21 - Speciation

Microevolution

Changes in allele frequencies overtime in a POPULATION

-> still the SAME species

Macroevolution

Large changes in allele frequencies

-> NEW species

Speciation

One species that splits into 2 (or more) species

Leads to diversity of life (~1.8 million spp identified)

Morphological Species Concept

Divides spp into body shape and other structural features

What does the morphological species concept apply to?

Asexual organisms

Sexual organisms

Fossils

Ecological Species Concept

Ecological Niche

-> How a spp interacts with its living AND non-living environment

What does the ecological species concept apply to?

Sexual organisms

Asexual organisms

Ernst Mayer: Species

- A group of populations that have the potential to interbreed in nature and reproduce viable, fertile, offspring

- Share common Gene Pool

- Gene flow between populations of the same spp

- Reproductive Isolation

Ernst Mayer: Reproductive Isolation

Species do not exchange genes with DIFFERENT species

What does Ernst Mayer's theory not apply to

Asexually reproducing organisms

Fossils

What is Reproductive Isolation

Mechanisms that PREVENT members of different spp from interbreeding and producing viable, fertile, offset

What does reproductive isolation do?

Prevents gene flow between species

When does a Pre-Zygotic Barrier happen

Occurs BEFORE the zygote is formed

-> Prevents FERTILIZATION from happening

Prevent Mating Attempts

- Habitat Isolation

- Temporal Isolation

- Behavioral Isolation

What is habitat isolation?

Species live in the same geographic area but live and breed in different habitats (located in the same area)

What is temporal isolation?

Breed at different times (day, seasons, years)

What is behavioral isolation?

Behaviors that are unique to a spp that ENABLES individuals to recognize potential mates

What is an example of behavioral isolation?

Courtship rituals

Females respond to males who do the right behavior

What are the two ways mating IS attempted but fertilization is PREVENTABLE?

Mechanical Isolation

Gametic Isolation

What is mechanical isolation?

- The make reproductive organ shape is compatible with female of SAME spp

- Lock and Key genitalia

What are some examples of mechanical isolation?

- Wide flower -> Bees

- Long, tube flower -> Hummingbirds

What is gametic isolation?

- Molecular or chemical differences between species

- Egg and Sperm are incompatible and fertilization is PREVENTED

When does a Post-Zygotic barrier happen?

Occurs AFTER the zygote is formed

What does a post-zygotic barrier do?

PREVENTS hybrid zygote from developing into a viable, fertile adult (can not produce offspring)

What are the post-zygotic barriers?

Reduced Hybrid Viability

Reduced Hybrid Fertility

Hybrid Breakdown

What is reduced hybrid viability?

Genetic incompatibility -> embryo dies early into development

What is reduced hybrid fertility?

The hybrid is produced but are sterile or not very fertile

What is the typical cause of reduced hybrid fertility?

Usually because meiosis isn't normal

What is an example of reduced hybrid fertility?

Female horse (2n=64) + Male Donkey (2n=62) = Mule (2n=63)

What is hybrid breakdown?

The first generation of offspring is fertile and viable

Hybrids mate with each other or parent generation

Offspring frail and infertile

What is the process of Speciation?

- Formation of 2 spp from a single spp

- Reproductive isolation from other populations of a spp AND gene pool

What are the two mechanisms of speciation?

Allopatric Speciation

Sympatric Speciation

What is the most common type of speciation?

Allopatric speciation

What is allopatric speciation?

One population is separated -> Gene flow is separated and interrupted -> Evolve by natural selection and/or genetic drift

("Other Homeland")

What can cause the separation in allopatric speciation?

Geographic barriers

Migration

What is an example geographic barriers?

Mountain ranges river changes its course because of the mountain, so lake turns into smaller separate pools

What happens once geographic separation occurs?

Separate gene pools may diverge and they can NOT interbreed, even if populations come back together

What is migration?

Individuals from parent population colonize new region

What can be connected to Migration?

The Founder Effect

What is sympatric speciation?

- A new spp arises within range of the parent population

- Reproduction isolation without geographic isolation

("Together Homeland")

What is Polyploidy?

More than 2 sets of chromosomes leads to an error

What is polyploidy common in?

It is common in plant species (NOT animal)

What are the mechanisms of polyploidy?

Autopolyploid

Alloploidy

What is Autopolyploid?

An individual has less than 2 sets of chromosomes and all sets are derived from a single species

Doubling of chromosome number BEFORE meiosis

An example of autopolyploid speciation

2n=6 —Cell Division Error—> Tetraploid 4n=12 —Meiosis—> Two 2n cells produced by tetraploid —> New spp is 4n

4n spp IS able to self or cross fertilize with other 4n spp but can NOT interbreed with 2n parent spp

What is alloploidy?

2 different species interbreed and produce hybrid offspring

What are hybrids like in alloploidy?

- Usually sterile

- May be able to propagate asexually

- After generations, it may develop into a fertile alloploidy (can mate with each other but NOT parent generation)

Example of alloploidy speciation

Spp A 2n=6 —Normal Gamete—> 2n=3

Spp B 2n=4 —Normal Gamete —> 2n=2

2n=3 and 2n=2 leads to sterile hybrid with 5 chromosomes —Mitotic or meiotic error doubles chromosome number—> New spp: Viable, Fertile hybrid 2n=10 (allopolyploid)

How rapidly do new species arise?

Figure out the rate of speciation, but this is difficult to observe directly

What patterns do we see in fossil records?

Many spp appear suddenly, persist unchanging for some time and then disappear with no transitional spp found

Why can we not find a transitional species?

- Not entirely sure

- Record could be incomplete, were the transitional species there or not?

What are the two models that explain evolution as observed in the fossil record?

Punctuated Equilibrium

Gradual Model

What is punctuated equilibrium?

- Long periods with little to no evolutionary change

- Punctuated by rapid bursts of speciation that is triggered by an environmental change

- Fossil record is complete, there is no transitional species

What is the gradual model?

- Darwin and current model

- Slow and constant accumulation of adaptive changes

- Complete fossil record rarely observed (requires millions of years of subtle stable environment conditions)

What are the speciation rates?

- Studies of different species

- 4000-40mil years

- Average: ~6.5 mil years

How many genes must change to form new species?

It varies, it depends on the number of genes involved in causing reproductive isolation

Example of genetics of speciation

Japanese snails of genus Euhadra

- Change in 1 gene, shell spirals in different direction

- Changes position of genitalia

- Can't mate

= Mechanical barrier reproduction