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Difficulty: HardAdaptive Radiation and Mechanisms of Speciation

A small group of lizards is dispersed by a rafting event to an isolated uninhabited island, initiating peripatric speciation. Arrange the following evolutionary events in the correct chronological sequence from earliest to latest.

  1. 1Geographic isolation occurs as a small peripheral subpopulation is physically separated from the mainland population.
  2. 2Rapid genetic divergence takes place in the island subpopulation due to founder effect and novel directional selection pressures.
  3. 3Intrinsic pre-zygotic reproductive barriers, such as altered courtship displays and dewlap signals, evolve as by-products of divergence.
  4. 4Biological species status is confirmed upon secondary contact as zero effective gene flow occurs between the island and mainland populations.

Answer

The correct chronological sequence is: Geographic isolation occurs as a small peripheral subpopulation is physically separated from the mainland population → Rapid genetic divergence takes place in the island subpopulation due to founder effect and novel directional selection pressures → Intrinsic pre-zygotic reproductive barriers, such as altered courtship displays and dewlap signals, evolve as by-products of divergence → Biological species status is confirmed upon secondary contact as zero effective gene flow occurs between the island and mainland populations.
Peripatric speciation initiates when a small peripheral subpopulation becomes geographically isolated from the main population. Once isolated, the small gene pool experiences strong genetic drift via the founder effect alongside novel selective pressures in the new environment, causing rapid genetic divergence. Over time, these genetic alterations produce intrinsic pre-zygotic reproductive barriers (such as modified courtship displays). Finally, when secondary contact occurs, complete reproductive isolation prevents gene flow, confirming the formation of a distinct biological species.

Step-by-Step Solution

1
Identify the initial physical event required for peripatric speciation.
Geographic separation isolates a small peripheral group from the main ancestral population.
An external physical barrier is required first to block gene flow between populations.
2
Determine the evolutionary mechanisms acting immediately after isolation.
Founder effect and local directional selection drive rapid genetic divergence.
Small founder population size accelerates genetic drift while novel island conditions favor specific adaptations.
3
Identify the emergence of biological reproductive barriers.
Pre-zygotic isolating mechanisms develop, changing reproductive traits and mating signals.
Divergent selection and accumulated mutations lead to behavioral or physiological incompatibility.
4
Recognize the final outcome confirming biological speciation.
Secondary contact demonstrates complete reproductive isolation and zero gene flow.
Speciation is complete when populations remain reproductively isolated upon sympatric re-exposure.

Key Concept

Peripatric Speciation and Stages of Reproductive Isolation
Estimated Time:2m 0s
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Topics

Adaptive Radiation and Mechanisms of Speciation

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