Week 1 Flashcards
artificial selection. why are these traits often not seen in the wild?
Used to increase the frequency of desirable traits in their stocks
Lots of traits developed through artificial selection are deleterious in the wild and therefore do not naturally occur
Darwin’s four postulates:
1.The individuals within a population differ from each other
2.The differences are passed onto offspring if they are heritable traits
3.Some individuals are more successful in reproduction that others - competition so that there can be differential success
4.The successful individuals succeed because of the traits they have inherited
natural selection
a process that results in descent with modification or evolution.
No goal in mind, no intent
What survives better is passed on
Darwinian fitness
an individual’s ability to survive and reproduce
adaptation
a trait that increases an organism’s fitness relative to individuals lacking it.
selection vs evolution
Selection occurs during generations, evolution occurs between generations**
nature of natural selection
Natural selection acts on individuals but its consequences occur in populations
Natural selection acts of phenotypes but evolution consists of changes in allele frequencies
Although selection acts on existing traits, new traits can evolve - recombination and mutation
Natural selection does not lead to perfection
Natural selection is nonrandom but it is not progressive - there is no such thing as a higher or lower plant or animal
Selection acts on individuals, not for the good of the species
exaptation
a trait that is used in a novel way
the modern synthesis
Individuals vary as a result of mutation and segregation and independent assortment
Individuals pass their alleles on to they offspring intact
In every generation some individuals are more successful at surviving and reproducing than others
The individuals most successful at surviving and reproducing have the alleles best suited to the environment
directional selection
fitness consistently increases with the value of a trait. Reduces variation in a population
stabilising selection
individuals with intermediate values of a trait have highest fitness.
disruptive selection
individuals with extreme values of a trait have the highest fitness.
how is variation maintained?
Most populations are not in evolutionary equilibrium - not fixed alleles yet as mutations slowly keep occurring
There is a balance between deleterious mutations and selection
Disruptive selection may be more common than thought
frequency dependent selection
Selection can maintain two alleles in a population if each allele is advantageous when it is rare
Common flowers are less selected for by bees than rare flowers
A type of balancing selection
why are cheetahs so fast?
Proximate reasons - body form, flexible spine, balance from tail, thin and streamlined, light frame and bones, long legs, big heart
Ultimate reasons - to be able to hunt fast prey, can get food to survive and reproduce
what selection type is acting on cheetahs?
We see a bell-shaped curve of speed
Faster are more likely to survive
Directional selection
Selection favours faster runners
Hypothesis: If there is a heritable basis then the population will get faster over time
how could we study cheetahs?
Can look at phylogeny - comes from a fast clade but is faster than the others in that clade
Is it fast because it has evolved from fast ancestors? Comes from a fast clade but is the fastest
Is it fast because of the region it lives in? African species are faster generally than from other regions. Africa selects for fast running - could be due to the habitat - flat savannah, open grasslands
Longitudinal study looking at phenotype and fitness - hard, time-consuming and costly to do but has merit
type of selection acting on golden rod gall flies
Inject eggs into goldenrod stem - larva eat the inside tissue, saliva caused the plant to grow a gall
Selection on gall size
Parasitic wasps find galls, lay eggs in them and then their larva eat the gall fly larva
Parasitic wasps are better at parasitising small galls
Large gall can be a selective advantage - directional selection??
But… woodpeckers eat the gall fly larva and they have more success in large galls
The intermediate phenotype or gall size is favoured - stabilising selection
black bellied seed cracker selection
Small beak and large beak sizes but breed randomly
Juveniles are bell-shaped in distribution but the adults that survive either have large or small beaks (no intermediate)
Disruptive selection
elderflower orchids selection
Yellow and purple flowers
Provide no nectar for bees
Bees alternate between flower colours to try and find a reward
In theory, rare flowers should receive more visits
This is negative frequency dependent selection - evolutionary advantage to being the rarer colour morph
Measured by how much pollen was taken from male flowers and pollen acquisition for female reproductive success
Balancing selection: acts to maintain variation in a population so this is a type of balancing selection
define evolution
change in gene frequencies over time.
macro-evolution
morphological change across time. Long term changes
Transitional forms in the fossil record help us test this such as archaeopteryx - modern feathers but reptilian features
Transition between dinosaurs and birds
Can find remnant traits in extant species to test as well - wings of kiwis that are tiny vestigial wings and do not serve for flight
Vestigial hind limbs (tiny) on snakes
microevolution
rapid phenotypic change within populations over successive generations
Threespine stickleback - marine varieties are more armoured than freshwater varieties
Marine variety invaded Loberg lake and frequency of fully plated decreased. Selection against fully plated and selection for lightly plated freshwater form
How did this happen? Mutation or standing genetic variation for armament phenotype (very few freshwater ones also invaded but were not detected)
genes and alleles
Much of our DNA is silent but those that provide phenotypic changes are genes
Genes encode proteins
DNA can mutate resulting in versions of genes called alleles
Some alleles have no affect on phenotype, some do
Genes evolve due to differential survival of alleles
is all evolution adaptive?
No
It can result in gene frequencies and phenotypes that are not helping
This occurs through genetic drift
genetic drift
random loss or change of frequencies of alleles
Unpredictable stochastic changes in allele frequencies across generations due to chance
More prevalent in small populations that have been bottlenecked
the four postulates - example with the finches
1.Variability - bell shaped curve of beak depth
2.Heritability - parents with big beaks produce offspring with big beaks etc. (limitation - this could be because of food supply and not heritability)
3.Not all finches survived - due to drought (huge bottleneck). This meant that seed abundance crashed. Large seeds were most abundant
4.Differential survival - deeper beaks were more likely to survive and offspring were more likely to have deep beaks
