologist studying Drosophila early in the 1900's. Morgan was the first to discover sex-linkage and genetic recombination, which placed the small fly in the forefront of genetic research. Due to it's small size, ease of culture, and short generation time, geneticists have been using Drosophila ever since. It is one of the few organisms whose entire genome is known and many genes have been identified. Fruit flies are easily obtained from the wild and most biological science companies carry a variety of different mutations. In addition these companies sell any equipment needed to culture the flies. Costs are relatively low and most equipment can be used year after year.

Today, there are about 7,500 researchers devoted to the study of fundamental problems in biology working with Drosophila. Many advances in our understanding of human development and human disease have come from this work, a fact recognized by the award in 1995 of the Nobel Prize for Physiology or Medicine to three Drosophila workers: Ed Lewis, Eric Weischaus and Christiane Nüsslein-Volhard.

Fruit flies are major problems in farming. They will "attack" a wide variety of plants ranging from avocados, to tomatoes. They also enjoy citrus a lot. To deal with this problem insecticides are used, but a common solution is vinegar traps. Also, to deal with the problem farmers have had to resort to early harvesting. However, the problem continues to rage on and results in large crop loss.

Major tests have been undergone using fruit flies to test the genetics behind alcoholism. Fruit flies are helpful in this pursuit because they have evolved to eat rotting fruit which had fermented and become partially alcoholic.In particular, fruit flies have been used in studying the KCNQ family of genes, which affect potassium gated signaling pathways in the brain that connect to an individual's natural disposition towards alcohol.


Habitat and niche
They live anywhere where fruit is present. (ie. restaurants, hotels, cafeterias,food processing plants, homes, etc...) They cause high contamination rates. More species live in tropical regions and many of them attract to fermented bananas and mushrooms.

Drosophila will breed in drains, garbage disposals, empty bottles and cans, trash containers, mops and cleaning rag. Their development required a moist film of fermenting material.

Predator Avoidance
Drosophila are the prey of many other insects such as bees and ants. These predators tend to attack the larvae or eggs. Drosophila does not have very much defense against predation besides sheer force of number. The organisms proliferate so rapidly that reproduction outweighs heavy predation.

While they do not have much defense mechanisms per say, the drosophila is quite adept at quickly moving/flying away to safety from predators. Because it is so quick, sometimes predators have a hard time catching them. (Prashant)

Nutrient acquisition
Drosophilia ingests food through the mouth. The food then passes through the foregut and into the crop (sac that stores food). Next, the food moves to the gizzard, which is an organ that grinds large food particles into smaller particles. The food then enters the midgut and intestines and the food is digested and the nutrients are absorbed. [1]

Reproduction and life cycle
Within 8 hours of their existence, Drosophila is genetically programmed to reproduce. Adult males will chase females and perform a courtship song with his wings to the females which accept his advances. The egg, while going through Meosis I, will have Zygotes will then experience a 2-week lifespan in which it will turn from egg to a larva to a pupa then an adult.[1]

The drosophila egg is approximately half a millimeter long.They commonly lay eggs just under fruits surfaces. (http://www.yates.com.au/problem-solver/problems/fruit-fly/) After fertilization occurs, it takes about one day for the embryo to develop and hatch into its primary, larval stage. The worm-like larva eats and grows continuously, eventually molting after one day (first instar), two days (second instar), and three days (third instar). The passage of two more days as a third instar larva allows the young drosophila to molt a fourth time and form an immobile pupa, inside of which the organism undergoes a complete structural remodeling to yield the mature, adult winged form. This adult stage drosophila hatches from the pupal case and is rendered fertile within about twelve hours. Depending on the ambient temperature, the course of the organism’s development could take longer, with each of the stages taking twice as long at 18 degrees Celsius, as opposed to normal 25 [degree Celsius] conditions. (Alexander Soloviev)
external image fcycle2.gif
Life Cycle of the Drosophilia

Growth and development
The fertilization, while undergoing Meiosis I, will have the genes to some traits experience crossing over. This will cause some traits, such as body color and eye color, to be inherited together. The embryo is multinucleate, due to the lack of cytokinesis for 13 divisions, and causes it to differentiate. Its maternal effect genes will determine which part of it is the anterior position. Ultimately, this leads to the segmentation and Hox genes which will determine placement of the different segments. There are 12 different segments (1 anterior head, 3 thoracic segments, and 8 abdominal segments. There will be considerably more growth when the fruit flies develop in a hyperoxic conditions. [1]

The inscets have a feathery, bristling cover of the head and thorax.
Interestingly, the drosophilia contains an outerlayer of lipids in intact eggs which give the insect an easy ability to reproduce and mate (evan). http://www.ncbi.nlm.nih.gov/pubmed/21520886

Drosophila has wings and thus travels through flight. These form in the pupa stage in the second and third segments, and can be different due to the crossing over earlier discussed. [1]

An enlarged image of a fruit fly's wing
An enlarged image of a fruit fly's wing
A closer look at the wing of drosophilia

Sensing the environment
Drosophila have compound eyes, each made of hundreds of ommatidia (optical units) that are responsible for perceiving the fly's environment. The light passes through the corneal lens and a crystalline cone before reaching hitting the specialized neurons that detect light (photoreceptors). The inside border is lined with microvilli (increases surface area) that traps light. The stimulated photoreceptors send signals to their axon that transmits the messages to the brain.
http://silverdialogues.fas.nyu.edu/docs/IO/24390/Desplan_Silver_Essay.pdf (BHu)

Flies also have a collection of sensory cells found on the antennae called Johnston's organ. Johnston's organ detects motion in the flagellum. The organ is also capable of sensing gravity and wind.
http://jeb.biologists.org/content/205/9/1199.full.pdf+html (BHu)

external image flyeye.GIF

A Drosophila's Eye

Gas exchange
Drosophilia uses the tracheae (tubes composed of chitin) to exchange gas with the environment. Air comes in through the spiracle (small openings on the thorax and abdomen) and the air travels through the tracheae which then splits into tracheoles. The tracheoles then lead to air capillaries, where gas exchange between the cells and environment occur. [1]
Tracheal System of the Insect

Waste removal
In general insects consume significantly more nitrogen than they need. As a result most insects excrete heavy amounts of nitrogen compounds typically through their rectums. (http://link.springer.com/article/10.1007%2FBF03179946?LI=true)

Environmental physiology
The lifespan of a fruit fly will be lowered if the temperature falls below 65 degrees or rises above 85 degrees.

Internal circulation
Drosophilia has one vessel which is classified as the tubular heart. Thus the drospohilia has an open circulatory system. (Cam Somers)

Wing Image: Circulation in the wings, antennae, legs, etc. is not controlled by the tubular heart. Instead, additional circulatory systems evolved. For the wing, circulation is controlled by the "wing hearts", which are basically two independent muscles located in the 2nd thoracic segment. There are suspicions that this "heart" originated from the tubular heart itself. (http://www.sdbonline.org/fly/aimorph/wing.htm)
wing anatomy.gif

Chemical control (endocrine system)
The endocrine system of insects consist of four main hormone-producing cells. The first type make up endocrine glands, which are structures that secrete hormones, releasing into the circulatory system of the insect. The second type of hormone-producing cell compose neurohemal organs, which are similar to glands but the release of hormones from these organs are triggered by signals from the nervous system or another hormone. Neurosecretory cells are specialized neurons that also secrete chemical messengers when stimulated, but they serve more as a link between the nervous system and the endocrine system. Lastly, the fourth category of hormone-producing cells make up the internal organs of insects; these cells make up bodily structures such as reproductive organs, the fat body, and the digestive system and their ability to control chemicals affect the associated functions of these structures. (
http://www.cals.ncsu.edu/course/ent425/tutorial/endocrine.html) [GW]

Review questions
1. Fruit flies are extremely important in the field of genetics and genome mapping. Almost 75% of the genes found in humans are found in Drosophilia as well. Explain the significance of the Drosophilia genome and give at least two examples of how it has lead to important discoveries in understanding genetics, DNA recombination, and the human species.
2. Since drosophilia do not have strong predator avoidance, what do they do to avoid heavy predation?
3.Name the three main stages in the reproduction cycle of the drosophilia. How long does each stage last and what specifically happens in each stage?

1. Hillis, David M., David Sadava, H. C. Heller, and Mary V. Price. Principles of Life High School Edition. Sudnerland, MA: Sinauer Associates, 2012. Print.