Lecture 7 - Phenotypic evolution Flashcards
How have humans harnessed evolution?
Through selective breeding
Allowed us to feed the world
Also have used for pets to make dogs
Quantitative traits
Traits that vary continiously
e.g. height, blood pressure and plumage colour
Quantitative genetics
Study of how quantitative traits are inherited and how they evolve
Phenotypic variance
Variance in a population for a particular trait
What explains phenotypic distributions?
Genes and the environment
Phenotypic plasticity
The capacity of an organism to develop any of several phenotypic states depending on the environment
Example of inducible defences of Crucian carp
With no exposure to predator cues the body shape is shallow which gives a competative advantages in the abscence of predators as more streamlined
With exposure to predator cues changes body shape to a deeper body shape, hey can attain higher speed, acceleration and turning rate. Also harder to be eaten
Reaction norms
Range of phenotypes expressed by a genotype along a range of environments
Why did lizards develop horns?
Birds capture lizards and put them on trees and fences to show off to mates
However the larger the horns the less this occurs
What are the 4 different types of selection outcomes?
Directional
Diversifying
Stabalising
Correlational
Directional selection
Selection towards a particular trait
Example of directional selection?
Finch
There was a major draught causing only large seeds to be available
ONly birds with large beaks could eat the large seeds
Powerful selection event
Diversifying selection
Extreme traits are selected for
Example of diversifying selection
Beaks in birds
Small beaks specialised in smaller food items and large beaks specialise in larger food items
Stabilizing selection
Selection towards the mean
Example of stabilizing selection?
Birth weight in babies
Correlational selection
Selection operates on multiple traits
Example of correlational selection
Snakes vary in stripes and behaviour
Found that certain behaviours only work with distinct colour patterns
Selection gradients
Measures the strength of directional selection acting on a quantitative trait
What is needed to calculate selection gradients
Trait measurments
Fitness of a set of individuals
How do you measure fitness
Lifetime fitness is ideal but hard to measure
Instead can use survival, growth and reproductive success
What is the symbol for selection gradient?
Beta
General findings of experimental evolution?
Almost all traits evolve when selected
Selection can cause a trait to evolve far beyond its original range of variation
Large populations evolve faster than small populations
Strong selection on one trait often has negative consequences for other traits
Genetic correlation of traits
Many traits are correlated
This is partly heritable
Selection can act to increase one trait but can also indirectly increase correlated traits
Can lead to traits evolving in opposite directions to selection
