Lecture 11 - evolution in real time Flashcards
What is evolution in real time?
- examples of evolution in action
- applications - disease & epidemiology
How did evolution occur in the distant past?
accumulation of lots of small changes at the genetic level that then translates into changes at the phenotypic level
What is evolution?
- evolution is gradual
- proceeds by the accumulation of small changes
- big jumps are thought to be unlikely
- the rate of evolution varies through time
- macro-evolution is slow
- micro-evolution is fast
What is a well known example of rapid micro evolution?
biston betularia - very fast responses to change (deposition of soot on trees turned them black leading to a change in environment) - selective force, occurred over a few years
What causes rapid evolutionary change?
- competition
- exploitation
- climate change
- parasites
What is competition?
- competition occurs when 2 species have similar requirements
- e.g. food/shelter
- 2 species with very similar requirements can’t coexist
- 1 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
Describe Darwin’s finches
different features for different pressures - classic example of radiation wide species
- competition is shaping the evolution of species
What occurred in response to competition?
the evolution of bill size
- different bills for different food sources
- increase in competition led to a reduced bill size (alternative food source - smaller seeds)
- rates of change are close to values predicted from heritability of the trait
What is exploitation?
humans do something to natural populations because we want to harvest them for food or another resource
- 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
How can human impacts lead to rapid evolution?
- hunting of Bighorn sheep
- hunted as ‘trophies’
- large rams are a target
Describe the effects of selective hunting on fitness & population size
- reduction in animal size
- reduction in horn length
- fluctuations in population size
Describe the evolution of body size & maturity in cod
- cod are fished for food
- nets target larger fish
- contain an intermediate life cycle (sexual maturity depends on size)
- cold environments often lead to slower development and as a result can reach sexual maturity a lot later
- fishing removes the larger fish from the population. This imposes a natural selection on reproduction. If an individual takes too long to get to maturity, it doesn’t reproduce and therefore isn’t able to pass on their genes (selective pressure on maturation)
Describe changes in maturation schedules
- maturation in 1987 was at a younger age & smaller than 1980
What is a good environment?
lots of resources, temperature is good, suitable conditions = large tree growth
What is a poor environment?
(e.g. much colder/hotter) = don’t grow as fast, some die, they don’t do as well as they could’ve
What does a poor environment lead to?
plant changing time of flowering
Describe phenology & climate change
- negative relationship between flowering date & temperature in British plant
- averaged across 250 years & 405 species
- flowering later as it gets warmer, as predicted from model
What are parasites?
parasites are reliant on their host to be able to spread from host to host. As a result there is a lot of selective pressure - as the hosts don’t want to spread the parasite
Describe rabbits & myxomatosis
myxomatosis - used to try and control their spread
Describe co-evolution in real time
- European rabbits were introduced to Australia in 1859
- Enormous capacity for reproduction
- Reached pest status
- Biological control - myxoma virus
Rabbits have rapid enthusiastic reproduction. Few natural predators. Created a huge population.
- became a pest
- virus (myxoma) introduced to reduce rabbit population
What is coevolution of virulence & resistance?
1st epidemic - 99% mortality
2nd epidemic - 90% mortality
3rd epidemic - 40-60% mortality
What are selection pressures on parasites?
- death of hosts stops spread of parasite
- high virulence of parasite leads to short period of spread
- lower virulence leads to more secondary cases
- hence selection on parasites for less virulence
- higher exposure –> resistance
What is the link between parasites & evolution?
- parasites provide some of the best evidence for evolution in action
- parasites have a large number of generations in short time
- intense ell ruin pressures on host
- hence rapid evolution
This has important biomedical applications
What is phylodynamic data?
- virus gene sequences sampled at different points in time
- immunological, epidemiological or medical data is often also available
- phylogenetic history estimated on real time-scale (e.g. years)
Measles & influenza have different phylogeny
What can phylogeny tell us?
- phylogeny tells us about the evolutionary history of a group
- it tells us which lineages have gone extinct & when they did
- as well as which ones have survived
- can map on other data & look at phylodynamics
What is the selection of measles?
no selection on measles virus - spread randomly
What is the selection of influenza?
the shape of this phylogeny reveals imprint of selection
What are other applications of fast evolution?
- evolution of pesticide resistance
- cancer treatment & drug resistance
- superbugs
