Question

When the ranges of two different species meet, a stable "hybrid zone" occupied by hybrid individuals may form. How is this possible? a. Hybrid individuals may have intermediate characteristics that are advantageous in a given region. b. Hybrid individuals are always allopolyploid and are thus unable to mate with either of the original species. c. Hybrid individuals may have reduced fitness and thus be strongly selected against. d. One species has a selective advantage, so as hybridization continues, the other species will go extinct.

Short answer

A stable "hybrid zone" may form when the ranges of two different species meet because hybrid individuals might have intermediate characteristics that are advantageous in a given region, allowing them to survive and reproduce.

Step-by-step solution

Option a: Hybrid individuals may have intermediate characteristics that are advantageous in a given region.

This option explains that hybrid individuals may have characteristics that are a combination of both parent species, which could be advantageous in a specific region. These advantageous traits may allow hybrid individuals to survive and reproduce, maintaining a stable hybrid zone.

Option b: Hybrid individuals are always allopolyploid and are thus unable to mate with either of the original species.

This option is not a valid explanation for the formation of a stable hybrid zone, as it incorrectly states that hybrid individuals are always allopolyploid. While allopolyploid hybrids can indeed occur, it is not the only type of hybrid, and it does not explain how a stable hybrid zone is maintained.

Option c: Hybrid individuals may have reduced fitness and thus be strongly selected against.

This option opposes the formation of a stable hybrid zone. If hybrid individuals have reduced fitness and are selected against, they would not be able to maintain a stable hybrid zone. This answer is not a valid explanation for the presence of a stable hybrid zone.

Option d: One species has a selective advantage, so as hybridization continues, the other species will go extinct.

This option suggests that one species will eventually go extinct due to hybridization. While the one species may have a selective advantage, this option does not explain how a stable hybrid zone can exist. A stable hybrid zone would suggest that both species and their hybrid individuals can coexist and maintain their respective populations. Based on the analysis of each option: The most appropriate answer to the question: "When the ranges of two different species meet, a stable "hybrid zone" occupied by hybrid individuals may form. How is this possible?" is: a. Hybrid individuals may have intermediate characteristics that are advantageous in a given region.

Key concepts

Species Coexistence

Species coexistence is the scenario where two or more species live in the same geographic area without one outcompeting the other to extinction. In the context of hybrid zones, species coexistence occurs as both parent species and their hybrid offspring find ways to maintain their populations. This coexistence can be attributed to a variety of factors that mediate competition and facilitate balance in biodiversity.

• Ecological Niches: Each species, including hybrids, might occupy slightly different ecological niches, minimizing direct competition for resources.
• Temporal Separation: Different species or hybrids might have different active times or breeding seasons, reducing overlap and direct competition.
• Environment: The physical conditions of a hybrid zone may be such that neither parent species would thrive alone, but hybrid individuals can survive, leading to species coexistence.

Stability in hybrid zones is possible when these factors align such that no single group consistently outperforms the other.

Hybrid Fitness

Hybrid fitness refers to the ability of hybrid individuals to survive, reproduce, and contribute to future generations. While commonly believed to have reduced fitness due to disrupted gene compatibility, some hybrids can exhibit increased fitness in certain environments, known as 'hybrid vigor' or 'heterosis'.

• Advantageous Traits: Hybrid individuals may possess genetic combinations from both parent species that confer new advantages, like disease resistance, better survival skills, or adaptations to specific niches.
• Environmental Factors: The fitness of hybrids can vary depending on the specific environmental conditions of the hybrid zone, which may favor intermediate or mixed traits.
• Equilibrium: In some cases, a balance exists where hybrids do well enough to maintain their populations without completely replacing the parent species, promoting stability in the hybrid zone.

The successful formation of a stable hybrid zone depends on whether the hybrids have fitness levels comparable to or exceeding those of their parent species.

Genetic Diversity

Genetic diversity refers to the variety of genes within a population or species, and it is a critical component of resilience in ecosystems. In hybrid zones, genetic diversity can be particularly high due to the mixing of genetic material from two different parent species.

• Increased Variation: Hybrids contribute to genetic diversity by combining alleles from both parent species, potentially leading to new genetic traits and increased adaptability.
• Adaptive Potential: Higher genetic diversity allows populations to better adapt to changing environments, as there is a wider range of traits that can be 'selected' for natural advantages.
• Survival and Stability: The introduction of new genetic combinations via hybridization can boost the survival prospects of hybrids, promoting stability and resilience in the hybrid zone.

Genetic diversity in hybrid zones is vital for the long-term stability and survival of both the hybrid population and the parent species.