Fruit Fly has Opened New Era of Taste Behavior

Fruit Fly has Opened New Era of Taste Behavior

If you have been seeing small flies or gnats in your kitchen, they're probably fruit flies. Fruit flies can be a problem year round, but are especially common during late summer/fall because they are attracted to ripened or fermenting fruits and vegetables.Normal fruit flies have red eyes, but his
mutant male had white eyes.


Tomatoes, melons, squash, grapes and other perishable items brought in from the garden are often the cause of an infestation developing indoors.Fruit flies comprise several different species belonging to the genus Drosophila. The most common species encountered in homes and other structures is D.melanogaster. Fruit flies are also identified as pomace flies or vinegar flies. These pests can be found throughout the world, in homes, food processing plants, warehouses, grocery stores, wineries, restaurants and other structures.

Vinegar flies may become a nuisance in homes, restaurants, fruit markets, canneries, etc., especially when associated with decaying or rotting fruit and vegetables. Indoors, flies may be seen hovering around overripe fruit and vegetables, baked goods containing yeast, garbage cans and beverages such as fruit juices, cider, soft drinks, beer, wine and vinegar.

Genetically speaking, people and fruit flies are surprisingly alike, explains biologist Sharmila Bhattacharya of NASA's Ames Research Center. "About 61% of known human disease genes have a recognizable match in the genetic code of fruit flies, and 50% of fly protein sequences have mammalian analogues."

The researchers found that fruit flies make subtle changes in the tilt of their wings relative to the ground and the size of each wing flap to generate the forces that allow them to turn. Flies then create an opposite twisting force with their wings to stop the inertia of the turn, preventing an out of control spin.

The researchers had noticed that specific inversions in the European flies varied in a predictable pattern according to the average temperature of the region where the flies lived. But the invading American flies did not, at first, appear to exhibit the same predictable chromosomal changes expected as they spread into warmer and colder latitudes.

The fly in question, Drosophila melanogaster, is about as common a fruit fly as you'll ever come across. While there are some 900 species of Drosophila worldwide, melanogaster is the one you've probably seen yourself—the tiny flies, maybe an eighth of an inch long, that you'll find hovering around your overripe bananas.The fruit fly also has a small genome—about 13,600 genes, compared with the estimated 40,000 genes of humans.

Fruit flies can reproduce anywhere there is fermenting organic matter that stays wet or moist. In the house, likely places for flies to breed include slow-moving or seldom-used sink, bathtub, shower, or floor drains in which a layer of slime (gelatinous film) has built up above the water line. Other moist accumulations of fermenting organic matter are possible such as wet areas under dripping pipes and refrigeration equipment, garbage containers, and discarded bottles and cans. Regardless of where the flies originate, they will be at windows throughout the house and at sinks because they are attracted to light and to moisture.

In a series of experiments, the researchers found that females given the male variant of the gene acted exactly like males in courtship, madly pursuing other females. Males that were artificially given the female version of the gene became more passive and turned their sexual attention to other males.

The two forms are naturally occurring fly mutations, providing the opportunity to study the molecular basis for behavioral polymorphism. Research at the Institute has revealed that interaction between gene and metabolic networks influence expression of mRNA and metabolite molecules between the two forms.

Researcheers noted that there must be an evolved function in the fly brain which leads to spontaneous variations in fly behavior.They indicate a mechanism which might be common to many other animals and could form the biological foundation for what we experience as free will.The next step will be to use genetics to localize and understand the brain circuits responsible for the spontaneous behavior. This step could lead directly to the development of robots with the capacity for spontaneous nonrandom behavior and may help combating disorders leading to compromised spontaneous behavioral variability in humans such as depression, schizophrenia or obsessive compulsive disorder.

The researchers show that, in the fruit fly, the expression of many genes is modified by exposure to alcohol, and that mutations in some of these genes affect the flies' sensitivity to alcohol. Many of the genes analysed are also found in humans and the authors of the study conclude that studies in the fruit fly Drosophila could shed light on the genetic basis of human response to alcohol, including the susceptibility to alcohol abuse.

Scientists recently reached an important milestone in the understanding of genetic contributions to behavior. A new study
demonstrated the role of a single gene in specifying sexual behavior in the fruit fly Drosophila melanogaster. The findings prompt provocative thinking about the contribution of genetic factors to sexual orientation in humans, as well as about genes that might underlie a broader spectrum of human behaviors.

Biological invasions occur when a plant or animal relocates to a new, favorable environment. Eliminating other competitors, predators or diseases, the species can rapidly expand its habitat, crowding out and otherwise harming native species. Many scientists believe the spread of exotic species is one of the most serious yet least known threats to biodiversity.

Fruit flies are being uses as research subjects in an effort to speed up genetic research into Alzheimer's as well as other diseases that affect a humans brain cells. The scientists choose to study the fruit fly because they have many genes with the same functions as human genes. Defects in the fly's gene that is the equivalent of the genes in humans that cause brain diseases cause the flies to lose brain function as they age, the same way the diseases do in humans.

That fruit fly hovering over your kitchen counter may be attracted to more than the bananas that are going brown; it may also want a sip of your carbonated water. Fruit flies detect and are attracted to the taste of carbon dioxide dissolved in water, such as water found on rotting fruits containing yeast, concludes a study appearing in the issue of the journal Nature. Scientists at the University of California, Berkeley, who conducted the study, suggest that the ability to taste carbon dioxide may help a fruit fly scout for food that is nutritious over that which is too ripe and potentially toxic. The research is partly funded by the National Institute on Deafness and Other Communication Disorders (NIDCD), one of the National Institutes of Health.

"Fruit flies contain similar versions of many human genes, which is why we study them for a variety of health issues, including taste," says James F. Battey, Jr., M.D., Ph.D., director of the NIDCD. "This research raises the question of whether people also may have the ability to taste carbon dioxide and perhaps other chemicals in food. If this were found to be true, our sense of taste could be even more complex than we realize." Currently, scientists recognize five tastes in humans: sweet, salty, bitter, sour, and umami, or savory. Before today’s findings, fruit flies were known to be able to taste sweet, bitter, and salty.

The researchers note that a fruit fly’s attraction for the taste of carbon dioxide is on a much smaller scale than for sugar, so it may be used more as a possible flavor enhancer as opposed to a full-fledged taste. This makes sense, they say, since carbon dioxide offers no nutrition to the fly.

In humans, taste occurs by way of taste cells, sensory cells that are clustered in the taste buds of the mouth, tongue, and throat, and that express certain proteins, called receptors. These receptors are activated by specific chemicals — called tastants—found in foods and drinks. When a receptor is activated by a tastant, an electrical signal is generated, which travels to the brain. Taste in the fruit fly, or Drosophila melanogaster, operates much the same way, except fruit flies have taste neurons instead of taste cells, and the taste neurons are found in structures called taste pegs and taste bristles instead of buds. Although taste pegs and bristles can be found all over a fruit fly’s body, most are concentrated on the labellum—the equivalent of a tongue—which is housed in the proboscis, a long tubular structure originating from the fly’s head.

To arrive at their findings, senior author Kristin Scott, Ph.D., and her research team made use of a powerful genetics technique that enables fruit fly researchers to tightly control which genes are expressed in a cell and which remain silent. The team first homed in on a class of taste neurons, called E409, found on taste pegs in the fruit fly’s labellum. These neurons had not been characterized before and were not already associated with known taste receptors for sweet and bitter. They then labeled the neurons with a fluorescent protein and found that their projections extended to separate parts of the taste area of the brain in comparison to the sweet and bitter neurons. Next, the researchers tested the E409 neurons’ response to an array of compounds and found that substances high in carbon dioxide, such as beer, yeast, and carbonated water, elicited heightened neuron activity as opposed to substances low in carbon dioxide. Finally, they found that fruit flies were attracted to solutions with high carbon dioxide concentrations, while those whose E409 neurons were shut off were not.

Because fruit flies are also able to smell carbon dioxide, the team also wanted to learn if the two senses influenced one another. Under normal conditions, when fruit flies smell carbon dioxide in the air, they are repelled by it. Scott and her team showed that fruit flies that had their E409 neurons shut off avoided high carbon dioxide concentrations in the environment; likewise, flies that were missing antennae, the structures they use to smell their surroundings, were attracted to solutions with high carbon dioxide concentrations. These results indicate that the senses of taste and smell operate independently. As a result, the team concluded that fruit flies use both senses of taste and smell separately to gauge their environment for a potential food source.

"Our model is that flies like high local concentrations of carbon dioxide," says Scott. "So if carbon dioxide is being produced by the yeast, flies taste it and they like it. But if there are increased global levels of carbon dioxide in the air—such as if a food source becomes spoiled and potentially toxic—then flies are repelled by it. So we think by having these two different carbon dioxide detectors, flies are able to compare global to local levels of carbon dioxide and then regulate their behavior accordingly."

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