Amphibian populations are declining rapidly worldwide. The fungus Batrachochytri

Question

Amphibian populations are declining rapidly worldwide. The fungus Batrachochytrium dendrobatidis (Bd) has contributed to this decline: This pathogen causes severe skin infections in many amphibian species, leading to massive die-offs. Efforts to save amphibians from Bd have met with limited success, and there is little evidence that frogs and other amphibians have acquired resistance to Bd on their own.

In this exercise, you will investigate whether amphibians can acquire resistance to the fungal pathogen Bd. The principle guiding your investigation is that prior exposure to a pathogen can enable amphibians to acquire immunological resistance to that pathogen. To see whether this occurs after exposure to Bd, you will analyze data on acquired resistance in Cuban tree frogs (Osteopilus septentrionalis).

To create variation in number of prior exposures to Bd, Cuban tree frogs were exposed to Bd and cleared of their infection (using heat treatments) from 0 to 3 times; frogs with 0 prior exposures are referred to as “naive.” Researchers then exposed frogs to Bdand measured mean abundance of Bd on the frog’s skin, frog survival, and abundance of lymphocytes (a type of white blood cell involved in the immune response).

Which of the following best describes the abundance of Bd on a frog's skin following exposure to Bd?

The abundance of Bd on a naïve frog’s skin is roughly equal to the abundance of Bd on the skin of frogs that have been exposed to Bd.

B) Which of the following best describes the change in frog survival following exposure to Bd?

C)

Examine the data in the table, and select the graph that best represents the abundance of lymphocytes (per g frog) by treatment group.

D) Based on the evidence, identify the most appropriate statement describing the relationship between prior exposure to Bd and acquired resistance.

E) Breeding populations of amphibian species threatened by Bd have been established in captivity. Evidence from captive-bred Cuban tree frogs suggests that frogs can acquire resistance not only from exposure to live Bd,  but also dead Bd. Which of the following strategies do you think is most appropriate if the goals are to maximize survival rates of the captive frogs and repopulate regions decimated by Bd?

The abundance of Bd on a frog’s skin is close to 0 for all sampled frogs. The abundance of Bd on a frog’s skin is lower for naïve frogs than it is for frogs with prior exposure to Bd. The abundance of Bd on a frog’s skin is higher for naïve frogs than it is for frogs with prior exposure to Bd.

The abundance of Bd on a naïve frog’s skin is roughly equal to the abundance of Bd on the skin of frogs that have been exposed to Bd.

B) Which of the following best describes the change in frog survival following exposure to Bd?

The survival rate for naïve frogs is roughly equal to the survival rate of frogs previously exposed to Bd. Frogs with prior exposure to Bd survived at lower rates than frogs with no prior exposure to Bd. Frogs with prior exposure to Bd survived at higher rates than frogs with no prior exposure to Bd. Exposure to Bd resulted in the death of all frogs. 260 240 220 200 2180 O160 140 120 100 2 Number of prior Bd exposures

Explanation / Answer

A] The abundance of Bd on the frog's skin is higher for naive frogs than it is for frogs with prior exposure to Bd.

This is so because prior exposure to Bd triggers the immune system to acquire resistance to the fungi. This will prevent the growth of the Bd on the frog's skin

B] Frogs with prior exposure to Bd survived at higher rates than frogs with no exposure to Bd.

This is so because prior exposure to Bd has armed the immune system of the frog with antibodies to fight the pathogen .

C] The first graph best represent the given data.

Because the number of exposures to Bd will be kept on the x-axis and number of lymphocytes will be kept on the y-axis.

D] Prior exposure to Bd stimulates the frog's immune response ,enabling the frog to acquire some degree of resistance to Bd.

E] Cuban tree frogs could be bred in captivity and exposed to dead Bd. The exposed frogs could then be released to regions where their populations has been severely affected by Bd.

This is so because the resistant frogs will be able to survive in the wild also and breed and increase their population.

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