Evolution: co-evolution - PowerPoint Presentation

Slide1

Evolution: co-evolution of the Red Queen

CfE

Advanced Higher Biology

Unit

2:

Organisms and Evolution

SQA mandatory key informationA change in the traits of one species acts as a selection pressure on the other species. Co-evolutionary ‘arms race’ between a parasite and host as an example of the Red Queen Hypothesis. WATCH:https://www.youtube.com/watch?v=a8GMNEg6c6U

Key conceptsCo-evolution is frequently seen in pairs of species that interact frequently or closely. Examples include herbivores and plants, pollinators and plants, predators and their prey, and parasites and their hosts The co-evolutionary ‘arms race’ between a parasite and host is known as the Red Queen Hypothesis as both organisms must ‘keep running in order to stay still’. Hosts better able to resist and tolerate parasitism have greater fitness. Parasites better able to feed, reproduce and find new hosts have greater fitness.

What is co-evolution?Definition - The term co-evolution describes a change in the genetic characteristics of one (or more) species in response to a change in the genetic characteristics of another. It is a reciprocal arrangement where two of more species affect each others evolution.Co-evolution is frequently seen in pairs of species that interact frequently of closely. Examples of these strong ecological interactions include:Herbivores and plants

Pollinators and plants

Predators and prey

Parasites and hosts

Herbivores and PplantsHerbivorous defences: Plants have evolved an impressive array of physical and chemical defences to avoid herbivory. Herbivores need to eat plants in order to obtain energy and have therefore coevolved mechanisms to overcome these defences.

Physical adaptations

Herbivores have evolved specially adapted teeth allowing them to break down their plant of choice. Herbivorous mammals have large molars for crushing and grinding material whereas seed eating birds have specially adapted beaks.

Herbivores and plantsChemical adaptationsSome herbivores are able to detoxify plant secondary metabolites (PSMs) which are used by plants as chemical defences

. It was found that the common

brushtail

possums

(

Trichosurus

vulpecula

) use various combinations of oxidation, hydrolysis, and conjugation with

glucuronic

acid (GA) or glycine to detoxify six PSMs to their evolutionary advantage.

Herbivores and plantsHerbivores can also increase their success in obtaining food through behavioural adaptations such as eating plants at different times of the growing season when tannins and chemical toxins are lower. They can also use symbiotic relationships with cellulose digesting bacteria to allow them to break down the tough plant structural protein eg. ruminants.How do plants defend themselves against herbivore attack?

Physical defences

eg

.

s

tings, thorns and spines.

eg

. stinging nettle,

Urtica

dioica

eg

. Thorns on an Acacia Tree,

Acacia

smallii

eg

. spines on a Blackberry plant,

Rubus

fruticosus

Herbivores and plants How else do plants defend themselves against herbivore attack?Chemical defences: Production of tannins and cyanidesIsolation of affected areas: Production of resins to localise fungal and bacterial infection and prevent spread to the rest of the plant.Mechanisms to reduce the effect of grazing: Low growing point (meristems), good powers of regeneration.

Lima beans or butter beans

Phaseolus

lunatus

are one of many plants that contain cyanide.

Pine resin

Pinus

radiata

surrounds areas of infection and limits spread.

Pollinators and plantsTegeticula moths pollinate Yucca flowers. Moths are nocturnal and have a good sense of smell. The Yucca flower is white and therefore visible at night and has a sweet smell. Yucca flowers are a certain shape so only that tiny moth can pollinate them. The moths lay their eggs in the yucca flowers and the larvae (caterpillars) live in the developing ovary and eat yucca seeds.

Pollinators and plantsAcacia ants Pseudomyrmex ferruginea on Acacia trees. Acacias are small, Central American trees. They have large, hollow thorns. The acacia ants live in the thorns. On the tips of its leaflets, the plant makes a substance used by the ants as food. The ants defend the tree from herbivores by attacking/stinging any animal that even accidentally brushes up against the plant. The ants also prune off seedlings of any other plants that sprout under “their” tree.

Predators and their preyPredation in Biology is defined as:The interaction between populations in which one organism (the predator) consumes another (the prey).Typically, the predator catches, kills and eats its prey but predation is also used to describe feeding by insectivorous plants and even grazing by herbivores.

Predators and their preyLions and Zebra: The fastest lions are able to catch food and eat, so they survive and reproduce, and gradually, faster lions make up more and more of the population. The fastest zebras are able to escape the lions, so they survive and reproduce, and gradually, faster zebras make up more and more of the population. An important thing to realize is that as both organisms become faster to adapt to their environments, their relationship remains the same. This is true in all predator-prey relationships.

Predators and their preyPolar bears and seals: In this Arctic environment, the white coat of the polar bear makes it hard to spot against the snow but seal pups are also white so they can’t be seen by the Polar bear!Australian broadheaded snake

feeds primarily on

velvet geckos.

Velvet geckos that are in the same environment as the snakes are able to detect and react to the scent of the snake and avoid entering crevices where the smell has been detected.

Parasites and their hostsIn co-evolution, a change in the traits of one species acts as a selection pressure on the other species.According to the Oxford Dictionary – the definition of a parasite is:An organism which lives in or on another organism (its host) and benefits by deriving nutrients at the other’s expense.Examples of co-evolution of parasites and hosts:

Influenza and its human hosts -

Influenza is an example of an RNA virus and it has many hosts. As we race to develop flu vaccines on an annual basis, the virus is more than able to keep up the evolutionary arms race due to the fact it has a high rate of mutation.

Parasites and their hostsThe nematode Caenorhabditis elegans and its bacterial microparasite Bacillus thuringiensis.

Both organisms have been extensively

studied and evidence of mutual co evolution

and genetic change were found.

The relationship between a parasite and its host is very dynamic. This co-evolutionary ‘arms race’ is known as the

Red Queen Hypothesis.

The term is taken from the Red Queen's race in Lewis Carroll's

Through the Looking-Glass

. The Red Queen said:

"

It takes all the running you can do, to keep in the same

place

."

Entrance of ‘The Red Queen’The Red Queen Principle can be stated as follows:In reference to an evolutionary system, continuing adaptation is needed in order for a species to maintain its relative fitness amongst the systems being co-evolved with.What this means:Hosts better able to resist and tolerate parasitism have greater fitness. Parasites better able to feed, reproduce and find new hosts have greater fitness.

An example of The Red QueenThe New Zealand freshwater snail Potamopyrgus antipodarum and its different trematode parasites represent a rather special model system. Populations of P. antipodarum consist of asexual clones and sexual individuals and therefore can be used to study the evolution and advantages of sexual reproduction.

Long term laboratory experiments and field studies revealed that there is a high correlation between the presence of parasites and the frequency of sexual individuals within the different populations. This result is consistent with the Red Queen hypothesis that sexual reproduction is favoured during host–parasite co evolution

TUTORIAL 1: Selection TutorialRead chapter 1 of The Red Queen:You will be given 1 discussion point to research. You must then be prepared to be able to answer fully and promote discussion on your question with the rest of the class during the tutorial.