Speciation II (DONE)

Question 1

What is genetic drift, and how can it affect populations?

Answer 1

a mechanism of evolution that involves random changes in the genetic composition of small populations- can reduce genetic variability and, over time may contribute to speciation

Question 2

What was Ernst Mayr’s idea about genetic drift and speciation in island populations?

Answer 2

Isolated populations may undergo a genetic revolution, creating reproductive barriers and potentially leading to speciation.

Question 3

How does the bottleneck effect influence genetic variability in small populations?

Answer 3

bottleneck effect occurs when a small number of individuals form a new population, resulting in a loss of genetic variability. This reduced variability can be compounded by challenges in adapting to new environments, potentially leading to further genetic changes.

Question 4

What happens to genetic variability if a small population survives over time?

Answer 4

If the small population survives, genetic variability may eventually rebuild. However, the genetic composition will differ from the original population, which could lead to reproductive isolation and speciation.

Question 5

What did the Drosophila study reveal about assortative mating after genetic drift?

Answer 5

Drosophila study, which involved extreme bottlenecks, found no overall increase in assortative mating within isolated populations- suggests that genetic drift alone may not drive speciation.

Question 6

What is Assortative Mating?

Answer 6

a pattern where individuals prefer mates based on similarity (positive assortative mating) or difference (negative assortative mating) in certain traits

Question 7

Why is genetic drift alone unlikely to produce speciation?

Answer 7

While genetic drift can cause random changes in genetic makeup, the specific differences required for speciation, like mate choice preferences or hybrid incompatibility, are unlikely to arise solely from this mechanism.

Question 8

What are key factors that typically drive speciation?

Answer 8

usually driven by a combination of mechanisms, such as natural selection, sexual selection, and geographic isolation, rather than by genetic drift alone.

Question 9

What is polyploidy?

Answer 9

individuals have three or more sets of chromosomes.

Question 10

What are the two main types of polyploidy, and how do they differ?

Answer 10

Autopolyploid: Chromosome doubling within a single species.
Allopolyploid: Chromosome doubling from hybridization between closely related species.

Question 11

Why does polyploidy create reproductive isolation?

Answer 11

Mating between individuals with different chromosome numbers (e.g., 2x and 4x) often produces sterile or unviable offspring, such as those with 3x chromosomes.

Question 12

Is polyploidy considered instant speciation?

Answer 12

Theoretically, yes, but in reality, some hybrids survive, allowing limited gene flow. However, reproductive isolation is still extensive.

Question 13

Is polyploidy more common in plants or animals?

Answer 13

It is much more common in plants, accounting for only 2-4% of speciation events.

Question 14

Why might polyploid organisms thrive?

Answer 14

They often produce more genetic products, grow faster, and are better suited to extreme environments.

Question 15

How significant is polyploid speciation in evolution?

Answer 15

It is a key mechanism for some species, though less common than originally thought. Genetic drift is now considered less significant compared to mechanisms like polyploidy.

Question 16

What is hybrid speciation?

Answer 16

occurs when two closely related species produce hybrids that form a new, viable species, often thriving in extreme environments.

Question 17

How do hybrids usually perform in natural environments?

Answer 17

Most hybrids struggle to survive, but some adapt well in extreme or unique conditions, leading to hybrid speciation.

Question 18

What does chromosomal mapping reveal about hybrids?

Answer 18

Hybrids often contain large chromosome segments from both parental species, reflecting their mixed genetic origin.

Question 19

Why are extreme environments important for hybrid speciation?

Answer 19

These environments may favor unique hybrid traits, giving them a survival advantage over parental species.

Question 20

Where does hybrid speciation commonly occur?

Answer 20

It happens in regions where distinct species overlap due to historical or environmental changes, such as cichlids in East Africa or sparrows in the Mediterranean.

Question 21

How does hybridization contribute to adaptive radiations?

Answer 21

Hybridization can introduce genetic diversity, fueling rapid diversification in environments like lakes or extreme habitats.

Question 22

How does divergent natural selection lead to speciation?

Answer 22

Populations in different environments experience unique selective pressures, evolving distinct genotypes. This divergence reduces hybrid fitness and reinforces reproductive isolation, resulting in ecological speciation.

Question 23

What is uniform selection, and how does it differ from divergent selection?

Answer 23

Uniform selection occurs when populations in similar environments evolve different genotypes due to random mutation order. Unlike divergent selection, it does not rely on environmental differences to drive genetic divergence.

Question 24

What is mutation order speciation, and what causes it?

Answer 24

Mutation order speciation occurs when isolated populations accumulate mutations in different sequences. These mutations fix in their respective populations and lead to genetic incompatibilities when the populations come into secondary contact.

Question 25

What does the Dobzhansky-Muller model describe?

Answer 25

It explains how genetic incompatibilities arise between populations due to mutations at different loci during isolation, which disrupt hybrid fitness upon secondary contact.

Question 26

How does the Dobzhansky-Muller model work?

Answer 26

1. A population splits into two isolated groups (allopatric speciation).
2. Each group accumulates mutations at different loci (e.g., A and B).
3. Mutations fix in each population if advantageous.
4. When populations re-contact, hybrids (AaBb) face disrupted genetic networks, lowering hybrid fitness.

Question 27

What is parallel evolution, and how does it relate to speciation?

Answer 27

occurs when populations in similar environments evolve along the same genetic pathways independently, leading to similar traits and potential reproductive barriers.

Question 28

Why is the order of mutations significant in speciation?

Answer 28

The order of mutations determines whether genetic incompatibilities develop. Different mutation sequences in isolated populations can create barriers to reproduction, even in identical environments.

Question 29

How do divergent and uniform selection mechanisms differ in their role in speciation?

Answer 29

Divergent selection arises from different environments causing genetic divergence, while uniform selection involves different mutation orders in similar environments, leading to incompatibilities without environmental variation.

Question 30

What is ecological speciation?

Answer 30

Ecological speciation occurs when populations diverge due to different ecological pressures (e.g., food sources, climate). Over time, genetic differences accumulate, leading to reproductive isolation and eventually new species.

Question 31

What is allopatric speciation and how does divergence occur?

Answer 31

Allopatric speciation happens when a population is geographically separated by a barrier (e.g., mountain, river). Isolated populations adapt to different environments and experience different selection pressures. Over time, genetic differences accumulate, reducing interbreeding, and leading to reproductive isolation and speciation.

Question 32

What happens when diverged populations come into secondary contact?

Answer 32

When diverged populations meet again, their hybrids often have reduced fitness due to genetic incompatibilities. These hybrids are less fit in either environment, lowering their survival or fertility.

Question 33

What is reinforcement in speciation?

Answer 33

when natural selection strengthens reproductive isolation between two diverging populations. If hybrids are less fit, individuals that avoid mating with the other population are favored, further isolating the populations and promoting speciation.

Question 34

How does reduced willingness to mate across environments support ecological speciation?

Answer 34

shows that ecological factors, such as resource use, can lead to reproductive isolation. As populations adapt to their environments, they become less likely to interbreed, reinforcing speciation.

Question 35

What are the predictions of the ecological speciation model?

Answer 35

1. Strong divergent selection leads to faster evolution of reproductive isolation.
2. Ecological selection reduces hybrid fitness due to trade-offs in traits for different niches.
3. Traits under divergent selection can fuel reproductive isolation (by-product mechanism).
4. Parallel evolution of mating incompatibilities occurs in populations from similar environments.

Question 36

How is the rate of evolution of reproductive isolation related to divergent selection?

Answer 36

When environments are highly different, strong divergent selection leads to faster evolution of reproductive isolation. The greater the ecological difference, the quicker the speciation process.

Question 37

How does ecological selection affect hybrid fitness?

Answer 37

Ecological selection reduces hybrid fitness because hybrids may fall between the ecological requirements of both parental niches, making them less fit in both environments.

Question 38

How do traits under divergent selection influence reproductive compatibility?

Answer 38

Traits under divergent selection, such as those related to ecological adaptation, can contribute to reproductive isolation. These traits may also become linked to mate choice, reinforcing isolation between populations.

Question 39

How does parallel evolution relate to mating incompatibilities in ecological speciation?

Answer 39

In similar environments, populations evolve similar traits, making reproductive incompatibilities less likely. However, when populations are in different environments, environmental factors drive divergence in traits, leading to stronger reproductive isolation.

Question 40

What is expected in terms of trait overlap over time during ecological speciation?

Answer 40

If genetic divergence follows ecological divergence, we expect a correlation between ecological trait differentiation and genetic divergence. Over time, as populations adapt to different niches, the likelihood of overlap in traits and gene flow decreases.

Question 41

What is a by-product mechanism in ecological speciation?

Answer 41

A by-product mechanism occurs when ecological traits, such as body size or coloration, influence reproductive isolation indirectly. These traits may affect mate choice, and differences in these traits may arise due to adaptation to different environments.

Question 42

How does beak shape relate to song in Galapagos finches (by-product mechanism)?

Answer 42

In Galapagos finches, beak shape and song are correlated. Since song is used as a mate choice cue, ecological factors influencing beak shape can also indirectly affect mating preferences, contributing to reproductive isolation.

Question 43

How does body size influence mate choice in sticklebacks (by-product mechanism)?

Answer 43

Sticklebacks prefer mates with similar body sizes. This preference is influenced by ecological differences in body size, showing that traits shaped by the environment can play a role in mate choice and reproductive isolation.

Question 44

How does coloration affect mate choice in sticklebacks (by-product mechanism)?

Answer 44

Sticklebacks from different environments exhibit different nuptial coloration, influenced by water color. Females prefer males with coloration that matches their environmental background, demonstrating that ecological factors influence mate choice and reinforce reproductive isolation.

Question 45

How does temporal isolation contribute to speciation in apple maggot flies (by-product mechanism)?

Answer 45

Apple maggot flies and hawthorn flies emerge at different times, preventing mating. This temporal isolation, driven by their food sources, leads to reproductive isolation and helps form distinct ecotypes.

Question 46

How does assortative mating occur in apple maggot flies (by-product mechanism)?

Answer 46

Apple maggot flies have a strong preference for apples, while hawthorn flies prefer hawthorns. This preference for specific food sources results in assortative mating, further promoting reproductive isolation between the two ecotypes.

Question 47

How does parallel evolution relate to mating incompatibilities in ecological speciation?

Answer 47

When populations evolve in similar environments, they tend to evolve similarly. This can lead to the development of mating incompatibilities in both populations, which reinforces reproductive isolation and drives speciation.

Question 48

What evidence supports parallel evolution in sticklebacks?

Answer 48

In studies of benthic and limnetic sticklebacks from different lakes, both populations showed similar mating preferences and avoided mating with individuals from different ecotypes, suggesting ecological speciation driven by similar environmental pressures.

Question 49

How does reinforcement contribute to ecological speciation in sticklebacks?

Answer 49

In an experiment with limnetic-like and benthic-like populations, the mating preferences between ecotypes were strengthened, supporting the idea of reinforcement, where selection favors mating between similar ecotypes to avoid hybrid incompatibilities.

Question 50

How can phylogenetic constraints affect parallel evolution in ecological speciation?

Answer 50

If two populations evolving in similar environments share a common origin, it suggests that their evolutionary path is constrained by their phylogenetic history, reducing the independence of their evolution and undermining the idea of complete parallel evolution.

Question 51

How does ecological compatibility influence mating in beetles?

Answer 51

In beetles feeding on different plants (e.g., willows vs. maples), populations that share the same food source are more likely to mate with each other, even if they are distantly related. This supports the idea that ecological compatibility influences mating preferences, driving speciation.