Co-evolution

Co-evolution

• This is the genetic change in one species in response to a genetic change in another.

• E.g. the battle between plants and herbivores.

• A plant may produce chemical defences against insects.

• The insect then evolves the biochemistry to neutralise these toxins.

• The plant then evolves new toxins etc.

Remember Pyrethrines.

• Some chrysanthemums produce a chemical in their leaves that is very poisonous to insects, preventing them from eating the leaves.

• The caterpillars of certain moths and butterflies have developed an enzyme have developed an enzyme that can detoxify the pyrethrin, and these can eat the leaves unharmed.

Ants and Acacia• This is another example of Co-evolution.• Without each other neither can survive.• The acacia provides a hollow thorn base for

the ants to make their home in and nectar and special fat and protein-rich leaves for the ants to eat.

• The ants guard the tree, stinging and biting any insects that they find on it.

• Even large mammals avoid the stings of the ants.

IMPORTANT

• A key feature of co-evolution is that there are traits in BOTH species that are not present in related species.

• The changes are reciprocal, i.e. the changes have evolved in both species as a response to each other.

Gradualism and Punctuated equilibrium

Traditional Concept of Evolution

• The traditional concept of evolution was that there was a mutation here and a change or microevolution there, leading to a change in the structure and physiology of a species.

• The new forms emerged gradually over a long period of time.

Gradualism and Punctuated Equilibrium

• In the fossil record, new forms often appear suddenly and then they remain unchanged for a long time.

• They may then disappear.• This has led to the theory of punctuated

equilibrium, where long periods of stable, unchanged forms are punctuated by episodes of relatively rapid speciation and change.

Punctuated Equilibrium

• This theory was put forward by Eldredge and Gould.

• Based on their study of fossil records, they suggest that most allopatric speciation events are a result of a crisis or major genetic alteration that punctuates long periods of stability where the structure and physiology of a species remains relatively stable.

Punctuated Equilibrium

• Remember in evolutionary terms “sudden change” can mean up to 100 000 yrs.

Example

• After the Cambrian explosion about 550 million yrs ago, there was a “sudden” appearance of complex animals.

• The huge radiation of mammals after the elimination of the dinosaurs in a global disaster after the Cretaceous – Tertiary boundary.