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Difficulty: MediumAdaptive Radiation and Mechanisms of Speciation

Two distinct populations of cichlid fish inhabit the same African lake without any physical barriers separating them. Over time, one group adapts to feeding in deep water while the other feeds in shallow water. Females of each population gradually develop mate preferences exclusively for males displaying specific nuptial coloration suited to their respective water depths. Which evolutionary mechanism best describes the formation of separate species in this scenario?

  1. Sympatric speciation driven by ecological niche partitioning and behavioral reproductive isolationAnswer
  2. B
    Allopatric speciation caused by physical geographical fragmentation of the lake basin
  3. C
    Convergent evolution driven by unrelated lineages occupying similar ecological niches
  4. D
    Lamarckian inheritance caused by individual fish acquiring new nuptial colors during their lifetime

Answer

Sympatric speciation driven by ecological niche partitioning and behavioral reproductive isolation
The correct answer correctly identifies sympatric speciation. Sympatric speciation occurs when a single population diverges into distinct reproductive species within the same geographical boundary. In this scenario, ecological niche partitioning (shallow vs. deep water feeding) combined with sexual selection (female mate preference for specific nuptial colors) forms pre-zygotic reproductive barriers without any physical separation.

Step-by-Step Solution

1
Identify the geographical context of the populations
The two fish populations inhabit the exact same lake without physical geographic barriers.
Determining whether geographic isolation is present distinguishes allopatric speciation from sympatric speciation.
2
Analyze the mechanism causing reproductive isolation
Adaptation to different water depths led to female mate choice based on nuptial coloration, establishing a pre-zygotic behavioral barrier.
Sexual selection combined with ecological niche differentiation leads to genetic divergence within the same territory.
3
Match the scenario to the correct evolutionary process
Speciation occurring within the same geographical location due to reproductive and ecological barriers is defined as sympatric speciation.
This directly aligns with the definition and classic examples (e.g., African Rift Lake cichlids) of sympatric speciation.

Key Concept

Sympatric Speciation and Ecological Reproductive Isolation
Estimated Time:1m 15s
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Topics

Adaptive Radiation and Mechanisms of Speciation

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