L12. Diversification: Adaptive Radiation

Question 1

Adaptive Radiation

Answer 1

• evolutionary changes shape traits allowing organisms to adapt to their environment, and convey fitness advantages
• evidence: a significant association between environments and the morphological and physiological traits used to exploit those environments
• leads to the development of many species in a relatively short time
• seems to correlate with a sudden abundance of open niches

Question 2

Ecological niche

Answer 2

• specific place a species holds in its biotic and abiotic environment
• the physical space where it feeds/reproduces, the role it plays in the food chain of its community, and its interactions with other organisms
• no two species can hold the same niche in the same environment because one will always outcompete the other

Question 3

Creation of new open niches

Answer 3

• could occur through dispersal to a new environment
• innovation traits can create new previously unexploited niches
• modification of habitat is called ecosystem engineering
• could happen through mass extinction
• change in physical landscape (creation of new land by volcanic processes) (actually what happened in Darwin’s finches)

Question 4

New habitat volcanic island example

Answer 4

• single colonizing finch species gave rise to many species that evolved to fill diverse open niches
• common ancestor arrived 2 million years ago
• now 18 species
• differ in body size, beak shape, song and feeding behaviour
• Galapagos island

Question 5

New habitat rift lake example

Answer 5

• one of the largest adaptive radiations: East African cichlid fishes
• so many evolved in a short time (less than 10 million years)
• different sizes, variation in appendages and jaws
• eat different things

Question 6

Emptying niches: End-cretaceous extinction

Answer 6

• mass extinction (meteor impact and possibly other factors)
• loss of dinosaurs caused an abundance of empty niches
• led to incredible adaptive radiation in mammal species
• resulted in the domination of mammal species today

Question 7

Why did mammals recover and dinosaurs did not?

Answer 7

• up to 90% of mammals species may have been lost during extinction event but they were able to come back
• small size gave them a fast reproduction rate
• generalist habit means they could survive on a diverse range of foods

Question 8

Cambrian Explosion

Answer 8

• massive radiation
• rapid emergence of new traits
• maybe new environmental niches

Question 9

Key innovations in flowering plants

Answer 9

• coevolved with insect pollinators
• creation of niches through ecosystem engineering
• adaptive radiation: became attractive to pollinators, this is because pollinators greatly improved pollen transmission since an insect can travel much farther than wind dispersed pollen
• major diversification of angiosperm pollinators along with angiosperms (new pollination niches)
• first angiosperms arose in forests dominated by conifers
• over 35 Ma dominant plant group changed form conifers to angiosperm, one they were dominant they changed the abiotic and biotic landscape to favour their own growth
• explains why we see the majority of conifers in colder areas where angiosperms cannot thrive due to short growing seasons

Question 10

What about when species become more similar?

Answer 10

• convergent evolution: independent evolution of analogous traits in two or more lineages (trait in question is not present in the last common ancestor of both groups)

Question 11

Examples of convergent evolution

Answer 11

• bats and birds
• venom injection arose separately in cobras and vipers
• platypus and ducks
• scorpions and bees
• crabs
• seeds in plants

Question 12

Carcinization

Answer 12

“the urge to become a crab”
- a crab-like body plan has arisen independently 5+ times

Question 13

How to prove convergent evolution

Answer 13

map a trait into a phylogeny, look for the presence of trait in fossil ancestors

Question 14

What is the mechanism of convergent evolution

Answer 14

• similar environments shape similar traits
• certain traits are more easily modified (fewer gene mutations required, co-option of existing structures)

Question 15

Mimicry

Answer 15

• example of convergent evolution
• ex. non-toxic species evolving to resemble an unrelated/dangerous one to deter predation

Question 16

Parallel evolution

Answer 16

similar development of a trait in distinct species that are not closely related, but share a similar original trait, in response to similar evolutionary pressure
- this is different from convergent in that ancestors shared the trait
- ex. placental mammals and marsupials (each lineage developed similar forms on different continents after they diverged to fill similar niches

Question 17

Founder effect

Answer 17

• new population colonizing an island
• smaller than source population
• contains only a sub-set of the genetics of the original population
• may also have harmful recessive founder mutations
• leads to faster evolution because of genetic drift and the bottleneck effect (new mutation in a small gene pool makes a large overall contribution to genetic diversity compared to a large population)

Question 18

Founder mutation

Answer 18

rate mutation in one of the founding members of population
- makes super rare trait everywhere else super common in community

Question 19

Modern Genetic diversity

Answer 19

• like discussed before: highest diversity in Africa, lower in Europe, lowest in South America
• more rare alleles in Africa, this is because rare alleles are more likely to become lost in founder population unless they become dominant