Examkin

Question

Difficulty: MediumAdaptive Radiation and Mechanisms of Speciation

A population of phytophagous insects undergoes ecological sympatric speciation following the introduction of a new host plant species into its native habitat. Arrange the following evolutionary events in the correct chronological sequence from earliest to latest:

  1. 1A subset of the insect population shifts to exploit and oviposit on the newly introduced host plant.
  2. 2Divergent natural selection favors distinct physiological and morphological traits suited to each host plant.
  3. 3Assortative mating on preferred host plants creates pre-zygotic reproductive barriers between the two groups.
  4. 4Substantial genetic divergence accumulates over generations, resulting in distinct daughter species.

Answer

The correct chronological sequence begins with a subpopulation shifting to oviposit and feed on the new host plant (item 1), followed by divergent natural selection acting on host-specific adaptations (item 2), leading to assortative mating and pre-zygotic reproductive isolation (item 3), and culminating in full genetic divergence and speciation (item 4).
Sympatric speciation via host shift begins when a portion of the population colonizes a novel host plant (item 1). This habitat shift creates contrasting selective pressures, driving divergent selection for traits adapted to each host (item 2). Because mating takes place on the host plant, host fidelity promotes assortative mating and establishes pre-zygotic reproductive barriers (item 3). Over time, suppressed gene flow enables genomic divergence and complete speciation (item 4).

Step-by-Step Solution

1
Identify the initiating event of sympatric host-shift speciation.
The first step is the behavioral colonization or host preference shift where a portion of the insect population starts using the new host plant (item 1).
Ecological speciation driven by host shift requires initial exposure and utilization of an unexploited ecological niche within the same geographic area.
2
Determine the selective process occurring after host colonization.
Divergent natural selection acts on traits relevant to feeding efficiency, toxin tolerance, and survival on the different hosts (item 2).
Alternative host species present contrasting chemical, physical, and microclimatic selective pressures.
3
Determine how reproductive isolation develops in sympatry.
Host fidelity during mating leads to assortative mating, establishing pre-zygotic isolation between groups (item 3).
Insects that court and mate on their specific host plant experience reduced interbreeding with insects on the original host plant.
4
Identify the final evolutionary outcome.
Accumulation of genetic differences leads to permanent speciation (item 4).
Sustained reduction in gene flow allows selection and genetic drift to lock in distinct species boundaries.

Key Concept

Sympatric Ecological Speciation via Host-Shift
Estimated Time:1m 30s
Rate this question

Topics

Adaptive Radiation and Mechanisms of Speciation

More questions from this topic