Writing & Grammar - Academic Activities

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👨‍🏫 در وبینار رایگان روز دوشنبه ساعت 19 تا 20، متن ریدینگ NEO 114 بررسی میشه:
Honeybee Juvenile Hormone

The activities of honeybee hives are highly coordinated. Honeybees live in colonies made up of a single queen and up to 80,000 workers. The tasks of a worker usually change dramatically with age, a phenomenon known as age polyethism. A typical honeybee worker newly emerged as an adult, winged insect will live for approximately six weeks and during this time moves through an orderly progression of tasks: Young adults (4 to 12 days old) tend the queen and the pupae (pre-adult insects); middle-aged bees (13 to 20 days old) perform various tasks associated with nest maintenance and food storage; and the oldest bees (over 20 days of age) concentrate on foraging (searching for food) outside the nest. In general, young workers mostly stay inside the hive and tend to nursing and housekeeping, and older workers often leave the hive to forage. Keep in mind, however, that the actual changes in the duties performed by a worker usually involve only changes in the frequencies of particular types of behaviors with age, rather than the addition or loss of entire categories of behaviors. Also, the sequence is flexible, allowing duties to be reassigned if the hive's needs change.

Age polyethism in worker honeybees is regulated by juvenile hormone (JH); levels of JH increase with age and mediate changes in work habits. These levels vary with age because of changes in the rate of its synthesis by the corpora allata, a pair of glands near the brain. Not only are the naturally occurring levels of JH correlated with a worker's change in duties but also experimental manipulations of JH levels have resulted in the expected changes in behavior. Treating newly emerged worker bees with a chemical similar to JH speeds up behavioral maturation. On the other hand, removing the corpora allata delays but does not prevent the development of a worker into a forager. But that delay can be eliminated by juvenile-hormone treatments.

How does JH cause an adult worker's behavior to change so dramatically? At least part of the answer is that JH affects brain structure. The most striking change in behavior during the usual progression of duties occurs when a worker becomes a forager. Unlike younger hive bees, foragers take long-distance flights; learn rapidly and form long-term memories; use the sun as a compass for orientation; and communicate to other foragers the distance to and direction of a food source. As a honeybee matures, there is a 20 percent increase in the size of the insect brain structures known as mushroom bodies. The mushroom bodies are important in learning, memory, and the processing of sensory information. The increase in volume is due to increases in the number of branches on the neurons, which increase the number of synapses (points at which nerve impulses pass from one neuron to another), thereby boosting the brain's ability to process information. Thus, these changes in the mushroom bodies may prepare a worker to learn to navigate during foraging flights and to find its way back to the hive.

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976 viewsApr 26 at 08:10

👨‍🏫 در وبینار رایگان روز دوشنبه ساعت 19 تا 20، متن ریدینگ NEO 114 بررسی میشه:
Honeybee Juvenile Hormone

The activities of honeybee hives are highly coordinated. Honeybees live in colonies made up of a single queen and up to 80,000 workers. The tasks of a worker usually change dramatically with age, a phenomenon known as age polyethism. A typical honeybee worker newly emerged as an adult, winged insect will live for approximately six weeks and during this time moves through an orderly progression of tasks: Young adults (4 to 12 days old) tend the queen and the pupae (pre-adult insects); middle-aged bees (13 to 20 days old) perform various tasks associated with nest maintenance and food storage; and the oldest bees (over 20 days of age) concentrate on foraging (searching for food) outside the nest. In general, young workers mostly stay inside the hive and tend to nursing and housekeeping, and older workers often leave the hive to forage. Keep in mind, however, that the actual changes in the duties performed by a worker usually involve only changes in the frequencies of particular types of behaviors with age, rather than the addition or loss of entire categories of behaviors. Also, the sequence is flexible, allowing duties to be reassigned if the hive's needs change.

Age polyethism in worker honeybees is regulated by juvenile hormone (JH); levels of JH increase with age and mediate changes in work habits. These levels vary with age because of changes in the rate of its synthesis by the corpora allata, a pair of glands near the brain. Not only are the naturally occurring levels of JH correlated with a worker's change in duties but also experimental manipulations of JH levels have resulted in the expected changes in behavior. Treating newly emerged worker bees with a chemical similar to JH speeds up behavioral maturation. On the other hand, removing the corpora allata delays but does not prevent the development of a worker into a forager. But that delay can be eliminated by juvenile-hormone treatments.

How does JH cause an adult worker's behavior to change so dramatically? At least part of the answer is that JH affects brain structure. The most striking change in behavior during the usual progression of duties occurs when a worker becomes a forager. Unlike younger hive bees, foragers take long-distance flights; learn rapidly and form long-term memories; use the sun as a compass for orientation; and communicate to other foragers the distance to and direction of a food source. As a honeybee matures, there is a 20 percent increase in the size of the insect brain structures known as mushroom bodies. The mushroom bodies are important in learning, memory, and the processing of sensory information. The increase in volume is due to increases in the number of branches on the neurons, which increase the number of synapses (points at which nerve impulses pass from one neuron to another), thereby boosting the brain's ability to process information. Thus, these changes in the mushroom bodies may prepare a worker to learn to navigate during foraging flights and to find its way back to the hive.

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