real time Flashcards
what do we know about evolution
-Evolution is gradual
-Proceeds by the accumulation of small changes
-Big jumps are thought to be unlikely
-But the rate of evolution varies through time
-macro-evolution is slow….
-…but micro evolution can be fast
whats a well known example of rapid microevolution
-Biston betularia
-Very fast response of species to change
-before the industrial revolution, individuals of this species were of a light mottled form. This allows the moths to blend in with their background and to be camouflaged from predators.
-In 1848 for the first time it was noticed that dark forms of the peppered moth had started to appear, and by the 20th century this form was as frequent as 90% of the moth population
components of rapid evolutionary change
-Competition
-Exploitation
-Climate change
-Parasites
whats competition as an ecological process
-Competition occurs when two species have similar requirements
-E.g. food, shelter
-Two species with very similar requirements cannot coexist
-One species must either go extinct or evolve different requirements
-It is usually thought that ecological process of extinction is faster than evolution
-Hence extinction is thought to be more likely
-Basically if two species with similar resource (e.g. food) requirements live in the same place at the same time, then ecological theory says that they cannot coexist. Usually in ecology it is thought that this means that one or other of the species has to become extinct. This has been the conventional ecological wisdom for some time
whats Darwin’s finches
-slow rapid evolution
-competition within species drives evolution
-this group of birds lives on the galapagos islands, a small group of volcanic islands off the coast of Ecuador. They colonised the islands some time ago, in the first instance beginning with an ancestor from the South American Mainland.
Evolution of bill size in response to competition
-Darwin’s finches have been studied for some time by the Grants: they have been looking at one island in parrticular called Daphne major. This was initially inhabited by just one species, Geospiz fortis, but a second species invaded, Geospiza magnirostris. Both species eat seeds and there is some degree of competition between them.
Evolutionary changes in bill size of Geospiza fortis
-Through time there have been lots of changes in bill size in Geospiza fortis as an evolutionary response to competition within and between species, as well as to droughts as you will have heard before
-1978 – drought and selection for feeding on new food sources and an increase in beak size.
-1983 Geospiza magnirostris starts to breed on the island and quickly establishes a large population.
-Combined effects of drought and competition: Geosiza magnirostris is now feeding on the larger seeds and hence there is selection for G fortis to feed on smaller seed. Here there is a very rapid shift in the mean phenotype of the population.
whats exploitation
-Many species are exploited by humans in some way
-Much exploitation is selective
-E.g. harvest the biggest
-This is exactly like the process of natural selection
-Some of the best examples of rapid evolutionary change come from systems in which species have been exploited by humans in some way. Some of the best examples of this are actually in the Origin of Species. Darwin used domestication, specifically of pigeons, as an example of the acquisition of traits through selection.
what are the Human impacts leading to rapid evolution
-Hunting of Bighorn sheep
-Hunted as ‘trophies’
-Large rams are a target
-examples of human exploitation:
= Bighorn sheep - these are reasonable common living wild in North America. They are targeted by sports hunters, with the largest rams with the biggest horns being a particular targe
=Because hunting is selective, that might be expected to put an evolutionary pressure on this species, and indeed it does: by targeting the largest individuals with the biggest horns, hunters are selectively removing those individuals with the genes for large horns and large body sizes. That is then leading to effects on the population as shown in this next slide
what are the Effects of selective hunting on fitness & population size
-Reduction in animal size
-Reduction in horn length
-Fluctuations in population size
whats Evolution of body size & maturity in cod
-Cod are fished for food (heavily)
-Nets target larger fish
-Sexual maturity depends on size
what are the Changes in cod maturation schedules
-Maturation in 1987 was at a younger age & smaller than in 1980
-For a cod to become sexually mature it has to cross a threshold of size and age. Research has shown that this threshold has changed markedly over recent years. The dashed line on this graph shows the average growth trajectory of a cod
how does the climate affect evolution of life histories
-in a good environment it pays to spend time growing and to take advantage of great conditions as long as possible.
-On the other hand, in a poor environment in which there are few resources and you are likely to die, it makes sense to reproduce as early as possible and not take a risk of dying before you can reproduce
Phenology & climate change
-Negative relationship between flowering date and temperature in British plant
- Averaged across 250 years and 405 species
-And this prediction is actually borne out by data: plants now flower earlier than they did 250 years ago, as borne out by analysis of long term phenological data.
Rabbits & myxomatosis
-pathogen of rabbits
-The background for this is that the myxoma virus is orginally from South America, where it was discovered and isolated. This was done with the purpose of using it as a biological control agent to kill rabbits wherever they had become pests.
whats Co-evolution like in real time
-European rabbits were introduced to Australia in 1859, few predators, population increased massively
-Enormous capacity for reproduction
-Reached pest status
-Biological control (more sustainable)- myxoma virus
whats Coevolution of virulence & resistance
-1st Epidemic - 99% mortality
-2nd Epidemic - 90% mortality
-3rd Epidemic - 40-60% mortality
Decrease & stabilisation of virulence
-The outbreaks of the disease were classified according to 5 different virulence grades: I is high virulence, causing nearly 100% mortality, V is low virulence causing virtually no death. The two sets of graphs here show what happened in Australia, where the disease was first introduced, and also in Britain, where it subseqeuntly established as the virus escaped from its initial range.
-Essentially the same pattern of evolution happened in both Australia and Britain: Initially the disease started as a high virulence strain, with all cases being of Type I. However as time progressed, the virulence of the disease declined, eventually stabilising at a much lower level
Parasites & evolution
-Parasites provide some of the best evidence for evolution in action
-Parasites have a large number of generations in short time
-Intense selection pressure on hosts
-Hence rapid evolution
photodynamic data
-what scientists and doctors do is to take samples of viruses from patients and look at the genetic sequences. They are able to do this at various points in time and then use the degree of different between the sequences to reconstruct the phylogeny for the viruses. This information is then combined with other information – epidemiological, immunological, medical or even social, and this allows the history of the outbreak to be precisely traced and analysed
measles and influenza
-It is immediately apparent that these two phylogenies look very different indeed. The measles phylogeny has quite a balanced looking tree-like structure. On the other hand, the flu phylogeny is much more ladder-like: most lineages on the phylogeny appears then disappear very rapidly.
What can the phylogeny tell us
-Phylogeny tells us about the evolutionary history of a group
It tells us which lineages have gone extinct and when they did
As well as which ones have survived
Can map on other data and look at phylodynamics
immunological vs genetic change in flu
-The phylogeny of the flu virus reflects a great deal of evolutionary pressure
-The phylogeny then shows how evolution has proceeded in this virus over a period of 20 years or so, with one strain successively replacing the next: so a particular new strain emerges, and becomes frequent causing lots of cases. However, the host population soon develops immunity – or vulnerable hosts are lost – with the consequence that the strain is no longer able to persist. As that strain goes extinct, it is replaced by another antigenically distinct one that the host is not able to fight off.
what are other applications of fast evolution
-Evolution of pesticide resistance
-Cancer treatments & drug resistance
-Superbugs
