Speciation

What is the Biological Species Concept

Group of organisms capable of producing fertile offspring

What is a Ring Species?

2 end populations reproductively isolated but indirectly connected by a continuous chain of reproducing populations (w/ gene flow)

What is the Morphological Species Concept?

Defines a species by morphological characteristics

What is the Morphological Species Concept mainly used for?

Extinct species where other info is unavailable

What does the Morphological Species Concept rely on?

Subjective criteria - depends on individual

What is the issue with Morphological Traits?

May not be meaningful in terms of bio species concept

What is a Cryptic Species?

Species that are reproductively isolated but morphologically similar

What is Speciation?

The origin of new species, occurs by reproductive isolation

What is Allopatric Speciation?

Gene flow interrupted when a population is divided by an environment - mental barrier

What is Sympatric Speciation?

Speciation in geographically overlapping populations

How does Allopatric Speciation work?

• 2 populations become reproductively isolated

• Differences build up

• If re-introduced, won’t interbreed

How does Sympatric Speciation work?

• Reproductively isolated

• Not geographic - some other mechanism

What is Reproductive Isolation?

Reproductive barriers stop 2 species interbreeding to produce fertile offspring

Fertility of Hybrids

Occasionaly fertile but infertile if reproductive barriers are incomplete

How are reprodutive isolation mechanisms classified?

Whether factors act before or after fertilisation

What is a pre-zygotic barrier?

Act before fertilisation of zygote

What is a post-zygotic barrier?

Act after fertilisation of zygote

How do Prezygotic barriers block fertilisation?

• Impeding different species from mating

• Preventing successful completing of mating

• Hindering fertilisation is mating is successful

How do Prezygotic Barriers impede different species from mating?

Habitat Isolation, Temporal Isolation

What is Temporal Isolation?

Breed at different times, seasons, years

What is the effect of mechanical isolation?

Morphological differences prevent mating, eg genitals on different sides

What is behavioural isolation?

Different courtship rituals or unique behaviours

What is Gametic Isolation?

Sperm may not fertilise eggs

How do post-zygotic barriers block hybrid survival & reproduction

• Reducing hybrid survival

• Reducing hybrid mating success

What is the effect of reducing hybrid survival?

Reduces hybrid viability

What is the effect of reducing hybrid survival?

Reduces hybrid fertility in 1st generation

What is the effect of reducing ongoing hybrid mating success?

Hybrid breakdown in 2nd generation

When can Hybrids occur?

When reproductive barriers are incomplete

What is a Hybrid Zone?

Region where members of different species mate and produce hybrids

What is the benefit of Hybrid Zones?

Can tell us about mechanisms of reproductive isolation

Long-term Outcomes of Hybrid Zones

• Reinforcement - Differences increase until no more hybrids

• Fusion - Barriers weaken until there’s 1 species

• Stability - Hybrids continue to be produced

How does reinforcement of Hybrid Zones work?

• Rate of hybridization decreases

• Pre-zygotic mechanisms appear

• Reproductive isolation so complete speciation (no gene flow)

How does Reinforcement of Hybrid Zones compare to Allopatric/Sympatric Speciation?

Stronger

Barriers of Allopatric Speciation

Strong geographic barriers

Barriers of Sympatry Speciation

Reproductive barriers have to be reinforced

When can Hybrid Zone Fusion occur?

If there’s continued substantial gene flow in hybrid zone

What is the product of Hybrid Zone Reinforcement?

2 species without gene flow

How does Hybrid Zone Fusion happen?

Reproductive barriers weaken & separated species can fuse

What is the product of Hybrid Zone Fusion?

1 species

When are Hybrid Zones stable?

If gene flow continues to occur

How is fusion/reinforcement prevented in Hybrid Zone Stability?

Involves a small overlap between populations

What is the product of Hybrid Zone Stability?

2 species w/ gene flow