Transcript Co-evolution and the Red Queen

Evolution:
co-evolution of the Red Queen
CfE Advanced Higher Biology
Unit 2: Organisms and Evolution
SQA mandatory key information
• A 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=a
8GMNEg6c6U
Key concepts
• Co-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 Pplants
Herbivorous 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 plants
Chemical adaptations
Some 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 plants
• Herbivores 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. stings, thorns and spines.
eg. spines on a Blackberry plant,
Rubus fruticosus
eg. Thorns on an Acacia Tree,
Acacia smallii
eg. stinging nettle, Urtica
dioica
Herbivores and plants
How else do plants defend themselves against herbivore attack?
• Chemical defences: Production of tannins and cyanides
• Isolation 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.
Pine resin Pinus
radiata surrounds
areas of infection
and limits spread.
Lima beans or butter beans
Phaseolus lunatus are one
of many plants that contain
cyanide.
Pollinators and plants
Tegeticula 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 plants
Acacia 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 prey
Predation 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 prey
Lions 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 prey
Polar 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 hosts
In 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 hosts
The 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 Queen
The 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 Tutorial
• Read 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.