Lecture 17: Evolution in real time

Question 1

Evolution is..

Answer 1

gradual.
proceeds by the accumulation of small changes. Big jumps are thought to be unlikely, but the rate of evolution varies through time.

Question 2

Macro-evolution is

Answer 2

slow

Question 3

micro-evolution

Answer 3

can be fast

Question 4

Microevolution example:

Answer 4

Biston bettlarna.

• very fast response of species to change.
• industrial revolution
• 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.

Question 5

when does competition: occur?

Answer 5

when two species have similar e.g. food /shelter.
two species with very similar requirements cannot coexist
-one species must 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..
—e.g. Darwin’s finches

Question 6

exploitation:

Answer 6

• 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

Question 7

e.g. of exploitation:

big horn sheep

Answer 7

• Hunting of Bighorn sheep
• Huunted as ‘trophies’
• large rams are a target
• selection pressure on species? –> reduction in animal size, horn length & fluctuations in population size

Question 8

e.g. of exploitation: COD

Answer 8

-Cod are fished for food
-Nets target larger fish
-Sexual maturity depends on size.
due to fishing;
- Age at maturity was 1 year younger by 2002
- Growth rates declined by up to 50%
- Resulting from reductions in survival of 50%+

Question 9

phenology;

Answer 9

the study of cyclic and seasonal natural phenomena, especially in relation to climate and plant and animal life.

Question 10

climate change:

Answer 10

• So 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.

Question 11

parasites e.g. rabbits & myxomatosis.

background:

Answer 11

• pathogen in rabbits
• 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.

Question 12

rabbits & myxomatosis ; coevolution in real time

Answer 12

• European rabbits were introduced to Australia in 1859.
• Enormous capacity for reproduction
• reached pest status
• Biological control - myxoma virus (eventually spread worldwide)

Question 13

rabbits & myxomatosis ; 3 epidemics

Answer 13

1st epidemic - 99% mortality
2nd epidemic - 90% mortality
3rd epidemic - 40-60% mortality

Question 14

5 different virulence grades

Answer 14

I is high virulence, causing nearly 100% mortality, V is low virulence causing virtually no death.

Question 15

rabbits & myxomatosis ; 3 epidemics EXPLAINED

Answer 15

• Death of hosts stops spread of parasite
• High virulence of parasite leads to short period of spread (DIE EARLY)
• Lower virulence leads to more secondary cases
• Hence selection on parasites for less virulence (more likely to spread disease)
• Higher exposure –> resistance

Question 16

parasites provide some of the..

Answer 16

best evidence for evolution in action: parasites such as viruses and bacteria in particular are able to cycle through a large number of generations in a short time. This has a dual effect: first, it means that there is a good chance of new variants of existing genes arising; second, new genes are able to spread very quickly through a population of parasites.

Question 17

parasites cause ____ ____ on hosts

Answer 17

intense selection pressure.
-viruses such as myxoma which are initially fatal, any individual possessing genes allowing them to resist the disease will be at a huge selective advantage. Consequently, genes for resistance are also likely to spread very quickly indeed.

Question 18

Phylodynamic Data (evolutionary models & diseases)

Answer 18

• Virus gene sequences sample at different points in time.
• Immunological, epidemiological or medical data is often also available.
• -Phylogenetic history is estimated on a real time-scale (e.g. years)

Question 19

e.g. to show phylogenetic graphs - measles and influenza

Answer 19

measles- tree like, balanced
flu- ladder like, most lineages on the phylogeny appear then disappear rapidly.
REPRESENTS; different evolutionary processes;-
measles; driven largely by school calendar.
Flu; adapting a lot,evolutionary pressure

Question 20

what can the phylogeny tell us? (disease)

Answer 20

• 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 and look at phylodynamics

Question 21

phylogeny showing tree like balanced vs ladder like short lived comment on selection

Answer 21

tree like; no selection - spread randomly

ladder; shape of phylogeny imprint of selection

Question 22

other applications of fast evolution;

Answer 22

• evolution of pesticide resistance
• cancer treatments & drug resistance
• superbugs