Metamorphosis in Frogs the Adaptive Significance of Metamorphosis
There are animals that undergo a specific phase of transformation called metamorphosis. Animals like butterflies, frogs, newts and mosquitoes all experience metamorphosis before they reach the imago phase of their life. Metamorphosis is associated with the different stages in life before coming out in adult form. One of the significant associations of metamorphosis is the adaptive changes incur in the organism in the way the organism interacts with its environment. The environmental cues play an important role in the metamorphosis of some organisms. The environmental cues trigger or send a message to hormones that yield to metamorphosis. The bull frog is an animal that undergo metamorphosis and the environmental cues as well as the genetic control are responsible for its development. The genetic control is the turning on and transcription of genes that incur changes in the gene expression which causes the metamorphosis in all animals. The paper aims to evaluate the significant adaptive changes and the genetic control in the development and metamorphosis of bull frogs.
Genetic Control and Metamorphosis
All of the cells in the body are composed of genes, which is made up of a set of instructions for making proteins. The creation of a protein from its gene is called gene expression (Saltsman, 2010). The gene expression is capable of genetic control in development of all organisms. In the case of metamorphosis of most amphibians and insects, the initiation and completion of metamorphosis id under the obligatory hormonal control which distinguishes it from other hormone-dependent late developmental stages. The hormone serves to trigger a predetermined programme of developmental changes in order to prepare the embryo for an environment suitable for adult life. The hormone does not direct the cell to acquire different characters but allows already differentiated but immature cells to acquire adult structures and functions (Khanna Yadav, 2005).
The role of hormones in organisms is very important. In organisms undergoing metamorphosis, the hormones play a vital role in carrying out the biological process of change in the bodys structure and function, which is accompanied by cell growth and differentiation. Some species of insects, cnidarians, crustaceans, amphibians, tunicates, echinoderms and mollusks undergo metamorphosis. Metamorphosis is any developmental change in an animals structure that is accompanied of changes in the physiological, behavioral and biochemical aspects. The morphological changes in an organism in the internal and external facets of an organism takes place in a short span of time and is triggered by a combination of external and internal cues. The extent of morphological changes ranges differently among the species. Even though the changes in the metamorphosing organism are very slight, metamorphosis sometimes brings considerable changes in the habitat and lifestyle of the organism (Metamorphosis, 2010).
A metamorphosing organism may undergo two paths of development, which are the direct and indirect development. Direct development or often referred to as simple metamorphosis or incomplete metamorphosis is not associated with drastic changes in the physical aspects of the organism. The young often resembles its adult form. Crickets and grasshoppers undergo this type of metamorphosis. Indirect development or complete metamorphosis, on the other hand, is the transformation of organisms that is associated with drastic physical changes. The adult form no longer has the traces of its young form. The larva is completely different from the imago and they often occupy different habitat or niches (McDarby, 2010). Organisms undergoing complete metamorphosis are often characterized by different life stages from egg to larva to pupa and to adult form. Butterflies and frogs are some of the examples of organisms that undergo complete metamorphosis.
Animals that Undergo Metamorphosis
Insects
Some insects undergo metamorphosis before it becomes an adult. Metamorphosis in insects often proceeds in distinct stages that start with larval stage then optionally passing through pupa stage before becoming fully an adult or imago. The stages differ among the insects and the distinction of the stages depends on the nature of metamorphosis. There are two types of metamorphosis in insects which are hemimetabolism and holometabolism. In hemimetabolism, the development of the larva often proceeds in repeated stages of growth and ecdysis or molting. The juvenile form of the organism resembles its adult form and if the adult form has wings, the young lack wings. The main difference between the juvenile and adult form of an insect undergoing this type of metamorphosis is the body proportion and the number of segments. In holometabolism, on the other hand, the larva largely differs from the adult. Insects that undergo holometabolism often undergo the inactive state called pupa or chrysalis before emerging as adults. During the pupa stage, the insect will excrete juices that aim to destroy the larvas body and leave a few cells intact. These cells will grow as the adult form of the insect.
Metamorphosis has benefits to the organisms undergoing the process, especially to its adaptation in the environment. Metamorphosis is associated with changes in the way the organism interacts with its environment. In insects, the larva and the imago eat very different foods. The larva has different physical built compared to its adult form. It has unique structures and organs that do not occur in the adult form. A larvas diet can be considerably different from the adults. Thus, the adults and larvae do not have to compete for the same food, which is a limiting resource in the environment. There is a reduced competition in the food sources. The larvae are often adapted to a different environment and by living in two distinct environments the larvae are given shelter from the predator and reduce the competition for resources with the adult population (Metamorphosis General Features, 2010).
Amphibians
The typical development of amphibians starts with eggs that are often laid in the water. The offspring are adapted in the aquatic lifestyle. Frogs, toads and newts are hatched from eggs as larvae with external gills. The specific stages are dependent on the threshold values for the different tissues. Because most of the embryonic development occur independently, the tissues and organs is subjected to a lot of adaptations due to specific ecological circumstances. After the metamorphosis, these organs will die controlled by cell death called apoptosis.
In frogs, the external gills and gill sac were formed after they were hatched in eggs. The pace of metamorphosis is really fast and the front and hind legs are visible a few days later. The tadpoles grow in a vegetarian diet due to its environment which is aqueous. Quick and immense changes occur when the frog changes completely. The unused organs and tissues which adapted in the tadpoles environment are reabsorbed. New tissues and organs developed for the adaptation of the adult form of a frog.
The adaptive changes in the metamorphosis of tadpoles to frogs render significance to the organism. The young and the adult form of frogs live in two distinct environments and adapted to the mechanisms of their environments. The two also has completely different diet as the tadpoles are herbivore and the frogs become predators of insects. By living in the aquatic environment, the larvae are given shelter and reduce food competition with the adult population.
Environmental Cues for Metamorphosis
Insects
Not all species of insects undergo metamorphosis. Metamorphosis in insects is often associated with wing development. It was discovered that PTTH, a brain-produced hormone triggers the metamorphosis in insects by acting like a key fitting in a lock. PTTH is a neuropeptide that is similar to the pituitary hormones released in humans pituitary glands. The metamorphosis of insects is quite similar to the transition of humans on the onset of puberty. When the insect reach the threshold body weight, a signal was sent to the brain releasing the PTTH and received by a receptor molecule located in the main endocrine organ in the insect and initiating metamorphosis. The researchers found out that the receptor is an enzyme that serves as the switch in turning on other enzymes that yield to the different changes that occur during metamorphosis (Morrison, 2009).
Amphibians
The duration of metamorphosis is measured from the time of hatching until the transition from the aquatic to terrestrial habitat. The metamorphosis of amphibians is influenced by both biotic and abiotic factors. In most cases, metamorphosis is influenced by hypothalamic-pituitary axis. The larva of most amphibians like frogs, the rapid and accelerated development is a response to desiccation and other stress-related environmental factors. The response is involved with corticosteroidstimulationof thyroid stimulating hormone, which results inTH synthesis and accelerated restructuring of the tadpole towardmetamorphic climax. (Heyland Moroz, 2006, p.747).
In all organisms undergoing metamorphosis, environmental cues play an important part in the biological process. Many insects often enter the dormant or the inactive state of development during winter. The low temperature triggers metamorphosis in most insects. The length of light and darkness or the solstices trigger the metamorphosis of some organisms. These environmental factors send message to the brain and signal the onset of metamorphosis.
Indirect Development of Bull Frogs
The eggs are fertilized externally as they are laid in the water. The little larva which hatches in a few days has two pairs of long, branched, external gills projecting from the dorsal ends of the third and fourth visceral arches. It is really inactive and clinging to vegetation in the aquatic environment through the glandular adhesive organ under lower jaw. Once the reserve yolk has been used up, however, the larva swims more actively and the adhesive organ disappears. The bases of the external gills are gradually covered by the growth of opercular folds and the so-called internal gills growing from the lower ends of the visceral arches that take over the respiratory function. Horny teeth and jaw coverings appear around the mouth that comprised a typical tadpole that is capable of swimming and breathing in water and for rasping away the surface of the vegetation that is his food source (Lynn, 1961).
The metamorphic changes occur and the most obvious changes are seen in the physical and external changes. There is a rapid growth and development of hind legs. There is a loss in the horny teeth and a change in the structure in the head and mouth, including the protrusion of eyes and sudden appearance of fore limbs within the opercular cavity. The tail and other useless body tissue undergo resorption. The gills used for breathing and the spiral gut used for digesting are lost (Lynn, 1961).
The changes during metamorphosis are brought about by the secretion of thyroxine (T4) and triiodothyronine (T3) from the thyroid gland. The environmental cues send signal to the thyroid gland that excretes hormones responsible for the inception of the metamorphosis. Thyroid hormones activate the transcription of some genes while at the same thing repressed other genes. At the onset of metamorphosis, the levels of thyrothropin increase that is probably due to the developmental maturation of the pituitary gland. Due to this maturation, there is an increase in the amount of T3. The T3 binds with the receptor mRNA. The other T-induced proteins are also needed for the transcription of more T3 message.
Both the larval and adult developmental programare under the control of various endogenous factors, 2 essentialones being the levels of thyroid hormone receptors (TRs) andthe concentration of intracellular free thyroid hormone (TH).Triiodo-L-tyrosine (T3) is the active hormone in amphibian metamorphosisthat binds with very high affinity to TRs. The action of THin metamorphosis can be best described by the so-called dual-functionmodel. Based on this model, TR without its ligand functions as a repressor of TH-regulatedgenes, while the conformational changes that occur upon ligandbinding change TR into an activator of TH-regulated genes. Sucha mechanism fulfills the very important function of repressingthe metamorphic genes by TR until the larva is ready to undergothe metamorphic transition in both a developmental and ecologicalsense (Heyland Moroz, 2006, p.746).
Metamorphosis is an important biological process in some organisms in order to achieve their adult form. Bullfrogs are examples of an organism that undergoes metamorphosis. The genetic control of the gene expression of an organism plays an important role in the onset of metamorphosis. Metamorphosis causes significant adaptive changes in the organism causing the m to adapt on the different facets of the environment. The metamorphosis of an organism is triggered by environmental cues that send signals to the biological aspects of the body that is responsible for the process of metamorphosis. Metamorphosis is an important process in some organisms and their adaptation in the inherent environment.
Genetic Control and Metamorphosis
All of the cells in the body are composed of genes, which is made up of a set of instructions for making proteins. The creation of a protein from its gene is called gene expression (Saltsman, 2010). The gene expression is capable of genetic control in development of all organisms. In the case of metamorphosis of most amphibians and insects, the initiation and completion of metamorphosis id under the obligatory hormonal control which distinguishes it from other hormone-dependent late developmental stages. The hormone serves to trigger a predetermined programme of developmental changes in order to prepare the embryo for an environment suitable for adult life. The hormone does not direct the cell to acquire different characters but allows already differentiated but immature cells to acquire adult structures and functions (Khanna Yadav, 2005).
The role of hormones in organisms is very important. In organisms undergoing metamorphosis, the hormones play a vital role in carrying out the biological process of change in the bodys structure and function, which is accompanied by cell growth and differentiation. Some species of insects, cnidarians, crustaceans, amphibians, tunicates, echinoderms and mollusks undergo metamorphosis. Metamorphosis is any developmental change in an animals structure that is accompanied of changes in the physiological, behavioral and biochemical aspects. The morphological changes in an organism in the internal and external facets of an organism takes place in a short span of time and is triggered by a combination of external and internal cues. The extent of morphological changes ranges differently among the species. Even though the changes in the metamorphosing organism are very slight, metamorphosis sometimes brings considerable changes in the habitat and lifestyle of the organism (Metamorphosis, 2010).
A metamorphosing organism may undergo two paths of development, which are the direct and indirect development. Direct development or often referred to as simple metamorphosis or incomplete metamorphosis is not associated with drastic changes in the physical aspects of the organism. The young often resembles its adult form. Crickets and grasshoppers undergo this type of metamorphosis. Indirect development or complete metamorphosis, on the other hand, is the transformation of organisms that is associated with drastic physical changes. The adult form no longer has the traces of its young form. The larva is completely different from the imago and they often occupy different habitat or niches (McDarby, 2010). Organisms undergoing complete metamorphosis are often characterized by different life stages from egg to larva to pupa and to adult form. Butterflies and frogs are some of the examples of organisms that undergo complete metamorphosis.
Animals that Undergo Metamorphosis
Insects
Some insects undergo metamorphosis before it becomes an adult. Metamorphosis in insects often proceeds in distinct stages that start with larval stage then optionally passing through pupa stage before becoming fully an adult or imago. The stages differ among the insects and the distinction of the stages depends on the nature of metamorphosis. There are two types of metamorphosis in insects which are hemimetabolism and holometabolism. In hemimetabolism, the development of the larva often proceeds in repeated stages of growth and ecdysis or molting. The juvenile form of the organism resembles its adult form and if the adult form has wings, the young lack wings. The main difference between the juvenile and adult form of an insect undergoing this type of metamorphosis is the body proportion and the number of segments. In holometabolism, on the other hand, the larva largely differs from the adult. Insects that undergo holometabolism often undergo the inactive state called pupa or chrysalis before emerging as adults. During the pupa stage, the insect will excrete juices that aim to destroy the larvas body and leave a few cells intact. These cells will grow as the adult form of the insect.
Metamorphosis has benefits to the organisms undergoing the process, especially to its adaptation in the environment. Metamorphosis is associated with changes in the way the organism interacts with its environment. In insects, the larva and the imago eat very different foods. The larva has different physical built compared to its adult form. It has unique structures and organs that do not occur in the adult form. A larvas diet can be considerably different from the adults. Thus, the adults and larvae do not have to compete for the same food, which is a limiting resource in the environment. There is a reduced competition in the food sources. The larvae are often adapted to a different environment and by living in two distinct environments the larvae are given shelter from the predator and reduce the competition for resources with the adult population (Metamorphosis General Features, 2010).
Amphibians
The typical development of amphibians starts with eggs that are often laid in the water. The offspring are adapted in the aquatic lifestyle. Frogs, toads and newts are hatched from eggs as larvae with external gills. The specific stages are dependent on the threshold values for the different tissues. Because most of the embryonic development occur independently, the tissues and organs is subjected to a lot of adaptations due to specific ecological circumstances. After the metamorphosis, these organs will die controlled by cell death called apoptosis.
In frogs, the external gills and gill sac were formed after they were hatched in eggs. The pace of metamorphosis is really fast and the front and hind legs are visible a few days later. The tadpoles grow in a vegetarian diet due to its environment which is aqueous. Quick and immense changes occur when the frog changes completely. The unused organs and tissues which adapted in the tadpoles environment are reabsorbed. New tissues and organs developed for the adaptation of the adult form of a frog.
The adaptive changes in the metamorphosis of tadpoles to frogs render significance to the organism. The young and the adult form of frogs live in two distinct environments and adapted to the mechanisms of their environments. The two also has completely different diet as the tadpoles are herbivore and the frogs become predators of insects. By living in the aquatic environment, the larvae are given shelter and reduce food competition with the adult population.
Environmental Cues for Metamorphosis
Insects
Not all species of insects undergo metamorphosis. Metamorphosis in insects is often associated with wing development. It was discovered that PTTH, a brain-produced hormone triggers the metamorphosis in insects by acting like a key fitting in a lock. PTTH is a neuropeptide that is similar to the pituitary hormones released in humans pituitary glands. The metamorphosis of insects is quite similar to the transition of humans on the onset of puberty. When the insect reach the threshold body weight, a signal was sent to the brain releasing the PTTH and received by a receptor molecule located in the main endocrine organ in the insect and initiating metamorphosis. The researchers found out that the receptor is an enzyme that serves as the switch in turning on other enzymes that yield to the different changes that occur during metamorphosis (Morrison, 2009).
Amphibians
The duration of metamorphosis is measured from the time of hatching until the transition from the aquatic to terrestrial habitat. The metamorphosis of amphibians is influenced by both biotic and abiotic factors. In most cases, metamorphosis is influenced by hypothalamic-pituitary axis. The larva of most amphibians like frogs, the rapid and accelerated development is a response to desiccation and other stress-related environmental factors. The response is involved with corticosteroidstimulationof thyroid stimulating hormone, which results inTH synthesis and accelerated restructuring of the tadpole towardmetamorphic climax. (Heyland Moroz, 2006, p.747).
In all organisms undergoing metamorphosis, environmental cues play an important part in the biological process. Many insects often enter the dormant or the inactive state of development during winter. The low temperature triggers metamorphosis in most insects. The length of light and darkness or the solstices trigger the metamorphosis of some organisms. These environmental factors send message to the brain and signal the onset of metamorphosis.
Indirect Development of Bull Frogs
The eggs are fertilized externally as they are laid in the water. The little larva which hatches in a few days has two pairs of long, branched, external gills projecting from the dorsal ends of the third and fourth visceral arches. It is really inactive and clinging to vegetation in the aquatic environment through the glandular adhesive organ under lower jaw. Once the reserve yolk has been used up, however, the larva swims more actively and the adhesive organ disappears. The bases of the external gills are gradually covered by the growth of opercular folds and the so-called internal gills growing from the lower ends of the visceral arches that take over the respiratory function. Horny teeth and jaw coverings appear around the mouth that comprised a typical tadpole that is capable of swimming and breathing in water and for rasping away the surface of the vegetation that is his food source (Lynn, 1961).
The metamorphic changes occur and the most obvious changes are seen in the physical and external changes. There is a rapid growth and development of hind legs. There is a loss in the horny teeth and a change in the structure in the head and mouth, including the protrusion of eyes and sudden appearance of fore limbs within the opercular cavity. The tail and other useless body tissue undergo resorption. The gills used for breathing and the spiral gut used for digesting are lost (Lynn, 1961).
The changes during metamorphosis are brought about by the secretion of thyroxine (T4) and triiodothyronine (T3) from the thyroid gland. The environmental cues send signal to the thyroid gland that excretes hormones responsible for the inception of the metamorphosis. Thyroid hormones activate the transcription of some genes while at the same thing repressed other genes. At the onset of metamorphosis, the levels of thyrothropin increase that is probably due to the developmental maturation of the pituitary gland. Due to this maturation, there is an increase in the amount of T3. The T3 binds with the receptor mRNA. The other T-induced proteins are also needed for the transcription of more T3 message.
Both the larval and adult developmental programare under the control of various endogenous factors, 2 essentialones being the levels of thyroid hormone receptors (TRs) andthe concentration of intracellular free thyroid hormone (TH).Triiodo-L-tyrosine (T3) is the active hormone in amphibian metamorphosisthat binds with very high affinity to TRs. The action of THin metamorphosis can be best described by the so-called dual-functionmodel. Based on this model, TR without its ligand functions as a repressor of TH-regulatedgenes, while the conformational changes that occur upon ligandbinding change TR into an activator of TH-regulated genes. Sucha mechanism fulfills the very important function of repressingthe metamorphic genes by TR until the larva is ready to undergothe metamorphic transition in both a developmental and ecologicalsense (Heyland Moroz, 2006, p.746).
Metamorphosis is an important biological process in some organisms in order to achieve their adult form. Bullfrogs are examples of an organism that undergoes metamorphosis. The genetic control of the gene expression of an organism plays an important role in the onset of metamorphosis. Metamorphosis causes significant adaptive changes in the organism causing the m to adapt on the different facets of the environment. The metamorphosis of an organism is triggered by environmental cues that send signals to the biological aspects of the body that is responsible for the process of metamorphosis. Metamorphosis is an important process in some organisms and their adaptation in the inherent environment.
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