Questions and Answers
Which of the following is NOT an example of a prezygotic barrier?
Mimulus lewisii and Mimulus cardinalis provide an example of which type of prezygotic barrier?
What is the primary reproductive barrier observed in the case of the band-rumped storm-petrel?
Which mechanism eliminates the possibility of hybrid formation after mating has occurred?
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Which term describes the process where two species reinforce their reproductive barriers through selection?
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Sexual isolation in the Physalaemus frogs is primarily based on:
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What type of isolation is illustrated by the different feeding plants of ladybird beetles?
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Which of the following scenarios best exemplifies prezygotic isolation through mating preferences?
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Which type of isolation occurs when two species breed at different times of the day?
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What is the primary reason for sexual isolation in animals?
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Which postzygotic barrier involves decreased survival due to genetic incompatibility?
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What does ecological isolation prevent?
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Which factor strengthens prezygotic isolation between two populations?
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How is gametic isolation defined in the context of reproductive barriers?
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What is a consequence of extrinsic postzygotic barriers?
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Which process describes the increase in reproductive isolation through selection against hybridization?
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What is the primary distinction between prezygotic and postzygotic isolation in speciation?
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Which process describes the formation of new species due to divergent natural selection in different ecological environments?
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In which scenario would reinforcement of reproductive isolation most likely occur?
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What is a common mechanism through which speciation by genetic conflict occurs?
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Which of the following is a result of ecological speciation?
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What role does sexual selection play in the development of prezygotic isolation?
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Why does postzygotic isolation evolve later than prezygotic isolation?
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Which pattern is commonly observed in the evolution of strong prezygotic isolation?
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Study Notes
Premating Barriers
- Features that impede the transfer of gametes to other species.
- Ecological isolation: potential mates do not encounter each other.
- Temporal isolation: species breed at different times (season or day).
- Habitat isolation: species mate in different environments.
- Immigrants from diverging populations have low survival, preventing interbreeding.
Mating but No Zygote Formation
- Potential mates encounter each other but do not mate.
- Sexual isolation: individuals prefer mating within their species.
- Pollinator isolation: pollinators do not facilitate pollen transfer between species.
Postmating Prezygotic Barriers
- Mating occurs, yet zygotes are not produced.
- Mechanical isolation: reproductive structures do not align.
- Copulatory isolation: females are unresponsive to males of other species.
- Gametic isolation: fertilization fails to occur.
Postzygotic Barriers
- Hybrids can form but have diminished fitness.
- Extrinsic barriers: hybrids are poorly adapted to environments.
- Ecological inviability: hybrids struggle in parental habitats.
- Behavioral sterility: hybrid's mating success is low.
- Intrinsic barriers: hybrid fitness is low regardless of environment.
- Hybrid inviability: genetic incompatibility leads to reduced survival.
- Hybrid sterility: hybrids produce fewer viable gametes.
Speed of Reproductive Isolation Evolution
- Prezygotic isolation evolves faster than postzygotic isolation in organisms like flies and fishes.
- The strength of reproductive isolation corresponds to time since lineages diverged, measured by genetic distances.
- Example: Mimulus lewisii (pollinated by bees) and Mimulus cardinalis (pollinated by hummingbirds) show divergence in habitats and traits.
Prezygotic Isolation Mechanisms
- Separate species in different habitats reduces hybrid formation.
- Pollination by different animals limits gene flow between species.
- Seasonal and temporal isolation observed in species like the band-rumped storm-petrel and periodical cicadas.
- Gametic isolation crucial in marine invertebrates with external fertilization; arises from divergences in cell surface proteins.
Sexual Isolation Examples
- Female Physalaemus frogs selectively respond to calls of their species.
- Chemical signals in moths lead to sexual isolation.
- Strong prezygotic isolation emerges soon after species diverge, while postzygotic isolation strengthens later.
Causes of Speciation
- Ecological speciation: new species arise from divergent natural selection across different environments.
- Speciation by genetic conflict: occurs when an allele biases its transmission, harming others (e.g., X chromosome influencing offspring sex ratio).
- Speciation by sexual selection: mate preference and traits evolve simultaneously, causing prezygotic isolation.
- Reinforcement of reproductive isolation: enhances traits that reduce hybridization between sympatric or allopatric populations.
- Speciation by polyploidy: increases genetic material, contributing to species formation.
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Description
Test your understanding of premating barriers that affect species' ability to interbreed. This quiz covers various types of isolation, including ecological, temporal, and habitat isolation, as well as sexual isolation in animals. Dive into the complexities of reproductive strategies in different species.
