co-evolution
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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Co-evolution
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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.
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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.
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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.
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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.
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Gradualism and Punctuated equilibrium
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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.
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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.
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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.
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Punctuated Equilibrium
• Remember in evolutionary terms “sudden change” can mean up to 100 000 yrs.
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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.