The Chytrid Fungus Epidemic

The scientific community first suspected that frogs were dying out in the 1980s. Several cases of sudden disappearances of frogs from places where they were formerly common were noticed, and worryingly. these were places where the habitat was protected and in good health in other respects. Furthermore, these extinctions occurred in widely separated places, among them. liter frogs in Puerto Rico, stream-breeding frogs in Australia, western toads in Colorado’s Rocky Mountains, and frogs and toads from the mountainous rain forests of Costa Rica and Panama.

When scientists working on amphibians around the world began to exchange notes on their experiences, it became clear that the amphibian declines in pure and widespread habitats were occurring much more quickly than they could explain in terms of habitat destruction, pollution, or climate change even though these factors have undoubtedly had some effect on frog populations in some places, and may even have caused local extinctions. A fungal disease was discovered in amphibians in the early 1990s. The fungus belongs to a group called the chytrid fungi and, although there are over 1,000 different forms of chytrid fungi, this was the only species known to become parasites on a vertebrate host. In 1999 it was named Batrachochytrium dendrobatidis, or Bd for short. It is now known that Bd only lives on amphibian skin, and often causes the death of frogs. Importantly. Bd infects all species of amphibians, and so it remains a threat even after one or more species has disappeared from a region. The researchers reached the conclusion that Bd was the main cause of amphibian declines in pure habitats and set out to investigate it.

There were several factors at work. Frogs at higher elevations are more likely to be affected than those at lower ones, indicating that the fungus is stronger at the cooler temperatures experienced in mountains than the warmer conditions lower down. It seems that the optimal temperature for the fungus is 170-25°C (62.50-770F), which is also, unfortunately, the temperature at which frog diversity tends to be greatest. Frogs restricted to cool mountains, especially stream-breeders, are the most affected. Higher temperatures reduced the activity of the fungus and can even be used to cure infected frogs under laboratory conditions. Species that tend to aggregate, under rocks, for example, are more likely to catch Bd, and periods of stress, perhaps as a result of unusually warm or dry weather, may also trigger outbreaks (and may also increase the tendency of the frogs to aggregate). Researchers discovered that although all amphibians have bacteria and other microbes on their skin that help them to fight off diseases, including fungal infections.the effectiveness of this defense appears to vary from one species to another. Partially immune species can act as reservoirs of infection, or carriers, allowing the fungus to spread throughout a community of frogs. They also found that Bd can survive away from its hosts, at least for limited periods of time, and can be collected from wet rocks on which frogs were previously sitting, for instance.

So far, nobody has definitely established where Bd came from.One theory that is gaining favor among experts is that it has always existed in parts of sub-Saharan Africa, as the fungus was discovered on a museum specimen of an African clawed frog.Xenopus faseri, collected in West Africa as far back as 1933. It was also found in Xenopus laevis collected in Uganda in 1934 and Xenopus gilli from the Cape regions of South Africa in 1982. Furthermore, the fungus appears not to be fatal to frogs from the southern half of Africa, suggesting that they had acquired immunity to it over a long period of time. Certainly, Bd was present on all clawed frogs collected in the region in 1973 with no apparent ill-effects. Clawed frogs were transported around the world in the middle years of the twentieth century for testing and, just as some of the frogs were accidentally introduced to new regions, this too could have been an opportunity for the fungus to spread. Regardless of its origins, Bd has spread to much of the world since the 1980s.

 

1

The scientific community first suspected that frogs were dying out in the 1980s. Several cases of sudden disappearances of frogs from places where they were formerly common were noticed, and worryingly. these were places where the habitat was protected and in good health in other respects. Furthermore, these extinctions occurred in widely separated places, among them. liter frogs in Puerto Rico, stream-breeding frogs in Australia, western toads in Colorado’s Rocky Mountains, and frogs and toads from the mountainous rain forests of Costa Rica and Panama.

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

Atypically

Bonce

Csomewhat

Despecially

 

2

The scientific community first suspected that frogs were dying out in the 1980s. Several cases of sudden disappearances of frogs from places where they were formerly common were noticed, and worryingly. these were places where the habitat was protected and in good health in other respects. Furthermore, these extinctions occurred in widely separated places, among them. liter frogs in Puerto Rico, stream-breeding frogs in Australia, western toads in Colorado’s Rocky Mountains, and frogs and toads from the mountainous rain forests of Costa Rica and Panama.

According to paragraph 1, all of the following are true of the frog disappearances in the 1980s EXCEPT

AThey occurred quite quickly.

BThey occurred most often in regions lacking streams for breeding frogs.

CThey occurred in healthy habitats

DThey occurred in several places with different frog species.

 

3

When scientists working on amphibians around the world began to exchange notes on their experiences, it became clear that the amphibian declines in pure and widespread habitats were occurring much more quickly than they could explain in terms of habitat destruction, pollution, or climate change even though these factors have undoubtedly had some effect on frog populations in some places, and may even have caused local extinctions. A fungal disease was discovered in amphibians in the early 1990s. The fungus belongs to a group called the chytrid fungi and, although there are over 1,000 different forms of chytrid fungi, this was the only species known to become parasites on a vertebrate host. In 1999 it was named Batrachochytrium dendrobatidis, or Bd for short. It is now known that Bd only lives on amphibian skin, and often causes the death of frogs. Importantly. Bd infects all species of amphibians, and so it remains a threat even after one or more species has disappeared from a region. The researchers reached the conclusion that Bd was the main cause of amphibian declines in pure habitats and set out to investigate it.

According to paragraph 2, which of the following is true of the fungus Bd?

AIt caused a disease that was first seen by scientists in 1999.

BIt is one of several species of chytrid fungi that are parasites on vertebrate hosts.

CIt lives on all species of amphibians, not just frogs.

DIt disappears from a region after it has killed off all members of a species.

 

4

There were several factors at work. Frogs at higher elevations are more likely to be affected than those at lower ones, indicating that the fungus is stronger at the cooler temperatures experienced in mountains than the warmer conditions lower down. It seems that the optimal temperature for the fungus is 170-25°C (62.50-770F), which is also, unfortunately, the temperature at which frog diversity tends to be greatest. Frogs restricted to cool mountains, especially stream-breeders, are the most affected. Higher temperatures reduced the activity of the fungus and can even be used to cure infected frogs under laboratory conditions. Species that tend to aggregate, under rocks, for example, are more likely to catch Bd, and periods of stress, perhaps as a result of unusually warm or dry weather, may also trigger outbreaks (and may also increase the tendency of the frogs to aggregate). Researchers discovered that although all amphibians have bacteria and other microbes on their skin that help them to fight off diseases, including fungal infections.the effectiveness of this defense appears to vary from one species to another. Partially immune species can act as reservoirs of infection, or carriers, allowing the fungus to spread throughout a community of frogs. They also found that Bd can survive away from its hosts, at least for limited periods of time, and can be collected from wet rocks on which frogs were previously sitting, for instance.

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

Ausual

Bmaximum

Crequired

DBest

 

5

There were several factors at work. Frogs at higher elevations are more likely to be affected than those at lower ones, indicating that the fungus is stronger at the cooler temperatures experienced in mountains than the warmer conditions lower down. It seems that the optimal temperature for the fungus is 170-25°C (62.50-770F), which is also, unfortunately, the temperature at which frog diversity tends to be greatest. Frogs restricted to cool mountains, especially stream-breeders, are the most affected. Higher temperatures reduced the activity of the fungus and can even be used to cure infected frogs under laboratory conditions. Species that tend to aggregate, under rocks, for example, are more likely to catch Bd, and periods of stress, perhaps as a result of unusually warm or dry weather, may also trigger outbreaks (and may also increase the tendency of the frogs to aggregate). Researchers discovered that although all amphibians have bacteria and other microbes on their skin that help them to fight off diseases, including fungal infections.the effectiveness of this defense appears to vary from one species to another. Partially immune species can act as reservoirs of infection, or carriers, allowing the fungus to spread throughout a community of frogs. They also found that Bd can survive away from its hosts, at least for limited periods of time, and can be collected from wet rocks on which frogs were previously sitting, for instance.

According to paragraph 3, which of the following methods can be used to cure frogs infected with Bd?

AExposing the frogs to heat

BReducing the activity level of the frogs

CPlacing bacteria and other microbes on the frogs’ skin

DProviding rocks so the frogs can aggregate under them

 

6

There were several factors at work. Frogs at higher elevations are more likely to be affected than those at lower ones, indicating that the fungus is stronger at the cooler temperatures experienced in mountains than the warmer conditions lower down. It seems that the optimal temperature for the fungus is 170-25°C (62.50-770F), which is also, unfortunately, the temperature at which frog diversity tends to be greatest. Frogs restricted to cool mountains, especially stream-breeders, are the most affected. Higher temperatures reduced the activity of the fungus and can even be used to cure infected frogs under laboratory conditions. Species that tend to aggregate, under rocks, for example, are more likely to catch Bd, and periods of stress, perhaps as a result of unusually warm or dry weather, may also trigger outbreaks (and may also increase the tendency of the frogs to aggregate). Researchers discovered that although all amphibians have bacteria and other microbes on their skin that help them to fight off diseases, including fungal infections.the effectiveness of this defense appears to vary from one species to another. Partially immune species can act as reservoirs of infection, or carriers, allowing the fungus to spread throughout a community of frogs. They also found that Bd can survive away from its hosts, at least for limited periods of time, and can be collected from wet rocks on which frogs were previously sitting, for instance.

According to paragraph 3, which of the following statements is true of frogs that have some immunity to Bd disease?

AThey may lose their immunity by sitting on rocks where Bd is present.

BAlthough they do not have the disease, they may still contribute to its spread.

CThey are also protected against other fungal infections.

DThey help other species in their community avoid becoming infected.

 

7

So far, nobody has definitely established where Bd came from.One theory that is gaining favor among experts is that it has always existed in parts of sub-Saharan Africa, as the fungus was discovered on a museum specimen of an African clawed frog.Xenopus faseri, collected in West Africa as far back as 1933. It was also found in Xenopus laevis collected in Uganda in 1934 and Xenopus gilli from the Cape regions of South Africa in 1982. Furthermore, the fungus appears not to be fatal to frogs from the southern half of Africa, suggesting that they had acquired immunity to it over a long period of time. Certainly, Bd was present on all clawed frogs collected in the region in 1973 with no apparent ill-effects. Clawed frogs were transported around the world in the middle years of the twentieth century for testing and, just as some of the frogs were accidentally introduced to new regions, this too could have been an opportunity for the fungus to spread. Regardless of its origins, Bd has spread to much of the world since the 1980s.

Why does the author provide the information that Bd fungus was found in “Xenopus laevis collected in Uganda in 1934 and Xenopus gilli from the Cape regions of South Africa in 1982”?

ATo support the claim that Bd may have originated in sub-Saharan Africa

BTo demonstrate how long it takes to acquire immunity to Bd

CTo provide further evidence that Bd can survive in museum specimens

DTo argue that Bd took a long time to spread throughout subSaharan Africa

 

8

So far, nobody has definitely established where Bd came from.One theory that is gaining favor among experts is that it has always existed in parts of sub-Saharan Africa, as the fungus was discovered on a museum specimen of an African clawed frog.Xenopus faseri, collected in West Africa as far back as 1933. It was also found in Xenopus laevis collected in Uganda in 1934 and Xenopus gilli from the Cape regions of South Africa in 1982. Furthermore, the fungus appears not to be fatal to frogs from the southern half of Africa, suggesting that they had acquired immunity to it over a long period of time. Certainly, Bd was present on all clawed frogs collected in the region in 1973 with no apparent ill-effects. Clawed frogs were transported around the world in the middle years of the twentieth century for testing and, just as some of the frogs were accidentally introduced to new regions, this too could have been an opportunity for the fungus to spread. Regardless of its origins, Bd has spread to much of the world since the 1980s.

What can be inferred from paragraph 4 about African clawed frogs that were transported around the world during the mid-twentieth century?

AThey were introduced to new regions where Bd was common.

BThey had never before been exposed to Bd.

CThey were unlikely to have been carriers of Bd.

DThey were largely immune to the effects of Bd.

 

9

There were several factors at work. Frogs at higher elevations are more likely to be affected than those at lower ones, indicating that the fungus is stronger at the cooler temperatures experienced in mountains than the warmer conditions lower down. It seems that the optimal temperature for the fungus is 170-25°C (62.50-770F), which is also, unfortunately, the temperature at which frog diversity tends to be greatest. Frogs restricted to cool mountains, especially stream-breeders, are the most affected. Higher temperatures reduced the activity of the fungus and can even be used to cure infected frogs under

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

 

Frogs’ preferred behaviors as well as their physical condition may also influence the spread of Bd.

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

 

10

Bd, a type of chytrid fungus, caused the deaths of many frogs worldwide beginning in the 1980s.

AThe scientific community was slow to recognize the cause of frog extinctions because chytrid fungi had no parasitic species prior to the 1980s.

BCertain environmental conditions, such as temperature and the degree to which the weather is dry, can increase or decrease the level of Bd risk in frogs.

CWhen African frogs that had been immune to chytrid fungi were accidentally introduced to new regions, they developed Bd, much like the local frogs of the region.

DThe parasitic fungus that causes Bd disease can spread from the frog’s skin where it lives, travel on the backs of immune frogs, and even survive for brief periods away from its living host.

EThe collection of Bd from wet rocks on which frogs once sat provides evidence of how the fungus has adapted to a variety of different conditions and amphibian hosts.

FBd’s origins are currently unknown, although some scientists believe that Bd came from Africa and spread as African frogs were transported worldwide.

 

答案请付费后查阅：