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Difficulty: HardAdaptive Radiation and Mechanisms of Speciation

In an African rift lake, several closely related species of cichlid fish inhabit the same continuous, unfragmented water body. These species occupy distinct ecological niches—some feed on algae in shallow waters, while others crush snail shells in deeper zones. Females choose mates exclusively based on male breeding coloration that corresponds to specific light penetration depths, preventing interbreeding between populations. Which evolutionary process and speciation mechanism are best illustrated by this population?

  1. Sympatric speciation leading to adaptive radiationAnswer
  2. B
    Allopatric speciation leading to convergent evolution
  3. C
    Allopatric speciation driven by inheritance of acquired traits
  4. D
    Sympatric speciation resulting in continuous phenotypic variation

Answer

Sympatric speciation leading to adaptive radiation
The correct answer is sympatric speciation leading to adaptive radiation. Sympatric speciation occurs when reproductive isolation evolves between groups within the same geographical area without physical barriers, driven in this case by sensory drive and sexual selection (depth-dependent male color preference). As these isolated groups adapt to distinct feeding niches (shallow-water algae vs. deep-water snails), a single ancestral lineage rapidly branches into multiple specialized species, which is the definition of adaptive radiation.

Step-by-Step Solution

1
Analyze the geographic setting of the population.
The cichlids inhabit the same continuous, unfragmented water body without physical barriers separating them.
Speciation occurring within the same geographical location in the absence of physical barriers is defined as sympatric speciation.
2
Examine the reproductive isolation mechanism and ecological diversification.
Behavioral mate choice based on male coloration and depth preferences prevents gene flow, while populations specialize into distinct feeding niches (algae scraping, snail crushing).
Pre-zygotic behavioral isolation combined with ecological niche divergence drives reproductive isolation within a shared habitat.
3
Synthesize the evolutionary outcome.
A single ancestral lineage rapidly diversifies into a multitude of specialized species filling diverse ecological niches.
This rapid evolutionary diversification from a common ancestor into varied ecological forms is the hallmark of adaptive radiation.

Key Concept

Sympatric Speciation and Adaptive Radiation
Estimated Time:2m 0s
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Topics

Adaptive Radiation and Mechanisms of Speciation

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