Schistocephalus Solidus Essay
I. Introduction
The Schistocephalus solidus parasite was discovered and isolated from the cold areas of the Eastern and Western regions of North America (Poulin, 2000). This parasite is also common in the areas of Canada, Europe, and Eurasia. Schistocephalus solidus is a cestode that has been established to infect over 400 different types of bird species (Barber and Scharsack, 2010). The different types of the bird's species form the definitive hosts of the parasite. Schistocephalus solidus is also known to invade other species such as the mammals, fish, and Gasterosteus aceulatus (Poulin, 2010). This paper will focus on Schistocephalus solidus adaptations needed to ensure its survival such as mechanisms for manipulation and host preferences.
II. The physical description of the parasite
Schistocephalus solidus parasite exists in …show more content…
various anatomical forms owing to its complex life cycle. The body of the parasite changes depending on the host and the development stage. The parasite is produced from an egg; the form in which it exists after emerging from the egg is a coracidia (Schultz, Topper & Heins, 2006). The larvae form of a coricidia is ciliated thus, enabling it to quickly swim through the waters. Upon infecting the first intermediate host, the parasite undergoes morphological transitions (Heins, et al,2010). The short ciliated coccidia gradually changes to an elongated procercoid form. In addition, it loses its transparency and becomes more opaque.
In addition, there is the development of posterior hooks accompanied by the development of the posterior bulbs; which occurs on the body of the procercoid. When ingested by the second intermediate host, the procercoid shades off the posterior bulb and develops into a 60-80 proglottid chain referred to as a plerocercoid. The proglottid chain is the form in which the parasite is ingested by the final definitive host.
III. Reproduction Schistocephalus solidus parasite is a hermaphrodite that exhibits both asexual and sexual forms of reproduction (Heins, & Baker, 2008). The parasite carries out both self-fertilization and cross-fertilization. The preference of the mode of fertilization depends on some factors of the parasite. Recent research indicates that self-fertilization usually occurs in the cases where there is a limited number of sexual partners (Poulin, 2010). On the other hand, cross-fertilization occurs where there is a varied number of sexual partners. Large parasites will always have a tendency to mate with other large parasites. The mature parasites are known to produce over 20,000 eggs in their entire lifetime. Studies indicate that the parasites prefer the cross-fertilization mode of reproduction despite the ability to carry out self-fertilization. This is always done to reduce the cases of inbreeding depression, which results in low chances of survival of the produced parasites. Cross breeding leads to a better and more adapted species that have proper survival in the second intermediate host.
IV. Lifecycle
The Schistocephalus solidus parasite has been formed to have a complex life cycle that comprises of three hosts which are a significant adaptation that ensures its survival. The parasite carries out its reproduction stage in the intestines of the bird. The gastrointestinal tract of the birds’ forms an excellent habitat for the adult worms to carry out the proper reproduction period. Consequently, the eggs produced by the parasite are passed through the droplets of the birds into the water; where they hatch into larvae (Barber, & Scharsack, 2010). Within this specific environment, the coracidia, may be viable for as long as 22 days. Schistocephalus solidus have adapted the ability to survive on the water bodies before they are consumed by the first intermediate host, the copepod. In this host, the second larval stage of the parasite develops and grows into the body tissues (Schultz, Topper & Heins, 2006). After a period of about two weeks, the copepod is ingested by a fish, which forms the second intermediate host. The fish, a three-spined stickleback for example, creates a new habitat where the plerocercoid larvae grows and expand in size. The birds target the fish, and upon ingestion, the larvae grow into a mature parasite which reproduces eggs within the intestines of the birds within two days. The reproduction period of these parasites occurs within a period of two weeks after which the parasite dies. Each developmental transition is smooth, and each host serves as a proper habitat for the parasite (Heins et al.,2010). In a nutshell, the habitat of the parasite depends on the development stage and the inhabiting host.
V. Lifespan The whole lifespan of the Schistocephalus solidus parasite depends on the amount of time each stage of the parasite occurs. The eggs typically take a period of 22-29 days before they hatch (Thomas, Poulin, & Brodeur, 2010). It takes approximately 24-48 hours before the produced coracidium finds a suitable first intermediate host. The coracidium develops for about 3-4 weeks in the first intermediate host before infecting the second host. The coracidium develops into a plerocercoid that takes about 17 days to develop significantly (Poulin, 2010). The definitive hosts then consume the plerocercoid which develops into the adult parasite. The adult parasite takes about 3-4 days to begin the production and release of the eggs (Thomas, Poulin, & Brodeur, 2010). Several studies indicate that the lifespan of the adult parasites depends on the type of the host. For instance, the parasite survives approximately six days in rats and about 14 days in ducks.
VI. Manipulation of the parasite in the host According to recent research, Schistocephalus solidus is adapted to survive due to its ability to change in different hosts (Barber, et, al, 2008). A major adaptation of the parasite is its ability to manipulate the character of the host. Change in the behavior of the host leads to better parasite survival within the host. For instance, Schistocephalus solidus consumes vast amounts oxygen gas when in the specific fish species targeted, forcing the fish to reach out to the water surface in search of enormous amounts of oxygen (Barber, et, al, 2008). In doing so, the fish becomes vulnerable to the birds which increases predation. The parasite is thus able to reach its definitive host where it carries out its reproduction. There are various ways Schistocephalus solidus manipulates the behavior of the hosts, to whom shall be highlighted and the pros and cons of these manipulations also considered (Barber, et, al, 2008). For instance, the feeding changes and the feeding motivation of the infected fish and how that is important in the ensuring the survival of Schistocephalus solidus.
VII. Behavior The infection intensity of the parasite in a particular host is governed by the number of parasites within a specific host. host. Recent research indicates that no more than four parasites are found within a single host. This is mainly an adaptation to ensure optimal growth of the parasite that ensures optimal survival (Overli, et al., 2001). However, other studies indicate that the prevalence of Schistocephalus solidus within different hosts can highly vary. There have been reports showing about 75-90% prevalence in some individuals to as minimum as 1% in other persons (Barber, et, al, 2008).
VIII. Feeding habits Schistocephalus solidus resides within the body of the host therefore, entirely depending on the host for nutrition (Overli, et al., 2001). Thus, parasite is adapted to carry out anaerobic respiration since it majorly exists in the gut of the host. The parasite increases the energy requirements of the hosts thus, increasing the amounts of food consumed by the various hosts. The parasite is mainly known to consume glycogen from the intermediate host’s. The deprivation of the host's glycogen deprives these hosts of sufficient oxygen.
According to a recent study, the energy requirement of an infected stickleback fish is quite enormous as compared to that of uninfected fish (Thomas, Poulin, & Brodeur, 2010). Now, the infected fish requires massive feeding to meet its optimal needs. Increased feeding of the host consequently enhances a number of nutrients to the parasite. The increased amount of energy to the parasite contributes largely to its quick and drastic growth before it is transferred to the next host (Franz, & Kurtz, 2002).
The increased nutrients levels of the, first intermediate host, the copepod, leads to the enormous growth of the coracidium larvae. The increased size of the parasite larvae is required to ensure proper transfer to the next host. The parasite also ensures that the copepod host is not exposed to the predators before the appropriate development of the host is reached (Poulin, 2010). This provides optimum maturation of the parasite since the transfer of immature larvae stage leads to the destruction of the lifecycle. In the case where the coracidium has completely matured, the parasite manipulates the copepod to be more vulnerable to the predator by decreasing its activity and mobility. As a result, the copepod is easily ingested by the fish thus ensuring the continuity of the life cycle of the parasite.
IX. Movement from one host to another Schistocephalus solidus, as earlier indicated has a complex life cycle that involves three distinct hosts. It is, therefore, paramount that the parasites have a well-defined coordinated mechanism that facilitates its movement from one host to another at the most appropriate stage (Seppälä, Karvonen, & Valtonen, 2005). Schistocephalus solidus have adapted the ability to manipulate the behavior and the character of the host, to facilitate its movement. The manipulation is in a such a coordinated manner such that, there is no transmission of the parasite prematurely. For instance, the parasite manipulates the physical characteristics of the fish in addition to its behavior thus making it more vulnerable to attack by the avian species (Parker, et.al, 2009). This ensures continuity of the life cycle in a coordinated manner.
X. Manipulation of the host's behavior To complete the life cycle, Schistocephalus solidus is highly adapted to influence the behavior of the host (Seppälä, Karvonen, & Valtonen, 2005). The parasite mostly contributes in the physiological and phenotypic characters of the host, to increase the parasites’ chances of growth and the predisposition of the host to the predator (Poulin, 2000). This is a significant adaptation that has significantly contributed to the proper survival of the Schistocephalus solidus and its effective transmission from one host to another.
XI. Manipulation of Phenotypic Characteristics Schistocephalus solidus is also known to manipulate the phenotypic characteristics of the stickleback fish.
Studies indicate that the Schistocephalus solidus in a heavily infested infection has the ability to gain the same weight as the host. This limits the movement of the fish making it very vulnerable to predators (Parker, et.al, 2009). The enormous size of the parasites also leads to the change in the size of the host. The change in the size of the host makes it quite distinct from the other uninfected fish in a shoal (Barber, Walker, & Svensson, 2004). Another adverse effect by the infestation of the parasite is the change in color of the infected fish (Thomas, Poulin, & Brodeur, 2010). The infected fish acquire a new white body color with black eyes. These phenotypic changes make the infected fish more distinct from uninfected fish thus becoming more exposed to predators than the uninfected fish (Heins, Baker, & Martin, 2002). An experiment performed indicates that these changes in phenotypic characteristics make the infected fish more vulnerable to attack by a bird predator, the final host of Schistocephalus
solidus.
The Schistocephalus solidus parasite was discovered and isolated from the cold areas of the Eastern and Western regions of North America (Poulin, 2000). This parasite is also common in the areas of Canada, Europe, and Eurasia. Schistocephalus solidus is a cestode that has been established to infect over 400 different types of bird species (Barber and Scharsack, 2010). The different types of the bird's species form the definitive hosts of the parasite. Schistocephalus solidus is also known to invade other species such as the mammals, fish, and Gasterosteus aceulatus (Poulin, 2010). This paper will focus on Schistocephalus solidus adaptations needed to ensure its survival such as mechanisms for manipulation and host preferences.
II. The physical description of the parasite
Schistocephalus solidus parasite exists in …show more content…
various anatomical forms owing to its complex life cycle. The body of the parasite changes depending on the host and the development stage. The parasite is produced from an egg; the form in which it exists after emerging from the egg is a coracidia (Schultz, Topper & Heins, 2006). The larvae form of a coricidia is ciliated thus, enabling it to quickly swim through the waters. Upon infecting the first intermediate host, the parasite undergoes morphological transitions (Heins, et al,2010). The short ciliated coccidia gradually changes to an elongated procercoid form. In addition, it loses its transparency and becomes more opaque.
In addition, there is the development of posterior hooks accompanied by the development of the posterior bulbs; which occurs on the body of the procercoid. When ingested by the second intermediate host, the procercoid shades off the posterior bulb and develops into a 60-80 proglottid chain referred to as a plerocercoid. The proglottid chain is the form in which the parasite is ingested by the final definitive host.
III. Reproduction Schistocephalus solidus parasite is a hermaphrodite that exhibits both asexual and sexual forms of reproduction (Heins, & Baker, 2008). The parasite carries out both self-fertilization and cross-fertilization. The preference of the mode of fertilization depends on some factors of the parasite. Recent research indicates that self-fertilization usually occurs in the cases where there is a limited number of sexual partners (Poulin, 2010). On the other hand, cross-fertilization occurs where there is a varied number of sexual partners. Large parasites will always have a tendency to mate with other large parasites. The mature parasites are known to produce over 20,000 eggs in their entire lifetime. Studies indicate that the parasites prefer the cross-fertilization mode of reproduction despite the ability to carry out self-fertilization. This is always done to reduce the cases of inbreeding depression, which results in low chances of survival of the produced parasites. Cross breeding leads to a better and more adapted species that have proper survival in the second intermediate host.
IV. Lifecycle
The Schistocephalus solidus parasite has been formed to have a complex life cycle that comprises of three hosts which are a significant adaptation that ensures its survival. The parasite carries out its reproduction stage in the intestines of the bird. The gastrointestinal tract of the birds’ forms an excellent habitat for the adult worms to carry out the proper reproduction period. Consequently, the eggs produced by the parasite are passed through the droplets of the birds into the water; where they hatch into larvae (Barber, & Scharsack, 2010). Within this specific environment, the coracidia, may be viable for as long as 22 days. Schistocephalus solidus have adapted the ability to survive on the water bodies before they are consumed by the first intermediate host, the copepod. In this host, the second larval stage of the parasite develops and grows into the body tissues (Schultz, Topper & Heins, 2006). After a period of about two weeks, the copepod is ingested by a fish, which forms the second intermediate host. The fish, a three-spined stickleback for example, creates a new habitat where the plerocercoid larvae grows and expand in size. The birds target the fish, and upon ingestion, the larvae grow into a mature parasite which reproduces eggs within the intestines of the birds within two days. The reproduction period of these parasites occurs within a period of two weeks after which the parasite dies. Each developmental transition is smooth, and each host serves as a proper habitat for the parasite (Heins et al.,2010). In a nutshell, the habitat of the parasite depends on the development stage and the inhabiting host.
V. Lifespan The whole lifespan of the Schistocephalus solidus parasite depends on the amount of time each stage of the parasite occurs. The eggs typically take a period of 22-29 days before they hatch (Thomas, Poulin, & Brodeur, 2010). It takes approximately 24-48 hours before the produced coracidium finds a suitable first intermediate host. The coracidium develops for about 3-4 weeks in the first intermediate host before infecting the second host. The coracidium develops into a plerocercoid that takes about 17 days to develop significantly (Poulin, 2010). The definitive hosts then consume the plerocercoid which develops into the adult parasite. The adult parasite takes about 3-4 days to begin the production and release of the eggs (Thomas, Poulin, & Brodeur, 2010). Several studies indicate that the lifespan of the adult parasites depends on the type of the host. For instance, the parasite survives approximately six days in rats and about 14 days in ducks.
VI. Manipulation of the parasite in the host According to recent research, Schistocephalus solidus is adapted to survive due to its ability to change in different hosts (Barber, et, al, 2008). A major adaptation of the parasite is its ability to manipulate the character of the host. Change in the behavior of the host leads to better parasite survival within the host. For instance, Schistocephalus solidus consumes vast amounts oxygen gas when in the specific fish species targeted, forcing the fish to reach out to the water surface in search of enormous amounts of oxygen (Barber, et, al, 2008). In doing so, the fish becomes vulnerable to the birds which increases predation. The parasite is thus able to reach its definitive host where it carries out its reproduction. There are various ways Schistocephalus solidus manipulates the behavior of the hosts, to whom shall be highlighted and the pros and cons of these manipulations also considered (Barber, et, al, 2008). For instance, the feeding changes and the feeding motivation of the infected fish and how that is important in the ensuring the survival of Schistocephalus solidus.
VII. Behavior The infection intensity of the parasite in a particular host is governed by the number of parasites within a specific host. host. Recent research indicates that no more than four parasites are found within a single host. This is mainly an adaptation to ensure optimal growth of the parasite that ensures optimal survival (Overli, et al., 2001). However, other studies indicate that the prevalence of Schistocephalus solidus within different hosts can highly vary. There have been reports showing about 75-90% prevalence in some individuals to as minimum as 1% in other persons (Barber, et, al, 2008).
VIII. Feeding habits Schistocephalus solidus resides within the body of the host therefore, entirely depending on the host for nutrition (Overli, et al., 2001). Thus, parasite is adapted to carry out anaerobic respiration since it majorly exists in the gut of the host. The parasite increases the energy requirements of the hosts thus, increasing the amounts of food consumed by the various hosts. The parasite is mainly known to consume glycogen from the intermediate host’s. The deprivation of the host's glycogen deprives these hosts of sufficient oxygen.
According to a recent study, the energy requirement of an infected stickleback fish is quite enormous as compared to that of uninfected fish (Thomas, Poulin, & Brodeur, 2010). Now, the infected fish requires massive feeding to meet its optimal needs. Increased feeding of the host consequently enhances a number of nutrients to the parasite. The increased amount of energy to the parasite contributes largely to its quick and drastic growth before it is transferred to the next host (Franz, & Kurtz, 2002).
The increased nutrients levels of the, first intermediate host, the copepod, leads to the enormous growth of the coracidium larvae. The increased size of the parasite larvae is required to ensure proper transfer to the next host. The parasite also ensures that the copepod host is not exposed to the predators before the appropriate development of the host is reached (Poulin, 2010). This provides optimum maturation of the parasite since the transfer of immature larvae stage leads to the destruction of the lifecycle. In the case where the coracidium has completely matured, the parasite manipulates the copepod to be more vulnerable to the predator by decreasing its activity and mobility. As a result, the copepod is easily ingested by the fish thus ensuring the continuity of the life cycle of the parasite.
IX. Movement from one host to another Schistocephalus solidus, as earlier indicated has a complex life cycle that involves three distinct hosts. It is, therefore, paramount that the parasites have a well-defined coordinated mechanism that facilitates its movement from one host to another at the most appropriate stage (Seppälä, Karvonen, & Valtonen, 2005). Schistocephalus solidus have adapted the ability to manipulate the behavior and the character of the host, to facilitate its movement. The manipulation is in a such a coordinated manner such that, there is no transmission of the parasite prematurely. For instance, the parasite manipulates the physical characteristics of the fish in addition to its behavior thus making it more vulnerable to attack by the avian species (Parker, et.al, 2009). This ensures continuity of the life cycle in a coordinated manner.
X. Manipulation of the host's behavior To complete the life cycle, Schistocephalus solidus is highly adapted to influence the behavior of the host (Seppälä, Karvonen, & Valtonen, 2005). The parasite mostly contributes in the physiological and phenotypic characters of the host, to increase the parasites’ chances of growth and the predisposition of the host to the predator (Poulin, 2000). This is a significant adaptation that has significantly contributed to the proper survival of the Schistocephalus solidus and its effective transmission from one host to another.
XI. Manipulation of Phenotypic Characteristics Schistocephalus solidus is also known to manipulate the phenotypic characteristics of the stickleback fish.
Studies indicate that the Schistocephalus solidus in a heavily infested infection has the ability to gain the same weight as the host. This limits the movement of the fish making it very vulnerable to predators (Parker, et.al, 2009). The enormous size of the parasites also leads to the change in the size of the host. The change in the size of the host makes it quite distinct from the other uninfected fish in a shoal (Barber, Walker, & Svensson, 2004). Another adverse effect by the infestation of the parasite is the change in color of the infected fish (Thomas, Poulin, & Brodeur, 2010). The infected fish acquire a new white body color with black eyes. These phenotypic changes make the infected fish more distinct from uninfected fish thus becoming more exposed to predators than the uninfected fish (Heins, Baker, & Martin, 2002). An experiment performed indicates that these changes in phenotypic characteristics make the infected fish more vulnerable to attack by a bird predator, the final host of Schistocephalus
solidus.