L5 adaptive radiation 1

Question 1

What is adaptive radiation?

Answer 1

A pattern of rapid species diversification where a lineage evolves into multiple forms occupying diverse ecological roles, with coupled ecological and phenotypic divergence.

Question 2

What key features characterize adaptive radiation?

Answer 2

Diversification into many forms with new phenotypes that improve organismal fitness in specific ecologies.

Question 3

What essential criteria define adaptive radiation?

Answer 3

Evolution of tightly linked phenotypic and ecological traits initiating rapid diversification driven by ecological opportunity.

Question 4

How does species diversification rate change over time in adaptive radiations?

Answer 4

It initially increases rapidly as niches are filled, then diminishes as ecological space saturates.

Question 5

What is phenotypic disparity?

Answer 5

The increase in morphological and physiological differences among new forms as they specialize into distinct ecological niches.

Question 6

Why does diversification slow down in adaptive radiations?

Answer 6

Because available ecological niches (adaptive peaks) become filled, reducing opportunities for further divergence.

Question 7

What is ecological opportunity?

Answer 7

The availability of unoccupied or newly available niches that drive adaptive radiation.

Question 8

How do new resources drive ecological opportunity? Provide an example.

Answer 8

Emergence of new resources (e.g., expansion of grasslands) opens niches for radiation, as seen in concurrent insect–plant radiations.

Question 9

How can extinction of species create ecological opportunity? Provide an example.

Answer 9

Removal of dominant species frees niches for radiating lineages, as after the K–Pg extinction mammals and birds diversified.

Question 10

How does colonisation of new environments drive ecological opportunity? Provide an example.

Answer 10

Entering isolated settings like islands or lakes with few competitors allows rapid niche filling, as early colonists diversify before others arrive.

Question 11

What are key innovations? Provide an example.

Answer 11

Novel traits that open access to new environments (e.g., wings in birds enabling flight into aerial niches).

Question 12

What occurs as lineages radiate and fill adaptive peaks?

Answer 12

The rate of new phenotypic and species diversification slows as niches become saturated.

Question 13

What are the two main categories of drivers of adaptive radiation?

Answer 13

Extrinsic drivers (ecological opportunity) and intrinsic drivers (evolvability).

Question 14

What role does standing genetic variation play in evolvability?

Answer 14

High genetic diversity in populations provides raw material for rapid evolutionary change under new ecological opportunities.

Question 15

How does introgressive hybridisation enhance evolvability?

Answer 15

It transfers genetic information between species through hybridisation and backcrossing, expanding variation and evolutionary potential.

Question 16

How do modularity and integration affect evolutionary change?

Answer 16

Modularity allows traits to change independently for diverse outcomes, while integration links traits, directing coordinated adaptations.

Question 17

What role does phenotypic plasticity play in adaptive radiation?

Answer 17

It enables flexible trait expression in new environments, allowing initial survival and subsequent genetic assimilation of beneficial traits.

Question 18

What are dynamic genomes and how do they drive diversity?

Answer 18

Structural genomic changes (e.g., inversions, transposable elements) provide new genetic material for adaptive evolution.

Question 19

What is the debate between trait modularity and integration?

Answer 19

Whether trait independence (modularity) facilitates diverse phenotypes or trait linkage (integration) coordinates adaptations but may constrain variation.

Question 20

Why are Darwin’s finches a model system for adaptive radiation?

Answer 20

They exhibit rapid phenotypic divergence in beak morphology tied to ecological resource use, illustrating extrinsic and intrinsic drivers at work.

Question 21

How do Darwin’s finches demonstrate the link between phenotypic and ecological divergence?

Answer 21

Variation in beak shapes corresponds to specialized feeding niches, showing morphological adaptation to ecological roles.

Question 22

What does convergent evolution in Caribbean anole lizards illustrate?

Answer 22

Independent lineages evolving similar phenotypes in similar island habitats due to geographic isolation and ecological opportunity.

Question 23

How do fitness landscapes help visualize adaptive radiation?

Answer 23

They depict adaptive peaks (niches) and valleys, showing how lineages diversify rapidly into peaks then slow as peaks fill.

Question 24

What explains the lag phase in Darwin’s finch speciation?

Answer 24

After arrival, ~1.3 M years passed before rapid speciation began, indicating ecological opportunity alone isn’t enough—intrinsic evolvability factors must align with external drivers.

Question 25

What diversity of bill forms occurs in Darwin’s finches?

Answer 25

Bills vary (crushing, probing, sharp, parrot-like), each matched to distinct diets and ecological niches.

Question 26

What sequence of geographic phases drove finch diversification?

Answer 26

Initial allopatry (island isolation → drift, local adaptation, beak/song divergence) followed by sympatry with character displacement and reinforcement via song differences.

Question 27

How does song divergence act as a pre-mating barrier?

Answer 27

Juveniles imprint on father’s bill appearance and song, guiding mate choice to reduce gene flow, though some hybridisation persists.

Question 28

How does hybridisation influence finch phenotypic variation?

Answer 28

Introgressive hybridisation increases heterozygosity and beak-shape variance, adding raw material for selection.

Question 29

What did whole-genome analyses reveal about finch species and beak genes?

Answer 29

There are 18 species (including cryptic ones); key beak-development genes predate the radiation and are repeatedly reused during speciation.

Question 30

What three components underlie Darwin’s finch radiation?

Answer 30

Geography (isolated archipelago with new islands), ecological opportunity (early arrival, environmental fluctuations), and high evolvability (standing variation, hybridisation, modularity/integration, behavioral flexibility).

Question 31

How does introgression help maintain adaptive potential?

Answer 31

By replenishing genetic diversity lost to drift or fixation, ensuring capacity to adapt to environmental changes.

Question 32

What do haplotype blocks tell us about beak-shape genetics?

Answer 32

~28 distinct genomic blocks on different chromosomes control beak variation, indicating a modular genetic architecture.

Question 33

What proportion of SNPs are shared between tree and ground finches, and why is that important?

Answer 33

~40% shared SNPs, showing ancient standing variation recycled across lineages.

Question 34

Which loci are key for beak shape and size in finches?

Answer 34

The ALX1 locus (shape) and HMGA2 locus (size).

Question 35

How is craniofacial integration measured, and what pattern emerges?

Answer 35

Landmark-based morphometrics show a strong positive correlation between beak and skull shape, reflecting tight integration.

Question 36

How does craniofacial integration relate to radiation rates across bird groups?

Answer 36

Groups with higher integration (Darwin’s finches, Hawaiian honeycreepers) radiate faster; those with lower integration (some mockingbirds, honeyeaters) radiate less despite similar niches.

Question 37

What are the contrasting views on modularity vs. integration?

Answer 37

One view: integration channels rapid shifts along a 'line of least resistance.' The other: modularity enables independent trait variation. Both may operate at different scales or phases.

Question 38

Give examples of behavioral flexibility in Darwin’s finches.

Answer 38

Vampire finch blood-feeding on seabirds; ground finches innovating seed- and egg-cracking techniques.

Question 39

What does the Flexible Stem Hypothesis propose?

Answer 39

Ancestral behavioral flexibility lets populations exploit niches first, with genetic assimilation later fixing advantageous behaviors.

Question 40

How does genetic assimilation follow behavioral innovation?

Answer 40

Initially plastic behaviors become genetically encoded over generations, stabilizing new ecological adaptations.

Question 41

What ecomorphs do Anoles in the Antilles evolve into?

Answer 41

Grass–bush, trunk–ground, trunk–crown, and crown–giant types, each adapted to distinct vegetation structures.

Question 42

How do morphological and molecular analyses of Anoles differ?

Answer 42

Morphology groups by similar ecomorph; molecular phylogeny groups by island, indicating single colonization followed by in situ radiation.

Question 43

What factors underlie convergent evolution in Antillean Anoles?

Answer 43

Similar adaptive landscapes across islands, evolutionary constraints, and historical contingency producing recurrent ecomorphs.

Question 44

How do evolutionary constraints channel Anoles trait evolution?

Answer 44

Genetic correlations and developmental pathways direct change along 'lines of least resistance,' although alternative morphologies can arise.

Question 45

What is historical contingency in adaptive radiation?

Answer 45

The initial ancestral phenotype of colonists biases which adaptive peak they occupy, leading to predictable outcomes when starting points match.

Question 46

How do single-peak vs. rugged adaptive landscapes affect radiation?

Answer 46

Single-peak landscapes yield similar endpoints regardless of start; rugged landscapes lead to different peaks based on starting conditions.

Question 47

What distinguishes microevolutionary from macroevolutionary adaptive radiations?

Answer 47

Micro: ~1–2 M yr in confined locales, filling fine niches (e.g., island finches). Macro: deep time, broad ranges, great morphological disparity (e.g., all bird bills).

Question 48

What pattern is seen in phylogenetic morphospace analyses of bird bills?

Answer 48

A rapid early increase in disparity (steep slope) followed by a plateau or decline as niches saturate.

Question 49

What are the two models describing micro vs. macro radiation?

Answer 49

Early morphospace expansion (quantum leaps) and later morphospace packing (fine-scale niche partitioning).

Question 50

Give an example of macroscale bill diversity in birds.

Answer 50

The wide range from long, curved hummingbird bills to large, pouch-bearing pelican bills.

Question 51

Why is ecological opportunity necessary but not sufficient for adaptive radiation?

Answer 51

Intrinsic evolvability (genetic variation, developmental features) must align with available niches for radiation to proceed.

Question 52

What intrinsic features predispose lineages to radiation?

Answer 52

Genetic variation, developmental modularity, evolutionary constraints, and historical contingency.

Question 53

Why shouldn’t micro- and macroevolutionary radiations be equated directly?

Answer 53

They operate on different timescales with potentially distinct dominant processes at each scale.

Question 54

Which methodologies are essential to study adaptive radiation comprehensively?

Answer 54

Morphological studies, molecular phylogenetics, and ecological modeling.

Question 55

Why is the Antillean Anoles radiation a prime example of convergence?

Answer 55

Independent island radiations repeatedly yield the same ecomorphs, showing predictable evolution under similar ecological pressures and constraints.