Question

When a biologist first tested a new pesticide on a population of insects, she found that only 1% of the insects survived their exposure to the poison. She allowed the survivors to reproduce and discovered that 10% of the offspring survived exposure to the same concentration of pesticide. One generation later, 50% of the insects survived this experimental treatment. What is a likely explanation for the increasing survival rate of these insects over time?

Short answer

The most likely explanation for the increasing survival rate is natural selection, where the insects that survive the pesticide pass on their genetic resistance to their offspring, leading to a higher percentage of the population that can survive subsequent exposures.

Step-by-step solution

Review the Survival Rates Over Generations

Notice the change in survival rates: initially 1% survive, then 10%, and then 50%. These numbers suggest that the ability to survive the pesticide is becoming more common in the population over time.

Consider Possible Explanations for Increased Survival

Think of potential reasons why more insects are able to survive exposure. These reasons could include natural selection, genetic mutations, or the development of resistance to the pesticide.

Determine the Most Likely Explanation

Given the context of biology and the data provided, the most likely explanation is that the pesticide selects for insects with a genetic resistance to the toxin. The insects that survived likely passed this advantageous trait to their offspring, causing an increase in the population's overall survival rate.

Key concepts

Genetic Resistance

Genetic resistance in a population can be thought of as a biological shield that some individuals possess, allowing them to withstand specific environmental challenges like diseases or pesticides. In the exercise where the insects were exposed to a new pesticide, the initial survival rate was a meager 1%. However, when the few survivors reproduced, their offspring showed a survival rate of 10%, and with another generation, this rate shot up to 50%. This substantial increase in survival rate suggests that the initial survivors had some form of genetic resistance to the pesticide.

This genetic resistance is not something the insects developed but rather, had inherently within their genetic makeup. It is possible the resistance was due to a particular gene that coded for proteins, which in turn could break down the pesticide or help the insect’s biological systems to be unaffected by it. Once these resistant individuals reproduce, they pass on their resistance genes to their offspring, thus increasing the proportion of resistant individuals in the population over generations. Genetic resistance is a natural phenomenon that can have a significant impact on the effectiveness of pesticides and the long-term composition of insect populations.

Pesticide Resistance Evolution

The concept of pesticide resistance evolution is closely tied to the principle of natural selection. It illustrates how a population can develop a reduced sensitivity to a pesticide over time, rendering the chemical less effective. This resistance is not due to the insects becoming stronger or actively adapting during their lifetime, but rather it is the result of the survival and reproduction of those individuals that by chance possess genetic traits enabling them to tolerate the pesticide.

When the population of insects in the exercise was exposed to pesticide, those without the resistant genes perished, while the ones with resistant traits survived and bred. Over time, the gene pool shifted. More and more offspring inherited the resistant genes simply because those were the genes available in the surviving breeding population. This is an evolutionary change driven by the increased reproductive success of the resistant individuals. Over generations, this process called selective pressure leads to a population consisting mainly of resistant individuals. As this case study shows, the evolution of pesticide resistance can be rapid, emphasizing the need for sustainable pest management practices that consider long-term ecological impacts.

Inheritance of Advantageous Traits

The inheritance of advantageous traits is a key concept underpinning evolutionary theory. When a certain characteristic provides a survival benefit within a given environment, organisms with this trait tend to have more offspring than those without it. Over generations, these traits become more common within the population. This is observable in the step-by-step analysis of the exercise where the insect population being exposed to the pesticide demonstrates increased survival over generations due to the inheritance of genetic resistance.

Surviving insects likely had a genetic makeup that allowed them to withstand the effects of the pesticide, an advantageous trait in the context of their environment. When these insects reproduced, the beneficial genes were inherited by their offspring, which, when subjected to the same environment, survived in greater numbers. In subsequent generations, the increased representation of these advantageous traits results in a greater proportion of the population being resistant, as the frequency of the resistance genes increases. This genetic change across generations is a fundamental aspect of evolutionary biology and illustrates the role of heredity in the adaptation of populations to their environments.