A team of evolutionary biologists is observing two bacterial colonies, Colony A and Colony B, grown from the same ancestral strain but under different nutrient conditions. Initially, both colonies are identical in composition and show genetic variations in their ability to metabolise nutrient X. After changing the nutrient composition by replacing 
with nutrient Y , they observe that Colony B begins to dominate the culture medium within 48 hours. Over a week, Colony B becomes the only surviving population. Meanwhile, a similar experiment on fishes involving a shift in food source does not result in significant population change even after several generations.
Which of the following best explains why bacteria adapted and evolved rapidly compared to fishes in this context?
Text Solution
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• The short life cycle and high mutation rate in bacteria allow faster selection of beneficial variants.
• The rate of appearance of new forms is linked to the life cycle or the life span.
• Microbes that divide fast have the ability to multiply and become millions of individuals within hours.
• A colony of bacteria (say A) growing on a given medium has built-in variation in terms of ability to utilise a feed component.
• A change in the medium composition would bring out only that part of the population (say B) that can survive under the new conditions.
• In due course of time this variant population outgrows the others and appears as new species. This would happen within days.
• For the same thing to happen in a fish or fowl would take million of years as life spans of these animals are in years. Here we say that fitness of 
is better than that of A under the new conditions. Therefore, nature selects for fitness.
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