5. Adaptive Radiation

Question 1

Structure of the lecture

Answer 1

1. Understanding adaptive radiation
2. Intrinsic drivers
3. Extrinction drivers
4. Scale of adaptive radiation
5. Case study: Drivers of adaptive radiation in Darwin’s finches
6. Case study: Drivers of convergent radiation in Anoles lizards

Question 2

Define adaptive radiation

1.1

Answer 2

A pattern of species diversification, in which one lineage of a species occupies a diversity of ecological roles

Has ecological and phenotypic diversity in a rapidly multiplying lineage

Usually accompanied by morphological and physiological changes that elevate capacity to use environment

Question 3

What are the major patterns that define adaptive radiation?

1.2

Answer 3

• Stems from a single ancestor
• Increase in phenotypic disparities
• Large differences between forms
• The increase in number of species or taxa at higher levels decreases as niches are formed

Question 4

What are the 4 main intrinsic drivers of adaptive radiation?

2.1

Answer 4

Intrinsic drivers offer ecological opportunities

1. The appearance of new resources (e.g., controversial radiation of horses dependent on grasslands in North America)
2. The extinction of species (e.g., diversification of mammals and birds after end-Cretaceous extinction)
3. The colonisation of a new environment with few/absent competitors (e.g., in lakes/archipelagos)
4. Key innovations (e.g., wings in birds/bats)

Question 5

How can we model intrinsic drivers of adaptive radiation?

2.2

Answer 5

Intrinsic drivers of adaptive radiation are driven by ecological opportunity. Can be modelled by lineage-through time plots in which we can study the radiation of a lineage to fill the peaks of an adaptive landscape

Question 6

What are the 4 extrinsic factors that drive adaptive radiation

3.1

Answer 6

1. High standing genetic variation and introgressive hybridisation
2. Modularity and integration of traits
3. High phenotypic plasticity, which allows for behavioural flexibility and genetic assimilation
4. Dynamic genomes

Question 7

What is the difference between micro- and macro- evolution?

4.1

Answer 7

Micro-evolution occupies little space/time with limited variation and is usually found in one species/genus

Macro-evolution has large variation and occupies lots of space/time with, and is looking at an entire clade (e.g., all of the birds)

Question 8

What are Darwinian ideas of adaptive radiations?

4.2

Answer 8

Based on microevolution within adaptive zones. Adaptive radiations involve the accumulation of small mutations and differences over time in one particular lineage

Question 8

What are Simpsonian ideas of adaptive radiations?

4.2

Answer 8

Large adaptive jumps into new adaptive zones

Question 9

How did Cooney et al., 2007 understand the scale of adaptive radiation?

4.3

Answer 9

Measured bill diversity and avian diversification.

Measured the bill morphology of >2000 birds, and found that bill morphology expanded early during avian diversification (morphospace expansion), before packing into a narrow range of forms (morphospace packing)

Question 10

What was the evolutionary history of Darwin’s finches?

5.1

Answer 10

Generic-looking species that arrived in the Galapagos ~2.3mya

Most of the radiation has occurred in the last 1mya.

Repeated cycles of speciation

Many bill forms

Question 11

What did Grant and Grant, 2008, find about phases of evolution in Darwin’s finches?

5.2

Answer 11

Underwent a period of allopatry before undergoing a period of sympatry

Allopatric phase allowed for adaption to local food conditions, with some drift and non-adaptive processes, creating pre-zygotic isolation

Sympatric phase involved some pre-mating barriers, which still allowed for hybridisation to occur. Reinforcement of diversification via song divergence, which kept them apart

Question 12

What did Losos et al., 2015 find from whole genome analysis of Darwin’s finches

5.3

Answer 12

Evolution did occur in the last 1mya

Lots of hybridisations throughout the radiation

New insights showed 18 new species

Specific genes developing for different beak morphs, including crushing, probing, sharp, grasping, warbler and parrot

Question 13

What are the three main drivers of adaptive radiation in Darwin’s finches?

5.4

Answer 13

1. Geography
2. Ecological opportunity
3. Evolvability

Question 14

Describe the impact of geography on the adaptive radiation of Darwin’s finches

5.4.1

Answer 14

Galapagos are an isolated archipelago with lots of variation between islands in terms of elevation, biotic and abiotic factors, isolation, habitats and ecological opportunity

Drives allopatry and subsequent sympatry

Question 15

Describe the influence of ecological opportunity (Intrinsic factors)on the adaptive radiation of Darwin’s finches

5.4.2

Answer 15

Sari and Bollmer, 2017

Presence of Mockingbirds (5.5-1.5 mya), Mohoidae family (17-14mya) and Hawaiian Honeycreepers (~5.7mya) dictated the ecological niches that were available to the finches, and the timing of their diversification

Question 16

Describe the influence of ecological evolvability (Extrinsic factors)on the adaptive radiation of Darwin’s finches

5.4.1

Answer 16

High standing genetic variation in the ALX1 and HGMA2 locus, which control beak size and shape

Introgressive hybridisation in Darwin’s finches maintained high levels of genetic diversity

Modularity and integration of traits increased access to many combinations

Behavioural flexibility in terms of feeding

Question 17

How have Anoles convergently evolved across Greater Antilles?

6.1

Answer 17

Anoles repeatedly evolved to form a number of different morphs, no matter the location of their radiation

Can study the mtDNA relationships of this to understand

Question 18

3 factors that drove the convergent radiation of Anoles?

6.2

Answer 18

1. Similar adaptive landscape
2. Evolutionary constraints
3. Historical contingency

Question 19

Describe the influence of adaptive landscape on the convergent radiation of Anoles?

6.2.1

Answer 19

Appears to be 1/2 ecomorphs that occur repeatedly

These forms are likely to occupy the highest evolutionary peaks in the adaptive landscape

Can predict this by measuring resource availability

Question 20

Describe the influence of evolutionary constraints on the convergent radiation of Anoles?

6.2.2

Answer 20

Evolution is more likely in some directions due to genetic covariance, or developmental pathways

However, this is unlikely in this scenario due to a lack of genetic variance, since other morphs have been found

Question 21

Describe the influence of historical contingency on the convergent radiation of Anoles

6.2.3

Answer 21

Each radiation started from the same ancestral species, and in this case, similar starting conditions