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Evolution - Adaptive Radiation

Grade 12CBSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Adaptive Radiation is the process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats).

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It is a classic example of divergent evolution, where a common ancestor gives rise to multiple forms to exploit different ecological niches.

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Darwin's Finches: On the Galapagos Islands, Darwin observed that the original seed-eating finches evolved into various forms such as insectivorous and vegetarian finches, with beaks modified for different food sources.

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Australian Marsupials: A diverse range of marsupials evolved from a single ancestral stock within the Australian continent, including the Kangaroo, Sugar Glider, and Marsupial Mole.

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Convergent Evolution: When more than one adaptive radiation occurs in isolated geographical areas (representing similar habitats), different groups of organisms may evolve similar features. Example: Placental mammals in North America and Marsupial mammals in Australia (e.g., Placental Wolf and Tasmanian Wolf).

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The survival of certain traits during radiation is often influenced by natural selection, which acts upon the phenotypic variations within a population.

📐Formulae

p+q=1p + q = 1

p2+2pq+q2=1p^2 + 2pq + q^2 = 1

Allele frequency of A=p\text{Allele frequency of } A = p

Allele frequency of a=q\text{Allele frequency of } a = q

💡Examples

Problem 1:

Explain why the beaks of Darwin's finches are considered a prime example of adaptive radiation.

Solution:

The beaks represent morphological adaptations to different feeding habits.

Explanation:

From an original seed-eating ancestor, various species evolved with beak shapes specialized for eating seeds, insects, or cactus fruit. This radiation from a single point to fill multiple ecological niches on the Galapagos Islands is the definition of adaptive radiation.

Problem 2:

In a population of finches, the frequency of a recessive allele for a small beak (qq) is 0.30.3. According to the Hardy-Weinberg principle, what is the frequency of the homozygous dominant genotype (p2p^2)?

Solution:

p2=0.49p^2 = 0.49

Explanation:

Since p+q=1p + q = 1, we find p=1−0.3=0.7p = 1 - 0.3 = 0.7. The frequency of the homozygous dominant genotype is p2=(0.7)2=0.49p^2 = (0.7)^2 = 0.49.

Problem 3:

The Marsupial Mole and the Placental Mole are not closely related but look similar. Name the evolutionary phenomenon and explain its cause.

Solution:

Convergent Evolution.

Explanation:

Both organisms independently underwent adaptive radiation in similar ecological niches (burrowing/subterranean) in different geographical locations (Australia vs. other continents). This led to the selection of similar adaptive traits, despite different ancestral lineages.