Origin of Species

What is at the focal point of evolutionary theory?

speciation

What must evolutionary theory explain?

How new species originate and how populations evolve

Microevolution

Consists of changes in allele frequency in a population over time

Macroevolution

Refers to broad patterns of evolutionary change above the species level

What can be used to define a species?

• Biological Species concept

• Morphological species concept

• Ecological species

• Phylogenetic species concept

Reproductive Isolation

The existence of biological factors (barriers) that impede two species from producing viable, fertile offspring

Hybrids

The offspring of crosses between different species

How can reproductive isolation be classified?

By whether factors act before or after fertilization

What the are prezygotic barriers?

• Habitat Isolation

• Temporal Isolation

• Behavioral Isolation

• Mechanical Isolation

• Gametic Isolation

What are the postzygotic barriers?

• Reduced Hybrid Viability

• Reduced Hybrid Fertility

• Hybrid Breakdown

What is Hybrid Breakdown?

Two related species can hybridize, and their F1 offspring are fertile.

• But successive generations (F2 and beyond) suffer lower viability or fecundity.

  • Thus, they cannot become an established population.

What is an example of hybrid breakdown?

Rice cultivars

• Cultivars have been artificially selected and some are related enough to hybridize

• F1 = fertile and viable

• F2 = stunted and sterile

What is Hybrid Sterility

• Example in explanation

Tigers and Lions are sister taxa, but seperate for millions of years

• Their hybrid offspring are viable and robust, but sterile.

• Chromosomes are not homologous, so they don’t migrate during meiosis normally

What is Hybrid Inviability

• Example in explanation

Tigers and Lions are sister taxa

• Their hybrid offspring are viable and robust, but sterile

  • A mating between a lion and leopard will produce sterile hybrids

  • A mating between a tiger and leopard will produce inviable hybrids

    • Zygotes divide, but embryo miscarries or is stillborn

What types or organisms can’t the biological species concept be applied to?

• Why?

Fossils or asexual organisms (including all prokaryotes)

• The biological species concept emphasizes absence of gene flow

Can gene flow occur between distinct species?

Yes; grizzly bears and polar bears can mate to produce “grolar bears”

What concepts emphasize unity within a species rather than separateness of different species?

• Morphological Species Concept

• Ecological Species Concept

• Phylogenetic Species Concept

What does the morphological species concept define?

• What does it apply to?

Defines a species by structural features

• It applies to sexual and asexual species but relies on subjective criteria

What are the different bacteria shapes?

Spheres (cocci), Rods (bacilli), Spirals

What does the ecological species concept view?

• What does it apply to?

It views a species in terms of its ecological niche

• It applies to sexual and asexual species and emphasizes the role of disruptive selection

What does the phylogenic species concept define?

• What does it apply to?

It defines a species as the smallest group of individuals on a phylogenetic tree

• It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate species (DNA Evidence)

• Based on DNA similarities

What are the ways in which speciation can occur?

1. Allopatric Speciation

2. Sympatric Speciation

What is allopatric speciation?

A population forms a new species while geographically isolated from its parent population.

What is sympatric speciation?

A subset of a population forms a new species without geographic separation.

Evidence of allopatric speciation?

• 15 pairs of sibling species of snapping shrimp (Alpheus) are separated by the Isthmus of Panama

• These species originated 9 to 13 million years ago, when the Isthmus of Panama formed and separated the Atlantic and Pacific waters

Barriers to reproduction are ________; separation itself is not a _________ _________

Barriers to reproduction are intrinsic; separation itself is not a biological barrier

Where does speciation take place in sympatric speciation?

Geographically overlapping populations

What is behavior isolation?

Courtship rituals and other behaviors unique to a species are effective barriers

What is polyploidy?

• Where is it common?

• How does it occur?

The presence of extra sets of chromosomes due to accidents during cell division

• Polyploidy is much more common in plants than in animals

• Polyploidy conditions occur through meiosis errors

What is an autopolyploid?

An individual with more than two chromosome sets, derived from one species

Common polyploid plants

• State the type

Seedless Watermelon = triploid

Banana = triploid

Blackberries = tetraploid

Peanuts = tetraploid

Sweet Potato = hexaploid

Wheat = hexaploid

Strawberry = octopoid

What is an allopolyploid?

A species with multiple sets of chromosomes derived from different species

What is the basic idea of the biological species concept?

That a group of organisms that can successfully interbreed and produce fertile offspring

What’s the difference between microevolution and macroevolution?

Macroevolution is broader, such as the evolution of lungs, or tetrapods.

Where can you determine that the species is different?

They may look alike, but there is some issue that prevents them from interbreeding.

What is habitat isolation?

Where organisms may be in the same environment, but in slightly different habitats so they never interact

• In the water and on land

What is temporal isolation?

Different mating periods, such as the season, time of day, etc.

What is behavioral isolation?

Different courtship rituals

• Dancing, singing

What is mechanical isolation?

Reproductive organs don’t line up

• Such as when snail shells are in the opposite ways

What is gametic isolation?

They can mate, butter gametes aren't chemically compatible

• The sperm and egg don’t merge, which means no zygote is made

Is geographic isolation the same as habitat isolation?

Nope

Are the species concepts perfect?

No, not all the time

What is reproductive isolation simply?

The absence of gene flow (intermitting, immigration, emigration)

What is the difference between allopatric and sympatric speciation?

Allopatric speciation is when a geological barrier prevents a population from interacting, so they are not able to reproduce with each other

• The reproductive barriers cause speciation

Sympatric speciation is when a population’s organisms evolve into unique species by different evolutionary pathways in the same environment until they are reproductively isolated from each other

What type of organisms are usually polyploids?

Plants, not animals bc they are too complex

How to polyploidy conditions occur?

Errors in meiosis

• Non normal meiosis

Explain an autopolyploid production

Both parents species are of the same species, and due to meiosis errors, their gametes have a full set of chromosomes. This then leads to an offspring with double the amount of chromosomes.

• Failure to reduce chromosome # during meiosis

Explain an allopolyploid production

• Two matings

One species(A) has a proper gamete and makes a zygote with a different species(B) whose gamete has had meiosis errors resulting in a gamete with a full chromosomal set. This hybrid then mates with an organism from species A. Species A again gives the proper gamete, and the hybrid has a meiosis error with a full chromosomed gamete. Together, they will make what the first mating should have properly had

• Hybridize between two species, and not reduce chromosome #

What type of speciation are allopolyploids and autopolyploids?

Sympatric Speciation

What type of speciation is habitat differentiation (habitat isolation)

• Why?

Sympatric because they are still in the same geographical area, just occupying slightly different habitats and niches

What can sexual selection be connected to?

• What’s an example of this connection?

Behavioral isolation

• A fish species’s slight was affected, changing how they saw the colors of other fish

  • This impacted the attraction between the fish species, eventually causing speciation

What can sexual selection drive?

Sympatric speciation

What is the punctuated equilibria?

A model that contrast with the model of gradual change

• A long period of no change followed by rapid changes or vice-versa

What would be considered a short time vs. a long time in an evolutionary standpoint

Thousands of years vs. Millions of years

What did punctuated equilibria ‘solve‘?

Examples of species from the fossil record that appear suddenly, persist essentially unchanged for some time, and then apparently disappear

What macroevolution in relation to speciation?

The cumulative effect of many speciation and extinction events