L4 ecological speciation

Question 1

What are the two primary forms of speciation focused on in this course?

Answer 1

Ecological speciation (via divergent natural selection) and mutation-order speciation (differential fixation of mutations).

Question 2

Why is speciation considered a continuous process rather than a single event?

Answer 2

Because reproductive barriers accumulate gradually, and markers (biological, morphological, phylogenetic, geographic) are proxies with exceptions.

Question 3

Define vicariance in allopatric speciation.

Answer 3

Physical separation of a population by a barrier (e.g., uplift isolating a small population).

Question 4

Define colonization in allopatric speciation.

Answer 4

Separation of a population by dispersal to a new area (e.g., mainland to island colonization).

Question 5

What level of gene flow and selection characterizes parapatric speciation?

Answer 5

Medium gene flow and medium selection across adjacent or stepping-stone populations.

Question 6

What conditions make sympatric speciation possible?

Answer 6

High gene flow but very strong divergent selection within overlapping distributions.

Question 7

Why measure gene flow directly rather than using geographic distance as a proxy?

Answer 7

Because actual connectivity can vary (e.g., human‐introduced isolated populations have zero gene flow despite proximity).

Question 8

How do selection, drift, and gene flow interact in speciation?

Answer 8

Their balance determines whether populations diverge to full reproductive isolation on a geographic stage.

Question 9

Under what scenario can genetic drift alone lead to speciation?

Answer 9

In allopatry with very low gene flow, drift can suffice without strong selection.

Question 10

What is the Biological Species Concept?

Answer 10

Groups of actually or potentially interbreeding natural populations that are reproductively isolated.

Question 11

What is ecological speciation?

Answer 11

Evolution of reproductive barriers due to ecologically based divergent selection between environments.

Question 12

What is mutation-order speciation?

Answer 12

Reproductive isolation arising because different populations fix the same beneficial mutations in different orders, causing incompatibilities.

Question 13

How can sexual selection contribute to speciation?

Answer 13

By driving divergence in mating signals or preferences, leading directly to reproductive isolation.

Question 14

What is an indirect mechanism of ecological speciation?

Answer 14

Reproductive isolation as a by-product of adaptive divergence in non-mating traits (e.g., genomic incompatibilities).

Question 15

Why are plants more capable of sympatric speciation than animals?

Answer 15

Because plants can survive polyploid mutations, instantly creating reproductive barriers without geographic separation.

Question 16

Give an example of hybrid speciation.

Answer 16

Formation of a new species through interbreeding of two distinct parent species.

Question 17

How does mutation-order speciation explain divergence under similar ecological conditions?

Answer 17

Random order of mutation fixation leads to different genetic combinations and incompatibilities.

Question 18

Summarize the roles of geography in speciation.

Answer 18

Geography (vicariance, parapatry, allopatry) sets the stage by modulating gene flow, serving as a proxy for connectivity.

Question 19

What are the two broad categories of speciation via natural selection?

Answer 19

Ecological speciation and mutation-order speciation.

Question 20

Why is it difficult to delineate species boundaries?

Answer 20

Because speciation is gradual, markers are proxies, and there is variability across taxa and exceptions.

Question 21

What does the three-spined stickleback system illustrate about divergence and speciation?

Answer 21

Divergence along separate fitness peaks can occur (different morphotypes) without complete reproductive isolation, showing speciation is a continuum.

Question 22

What are the three key requirements for ecological speciation?

Answer 22

(1) Source of divergent selection, (2) Pre- or post-mating reproductive isolation, (3) Genetic mechanisms linking ecological traits to isolation.

Question 23

Give two abiotic factors that drive divergent selection.

Answer 23

Altitude (e.g., high versus low elevation), temperature extremes (very cold vs. very hot environments).

Question 24

Name two biotic factors that can create divergent selection pressures.

Answer 24

Predation regimes (presence/absence of predators) and competition for food resources.

Question 25

What is ecological character displacement?

Answer 25

Evolution of extreme, divergent phenotypes in sympatric species due to direct competition for similar resources.

Question 26

How do reciprocal transplant experiments detect local adaptation?

Answer 26

By moving individuals between environments and observing 'crossover' fitness effects—high fitness in home habitat but low fitness in foreign habitat.

Question 27

Describe a field-based method for measuring divergent selection.

Answer 27

Tracking survival, growth, or reproduction of individuals with varying traits in natural populations (e.g., Western chorus frogs’ body shape under different predator regimes).

Question 28

How was the adaptive landscape 'reverse-engineered' in Darwin’s finch studies?

Answer 28

Measuring natural seed-size distributions on islands to model and predict corresponding beak-size adaptations across finch populations.

Question 29

What is pre-mating reproductive isolation via habitat preference?

Answer 29

When individuals preferentially remain and mate in their native habitat, reducing interbreeding (e.g., lake vs. stream sticklebacks in mark–recapture studies).

Question 30

What evidence shows sticklebacks exhibit habitat fidelity?

Answer 30

Mark–recapture data reveal that few individuals switch between lake and stream habitats, and those that do have intermediate morphologies.

Question 31

Define immigrant inviability with an example.

Answer 31

Reduced survival of migrants in non-native habitats, as shown by Atlantic Molly from sulphidic vs. non-sulphidic waters performing poorly when transplanted.

Question 32

What physiological adaptation allows Atlantic Molly to inhabit sulphide-rich waters?

Answer 32

Evolved detoxification and respiratory mechanisms counteracting hydrogen sulphide’s metabolic disruption.

Question 33

Name a post-mating, post-zygotic isolation mechanism in ecological speciation.

Answer 33

Ecologically dependent selection against hybrids or intrinsic genetic incompatibilities reducing hybrid fitness.

Question 34

Why might some divergent environmental factors fail to show selection effects?

Answer 34

Due to low statistical power or examining the wrong traits, making true divergent selection hard to detect.

Question 35

How do genomic tools aid in linking selection to reproductive isolation?

Answer 35

Whole-genome sequencing can identify loci under divergent selection that also contribute to mate choice or incompatibilities.

Question 36

Summarize how trade-offs underpin local adaptation in ecological speciation.

Answer 36

Organisms face fitness trade-offs across environments, so alleles beneficial in one habitat reduce fitness in another, promoting divergent adaptation and isolation.

Question 37

What is ecologically dependent selection against hybrids?

Answer 37

Environment‐dependent fitness reduction in hybrids beyond intrinsic genomic incompatibilities.

Question 38

In the leaf beetle study, how did F₁ hybrids perform compared to pure types?

Answer 38

F₁ hybrids had lower growth rates in both maple and willow environments, reflecting both environmental mismatch and intrinsic incompatibilities.

Question 39

How did backcross experiments isolate ecological effects in the leaf beetle study?

Answer 39

By comparing F₁×maple and F₁×willow backcrosses (same genetic load) across both host environments, revealing environment‐specific fitness trade-offs.

Question 40

What is sensory drive in ecological sexual isolation?

Answer 40

Adaptive divergence of signaling traits (e.g., coloration, calls) driven by habitat‐dependent signal transmission efficiency.

Question 41

Give an example of ecology influencing bird mate choice.

Answer 41

In some species, feeding strategy–induced beak morphology alters song structure, leading to assortative mating based on habitat‐tuned signals.

Question 42

Define pleiotropy linking ecological traits to reproductive barriers.

Answer 42

A single gene simultaneously affects an ecological adaptation and a mating or isolation trait, directly coupling divergence and isolation.

Question 43

How does linkage disequilibrium facilitate ecological speciation?

Answer 43

Close chromosomal proximity of ecological‐trait genes and isolation genes prevents recombination from breaking their association.

Question 44

What stickleback evidence suggests pleiotropy or tight linkage?

Answer 44

A ~16 Kb haplotype block shows high LOD scores for multiple phenotypes (e.g., armour plating), implying shared genetic control.

Question 45

Why is pleiotropy stronger than linkage disequilibrium in maintaining trait associations?

Answer 45

Pleiotropy has no chance of recombination separating traits, whereas linkage disequilibrium can be eroded by crossovers.

Question 46

How can reproductive isolation evolve without ecological divergence?

Answer 46

Geographic isolation and genetic drift can generate barriers first, with ecological differences arising later (e.g., Himalayan warblers).

Question 47

What scenario defines mutation‐order speciation?

Answer 47

Parallel adaptation to the same environment via different mutational paths in allopatry, leading to genomic incompatibilities.

Question 48

How do mitochondrial‐nuclear interactions drive mutation‐order speciation?

Answer 48

Different populations accumulate distinct mitochondrial mutations and compensatory nuclear restorers, causing hybrids to malfunction.

Question 49

What is meiotic drive and its role in speciation?

Answer 49

Selfish elements bias gamete transmission (e.g., disabling rival sperm), creating fertility costs and divergent genetic conflicts.

Question 50

How do transposons contribute to mutation‐order speciation?

Answer 50

Rapid movement creates lineage‐specific genomic changes, leading to incompatibilities and reduced hybrid fitness.

Question 51

Describe the Monkey Flower example of mutation‐order speciation.

Answer 51

Lineages evolved different mitochondrial distortions and nuclear restorer genes, so hybrids suffer inviability when crossed.

Question 52

Contrast gene‐flow requirements for ecological vs. mutation‐order speciation.

Answer 52

Ecological speciation can occur with gene flow under divergent selection; mutation‐order speciation requires reduced gene flow for distinct mutation paths.

Question 53

Why can mutation‐order speciation not generate ecologically based isolating barriers?

Answer 53

Because selective pressures are concordant across populations, not divergent ecologies driving isolation traits.

Question 54

How does ecologically dependent selection against hybrids reinforce reproductive isolation?

Answer 54

Hybrids incur additional environment‐specific fitness losses, strengthening postzygotic barriers via trade‐offs.

Question 55

What two genetic mechanisms bridge ecological adaptation and reproductive isolation?

Answer 55

Pleiotropy and linkage disequilibrium coupling adaptive traits with isolating traits.

Question 56

Why doesn’t every ecological divergence result in ecological speciation?

Answer 56

Divergence must evolve before or alongside isolation; if isolation precedes ecology, ecological differences are secondary, not causative.