Question

Why are American elm trees less likely to die of Dutch elm disease now than when the disease was first brought to North America from Asia?

1) The beetles that spread the disease do not survive in cities so the growth of cities has provided more disease-free habitat for American elms.
2) The most susceptible trees died in the initial outbreak and the more resistant survivors have passed their genes for resistance to their offspring.
3) Antibiotics have been developed to combat the disease, although untreated trees still quickly succumb to the disease once they are infected.
4) The fungus that causes the diseases began to die out as the number of new host trees dropped and the pathogen is now nearly extinct in North America.

Answer 1

The American elms are less susceptible to Dutch elm disease now due to natural selection, where the more resistant trees survived the initial outbreak and passed on their resistance to their offspring, thereby increasing the species' resilience to the pathogen over time.

Step-by-step explanation:

The American elm trees are less likely to die from Dutch elm disease now than when the disease was first introduced to North America largely because of natural selection. The initial outbreak killed the most susceptible trees, leaving behind those that had greater resistance to the disease. Over time, these surviving trees have propagated, passing their resistant genes on to their offspring, thereby increasing the overall resistance of the population to Dutch elm disease.

This is evidence of a classic evolutionary response to a pathogen, where the survival of the fittest plays a significant role in the overall health and resilience of the species. While some management strategies, like sanitation measures, selective breeding for resistant strains, and the use of fungicides have been employed to protect elms from the disease, the genetic resistance in naturally surviving trees has been key to the species' partial recovery.