Directions: Use the information provided and your knowledge of Life Science to answer the following questions. Show all work where necessary.
Directions: Use the information provided and your knowledge of Life Science to answer the following questions. Show all work where necessary.
In the 1950s, Australia introduced the myxoma virus to control invasive rabbit populations that were damaging crops and native ecosystems. When the virus was released, it caused extremely high mortality: in some regions, over
Initially, nearly all rabbits were highly susceptible to the virus. But a small number carried genetic variants that gave them partial resistance. These rabbits were far more likely to survive infection long enough to reproduce. As the virus continued to spread, resistant rabbits had a strong selective advantage: they survived, produced offspring, and passed their resistance alleles to the next generation.
Diagram 1.
Source: https://fuzzyrabbit.com/sudden-death-in-rabbits/
Because rabbits reproduce rapidly, each female producing multiple litters per year, the population had high reproductive potential - one of the key factors driving evolutionary change. Even if only a fraction of rabbits survived the virus, the surviving resistant individuals produced enough offspring to quickly shift allele frequencies in the population.
Competition also played a role. As susceptible rabbits died in high numbers, resistant rabbits faced less competition for resources such as food and space. Their increased survival and reproductive success created conditions for the rapid proliferation of the resistant trait.
Over time, the average mortality rate caused by the virus decreased, not because the virus became less deadly at first, but because the population of rabbits contained a much higher proportion of resistant individuals. Statistical analysis of rabbit populations showed clear upward trends in resistance frequency and downward trends in mortality.
This phenomenon illustrates the principles of:
Potentials for population increase allow traits to spread quickly.
Heritable genetic variation provides the raw material for evolution.
Competition and lethal selection pressures reduce survival of individuals lacking advantageous traits.
Organisms with advantageous traits increase in proportion across generations.
The evolution of myxomatosis resistance in Australia remains a key historical example of how strong selective pressures can rapidly shift trait frequencies in natural populations.
Diagram 2.
Source: https://www.slideserve.com/zenia-chaney/chapter-32
Table 1.
Year | Resistant Rabbits (%) | Susceptible Rabbits (%) |
|---|---|---|
1950 | 1 | 99 |
1955 | 8 | 92 |
1960 | 22 | 78 |
1965 | 38 | 62 |
1970 | 55 | 45 |
1975 | 71 | 29 |
Graph of Information - Figure 1.
Table 2.
Rabbit Type | Mortality Rate (%) |
|---|---|
Highly Susceptible | 96 |
Intermediate | 65 |
Resistant | 28 |
Graph of Information - Figure 2.
Using Table 1 and Figure 1, describe how the frequencies of resistant and susceptible rabbits changed between 1950 and 1975. Include one numerical example.
Using the reading, explain how genetic variation in rabbits contributed to the spread of myxomatosis-resistant traits across generations.
According to Table 2, which rabbit type has the highest mortality rate when exposed to myxomatosis?
Based on Diagram 2, which statement best explains why resistant rabbits became more common over time?
Using Table 2 and Figure 2, explain how differences in mortality rates among rabbit genotypes support natural selection during the myxomatosis epidemic.
Construct a CER explaining how environmental pressures from the myxoma virus caused shifts in trait frequencies among rabbit populations over time.