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Consider two species of birds that diverged while separated geographically but resumed their contact before reproductive isolation was complete. Which describes the first step in what would happen over time if the two species mated extensively and their hybrid offspring survived and reproduced more poorly than offspring from intra-species matings? a. Natural selection would cause prezygotic barriers to reproduction between the parent species to strengthen over time. b. The production of unfit hybrids would increase and the speciation process would complete. c. The extensive mating between the species would continue to produce large numbers of hybrids. d. The gene pools of the parent species would fuse over time, reversing the speciation process.

Step by step solution

01

- Understand the Scenario

Examine the situation where two species of birds that diverged in isolation come into contact again before complete reproductive isolation.

02

- Analyze Mating and Hybrid Offspring

Consider the extensive mating between the two species and note that hybrids produced are less fit compared to purebred offspring.

03

- Identify Natural Selection's Role

Understand that if hybrid offspring have reduced fitness, natural selection would favor traits that prevent inter-species mating.

04

- Evaluate Prezygotic Barriers

Realize that prezygotic barriers (such as differences in mating calls, timing, or behaviors) would strengthen to avoid producing unfit hybrids.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Natural Selection

Natural selection is a process where organisms better adapted to their environment tend to survive and produce more offspring. In our bird scenario, when the hybrid offspring are less fit than the purebred offspring, natural selection would favor traits that discourage hybridization. This means birds that avoid interbreeding will be more successful in passing on their genes. Over time, this selection process will reduce the number of unfit hybrids, enhancing the survival chances of the fitter offspring.

Hybridization

Hybridization occurs when two different species mate and produce offspring. These offspring are called hybrids. In the given scenario, extensive mating results in many hybrids. However, since these hybrids are not as fit, they struggle to survive and reproduce. Hybridization isn't always disadvantageous, but in cases where hybrids are less fit, it can slow the process of complete species differentiation or speciation. Mating between species could potentially result in a mix of traits, but if those traits don't offer survival advantages, these hybrids don't do well.

Prezygotic Barriers

Prezygotic barriers are mechanisms that prevent species from mating and producing hybrids. These barriers can include:

• Differences in mating calls or courtship behavior
• Different breeding seasons or timing
• Physical differences that prevent mating

In our bird example, as hybrids become less fit, natural selection will favor the development or strengthening of these prezygotic barriers. Over time, these barriers minimize the chances of inter-species mating, leading to fewer unfit hybrids.

Speciation

Speciation is the process where one species splits into two or more distinct species. It typically occurs because of geographic isolation or significant genetic differences over time. In this bird scenario, geographic isolation initially caused the two bird populations to diverge. When they come back into contact and hybrids are less fit, natural selection pushes for stronger prezygotic barriers. This will further drive the speciation process, ensuring that the two bird populations continue to evolve separately without merging back into one species.