Week 9 Flashcards
what is a gallwasp?
Forces a plant to make it a home
Tiny wasp injects eggs into the base of acorn flowers and they grow into galls not acorns
Wasp larvae feeds on gall flesh
Galls are shed by the oak tree with its leaves and the wasps leave (after 9 months)
Then it only lives for a few more weeks to mate and way eggs
Sexual females emerge from a turkey oak and lay in a English oak and then asexual female baby has to find the turkey oak
population genetics model system on gall wasps
System is based around knopper gallwasps (acorn ones)
Galls are plant tissues whose development is controlled by another organism
100 European gallwasp species that produce a variety of galls
During the ice ages there were less areas available for oaks to grow but when ice melted, the oaks expanded across Europe. But Turkey oak did not spread as far naturally. Humans spread it much further
Spread was slow because of slower move of turkey oak
Sampling design: native range and a broad range of invaded ranges
Genetic dataset: 827 wasps, 46 locations, 14 regions, 5 zones
Genetic markers: 6 marker loci, enclosed by nuclear genome, allozymes (proteins but reflect DNA variation), few alleles per locus
Selectively neutral
Co-dominant (can see both alleles in a heterozygote)
genetic markers
Something you can visualise that reveals heritable variation
Genetic markers must be heritable, usefully variable
Reflect DNA sequence variation
Show genetic diversity, connectivity, inbreeding etc.
Calculate allele frequencies and then genotype frequencies
Allele frequencies let us understand evolutionary changes
allelic diversity
Heterozygosity and expected heterozygosity
where does phenotypic variation come from?
Genetic variation
The environment
genetic basis of variation
Molecular diversity - simple genetic control (neutral to adaptive)
Eg. Haemoglobin variation and gallwasp allozymes
Changing DNA, changes protein, changes phenotype
Quantitative genetic diversity - complex genetic control (lots of genes involved) plus environment
Also neutral to adaptive
Many traits with large impacts on fitness are quantitative
Body size, reproductive success, stress-resistance, running speed, flowering time etc.
what are quantitative traits controlled by?
Quantitative traits are controlled by genetic variation + environmental variation
variation from genotype has three components
Additive genetic variation:
Among alleles
Phenotypic effect of inheriting one allele over another
Somewhat predicts evolutionary potential because it reflects allele frequencies
Is a key determinant of heritability
Dominance genetic variation:
Within genes
Some alleles are more influential than others in determining phenotype
Interaction (epistatic) genetic variation:
Among genes
Phenotypes depend on combinations of alleles inherited at different loci
allozymes
Mutation on allozymes is very very slow and so we are only looking at neutral alleles in gallwasps
heritability
Index of adaptive variation/potential
h^2 = Va/Vp (proportion of the phenotypic variation due to additive genetic variation)
Ranges from 0 to 1
What proportion of phenotypic variance passed from parents to offspring? To what extent are traits under selection controlled by genes and are variable?
Heritability is an estimate of the adaptive potential of a population
adaptive genetic variation
Changes phenotypes on which natural selection acts
Includes genes that code for proteins, regulate development or influence the way organisms respond to and sense their environment
Only happens through natural selection!
neutral genetic variation
Genetic variation that does not affect fitness and is invisible to natural selection
It may cause phenotypic variation that does not affect fitness
Reflects neutral evolutionary forces such as genetic drift, mutation and migration
Synonymous changes (don’t change protein sequence) can have strong fitness effects too
insights into evolutionary potential and rapid evolution
Rapid adaptive evolution is driven by changes in gene expression (regulatory variation)
Most traits are polygenic
Most recent adaptation is due to subtle shifts of allele frequencies
effective population size
The number of individuals that contribute to the next generation
Needed to make predictions about evolution, adaptation and persistence of populations
Ne accounts for factors that reduce the capacity of a population to hold genetic diversity such as deviating from even sex ratios, variation in family size, fluctuations in population size
Higher Ne means more selection and less drift
migration and Ne
Ne/N tells us how many actual migrants are needed to produce a given number of effective migrants
To have 2 effective migrants, we need 20 migrants
