The Cost of Venom

Venom,a poisonous substance that is produced by some animals and injected into an enemy or prey mainly by biting or stinging,is clearly an advantage for defense or hunting.But it is an expensive resource.Replenishing empty venom glands can greatly diminish an animal’s energy supply.Even though the venom supply in snakes makes up only a tiny fraction of their weight,refilling venom glands after use can increase a snake’s metabolic (energy use)rate by more than 20 percent.The cost of using venom is not restricted to the direct metabolic cost of replenishing it,however.Spending venom can result in temporary disarmament,so that,for instance,a predatory spider lacking its venom becomes defenseless prey.The speed of refueling venom glands varies considerably between groups.It can take theraphosid spiders-a group of mostly large and hairy spiders popularly known as tarantulas or bird-eating spiders-as long as 85 days to finish reloading their glands,while the tiny ceterpillar-killing paresitoid wesp Bracon brevicornis can reload its glands in less than three hours.The North American centipede regenerates about 85 percent of its venom volume within two days.

The great cost of venom,direct or indirect,is also indicated by the phenomenon of ‘venom metering”(monitoring the amount of venom used).Snakes can control the amount of venom they release so they do not use more than is necessary.A larger,more dangerous,or more agile prey receives a larger dose of venom to ensure it is subdued effectively.Although venom metering has been poorly studied in spiders,researchers know that they are also able to make decisions about when and how much venom to deliver.The Central American hunting spider Cupiennius salei injects more venom into larger prey.When dealing with prey that have body armor, such as beetles,and the armor prevents the spider from injecting venom into an optimal location,the spider also increases the dose. Remarkably,this spider can also distinguish prey that are more or less sensitive to its venom (crickets and cockroaches.respectively) purely on the basis of smell,and choose the more vulnerable prey when its venom glands are depleted.

Venom is not just metered during prey capture.Snakes, scorpions,and spiders also show defensive venom metering. Females of the western black widow spider,for example,can adjust the amount of venom in their defensive bites depending on the threat level.Squeezing the spider’s body provokes her to deliver almost twice the dose of venom than if her leg is pinched.Even so,more than half of her defensive bites contain no detectable venom at all. The defensive bites of some snakes and the defensive stings of scorpions can likewise be less costly.The South African thick-tail scorpion initially stings predators with a transparent prevenom that is poor in proteins but rich in pain-inducing potassium ions.The scorpion releases its milky venom,which is more protein rich and toxic-but also more expensive to produce-only when its prevenom fails to do the job.

The cost of venom does not only affect how venoms evove:it can also cause a loss of toxins.Some specialist venomous predators that have evolved to feed on only a limited number of species have streamlined their venoms by losing toxin types that are no longer useful.This removes the cost of producing obsolete toxins. Sea snakes,for example,have relatively simple venoms compared to their terrestrial relatives,with the venom consisting of only a few neurotoxins that effectively immobilize their fish prey.In a fascinating case of convergent evolution (in which species not closely related independently evolve similar traits),the venoms of sea kraits,which are related to sea snakes but independently adopted a marine fish- eating lifestyle,have undergone the same streamlining.In fact,the venom of sea kraits is so similar to that of sea snakes that it can be effectively neutralized by sea snake antivenom.Venom is such an expensive commodity that it is discarded if its ecological importance disappears.When the marbled sea snake switched to a diet consisting exclusively of fish eggs,it did not simply lose a few toxin types.It lost its venom,fangs,and even its venom gland.

 

 

1

Venom,a poisonous substance that is produced by some animals and injected into an enemy or prey mainly by biting or stinging,is clearly an advantage for defense or hunting.But it is an expensive resource.Replenishing empty venom glands can greatly diminish an animal’s energy supply.Even though the venom supply in snakes makes up only a tiny fraction of their weight,refilling venom glands after use can increase a snake’s metabolic (energy use)rate by more than 20 percent.The cost of using venom is not restricted to the direct metabolic cost of replenishing it,however.Spending venom can result in temporary disarmament,so that,for instance,a predatory spider lacking its venom becomes defenseless prey.The speed of refueling venom glands varies considerably between groups.It can take theraphosid spiders-a group of mostly large and hairy spiders popularly known as tarantulas or bird-eating spiders-as long as 85 days to finish reloading their glands,while the tiny ceterpillar-killing paresitoid wesp Bracon brevicornis can reload its glands in less than three hours.The North American centipede regenerates about 85 percent of its venom volume within two days.

Why does the author state that“refilling venom glands after use can increase a snake’s metabolic (energy use)rate by more than 20 percent’?

ATo emphasize the advantage that venom provides for defense or hunting

BTo suggest that venom makes up a larger fraction of a snake’s weight after it is replenished

CTo point out how much more energy the weight of a full venom gland requires snakes to use in their daily activities

DTo support the idea that maintaining venom supply decreases an animal’s available energy

 

2

The great cost of venom,direct or indirect,is also indicated by the phenomenon of ‘venom metering”(monitoring the amount of venom used).Snakes can control the amount of venom they release so they do not use more than is necessary.A larger,more dangerous,or more agile prey receives a larger dose of venom to ensure it is subdued effectively.Although venom metering has been poorly studied in spiders,researchers know that they are also able to make decisions about when and how much venom to deliver.The Central American hunting spider Cupiennius salei injects more venom into larger prey.When dealing with prey that have body armor, such as beetles,and the armor prevents the spider from injecting venom into an optimal location,the spider also increases the dose. Remarkably,this spider can also distinguish prey that are more or less sensitive to its venom (crickets and cockroaches.respectively) purely on the basis of smell,and choose the more vulnerable prey when its venom glands are depleted.

The word“Remarkably”in the passage is closest in meaning to

AAdditionally

BNaturally

COrdinarily

DImpressively

 

3

The great cost of venom,direct or indirect,is also indicated by the phenomenon of ‘venom metering”(monitoring the amount of venom used).Snakes can control the amount of venom they release so they do not use more than is necessary.A larger,more dangerous,or more agile prey receives a larger dose of venom to ensure it is subdued effectively.Although venom metering has been poorly studied in spiders,researchers know that they are also able to make decisions about when and how much venom to deliver.The Central American hunting spider Cupiennius salei injects more venom into larger prey.When dealing with prey that have body armor, such as beetles,and the armor prevents the spider from injecting venom into an optimal location,the spider also increases the dose. Remarkably,this spider can also distinguish prey that are more or less sensitive to its venom (crickets and cockroaches.respectively) purely on the basis of smell,and choose the more vulnerable prey when its venom glands are depleted.

Which of the following can be inferred from paragraph 2 about the use of venom metering by the Central American hunting spider Cupiennius salei?

ACupiennius salei does not use venom metering when hunting prey that have body armor.

BCupiennius salei uses its sense of smell to release venom into the optimal location in beetles.

CCupiennius salei preys on crickets when its venom supply is low.

DCupiennius salei releases less venom when hunting cockroaches than when hunting crickets.

 

4

Venom is not just metered during prey capture.Snakes, scorpions,and spiders also show defensive venom metering. Females of the western black widow spider,for example,can adjust the amount of venom in their defensive bites depending on the threat level.Squeezing the spider’s body provokes her to deliver almost twice the dose of venom than if her leg is pinched.Even so,more than half of her defensive bites contain no detectable venom at all. The defensive bites of some snakes and the defensive stings of scorpions can likewise be less costly.The South African thick-tail scorpion initially stings predators with a transparent prevenom that is poor in proteins but rich in pain-inducing potassium ions.The scorpion releases its milky venom,which is more protein rich and toxic-but also more expensive to produce-only when its prevenom fails to do the job.

In paragraph 3,the author mentions which TWO of the following as examples of defensive venom metering?To receive credit,you must select TWO answer choices.

AReleasing larger doses of venom for greater threats

BReleasing toxic chemicals in prevenom

CReleasing small doses of venom before releasing richer, pain-inducing potassium ions

DReleasing protein-rich venom only if protein-poor prevenom is not an effective defense

 

5

The cost of venom does not only affect how venoms evove:it can also cause a loss of toxins.Some specialist venomous predators that have evolved to feed on only a limited number of species have streamlined their venoms by losing toxin types that are no longer useful.This removes the cost of producing obsolete toxins. Sea snakes,for example,have relatively simple venoms compared to their terrestrial relatives,with the venom consisting of only a few neurotoxins that effectively immobilize their fish prey.In a fascinating case of convergent evolution (in which species not closely related independently evolve similar traits),the venoms of sea kraits,which are related to sea snakes but independently adopted a marine fish- eating lifestyle,have undergone the same streamlining.In fact,the venom of sea kraits is so similar to that of sea snakes that it can be effectively neutralized by sea snake antivenom.Venom is such an expensive commodity that it is discarded if its ecological importance disappears.When the marbled sea snake switched to a diet consisting exclusively of fish eggs,it did not simply lose a few toxin types.It lost its venom,fangs,and even its venom gland.

Why does the author state that sea snakes “have relatively simple venoms compared to their terrestrial relatives”?

ATo support the claim that venom’s expense can lead to an evolutionary loss of toxins

BTo provide an example of how limited the number of snake species with complex venoms is

CTo demonstrate that terrestrial snakes produce obsolete toxins

DTo show that sea snakes’ neurotoxins are more effective at immobilizing prey than terrestrial snakes’ venoms are

 

6

The cost of venom does not only affect how venoms evove:it can also cause a loss of toxins.Some specialist venomous predators that have evolved to feed on only a limited number of species have streamlined their venoms by losing toxin types that are no longer useful.This removes the cost of producing obsolete toxins. Sea snakes,for example,have relatively simple venoms compared to their terrestrial relatives,with the venom consisting of only a few neurotoxins that effectively immobilize their fish prey.In a fascinating case of convergent evolution (in which species not closely related independently evolve similar traits),the venoms of sea kraits,which are related to sea snakes but independently adopted a marine fish- eating lifestyle,have undergone the same streamlining.In fact,the venom of sea kraits is so similar to that of sea snakes that it can be effectively neutralized by sea snake antivenom.Venom is such an expensive commodity that it is discarded if its ecological importance disappears.When the marbled sea snake switched to a diet consisting exclusively of fish eggs,it did not simply lose a few toxin types.It lost its venom,fangs,and even its venom gland.

The word“exclusively”in the passage is closest in meaning to

Aincreasingly

Bonly

Cregularly

Dlargely

 

7

The cost of venom does not only affect how venoms evove:it can also cause a loss of toxins.Some specialist venomous predators that have evolved to feed on only a limited number of species have streamlined their venoms by losing toxin types that are no longer useful.This removes the cost of producing obsolete toxins. Sea snakes,for example,have relatively simple venoms compared to their terrestrial relatives,with the venom consisting of only a few neurotoxins that effectively immobilize their fish prey.In a fascinating case of convergent evolution (in which species not closely related independently evolve similar traits),the venoms of sea kraits,which are related to sea snakes but independently adopted a marine fish- eating lifestyle,have undergone the same streamlining.In fact,the venom of sea kraits is so similar to that of sea snakes that it can be effectively neutralized by sea snake antivenom.Venom is such an expensive commodity that it is discarded if its ecological importance disappears.When the marbled sea snake switched to a diet consisting exclusively of fish eggs,it did not simply lose a few toxin types.It lost its venom,fangs,and even its venom gland.

According to paragraph 4,for which of the following reasons did the marbled sea snake lose “It lost its venom,fangs,and even its venom gland’?

AThe snake no longer needed venom as a defense against sea kraits.

BVenom was no longer helpful for obtaining food because of changes in the snake’s diet.

CChanges in the snake’s environment caused the production of venom to become more expensive.

DThe snake’s prey evolved an ability to effectively neutralize the snake’s venom.

 

8

The cost of venom does not only affect how venoms evove:it can also cause a loss of toxins.Some specialist venomous predators that have evolved to feed on only a limited number of species have streamlined their venoms by losing toxin types that are no longer useful.This removes the cost of producing obsolete toxins. Sea snakes,for example,have relatively simple venoms compared to their terrestrial relatives,with the venom consisting of only a few neurotoxins that effectively immobilize their fish prey.In a fascinating case of convergent evolution (in which species not closely related independently evolve similar traits),the venoms of sea kraits,which are related to sea snakes but independently adopted a marine fish- eating lifestyle,have undergone the same streamlining.In fact,the venom of sea kraits is so similar to that of sea snakes that it can be effectively neutralized by sea snake antivenom.Venom is such an expensive commodity that it is discarded if its ecological importance disappears.When the marbled sea snake switched to a diet consisting exclusively of fish eggs,it did not simply lose a few toxin types.It lost its venom,fangs,and even its venom gland.

According to paragraph 4,the venom of sea snakes is very similar to the venom of sea kraits for which of the following reasons?

ASea snakes and sea kraits both feed on e wider variety of prey than do terrestnial snakes.

BSea kraits evolved from sea snakes.

CSea snakes and sea kraits have adopted similar diets over time.

DSea snakes and sea kraits have both adapted to the ability of some marine fish to effectively neutralize venom.

 

9

Look at the four squaresthat indicate where the following sentence could be added to the passage

The amount of venom delivered is determined by the specific characteristics of the prey.

Where would the sentence best fit？Click on a square  sentence to the passage.

10

Venom is a very useful but expensive resource.

AThe time it takes to replenish empty venom glands depends on the size of the animal,such that it takes snakes longer than it does some spiders and wasps to refuel venom glands.

BVenomous predators can choose different types of toxins to release. depending on which toxin will be most effective for each type of prey.

CIn cases where venomous predators evolve to feed on just a few species,their venom production becomes streamlined so that they produce no obsolete toxins.

DDepending on the species that has used up its venom,replacing that venom can take hours or days,during which the venomous animal may have few defenses.

ESome animals carefully control the amount of venom they release,and this phenomenon occurs both in hunting and in defense.

FBecause most modern sea reptiles have lost their ability to produce venom,they can feed on only a limited number of species.

 

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