Speciation and Reproductive Isolation

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Questions and Answers

According to the formula provided, what does a reproductive isolation (RI) value of 0 signify?

Complete reproductive isolation, with no heterospecific matings.

Equal frequency of heterospecific and conspecific matings. (correct)

A low rate of heterospecific matings compared to conspecific matings.

A high rate of heterospecific matings compared to conspecific matings.

How do the songs of green lacewings contribute to premating reproductive isolation?

Males and females perform complex duets that are species-specific, preventing mating between different species. (correct)

Females are attracted to the songs of any male, regardless of species, but only mate with males of their own species.

Males sing complex songs, but females don't use these to choose a specific species.

Male songs attract only females that are morphologically similar, which ensures mating with their own species.

What is a likely outcome of two coral species spawning at different times, as described in the text?

Reproductive isolation based on habitat segregation.

Reproductive isolation through asynchronous gamete release. (correct)

Reproductive isolation through post-zygotic mechanisms.

Increased instances of hybridisation between the species.

Which of the following is the best interpretation of 'sympatric species' mating at different times, as described?

Species in the same geographical area do not interbreed because their reproductive cycles do not overlap. (B) Signup and view all the answers

In terms of the lacewing study, which experimental observation would best suggest reproductive isolation in the species?

Females respond only to the songs of conspecific males. (D) Signup and view all the answers

What is the fundamental process underlying speciation?

The evolution of biological barriers to gene flow. (B) Signup and view all the answers

In the context of a 'tug-of-war,' what forces are considered to be in opposition during speciation?

Selection and Recombination/Gene Flow. (A) Signup and view all the answers

Which geographic scenario involves populations diverging while geographically separated?

Allopatric Speciation. (A) Signup and view all the answers

What is a key characteristic of parapatric speciation?

Divergence of neighboring populations with some gene exchange. (D) Signup and view all the answers

What is considered the primary limiting factor for sympatric speciation?

Recombination eroding genetic linkage. (D) Signup and view all the answers

According to the text regarding bird morphology, what is the consequence of recombination in sympatry?

It erodes linkage between color and bill size loci. (C) Signup and view all the answers

Why does allopatric speciation facilitate the divergence of traits like bill size and color in the birds mentioned in the text?

Because geographic isolation allows for independent divergence in traits. (C) Signup and view all the answers

In the context of speciation, what does 'secondary contact' refer to?

The reuniting of populations that have previously diverged in allopatry. (C) Signup and view all the answers

What observation supports the hypothesis that divergent populations in sympatry are 'good species'?

Stable coexistence despite introgression. (D) Signup and view all the answers

What is the most important distinction when categorizing reproductive isolation barriers?

Prezygotic vs. postzygotic barriers (D) Signup and view all the answers

Which of the following exemplifies a pre-mating, prezygotic isolation barrier?

Different mating seasons or times. (C) Signup and view all the answers

A scenario where potential mates meet but do not mate due to differing courtship rituals falls under which of the following categories?

Pre-mating, prezygotic isolation. (A) Signup and view all the answers

Which of the following is an example of a postmating, prezygotic isolating mechanism?

Incompatible gametes. (C) Signup and view all the answers

Which scenario describes an 'extrinsic' postzygotic isolation mechanism?

A hybrid that cannot fit into either parent's ecological niche. (D) Signup and view all the answers

In the case of Mimulus lewisii and M. cardinalis, what is considered the second most important barrier to gene flow?

Pollinator differences. (B) Signup and view all the answers

Which of these statements is true regarding reproductive isolation?

Several reproductive barriers can act in sequence. (C) Signup and view all the answers

What is a key finding from the phylogenetic analysis of Atlantic shrimp species?

The closest relatives of some Atlantic shrimp species are Pacific species. (B) Signup and view all the answers

Which factor can lead to the fragmentation of a widely distributed species resulting in allopatric populations?

Habitat fragmentation due to climate change. (A) Signup and view all the answers

In the example of the Holbrookia maculata lizards, what does the observation of mixed genotypes suggest?

Ongoing gene flow between the white sand and dark soil populations. (B) Signup and view all the answers

Which of the following best describes the genetic findings for the malaria mosquito species complex?

High levels of introgression with divergent regions in the X chromosome maintaining species boundaries. (B) Signup and view all the answers

What role does the X chromosome play in the maintenance of species boundaries in malaria mosquitoes?

It contains regions that resist homogenization and maintain species differences. (A) Signup and view all the answers

What is the relationship between geographic and reproductive barriers in the speciation process?

They often work together during the speciation process. (B) Signup and view all the answers

In the context of the content, what does 'introgression' refer to?

The movement of genes between species through hybridization. (C) Signup and view all the answers

What term describes genetic incompatibilities arising from new substitutions that have not been tested in the background of each other?

Dobzhansky-Muller Incompatibilities (D) Signup and view all the answers

Which of the following is NOT a step in the process of reinforcement?

Selection favors the evolution of greater post-zygotic reproductive isolation. (D) Signup and view all the answers

What is the primary driving force behind reinforcement?

Adaptation to prevent the production of unfit hybrids. (D) Signup and view all the answers

In the context of reinforcement, what type of reproductive mechanisms are directly influenced by selection?

Pre-zygotic isolation mechanisms (B) Signup and view all the answers

What outcome is favored within the area of sympatry when diverging populations that were previously in allopatry come into secondary contact?

Alleles that reduce the degree of interbreeding (D) Signup and view all the answers

What is the primary outcome of speciation?

The evolution of biological barriers to gene flow (B) Signup and view all the answers

Which of the following best describes a postmating, prezygotic isolating barrier?

Incompatible genitalia prevents successful mating (A) Signup and view all the answers

Which of the following would be considered an 'intrinsic' postzygotic isolation mechanism?

Hybrid lethality (D) Signup and view all the answers

What type of reproductive barrier is associated with pollen from one plant species being unable to fertilize the ovule of another plant species?

Postmating, prezygotic isolation (A) Signup and view all the answers

According to the Dobzhansky-Muller model, what underlies the evolution of intrinsic hybrid sterility or inviability?

Differentiation at multiple loci with complementary fitness effects (C) Signup and view all the answers

What type of isolation is exemplified when hybrids do not fit into the ecological niches of either parental species?

Extrinsic postzygotic isolation (ecological) (A) Signup and view all the answers

Which of the following best describes 'mate recognition' as a postzygotic barrier?

Hybrid mating behavior is not recognized by either parent species (D) Signup and view all the answers

Study Notes

Speciation

Speciation is the evolution of biological barriers to gene flow
Study of speciation bridges the evolution of populations and the evolution of taxonomic diversity
Each branching point (node) in the tree of life marks a speciation event (origin of two species from one)
Speciation can be considered a tug-of-war between two sets of forces: Selection & Recombination/Gene Flow

Geographic Modes of Speciation

Allopatric: Populations diverge while separated by a geographic barrier that prevents/reduces gene flow
Parapatric: Neighboring populations diverge while still exchanging some genes (but not freely). Adjacent populations adapt to different habitats/niches and selection favors divergence. Reduction of gene flow is due to strong selection preventing colonization of the other habitat or the formation of hybrids.
Sympatric: Two new species emerge from a single ancestor without any geographic isolation and while exchanging genes freely. This speciation mode is highly controversial and unlikely to happen in nature.

Reproductive Isolation and Reinforcement

Reinforcement is an adaptation to prevent the production of unfit hybrids
Reinforcement generates selection favoring the evolution of stronger prezygotic reproductive barriers between emerging species
Species may diverge in allopatry and then spread back into secondary contact and isolation is not complete.
Alleles that reduce the degree of interbreeding can be favored in the area of sympatry
This is a form of direct selection for reproductive isolation

Prezygotic Barriers

Pre-mating: Potential mates don't meet; different habitats, different mating seasons/times. Potential mates meet but don't mate; different mating behavior in animals, different pollinators in plants
Postmating, prezygotic: Potential mates try to mate but can't form a zygote; incompatible genitalia, incompatible gametes

Postzygotic Barriers

Postzygotic: Hybrids are formed but have low fitness; "Intrinsic" mechanisms: Hybrid lethality, Hybrid sterility (physiological or behavioral); "Extrinsic" mechanisms: Ecological: hybrids don't fit into either ecological niche, Mate recognition: mating behavior not appropriate for either species

Example of "Intrinsic" Hybrid Sterility/Inviability

Example of a horse and a donkey resulting in a mule
Mules are infertile (cannot reproduce)

The Dobzhansky-Muller Model

Dobzhansky and Muller provided a theoretical solution where reproductive barriers are based on differences at two or more loci that have complementary effects on fitness
Substitutions at two or more loci can generate incompatible genotypes.
These new substitutions have never been tested in the background of the other

Hybrid Sterility Results from Genetic Incompatibilities

X chromosome has a major effect on sperm motility
Divergence between interacting loci yields incompatible interactions in hybrids

Character Displacement and Reinforcement

Three steps:
1. Populations diverge in allopatry
2. The two divergent populations come back in secondary contact
3. Selection acts against interbreeding, if hybrids have lower fitness Selection favors the evolution of greater reproductive isolation
Important Consideration: Reinforcement can only act on the evolution of prezygotic reproductive mechanisms

Clarification about Barriers

Geographic and reproductive barriers are not mutually exclusive, and instead often work together during the speciation process

Specific Examples (various):

Birds of Paradise: 39 species
Malaria mosquito (genus Anopheles): Lots of introgression between species, but divergent islands in the X chromosome maintain species boundaries
Types of reproduction barriers: behavioral, ecological, gametic, temporal
Different types of reproductive barriers: premating (before mating), postmating/prezygotic (after mating but before zygote forms), postzygotic

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Description

This quiz explores key concepts related to reproductive isolation and speciation processes. Questions cover topics such as premating isolation mechanisms, geographic scenarios of speciation, and the implications of timing in mating among sympatric species. Test your knowledge on these fundamental biological principles!