User:Lexie523/Chemical defense

Terrestrial Arthropods
Many insects are distasteful to predators and excrete irritants or secrete poisonous compounds that cause illness or death when ingested. Secondary metabolites obtained from plant food may also be sequestered by insects and used in the production of their own toxins. One of the more well-known examples of this is the monarch butterfly, which sequesters poison obtained from the milkweed plant. Among the most successful insect orders employing this strategy are beetles (Coleoptera), grasshoppers (Orthoptera), and moths and butterflies (Lepidoptera). Insects also biosynthesize unique toxins, and while sequestration of toxins from food sources is claimed to be the energetically favorable strategy, this has been contested. Passion-vine associated butterflies in the tribe Heliconiini (sub-family Heliconiinae) either sequester or synthesize de novo defensive chemicals, but moths in the genus Zygaena (family Zygaenidae) have evolved the ability to either synthesize or sequester their defensive chemicals through convergence. Some coleopterans sequester secondary metabolites to be used as defensive chemicals but most biosynthesize their own de novo. Anatomical structures have developed to store these substances, and some are circulated in the hemolyph and released associated with a behavior called reflex bleeding.

Chemical alarms and detection are seen as extremely important defensive mechanisms because identifying predators and responding swiftly and appropriately is advantageous and leads to higher fitness. These defensive responses can include (but are not limited to): avoidance and escape responses, safeguarding offspring, and applying “direct defenses” (i.e. toxins or defensive chemicals similar to the strategy of the monarch butterfly discussed above). There are many defensive strategies that are incited via chemical communication and detection that result in a change in behavior. These behavioral changes can lead to avoidance or aggression. For example, the fruit fly (Rhagoletis basiola) can chemically detect a nearby parasitoid (an organism that acts as both a parasite and a predator) and halt their egg-laying. Delaying oviposition can reduce the risk of predation and falls under the category of protecting offspring. The spider mite (Tetranychus urticae) can respond to predator volatiles in the environment and choose to feed in areas without predator cues. Similarly, spider mites are also able to sense damaged body parts of individuals of the same species, or conspecifics, and present the same avoidance behavior as with predator cues. Additionally, spider mites exhibit a similar behavior with egg-laying and will elect to move to areas absent of predator cues before oviposition. Spider mites will not avoid areas with other, non-predator volatiles, meaning these organisms are able to chemically distinguish threats from non-threats. Parasitic wasps (Aphidius uzbekistanicus) also sense volatiles of their hyperparasitoid (a parasite who's host is another parasite) and fly to new areas devoid of the chemical cues, displaying similar avoidance behaviors as the spider mite.

Alternately, chemical detection of predators or threats can also instigate aggressive behaviors in some terrestrial arthropods. Polybia paulista, a vespid wasp, is a social species that forage and defend according to social structures. These wasps have evolved to detect pheromones from the venom of members of the same species. Identifying volatiles from the venom of conspecifics allows the vespid wasps to discern when a conspecific is threatened. When detected, these pheromones induce an attacking behavior within other members of the same species. Similarly, honeybees (Apis mellifera scutellata) release a warning pheromone when threatened. These pheromones intensify their defenses by increasing the duration of their stinging behavior.

Aphids, small insects that can be found feeding on the sap of plants, exhibit many strategies in terms of chemical defense. Aphids have structures called cornicles along the posterior side of their abdomen which are used to deliver secretions containing both volatile and nonvolatile compounds. Volatile compounds serve primarily as alarm pheromones, which are chemicals released from one individual that elicit a response from another. Nonvolatile compounds, such as wax, are used as noxious adhesives that the aphid will smear on their enemies. These smears are used to fatally bind predators' mouthparts, attenaes, legs, etc., meaning these compounds are used more for physical defense rather than chemical. Pea aphids (Acyrthosiphon pisum) produce a warning chemical called (E)-β-farnesene which is excreted as a volatile compound in the presence of general predators and threats. In many cases, the aphid will respond by leaving the feeding site in search for an area without alarm pheromones. Additionally, pea aphids are highly attune to which predators in their area as they can chemically identify what is posing as a threat and adjust their response accordingly. For example, pea aphids can identify Adalia bipunctata, the ladybird beetle, by their chemical predator cues. After sensing this predator, pea aphids are known to produce more offspring with wings. The winged offspring are able to better avoid predation; however, winged individuals are less fertile. This trade-off between wings and fertility shows the success of this particular defensive strategy. In “relaxed” conditions, or conditions in which predator cues are absent, more wing-less offspring are produced.

The chemical defense systems of aphids are highly specific. (E)-β-farnesene, the alarm pheromone discussed above, is used by many species of aphids. When released, (E)-β-farnesene will only extend 2-3 cm in diameter. This protects farther conspecifics from the alarm chemical so they do not experience any needless pause in feeding or respond unnecessarily. Furthermore, these chemical alarms are detected by structures on the antennae of aphids that utilize specialized binding proteins. Warning chemicals must accumulate to a certain minimum within the binding proteins before a response is produced. These factors are used to highlight the specificity of the chemical defense systems of aphids. Moreover, the chemical warnings used are also highly specific and the method in which the alarm pheromone is distributed can elicit different responses. For example, Ceratovacuna lanigera, the sugarcane wooly aphid, has two methods of distribution of alarm pheromones. When threatened, the alarm pheromones can either be released as a droplet or as a smear. When the alarm is released as a droplet from the aphid's cornicle, the local conspecifics will respond individually and will either avoid or escape the area. However, when alarm pheromones are spread on a predator, other members of the same species will launch a joint attack.

Other organisms have been able to take advantage of the elaborate chemical defenses of aphids to increase their own fitness. Lysiphlebus fabarum, a parasitoid of aphids, are able to mimic the secretions of specific aphids when infiltrating their colonies. This mimicry serves as a “chemical camouflage” and protects these parasitoids as they go undetected within aphid colonies. Chrysopa glossonae, a lacewing, uses the wax of the woolly alder aphid to chemically disguise itself from Formicine ants (of the sub-family Formicinea) who have learned to avoid attacking the aphid.

SOCIAL

There are many defensive strategies that are incited via chemical communication and detection that result in a change of behavior.

Terrestrial arthropods - final draft
There are many strategies terrestrial arthropods employ in terms of chemical defense. The first of these strategies include the direct use of secondary metabolites. Many insects are distasteful to predators and excrete irritants or secrete poisonous compounds that cause illness or death when ingested. Secondary metabolites obtained from plant food may also be sequestered by insects and used in the production of their own toxins. One of the more well-known examples of this is the monarch butterfly, which sequesters poison obtained from the milkweed plant. Among the most successful insect orders employing this strategy are beetles (Coleoptera), grasshoppers (Orthoptera), and moths and butterflies (Lepidoptera). Insects also biosynthesize unique toxins, and while sequestration of toxins from food sources is claimed to be the energetically favorable strategy, this has been contested. Passion-vine associated butterflies in the tribe Heliconiini (sub-family Heliconiinae) either sequester or synthesize de novo defensive chemicals, but moths in the genus Zygaena (family Zygaenidae) have evolved the ability to either synthesize or sequester their defensive chemicals through convergence. Some coleopterans sequester secondary metabolites to be used as defensive chemicals but most biosynthesize their own de novo. Anatomical structures have developed to store these substances, and some are circulated in the hemolyph and released associated with a behavior called reflex bleeding.

The use of chemical alarms and detection is another strategy of chemical defense. Identifying predators and responding swiftly and appropriately is advantageous and leads to higher fitness. These defensive responses can include (but are not limited to) avoidance and escape responses, safeguarding offspring, aggressive behaviors, and applying “direct defenses” (i.e. toxins or defensive chemicals similar to the strategy of the monarch butterfly discussed above). For example, the fruit fly (Rhagoletis basiola) can chemically detect a nearby parasitoid (an organism that acts as both a parasite and a predator) and halt its egg-laying. Delaying oviposition can reduce the risk of predation and falls under the category of protecting offspring. The spider mite (Tetranychus urticae) can respond to predator volatiles in the environment and will choose to feed in areas without predator cues. Similarly, spider mites are also able to sense damaged body parts of individuals of the same species, or conspecifics, and present the same avoidance behavior as with predator cues. Furthermore, spider mites exhibit a similar behavior with egg-laying as the fruit fly and will elect to move to areas absent of predator cues before oviposition. Spider mites will not avoid areas with other, non-predator volatiles meaning these organisms are able to chemically distinguish threats from non-threats. Parasitic wasps (Aphidius uzbekistanicus) also sense volatiles of their predator, a hyperparasitoid (a parasite who's host is another parasite), and fly to new areas devoid of the chemical cues, displaying similar avoidance behaviors as the spider mite.

Alternately, chemical detection of predators or threats can instigate aggressive behaviors in some terrestrial arthropods, rather than escape and avoidance behaviors. Polybia paulista, a vespid wasp, is a social species that forage and defend according to complex social structures. These wasps have evolved to detect pheromones in the venom of members of the same species. Identifying volatiles from the venom of conspecifics allows the vespid wasps to discern a nearby threat. When detected, these pheromones induce an attacking behavior within members of the same species. These wasps will then work together to defeat the threat. Similarly, honeybees (Apis mellifera scutellata) release a warning pheromone when threatened. These pheromones intensify the honeybees' defenses by increasing the duration of the stinging behavior in all nearby honeybees.

Aphids, small insects that can be found feeding on the sap of plants, exhibit many strategies in terms of chemical defense. Aphids have structures called cornicles along the posterior side of their abdomen which are used to deliver secretions containing both volatile and nonvolatile compounds. Volatile compounds serve primarily as alarm pheromones. Pheromones are chemicals released from one individual that elicit a response from another. Nonvolatile compounds, such as wax, are used as noxious adhesives that the aphid will smear on their enemies. These smears are used to fatally bind predators' mouthparts, antennas, legs, etc., meaning these compounds are typically used more for physical defense rather than chemical. Pea aphids (Acyrthosiphon pisum) produce a warning chemical called (E)-β-farnesene which is excreted as a volatile compound in the presence of predators or perceived threats. In many cases, the aphid will respond by leaving the feeding site in search of an area without alarm pheromones. Additionally, pea aphids are highly attune to which predators are in their area as they can chemically identify what is posing as a threat and adjust their response accordingly. For example, pea aphids can identify Adalia bipunctata, the ladybird beetle, by their chemical predator cues. After sensing this predator, pea aphids are known to produce more offspring with wings. The winged offspring are able to better avoid predation; however, winged individuals are less fertile. This trade-off between wings and fertility shows the success of this particular defensive strategy. In “relaxed” conditions, or conditions in which predator cues are absent, more wing-less offspring are produced.

The chemical defense systems of aphids are highly specific. (E)-β-farnesene, the alarm pheromone discussed above, is used by many species of aphids. When released, (E)-β-farnesene will only extend 2-3 centimeters in diameter. This protects farther conspecifics from the alarm chemical so they do not experience any needless pause in feeding or respond unnecessarily. Furthermore, these chemical alarms are detected by structures on the antennae of aphids that utilize specialized binding proteins. Warning chemicals must accumulate to a certain minimum within the binding proteins before a response is produced. These factors are used to highlight the specificity of the chemical defense systems of aphids. Moreover, the chemical warnings used are also highly specific and the method in which the alarm pheromone is distributed can elicit different responses. For example, Ceratovacuna lanigera, the sugarcane wooly aphid, has two methods of distribution of alarm pheromones. When threatened, the alarm pheromones can either be released as a droplet or as a smear. When the alarm is released as a droplet from the aphid's cornicle, the local conspecifics will respond individually and will either avoid or escape the area. However, when alarm pheromones are spread on a predator, other members of the same species will launch a joint attack. As discussed above, waxy cornicle smears are typically used to physically defend an aphid from a predator. In this case, however, the chemical alarms in the wax are eliciting a behavioral change; therefore, this particular strategy can be considered chemical defense.

Other organisms have been able to take advantage of the elaborate chemical defenses of aphids to increase their own fitness. Chemical mimicry is powerful tool in terms of chemical defense. Lysiphlebus fabarum, a parasitoid of aphids, is able to mimic the chemical secretions of specific aphids when infiltrating their colonies. This mimicry serves as a “chemical camouflage” and protects these parasitoids as they go undetected within aphid colonies. Chrysopa glossonae, a lacewing, uses the wax of the woolly alder aphid to chemically disguise itself from formicine ants (of the sub-family Formicinea) who have learned to avoid attacking the aphid. This means that nearby formicine ants will ignore the lacewing as it would the wooly alder aphid. This is another instance where waxy secretions are used for chemical defense rather than physical.

Marine Invertebrates
Marine invertebrates employ a diverse array of strategies in terms of chemical defense. Some of these strategies include: secondary metabolite production, storage and modification of another organism’s secondary metabolites, chemical warnings, predator warnings, phagomimicry, and chemical “clothing.” (CITE ALL)

Sea sponges, of the phylum Porifera, are filter feeders that have shown to benefit from the production of many secondary metabolites. Sponges do have the ability to produce their own secondary metabolites rather than rely on the storage and modification of another organism's chemical defense. The roles of all observed secondary metabolites are unknown; however, there is an inverse relationship between the quantity of secondary metabolites within a sponge and the number of spicules present on the sponge. Spicules are sharp, needle-like structures protruding from the sponge which are used as a physical defense for the sponge. The observed inverse relationship between the quantity of secondary metabolites and spicules means that as the amount of secondary metabolites increase, the number of spicules decrease. This leads to the idea that secondary metabolites are indeed used for defensive purposes. Additionally, many sponges are toxic to potential predators. Sponges that exhibit a larger production of secondary metabolites experience less predation, aiding in the idea that secondary metabolites are used as a defensive mechanism.

Nudibranchs, also known as sea slugs, exhibit both an “active” and “passive” form of chemical defense. Sea slugs are carnivorous and a central part of their diet consists of sea sponges who, as discussed above, produce their own defensive secondary metabolites. A key feature of sea slugs is their ability to store and reuse the defensive chemicals produced in the organisms they consume. For instance, a sea sponge produces pigments which gives sponges their vibrant colors. The pigments in the sponges accumulate in the sea slugs as they feed, allowing the sea slug to be camouflaged into its environment. The color of the sea slug is dependent on which sponge they consume. For example, a sea slug that appears pink when found feeding on a pink sponge can turn green when migrating to a green sponge. This camouflage can be regarded as an “accidental” or passive form of chemical defense. A more active form of chemical defense found in sea slugs is their ability to store the defensive secondary metabolites produced by sponges. Sea slugs exhibit two mechanisms of storing defensive chemicals. The first of these mechanisms is storing the chemicals within their dorsum (or “backside”). This storage mechanism is advantageous as the defensive chemicals are located near the surface of the sea slug in preparation of mucus secretion. The second mechanism of defensive chemical storage exhibited by sea slugs is to preserve the chemicals in other areas of their body. For example, some sea slugs store secondary metabolites within their digestive track. Sea slugs who use this strategy for secondary metabolite storage have mechanisms of deploying the defensive chemicals when needed. Sea slugs are phylogenetically related to sea snails. One of the most distinguishing factors between these two marine invertebrates is the sea snail posses a shell and sea slugs do not. This loss of shell provides insight to the success of the sea slug’s chemical defensive strategies. With the use of defensive chemicals, shells are unnecessary and energetically expensive, leading to the loss of these protective structures. The fact that sea slugs can effectively survive and evade predation without the use of the shell highlights the success of storing and modifying secondary metabolites as a defensive mechanism.

Chemical warnings and alarms as a defensive mechanism is used by many marine invertebrates. The mechanism relies on chemical cues to be released and sensed throughout their aquatic environment and the organisms ability to modify their behavior as a result. For example, clams have evolved to sense predator pheromones in the surrounding water and respond in a way that hides their presence from potential predators. Clams, referring to many species of mollusks, feed by pumping. “Pumping” occurs when clams pull surrounding water in, feed on microorganisms present in the water, and release the newly filtered water. Predators of clams, namely blue shell crabs and whelks, are able to identify their prey by sensing the chemical cues present in the surrounding environment by the release of the filtered water. Clams have evolved to chemically sense upstream predators. When a predator is sensed nearby, clams modify their behavior and discontinue their pumping to reduce consumer cues so their predators can no longer follow their chemical trail. Clams only restart their pumping when consumer cues are absent. In this scenario, both predator and prey are relying on the presence of secondary metabolites, predators are using these chemicals as a hunting mechanism while the clams are using them as a mode of defense. Blue shell crabs (Callinectes sapidus), a common predator of clams, have a similar mechanism of defense; however, instead of chemically sensing predators in the local environment, they are able to sense chemical warnings emitted by members of the same species. These crabs, when harmed, emanate a chemical warning that is species specific, meaning these chemical warnings are only detected by other blue shell crabs. These warnings can come from damaged whole crabs or body parts of blue shell crabs. These chemical signals warn others to avoid areas of high risk. The use of chemical warnings and alarm pheromones is mechanism used by many marine invertebrates, clams and blue shell crabs are only two examples of this defensive strategy. (MARINE CHEM ECO)

Sea hares use a form of chemical defense called phagomimicry. Unlike the widespread use of chemical warnings and alarms, phagomimicry is specific to sea hares. Phagomimicry, as the name suggests, is a type of chemical mimicry. Many organisms have evolved to use mimicry as it is a highly successful mechanism of chemical defense. Sea hares, when attacked, quickly release a fog of chemicals into the surrounding environment. The chemical cloud consists of two main parts: the ink and the opaline. The ink, when released into the water, physically obscures the sea hare from their predator. The opaline is synthesized and stored in the opaline gland. The opaline fog is a mixture of chemicals that mimic the signals of the predator's food and therefore acts as a food stimulus. The goal of the opaline chemicals cloud is to supply a stronger food stimulus than the sea hare itself provides. Altogether, the cloud works to overwhelm and distract the predator. Confused, the predator will attack the chemical mixture rather than the sea hare itself, allowing time for the sea hare to escape. (SEA HARES USE NOVEL)

Several marine invertebrates are able to acquire chemical defense by covering themselves in other organisms who possess their own defensive secondary metabolites. This defensive mechanism is described as "chemical clothing." Invertebrates have been observed using many different species as a form of clothing. These include sponges, bacteria, and seaweed. Interestingly, many marine invertebrates who capitalize on this mechanism of defense are herbivores. These herbivores choose to use seaweed as clothing rather than food, meaning they value the seaweed more for their defensive abilities rather than as potential food. In the field, invertebrates such as the Atlantic decorator crab (Libinia dubia) are observed to experience significantly less predation when "clothed" in noxious seaweed than their unclothes conspecifics. The marine invertebrate and the chemically defended organism are able to form a symbiotic relationship resulting in the marine invertebrate acquiring long-term chemical defenses.

Marine Invertebrates - Final draft
Marine invertebrates employ a diverse array of strategies in terms of chemical defense. Some of these strategies include: secondary metabolite production, storage and modification of another organism’s secondary metabolites, chemical warnings, predator warnings, phagomimicry, and chemical “clothing.” The success of these strategies is exemplified by the number of species who exhibit these chemical defenses.

Sea sponges, of the phylum Porifera, are just one example of marine invertebrates who benefit from the production of secondary metabolites. Sponges have the ability to produce their own secondary metabolites rather than rely on the storage and modification of another organism's chemical defenses. The roles of some observed secondary metabolites are still unknown; however, there is evidence highlighting that fact that a large number of secondary metabolites are used for defensive purposes. For example, there is an inverse relationship between the quantity of secondary metabolites within a sponge and the number of spicules present on the organism itself. Spicules are sharp, needle-like structures protruding from the sponge and are used as a form of physical defense. Secondary metabolites and spicules have an inverse relationship because, as the quantity of secondary metabolites increase, the number of spicules decrease. This leads to the idea that secondary metabolites are indeed used for defensive purposes and sponges no longer have to rely on physical defenses. Additionally, many sponges that produce secondary metabolites are toxic to potential predators. Sponges that exhibit a larger production of secondary metabolites experience less predation, aiding in the idea that secondary metabolites are used as a defensive mechanism.

Secondary metabolite storage and modification is a useful strategy for many marine invertebrates. They are able to sequester preexisting chemicals without needing to spend the energy producing the secondary metabolites themselves. For example, Nudibranchs, also known as sea slugs, exhibit both a “passive” and an “active” form of chemical defense. Sea slugs are carnivorous and a central part of their diet consists of sea sponges who, as discussed above, produce their own defensive secondary metabolites. A key feature of sea slugs' chemical defense is their ability to store and reuse the chemicals produced in the organisms they consume. For instance, a sea sponge produces pigments which gives them their vibrant colors. The pigments in the sponges accumulate in the sea slugs as they feed, allowing the sea slug to be camouflaged within its environment. The color of the sea slug is dependent on which sponge they consume. For example, a sea slug that appears pink when found feeding on a pink sponge can turn green when migrating to a green sponge. This camouflage can be regarded as an “accidental” or passive form of chemical defense. A more active form of chemical defense found in sea slugs is their ability to store the defensive secondary metabolites produced by sponges. Sea slugs exhibit two mechanisms of storing defensive chemicals. The first of these mechanisms is storing the chemicals within their dorsum (or “backside”). This storage mechanism is advantageous because the defensive chemicals are located near the surface of the sea slug and are readily available for any mucus secretion. The second mechanism of defensive chemical storage exhibited by sea slugs is preserving the secondary metabolites in other areas of their body. For example, some sea slugs store secondary metabolites within their digestive track. Sea slugs who use this strategy for secondary metabolite storage have mechanisms of deploying the defensive chemicals when needed. Sea slugs are phylogenetically related to sea snails. One of the most distinguishing factors between these two marine invertebrates is sea snails posses a shell while sea slugs do not. This loss of shell provides insight to the success of the sea slug’s chemical defensive strategies. With the use of defensive chemicals, shells are unnecessary and energetically expensive, leading to the loss of these protective structures. The fact that sea slugs can effectively survive and evade predation without the use of the shell highlights the success of storing and modifying secondary metabolites as a defensive mechanism.

The use of chemical warnings and alarms as a defensive mechanism is employed by many marine invertebrates. This mechanism relies on the invertebrates releasing and sensing chemical cues throughout their aquatic environment and modifying their behavior as a result. For example, clams have evolved to sense predator pheromones in the surrounding water and respond in a way that hides their presence from those predators. Clams, referring to many species of mollusks, feed by pumping. “Pumping” occurs when clams pull surrounding water in, feed on microorganisms present in the water, and release the newly filtered water. Predators of clams, namely blue shell crabs and whelks, are able to identify their prey by sensing the chemical cues present in the filtered water. Clams have evolved to chemically sense upstream predators. When a predator is sensed nearby, clams modify their behavior and discontinue their pumping to reduce consumer cues. Predators no longer have a chemical trail to follow when searching for the clam. Clams only restart their pumping when consumer cues are absent. In this scenario, both predator and prey are relying on the presence of secondary metabolites, predators are using these chemicals as a hunting mechanism while the clams are using them as an alarm that elicits their behavioral response. Blue shell crabs (Callinectes sapidus), a common predator of clams, have a similar mechanism of defense; however, instead of chemically sensing predators in the local environment, they are able to sense chemical warnings emitted by members of the same species. These crabs, when harmed, emanate a chemical warning that is species specific, meaning these chemical warnings are only detected by other blue shell crabs. These warnings can come from damaged whole crabs or body parts of blue shell crabs. These chemical signals warn others to avoid areas of high risk. The use of chemical warnings and alarm pheromones is a mechanism used by many marine invertebrates, clams and blue shell crabs are only two examples of this defensive strategy.

Sea hares use a form of chemical defense called phagomimicry. Unlike the widespread use of the previously discussed chemical defensive strategies, phagomimicry is specific to sea hares. Phagomimicry, as the name suggests, is a type of chemical mimicry. Many organisms have evolved to use mimicry as it is a highly successful mechanism of chemical defense. Sea hares, when attacked, quickly release a fog of chemicals into the surrounding environment. The chemical cloud consists of two main parts: the ink and the opaline. The ink, when released into the water, physically obscures the sea hare from their predator. The opaline fog is a mixture of chemicals that mimic the signals of the predator's food and therefore acts as a food stimulus. The goal of the opaline chemical cloud is to supply a stronger food stimulus than the sea hare itself provides. Altogether, the cloud works to overwhelm and distract the predator. Confused, the predator will attack the chemical mixture rather than the sea hare itself, allowing time for the sea hare to escape.

Several marine invertebrates are able to acquire chemical defense by covering themselves in other organisms who possess defensive secondary metabolites. This defensive mechanism is described as "chemical clothing." Invertebrates have been observed using many different organisms as a form of clothing. These include sponges, bacteria, and seaweed. Interestingly, many marine invertebrates who capitalize on this mechanism of defense are herbivores. These herbivores choose to use seaweed as clothing rather than food, meaning they value the seaweed more for their defensive abilities rather than as potential food. In the field, invertebrates such as the Atlantic decorator crab (Libinia dubia) experience significantly less predation when "clothed" in noxious seaweed than their unclothed conspecifics. The marine invertebrate and the chemically defended organism are able to form a symbiotic relationship resulting in the marine invertebrate acquiring long-term chemical defenses.

Marine Invertebrates - Final, Final Draft
Marine invertebrates employ a diverse array of strategies in terms of chemical defense. Some of these strategies include: secondary metabolite production, storage and modification of another organism’s secondary metabolites, chemical warnings, predator warnings, phagomimicry, and chemical “clothing.” The success of these strategies is exemplified by the number of species who exhibit these chemical defenses.

Sea sponges, of the phylum Porifera, are just one example of marine invertebrates who benefit from the production of secondary metabolites. Sponges have the ability to produce their own secondary metabolites rather than rely on the storage and modification of another organism's chemical defenses. The roles of some observed secondary metabolites are still unknown; however, there is evidence highlighting that fact that a large number of secondary metabolites are used for defensive purposes. For example, there is an inverse relationship between the quantity of secondary metabolites within a sponge and the number of spicules present on the organism itself. Spicules are sharp, needle-like structures protruding from the sponge and are used as a form of physical defense. Secondary metabolites and spicules have an inverse relationship because, as the quantity of secondary metabolites increase, the number of spicules decrease. This leads to the idea that secondary metabolites are indeed used for defensive purposes and sponges no longer have to rely on physical defenses. Additionally, many sponges that produce secondary metabolites are toxic to potential predators. Sponges that exhibit a larger production of secondary metabolites experience less predation, aiding in the idea that secondary metabolites are used as a defensive mechanism.

Secondary metabolite storage and modification is a useful strategy for many marine invertebrates. They are able to sequester preexisting chemicals without needing to spend the energy producing the secondary metabolites themselves. For example, Nudibranchs, also known as sea slugs, exhibit both a “passive” and an “active” form of chemical defense. Sea slugs are carnivorous and a central part of their diet consists of sea sponges who, as discussed above, produce their own defensive secondary metabolites. A key feature of sea slugs' chemical defense is their ability to store and reuse the chemicals produced by the organisms they consume. For instance, a sea sponge produces pigments which gives them their vibrant colors. The pigments in the sponges accumulate in the sea slugs as they feed, allowing the sea slug to be camouflaged within its environment. The color of the sea slug is dependent on which sponge they consume. For example, a sea slug that appears pink when found feeding on a pink sponge can turn green when migrating to a green sponge. This camouflage can be regarded as an “accidental” or passive form of chemical defense. A more active form of chemical defense found in sea slugs is their ability to store and use the defensive secondary metabolites produced by sponges. Sea slugs exhibit two mechanisms of storing defensive chemicals. The first of these mechanisms is storing the chemicals within their dorsum (or “backside”). This storage mechanism is advantageous because the defensive chemicals are located near the surface of the sea slug and are readily available for any mucus secretion. The second mechanism of defensive chemical storage exhibited by sea slugs is preserving the secondary metabolites in other areas of their body. For example, some sea slugs store secondary metabolites within their digestive track. Sea slugs who use this strategy for secondary metabolite storage have mechanisms of deploying the defensive chemicals when needed. Sea slugs are phylogenetically related to sea snails. One of the most distinguishing factors between these two marine invertebrates is sea snails posses a shell while sea slugs do not. This loss of shell provides insight to the success of the sea slug’s chemical defensive strategies. With the use of defensive chemicals, shells are unnecessary and energetically expensive, leading to the loss of these protective structures. The fact that sea slugs can effectively survive and evade predation without the use of the shell highlights the success of storing and modifying secondary metabolites as a defensive mechanism.

The use of chemical warnings and alarms as a defensive mechanism is employed by many marine invertebrates. This mechanism relies on the invertebrates releasing and sensing chemical cues throughout their aquatic environment and modifying their behavior as a result. For example, clams have evolved to sense predator pheromones in the surrounding water and respond in a way that hides their presence from those predators. Clams, referring to many species of mollusks, feed by pumping. “Pumping” occurs when clams pull surrounding water in, feed on microorganisms present in the water, and release the newly filtered water. Predators of clams, namely blue shell crabs and whelks, are able to identify their prey by sensing the chemical cues present in the filtered water. Clams have evolved to chemically sense upstream predators. When a predator is sensed nearby, clams modify their behavior and discontinue their pumping to reduce consumer cues. Predators no longer have a chemical trail to follow when searching for the clam. Clams only restart their pumping when consumer cues are absent. In this scenario, both predator and prey are relying on the presence of secondary metabolites, predators are using these chemicals as a hunting mechanism while the clams are using them as an alarm that elicits their behavioral response. Blue shell crabs (Callinectes sapidus), a common predator of clams, have a similar mechanism of defense; however, instead of chemically sensing predators in the local environment, they are able to sense chemical warnings emitted by members of the same species. These crabs, when harmed, emanate a chemical warning that is species specific, meaning these chemical warnings are only detected by other blue shell crabs. These warnings can come from damaged whole crabs or body parts of the blue shell crabs. These chemical signals warn others to avoid areas of high risk. The use of chemical warnings and alarm pheromones is a mechanism used by many marine invertebrates, clams and blue shell crabs are only two examples of this defensive strategy.

Sea hares use a form of chemical defense called phagomimicry. Unlike the widespread use of the previously discussed chemical defensive strategies, phagomimicry is specific to sea hares. Phagomimicry, as the name suggests, is a type of chemical mimicry. Many organisms have evolved to use mimicry as it is a highly successful mechanism of chemical defense. Sea hares, when attacked, quickly release a fog of chemicals into the surrounding environment. The chemical cloud consists of two main parts: the ink and the opaline. The ink, when released into the water, physically obscures the sea hare from their predator. The opaline fog is a mixture of chemicals that mimic the signals of the predator's food and therefore acts as a food stimulus. The goal of the opaline chemical cloud is to supply a stronger food stimulus than the sea hare itself provides. Altogether, the cloud works to overwhelm and distract the predator. Confused, the predator will attack the chemical mixture rather than the sea hare itself, allowing time for the sea hare to escape.

Several marine invertebrates are able to acquire chemical defense by covering themselves in other organisms who possess defensive secondary metabolites. This defensive mechanism is described as "chemical clothing." Invertebrates have been observed using many different organisms as a form of clothing. These include sponges, bacteria, and seaweed. Interestingly, many marine invertebrates who capitalize on this mechanism of defense are herbivores. These herbivores choose to use seaweed as clothing rather than food, meaning they value the seaweed more for their defensive abilities rather than as potential food. In the field, invertebrates such as the Atlantic decorator crab (Libinia dubia) experience significantly less predation when "clothed" in noxious seaweed than their unclothed conspecifics. The marine invertebrate and the chemically defended organism are able to form a symbiotic relationship resulting in the marine invertebrate acquiring long-term chemical defenses.

Marine Invertebrates

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Types of chemical defense strategies found in marine invertebrates (this is not an exhaustive list):


 * secondary metabolite production (ex: sponges)
 * Storage and modification of another organism’s chemical defenses (ex: sea slugs)
 * Chemical warnings (ex: blue shell crabs)
 * Predator sensing (ex: clams)
 * Phagomimicry (ex: sea hares)
 * Bioluminescence  (This I am unsure about, will require further discussion)

Sponges – Secondary Metabolite Production


 * Energetic trade-off: loss of spicules as secondary metabolites become primary mode of defense
 * Provide defensive chemicals to those who feed on them

Sea slugs – Storage and Modification of another organism’s chemical defense


 * Camouflage: “accidental” form of chemical defense
 * Pigments in sponges -> accumulate in sea slugs
 * Color of sea slugs -> dependent on which sponge they consume
 * Ex: pink when found on pink algae (symbiont with sponge) turn green if migrate to green algae


 * Defensive chemicals
 * Different mechanisms of storing
 * Within dorsum
 * Advantage: no chemical mobility required -> already present at surface for mucus secretion

Clams - behavioral response to predator chemical cues
 * Within another area of the body
 * Activation of defense and chemical movement required
 * Loss of shell: provides insight to success of chemical defense
 * Sea slugs -> phylogenetically related to sea snails
 * Success of defensive chemicals resulted in loss of shell
 * Shell became unnecessary and energetically expensive


 * pumping reduced when predators are sensed
 * predators include blue shell crab and whelks
 * what is pumping?
 * another term for feeding -> clams feed by filtering water
 * clams pull water in -> feed on microorganisms present in water -> release filtered water -> predators able to sense clams through cues present in released water
 * Clams: chemically sense upstream predators
 * Behavioral change - reduction of pumping
 * When consumer cues are absent, pumping restarts

Blue Shell Crabs - chemical warnings


 * Chemical signals from damaged crabs/body parts
 * Released into local environment
 * Other blue shell crabs avoid areas with chemical warning signals
 * Species specific
 * Ex: blue shell crabs only respond to chemical warnings from other blue shell crabs

Sea hares - Phagomimicry


 * Specific to sea hares
 * able to release chemical signals when attacked
 * chemical signals mimic specific food chemicals (ex: amino acids)
 * 2 parts to chemical "cloud":
 * Ink -> obscures sea hare
 * Opaline -> synthesized and stores in opaline gland
 * contains chemicals that mimic food
 * predator -> overwhelmed and distracted
 * will attack cloud rather than sea hare -> sea hare able to escape

[There is more to details to add here; however, an entire page already exists for phagomimicry so I am trying to decide how much to add. Any help is appreciated!]

Bioluminescence