Macroevolution

Macroevolution is the study of major biological changes evident in the fossil record

Includes the following:

1. Multiplication of species

2. Origin of structures like feathers and large brains

3. Diversification of species – like flowers

4. Mass extinctions that lead to explosions -like the explosion of mammals after the dinosaurs became extinct

speciation

Speciation is the origin of new species

Branching vs. non-branching

Branching – a lineage is split into two or more species

Non-branching – initial species becomes new species

Anagenesis vs. Cladogenesis

The Origin of Species

Biological species concept – groups of interbreeding natural populations whose members ONLY breed with each other to create fertile offspring.

What keeps members of different species apart?

Reproductive Barriers

Prezygotic barriers – occur before conception

Post-zygotic barriers – occurs after conception

Pre-zygotic Barriers

Temporal Isolation – mating or flowering occur at different time of the year/day

Ex. Western spotted skunks breed in fall, while eastern spotted skunks breed in the late winter

Habitat Isolation – species living in the same region may occupy different habitats

Ex. Some Garter snakes live in water/some on land

Behavioral Isolation-courtship rituals are very specific

Ex. Birds

Mechanical isolation-structural differences in genitalia or flowers prevent copulation or pollen transfer

Ex. Insects and flowers

Gametic isolation- male sperm cannot fertilize the egg

Post-zygotic Barriers

Hybrid Inviability – hybrid zygotes fail to develop or reach sexual maturity

Hybrid Sterility – Hybrid individuals fail to produce young

Speciation

When a population is somehow severed from the parent population and over time its gene pool is altered.

Allopatric and sympatric

Allopatric speciation

Isolation is the result of a geographic barrier

Ex. Galapagos finches

True speciation only occurs if the remaining populations will NOT breed

allopatric

Sympatric

When a sub-population arises in the midst of the parent population

Many plant species have accidental polyploidy in meiosis. They produce zygotes with multiple sets of chromosomes.

They can no longer reproduce with parental generation.

Evolution of Wheat

What is the tempo of speciation?

Gradual vs. punctuated

Punctuated equilibrium model – species most often diverge in spurts of rapid change instead of slow and gradually.

Over a few to ten thousand years, genetic drift and natural selection can change small, isolated species

Punctuated Equilibrium

Archaeopteryx

Exaptation

Term used to describe a structure that evolves in one context, but becomes adapted for another. However, natural selection cannot anticipate future need

Ex. Light bones in reptiles

Evo-Devo

How do evolution and development interface?

Genes control the development of an organism from zygote to adult

Turning these genes on and off at certain times can have a profound effect on development.

Paedomorphosis – the retention of juvenile features as an adult

Ex. axototl

Axototl

Chimpanzee vs. human skulls

We retain a skull more like that of our fetal skull

History of biological diversity

Macroevolution is tied to the history of the Earth

Fossils are recovered from various sources

Sedimentary rocks

Skulls

Petrified trees

Tracks

Body parts

Amber

Geological Time Scale

Four eras – Precambrian, Paleozoic, Mesozoic, Cenozoic

Fossils are dated by carbon dating

Handout

At the end of the paleozoic era (250mya), Pangaea was formed.

The formation of pangaea reduced coastline and changed the environment for many terrestrial species.

Changing ocean currents killed many marine species

Breaking of Pangaea

180 MYA during the mesozoic

Caused major geographic isolation

Continental drift

Patterns of Evolution

Divergent evolution – when two isolated population evolve independently (Ex. Brown and polar bears)

Adaptive radiation – rapid evolution of a variety of species from a single ancestor (ex. Darwin’s finches)

Convergent Evolution – when two organisms without a common ancestor occupy the same niche, so they have the same characteristics. (ex. Porpoise and penguin)

Patterns cont.

Parallel Evolution – two related species who have made similar evolutionary changes. Ex. Placental and marsupial wolf

Co-evolution – predator/prey relationships

Adaptive Radiation