Drosphila

= Drosophila = == By Alina Smithe ==

Classification/Diagnostic characteristics
Anatomy of the Fruit Fly Kingdom: Animalia, Phylum: Arthropoda, Class: Insecta, Order: Diptera, Family: Drosophilidae, Genus: Drosophila

Drosophila, more commonly known as fruit flies, are arthropods. There are around a billion billion arthropods living at any given time. Their distinguishing features include segmented bodies with muscles attached to their exoskeletons. Drosophila are insects, which is a subgroup of arthropods. They have bodies with three regions: the head, the thorax, and the abdomen. They have antennae extending from their head. They also have six legs extending from the thorax, making them hexapods. Insects do not have appendages extending off of their abdominal segments, unlike other arthropods.

Relationship to Humans
Drosophila are often used in biological research. Scientists conduct many experiments on them because of their small size, short life cycle, and easiness to breed. These experiments involving Drosophila include research on genetic linkage, body segmentation, evolution under hyperoxic (increased oxygen concentration) conditions, speciation, and Hox genes.

Humans are largely responsible for the dispersal of Drosophila and other insects throughout the world.

Fruit flies are considered a common pest to humans. However, as members of Drosophilia only feed on and lay eggs in overripe or rotting fruit, they are not as significant an agricultural pest as members of the closely-related Tephritidae family, which does feed on unripe and ripe fruits. Fruit flies in the home are typically only minor annoyances, but they may also contaminate food with disease-causing bacteria. Tools for dealing with infestations include traps and insecticides

Habitat and Niche
They live in terrestrial environments all over the world. Drosophila implant their eggs into rotting fruit, which is the ideal environment for their pupation. Drosophila are found on every continent in the world except for Antarctica. They require moist environments to live, and the name "Drosophila" literally means "lover of dew." The range of Drosophila is primarily limited by temperature; Drosophila cannot survive the colder temperatures at higher elevation or latitude.

Predator Avoidance
Drosophila do not have many defenses against predators, and they are the prey of many different species. Their rigid exoskeleton does provide some protection against predators but not much. Their only other effective defense mechanism is utilizing their compound eyes to detect predators and attempt to fly away from them.

In an experiment done in 2012 at the University of Houston, Drosophila was concluded to use redundant sensory modalities to detect and avoid predators. This kind of sensory device can be used to detect rhythm discrimination, maternal calling, orienting response, and associative learning. It is actually also prevalent in newborn babies who use it to gain and use sensitivity to differences in numerical and auditory responses. This kind of stimuli also allows for cognitive response. These characteristics are really useful to avoiding predators because it gives the organism quick ways to escape the threat and learn from the experience how to avoid it afterwards.

Nutrient Acquisition
Fruit flies are heterotrophs, gaining energy from consuming other organisms, specifically rotting plants and fruits. Food enters through the mouth, where digestion begins. The food is broken up and chemically digested in the foregut, midgut, and hindgut.

Reproduction and Life Cycle


The life cycle of Drosophila lasts two weeks, starting from a fertilized egg to reaching maturity. About 24 hours after fertilization, the egg hatches into a larva. Then, the larva becomes a pupa and finally an adult fly.

Only 8 hours after reaching adulthood, fruit flies are ready to mate. The males chase the females and tap their forelegs on the females’ bodies. Most of the time, the females flee, making it difficult for the males to find available mates. Once they do find females that don’t run away, they make courtship songs with their wings and lick the genitals of the females before beginning copulation.

Growth and Development
media type="custom" key="24505330" During development, different body segments are recognizable as early as 24 hours after fertilization during pupation. Maternal effect genes, segmentation genes, and Hox genes are responsible for development in fruit flies.

Drosophila undergo a process early in development called superficial cleavage. This happens when a cell undergoes mitosis without cell division, resulting in a cell with many nuclei called a syncytium. The nuclei then move toward the outside of the egg, and the cell membrane grows outward, enclosing the nuclei in individual cells surrounding a yolk core.

The process of growth happens very quickly in fruit flies, and they reach maturity after only a couple of weeks. Along with three pairs of legs, fruit flies have wings, which allow for movement through flying.

Integument
Drosophila have rigid exoskeletons to protect them. Layers of protein and chitin, a waterproof polysaccharide, thicken this exoskeleton. Although it provided protection, it made movement and gas exchange more difficult, leading to evolutionary adaptations that eliminated these problems.

Movement
Extending off of the exoskeleton, appendages in Drosophila are the source of movement. they contain muscles, which contract in various ways to produce movement. Each part of the segmented body has muscles that control the attached jointed appendages. Complex muscle movements are due to these jointed appendages.

Drosophila flap their wings up to 200 times a second horizontally, unlike birds, and when the organisms sweeps its wings forward, this creates a vortex of air on top of the wings, which results in a low pressure zone that allows it to fly and produces lift.

Sensing the Environment
Drosophila have antennae, which are appendages that help them sense the environment around them.

Arthropods, including Drosophila have compound eyes, consisting of hundreds of optical units called ommatidia. The ommatidia each has a narrow-angle lens that focuses light onto retinula. These photoreceptor cells are lined with microvilli, which contain rhodopsin and are responsible for capturing the light. Drosophila have 800 ommatidia, which creates a high image resolution. Each omnatidia is made of 8 photoreceptor neurons and 4 cone and pigment cells.

A close up of the drosophilia eye. Each individual omnatidia is visible.

Gas Exchange
Insects do not have a central respiratory system. Instead, they have a tracheal gas exchange system throughout their bodies to regulate oxygen levels. Air tubes bring oxygen to every cell in the body through diffusion. The spiracles, which are openings in the sids of the abdomen and thorax, open to allow the passage of air. The spiracles are connected to tubes called tracheae, which branch into tracheoles, which branch into air capillaries. The process of gas exchange occurs in the capillaries, which extend all over the body, allowing every cell to receive oxygen.

Waste Removal
The excretory system in Drosophila and all other insects is composed of Malpighian tubules. These tubules are blind-ended, meaning that they are sealed at one end, and they open between the midgut and hindgut. Since insects have open circulatory systems and can’t use pressure differences to transport extracellular fluids, they have to use energy for the active transport of uric acid, potassium ions, and sodium ions into the tubules. Water flushes the contents of the tubules towards the gut through osmosis, and it then must be regained. Sodium and potassium ions are actively transported by epithelial cells from the gut back to the extracellular fluid, which causes water to be pulled out of the waste products. Lastly, the waste, which is a mixture of uric acid and other substances, exits the body through the rectum.

Environmental Physiology (temperature, water and salt regulation)
The Malpighian tubule system in Drosophila is very effective at removing nitrogenous wastes and salts without losing a lot of water, making it possible for them to live in drier environments.

Drosophila are ectotherms, meaning that their body temperature depends on that of the environment around them, but they still have to produce heat metabolically when it comes to flight. The muscles needed for flying do not function properly if not at 35-40 degrees Celsius. This heat comes from contractions in the flight muscles.

Internal Circulation
Drosophila have an open circulatory system. Circulatory fluid called hemolymph exits vessels, and then it flows between cells and back into the heart or vessels.

Chemical Control (i.e. endocrine system)
Molting of the exoskeleton is controlled by two hormones: prothoracicotropic hormone (PTTH) and ecdysone. PTTH is produced by cells in the brain and is transported to and stored in structures surrounding the brain. To initiate molting, it is released, and it diffuses through the extracellular fluid until it reaches the prothoracic gland, which is stimulated to release ecdysone. Ecdysone diffuses to areas where molting will occur, and molting begins.

Juvenile hormone, produced in a structure called the corpora allata, controls the end result of molting in insects that have yet to reach maturity. It determines whether or not the insect will become an adult or simply grow to a larger size.



Review Questions
1) How do Drosphila exchange gas with the enviorment? Explain what mechanisms and body parts are involved and what they do. 2) What role do hormones play in the development of Drosophila? 3) How do Drosophila excrete waste? Explain the system of the Malpighian tubules. 4) Why are Drosophila useful in scientific experiments? What studies have involved Drosophila? 5) What is the life cycle of Drosophila? Explain each event/stage and how long each takes.