Speciation

Chapter 2.7, Bush

Speciation

What is a species?

The Process of Speciation

Models of Speciation

Interesting examples of Speciation

Speciation

What is a species?

The Process of Speciation

Models of Speciation

Interesting examples of Speciation

What is a species?

Morphological Species Concept

Biological Species Concept

Modern Species Concepts

Morphological Species Concept

Linnaeus invented the system of classifying organisms in the 1800’s

He based the classification of a species by appearance

Defining species is complicated

Phenotypic variation within species may make us think that there is more than one species

Different species may look remarkably similar

Different phenotypes within a single species

Hydrangea

Different species with similar appearance

Eastern and Western Meadowlarks look identical but differ in their song

Eastern Meadowlark

Western Meadowlark

Different species with similar appearance

Some species look similar even when they are only very distantly related = CONVERGENT EVOLUTION

Cacti (Americas) Euphorbia (Africa)

Biological Species Concept

“Species are groups of potentially or actually interbreeding natural populations that are reproductively isolated from other such groups”

-Mayr, 1942

Defining species is still complicated

Must revert to Linnaeus’ system for:

– extinct organisms– asexual organisms– some distinct species that can still

interbreed and produce viable offspring (e.g., coyotes, wolves, and dogs)

Modern species concepts

If >5% of amino acids are different, then consider two organisms to be of different species

Speciation

What is a species?

The Process of Speciation

Models of Speciation

Interesting examples of Speciation

The Process of Speciation

Speciation Evolution– populations can evolve too

e.g. Ground finch size during drought

SPECIATION:– is the process in which a new species is

formed from an initial one

The Process of Speciation

One species (set of interbreeding

organisms)

Genetic variant spreads through part of the species; bearers of this variant must mate only with other

bearers of the same variant

Two species. Further phenotypic, behavioural

and ecological differences may evolve

How Speciation occurs:

Evidence for both types of speciation

It is thought that most speciation has been allopatric

Sympatric speciation is thought to occur often among flowering plants (2-4% of species formed through this process)

Allopatric speciation

The Grand Canyon prevents dispersal of squirrels to opposite side, allowing divergence

Chance events influence evolution

Founder effects

Sympatric speciation via polyploidization

Chromosome evolution in animals

Barriers to interbreeding

Two species have been formed if breeding is prevented:

1) Prezygotic barrier – E.g. don’t live in the same habitat (e.g., squirrels in the Grand Canyon)

2) Postzygotic barrier – E.g. offspring are inviable or sterile (e.g., in polyploid vs. diploid species)

Speciation

What is a species?

The Process of Speciation

Models of Speciation

Interesting examples of Speciation

Models of Speciation

Gradualist Model:– Darwin thought species arose gradually

and slowly

Punctuated Equilibrium Model:– speciation occurs in quick bursts followed

by long periods of no change– Fossil record supports this model but is

incomplete

Gradualism vs. Punctuated Equilibrium

Speciation

What is a species?

The Process of Speciation

Models of Speciation

Interesting examples of Speciation

Adaptive radiation of Darwin’s finches

single ancestral species arrived from mainland S. America millions of years ago, radiated into 13 species with specialized feeding habits

Ring Species – One species or two?

Ensantina salamanders

Co-speciation of host and parasite

Changing Environments and Evolution

Ch. 2, 22.4-22.6, Bush

Changing environments and Evolution

Early Earth and the Origin of Life

Major events in the history of life

Continental drift and life as we know it

Present day environmental changes

Changing environments and Evolution

Early Earth and the Origin of Life

Major events in the history of life

Continental drift and life as we know it

Present day environmental changes

Early Earth

Earth was formed ~4,500,000,000 yrs agoEarth was very hot and constantly bombarded

by meteor showers from spaceAt this point there was no liquid water, life was

impossible

About 3,900,000,000 yrs ago, Earth was solidified enough and cool enough for liquid water

Life apparently arose shortly thereafter

Formation of ingredients for life

1950’s – Muller and Urey found that the input of electrical energy could spur the creation of organic compounds from inorganic compounds and ocean water

The transition from molecules to life

the step from amino acids to replicating life is still a mystery

biochemical clues suggest that there may have been life on the planet as early as 3.8 billion years ago

First fossils are 3.5 billion years old (resemble modern day bacteria)

Environment for early life forms

Essentially no atmospheric O2

– Highly corrosive, destroys molecules

Highly energetic– Lightning, volcanic

activity, UV radiation high

– Provide energy for chemical reactions

Could life originate elsewhere?

As our understanding of our own solar system has increased, the hypothesis that life is not restricted to Earth has received more attention.– Europa (a moon of Jupiter):

may have liquid water beneath the surface and may support life

– Mars: is cold, dry, and lifeless today, but was probably

relatively warmer, wetter, and had a CO2-rich atmosphere billions of years ago

Mars’ subsurface may still be capable of having lifeMany scientists see Mars as an ideal place to test

hypotheses about Earth’s prebiotic chemistry

Where did first life forms evolve?

Previously assumed to be on the surface of the ocean

Now, it is thought that life evolved in hydrothermal vents in the deep ocean where no photosynthesis takes place– sulphide-rich water and heat provided the

necessary elements for life’s reactions

Deep Sea vents

Changing environments and Evolution

Early Earth and the Origin of Life

Major events in the history of life

Continental drift and life as we know it

Present day environmental changes

Early Earth and the Origin of Life

Major events in the history of life

Continental drift and life as we know it

Present day environmental changes

A clock analogy for Life’s History

Major events are:– Photosynthesis– Multicellularity– Invasion of land– Humans (come into

the picture a few minutes to 12:00)

The Evolution of Photosynthesis

Photosynthesis: Using sunlight to create carbohydrate from CO2

First photosynthetic organisms used Hydrogen sulphide and created sulphur as a by-product

Modern day photosynthesis uses only CO2 and water and produces O2 as by-product

Oxygen changed the world

Over the next 3 billion years, the oceans became saturated with O2

organisms that could not tolerate O2 went extinct (or became very rare and restricted to O2-free environments)

800 million years ago, O2 starts seeping into atmosphere creating the ozone layer

Ozone layer allows life on land

By 400 million years ago, O2 levels were approximately at modern levels

Ozone layer blocks the UV radiation, which causes mutations, allowing organisms to invade land

Early changes in the environment

Cambrian Explosion of multicellular organisms

Earliest known fossils of multicellular organisms, 600 mya

540-505 mya huge diversity of organisms present in the fossil record

Best fossils displaying Cambrian explosion are in the Burgess Shales in the Canadian Rockies

Determining the Earth’s History

Fossils of Early life forms

microscopic found in 3.4 billion

year-old rock

Cambrian fossils

Other well-preserved fossils

Other well-preserved fossils

Other well-preserved fossils

Changing environments and Evolution

Early Earth and the Origin of Life

Major events in the history of life

Continental drift and life as we know it

Present day environmental changes

Continental Drift

continents ride across the surface of Earth, propelled by powerful volcanic forces

explains some basic patterns of similarity and dissimilarity of flora and fauna

Pangaea

Until 200 mya, all continents were clustered together at tropical latitudes

As plates of Pangaea broke off, each plate carried a different set of life forms

The Drifting of Continents

Australia and Antarctica

Have been isolated from the other continents for the longest time

Resulted in them having the most unique flora and fauna

e.g., marsupials

Unique flora and fauna of Australia

Changing environments and Evolution

Early Earth and the Origin of Life

Major events in the history of life

Continental drift and life as we know it

Present day environmental changes

Recent Ozone changes

• Human activities have:• increased ozone in

the troposphere• decreased ozone

in the stratosphere

“Good” ozone (protects Earth from UV radiation)

“Bad” ozone (reactive gas)

Increases in tropospheric ozone

By-products of burning fossil fuels (e.g., oil. gas) react with oxygen to make O3

O3 reacts with chlorophyll in plants, detrimental to growth

Decreases in stratospheric ozone

CFC’s, HCFC’s and other chemicals react with O3 to make O2

decrease in O3 increases UV radiation higher rates of cancer (in humans and other mammals), reproductive failure in birds and lizards, damage to plants, etc.

Summary Life began on Earth ~ 3.5 bya

The evolution of photosynthetic organisms resulted in the formation of the ozone layer, paving the way for life on land

Continental drift has played a large part in shaping the modern day distribution of organisms

Changes in the environment are happening today at a rapid pace