Week 6 Flashcards
What is coevolution?
The evolution of one species is affected by its interaction with another species and vice versa
What is antagonistic coevolution?
When the interactions are harmful to one of the two interacting species, such as interactions between predators and prey
What was the original case fatality rate (CFR) in rabbits from the myxoma virus?
99.8% then declined
What is an overview of the myxoma virus?
Myxoma virus is transmitted by biting arthropods
Original strain had case fatality rate (CFR) of almost 100%
Rapidly replaced by strains with 70-95% CFR
Some strains with less then 50% CFR
Selection favoured this because highly virulent strains had shorter infections periods then attenuated (weaker) strains
When was rabbits and the myxoma virus introduced to Australia?
Rabbits introduced in 1859 and bred rapidly and outcompeted native species
Myxoma virus was introduced in 1950 as it was deadly to European rabbits the ancestors to Australian rabbits but not American rabbits where it is natively from
Why do viruses become less virulent?
Virus strains that didn’t immediately kill their hosts got to live in their hosts longer and therefore got more opportunity to disperse to new hosts (mosquitos only bite living hosts)
What happened to the rabbit host in response to the myxoma virus?
Selection towards genetic resistance in the host
Tested by comparing the same viral strain at Lake Urana in a wild rabbit population 7 years apart
At the start of the trial the strain killed 90% of infected hosts
Seven years later only 26% of hosts were killed
What happened after the host evolved resistance and myxoma virus to become less virulent?
Viral lethality began to climb again but with high regional variation and frequent changes across the Myxoma phylogeny
Strains with <50% fatality became very rare
So now more virulent strains had longer infectious periods because they were less readily controlled by the host immune system
Highly virulent immunosuppressive strains began to appear
What were the different strains of myxoma virus and their virulence factors?
SLS = virulence grade of 1 (highest score) killed rabbits in about 2 weeks
BRK 4/93 = virulence grade of 1 (highest score) killed rabbits in about 12 days
SWH 805 = virulence grade of 2 70% killed rabbits in about 28 days
OB3 Y317 = virulence grade of 5 killed rabbits all rabbits recovered from strain
What happens to the rabbits with virulent later strains myxoma infection?
Lymph node lacking lymphocytes which should be highly prevalent
Also disection of lung was shown to have a secondary bacterial infection due to immune system being severly reduced from myxoma infection
What was the origin of each of the virual strains?
SLS = 1950 progenitor virus
BRK 4/93 = 1993 strain
SHW 805 = another 1993 strain
OB£ Y317 = 1994 strain
What is brood parasitism?
Bird species lay eggs in the nest of others for example Cowbird and Cuckoo
What traits may evolve from brood parasitism?
Host - recognition of parasite eggs
Brood parasitism - increased trickery/mimicry
What is an overview of cuckoo brood parasitism?
Cuckoos save energy required to build and maintain nests and raise chicks
So more energy can be put into producing eggs –> female cuckoo can lay up to 25 eggs in a season
Cuckoos can also migrate to wintering grounds earlier
What are the costs of brood parasitism to the host?
The chicks take the majority of food
The cuckoo chick may eject the hosts eggs
What species in britain do common cuckoos (Cuculus canorus) are primarily parasitic upon?
Meadow pipit (Anthus pratensis) in moorland
Reed warbler (Acrocephalus scirpaceus) in marshland
Dunnock (Prunella modularis) in woodland
Pied wagtail (Motacilla alba) in open country
10 other species are used occasionally
What species in britain do common cuckoos (Cuculus canorus) are primarily parasitic upon?
Meadow pipit (Anthus pratensis) in moorland
Reed warbler (Acrocephalus scirpaceus) in marshland
Dunnock (Prunella modularis) in woodland
Pied wagtail (Motacilla alba) in open country
10 other species are used occasionally
What is an overview of host specificity of common cuckoos (Cuculus canorus)?
Cuckoos lay mimetic eggs - match eggs to the host nest
Genetically determined
Dunnocks eggs don’t match
This is because dunnocks don’t eject parasitic eggs
Female cuckoos are thought to specialise in one particular host species
Cross mating in males maintains a single cuckoo species though
What did experimental evidence in warblers suggest about rejection?
Egg rejection was higher for more dissimilar looking eggs
Egg rejection was higher for larger eggs
What is a strategy that is used by cuckoos?
Cuckoos remove one egg when they lay
After the chick hatches it removes the rest of the eggs
Why are the rest of the eggs removed after the chick hatches?
Warblers desert single egg nests
The hatched cuckoo chick does what the mother couldn’t do
Maximises resources going to the cuckoo
Why doesnt Dunnock reject eggs?
Are dunnocks recent victims?
Is this why they lag behind in their counter adaptations to a new selective pressure
Is there a hidden cost to egg recognition? When cuckoos are rare host species that normally reject eggs reject less often
How did egg reject change between hosts?
Experimental tests between suitable and unsuitable hosts showed rejection of eggs was higher in suitable hosts and absent in unsuitable hosts
How can potentially cuckoos avoid egg rejection?
Maybe cuckoos switch hosts through evolutionary time when current host search patterns are too strong
What is the egg discrimination like in bird popualions without brood parasites?
In Iceland there are no cuckoos so pipits and wagtails have poor egg discrimination potentially as a result of not having brood parasites
What was the thought experiment by Van Valen in 1973 about?
Imagine that there is no co-evolution with other species
Evolution and adaptation only responded to the physical environmental pressures
If the environment remains constant you would expect species to adapt and evolve until they fitted their niche perfectly
They have all the adaptations needed to persist
If a new species arises via speciation maybe its not so well adapted to its environment and may become extinct
If this is true then the longer your species has existed for then the less likely it is that it will become extinct
There should be some genera in the fossil record that have lasted a very long time (hundreds of millions of years)
What would happen if Van Valens hypothesis is true?
If Van Valens hypothesis were true you would expect to see that some genera have adaptations that are so good that they persist indefinitely
What is the pattern for number of genera and survival time?
Lots of genera have survives a small amount of time a few general have survived a long time
What would happen if the probability of extinction if species around for a long time and recently evolved species was the same?
If you have a selection of genera, some of which have been around for a long time and some of which have recently evolved, and if there is no difference in their probability of extinction you get a linear distribution
What would happen if genera that had been around for a long time have a lower chance of extinction?
However you may expect genera that have been about longer to have a lower probability of extinction
If this was the case we would see a curved line
How was Van Valen proved the relationship between time spent existing and extinction chance?
He studied sea Urchins, sand pennies, ammonites and sponges
There was a declining linear relationship with a most species persisting a short amount of time and few species existing a long amount of time
What must be happening to cause equal chance of extinction in organisms based on time length?
So what must be happening is that the environment is changing
So new adaptations are required - you can never be perfectly adapted to your environment
What is the quote that inspired the red queen hypothesis?
“Here, you see, it takes all the running you can do, to keep in the same place”
Lewis Carrol
What is an overview of the biology of the alice and wonderland quote?
Running = evolving to a constantly changing environment
Most obvious change to your environment is other species for e.g. parasites and predators
Parasites and predators evolve to overcome host adaptations so everything is constantly evolving but they don’t become more fit
What is a brief overview of the red queen hypothesis?
Predator and prey in fluctuating population ie high predators = low prey = low predators = high prey = high predators constantly in a cycle
If the prey escapes the predator the population will increase until another predator replaces the old and the cycle restarts
What is a brief overview of the court jester hypothesis?
Predator and prey in fluctuating population ie high predators = low prey = low predators = high prey = high predators constantly in a cycle
Abiotic event happens which causes the predator population to rapidly to decline
Prey species escapes and increases in size
New predator species evolves which is a descendant to previous predator species
What is an overview of molluscs and their predators?
Molluscs are abundant as fossils and show a range of protective adaptations eg Thicker shells, Burrowing species. Cemented species and/or Shell repairs
So we can infer some behaviours from the shells thickness
Thick shells are more costly to make but better protection to predators
Geerat Vermeij looked at the change in prey properties through time and the types of predator present
Repeated constant evolution of new traits
What happened over time with the arms race between molluscivore and molluscs?
Molluscivores evolved more complex ways to eat molluscs eg from whole body ingestors to specialised shell breakers and shell drillers
Molluscs evolved a more increasing prevalence of protective mechanisms
