10 Speciation and The Origins of Biodiversity

Question 1

Phenotypic discontinuities can be misleading (2)

Answer 1

Cryptic species - look the same but actually independent

Polytypic species - look different but actually one species

Question 2

Species meaning and description

Answer 2

units with independent evolution because of barriers to gene flow

Interbreed with other members of the population + can‘t produce viable offspring with members of other species

Genetic isolation

Evolutionarily independent

Often appear discontinuous

Question 3

Gene flow definition

Answer 3

distinct in genetic composition (variant frequency, variant pressence) / absence of viable, fertile hybrids

Question 4

Prezygotic isolation - barriers before fertilisation

Answer 4

Temporal / ecological / behavioural / mechanical / gametic

Question 5

Gametic isolation (oceans example)

Answer 5

In oceans, selective use of sperm —> similarly, heterospeifc pollen doesn’t grow well in plants —> in insects, sperm competeion is biased to sperm of its own species

Question 6

Postzygotic isolation - barriers after fertilisation

Answer 6

Reduced hybrid fertility - babies sterile / babies die

Question 7

Allopatric species formation

Answer 7

complete geographical isolation

Question 8

The paradigm

Answer 8

Many mammal radiations come after the landscape, implying dispersal

Question 9

Sympatric species formation

Answer 9

reproductive isolation without graphical isolation —> consider a mutation which insect preference to lay eggs on new host plant / this gives genetic isolation when mating occurs on host plant

Single beneficial mutations - instantaneous mating barriers

Question 10

Unselected incompatibilities

Answer 10

Accumulation of mutations - overtime new variation will be added to isolated population via mutation, drift an selection (untested gene interactions if come in contact)

Question 11

Postzygotic isolation can aslo be ecological…

Answer 11

Selection for traits that help individuals with the local environment

Question 12

Divergence in allopatry may change diet / reproduction preferences

Answer 12

Alternatively do, interefere —> 2 outcomes (extinction of 1 species OR rescue through character displacement

selection favours individual species that don’t interefere)

Question 13

Ecological character displacement

Answer 13

selection for each species to utilise different niche

Question 14

Generation of biodiversity requires… (2)

Answer 14

1. Evolution of reproductive isolation (allopatry, peripatetic, sympathy —> divergence)
2. Distinctions between species that permit coexistence - resource use, mate choice

Natural selection may produce these through process of character displacement but may be constrained in doing so

Question 15

Diversification depends on niche space (description)

Answer 15

Lots of diversity to start (empty niches) (adaptive radiation) —> diversification then slows as niches become filled

Question 16

Diversification observed related to resource abundance

Answer 16

Generation of reproductive isolation initially important —> later, saturation —> new species limited by niche availability —> mating habitat —> resource abundance

Question 17

Adaptive radiation

Answer 17

burst of speciation in new unexploited habitats, as any new species formed can find new niches

Question 18

Initial barriers that allow divergence (3)

Answer 18

1. No dispersion - vicariance only source of isolation
2. Low dispersion - can reach new pla es occasionally, but population has integrity vs gene flow (vicariance is viable as well)
3. High dispersion - can reach new places easily but these then have gene flow to source - vicariance unlikely

Question 19

Speed of divergence when separate (mammals)

Answer 19

Mammals - very low tolerance to hybridisation - hybrid in viability evolves quickly (max 3MYA in mammals vs 20MYA in birds and amphibia)

Fast in mammals because placentation hypothesis —> foetal viability requires internal development and correct interface with the mother / immunological tolerance stretched - hybrids that are genetically distinct are rejected

Question 20

Biological innovation

Answer 20

allow new ways of living / new niche space —> diversification

Question 21

Taxa can vary intrinsically in speciation rate (2)

Answer 21

1. Dispersal capacity —> barriers to gene flow
2. Features of biology that affect rate of evolution of reproductive isolation (eg. Pregnancy)

Question 22

Mayr’s definition of a species

Answer 22

Biological species concept (BSC)

Species as a group of interbreeding populations that are reproductively isolated from other such groups.

This means individuals within a species can produce fertile offspring together, but they cannot reproduce successfully with members of other species.

Question 23

Hybrid in viability

Answer 23

The hybrid offspring do not develop properly or die early

Question 24

Hybrid sterility

Answer 24

Hybrid is sterile

Question 25

Geographic isolation

Answer 25

Species can become geographically isolated through physical barriers such as mountains, rivers, or oceans, which prevent gene flow between populations

Question 26

Allopatric speciation

Answer 26

Populations are geographically isolated and evolve separately

Question 27

Sympatric speciation

Answer 27

Same geographic area, typically due to ecological or behavioural differences

Question 28

Parapatric speciation

Answer 28

Populations are adjacent but experience different environmental pressures across a gradient

Question 29

Genetic divergence

Answer 29

Isolated populations accumulate genetic differences due to mutations, genetic drift, and different selective pressures

Question 30

Reproductive isolation

Answer 30

When populations come into contact again after long periods of isolation, genetic differences may prevent successful interbreeding (eg. through prezygotic or postzygotic isolation), leading to the formation of new species

Question 31

Niche space

Answer 31

The specific environmental conditions and resources a species uses in an ecosystem

Question 32

Adaptive radiation

Answer 32

The rapid diversification of a species into many different forms to exploit various ecological niches

This often occurs after a new habitat is colonized or after mass extinctions open up new niches

Question 33

Factors that enhance or constrain evolution

Answer 33

Available Niche Space - The greater the unfilled niche space, the more opportunities for adaptive radiation

Environmental Change - Environmental changes (continental drift / climate change) can create new ecological niches and drive speciation

Question 34

Example of adaptive radiation

Answer 34

Different finch species on the Galápagos evolved distinct beak shapes to exploit various food sources, showing adaptive radiation

Question 35

Dispersal definition

Answer 35

Movement of individuals from their birthplace to new areas

Dispersal biology affects gene flow and speciation

Question 36

Effect on speciation - high dispersal

Answer 36

Leads to greater gene flow between populations, slowing speciation

Question 37

Effect on speciation - limited dispersal

Answer 37

Populations that are isolated by distance or barriers experience reduced gene flow and more genetic divergence, increasing the potential for speciation.

Question 38

Pregnancy and isolation

Answer 38

Pregnancy in mammals can increase the rate of postzygotic isolation by prolonging the developmental period, which may lead to more genetic incompatibilities

Question 39

How does pregnancy effect evolution

Answer 39

Pregnancy allows for more complex interactions between maternal and paternal genes, increasing the possibility of genetic mismatches

Question 40

Example of biological change driving adaptive radiation

Answer 40

The Evolution of the Vertebrate Limb

The modification of the tetrapod limb allowed vertebrates to adapt to diverse terrestrial environments, leading to adaptive radiation into amphibians, reptiles, birds, and mammals.