Evolution and Ecology Flashcards
Evolution
Change in the heritable characteristics of biological populations over successive generations
Evolutionary tree of life
- Proposed by Darwin
- Idea that all organisms are related to each other via a common descent
- Organisms can be put into groups based on shared morphological traits. Molecular revolution shown that evolution by common descent written in DNA
- Ex. humans share common ancestor with all mammals and and vertebrates
Mechanisms of evolution
- Any process responsible for creating new species and diversity of life
- Includes mutation, natural selection, genetic drift, genetic exchange between populations
Darwin and “The origin of species”
- Published book in 1859
o Many biologists accepted idea of common descent and evolution as historical fact
o Natural selection was more controversial until heredity discovered and theory was more finalized in 1920
Discovery of Heredity/genes
Gregor Mendel
Key components of evolution by natural selection
- Variation in phenotype- some individuals are susceptible to infectious disease whereas others are resistant
- Natural Selection (covariance between fitness and phenotype)- when exposed to the infectious disease, susceptible phenotypes have reduced fitness compared to resistant phenotypes
- Variation in phenotype is heritable- there is variation in the genes (ie. Alleles) coding for immunity that confer susceptibility or resistance to infectious disease
Mice and fox evolution by natural selection
- Foxes will eat the mice with dark fur, and they are less likely to eat the mice with light fur
- This causes a decline of the allele for dark fur in the population
» Change in allele frequency over time which means that the fox is an agent for natural selection
Evolution of mammals/morphological tree
- Morphology and molecular biology largely agree with respect to the monophyly of the 18 placental orders
- Morphologic tree recognizes four major clades
»Based on rare genomic changes (RGCs)
Rare genomic changes
- Include insertions, deletions, changes in gene order, gene duplication
- Very rare, so when a group of animals have them, you can assume that they are related by a common ancestor
Major clades discussed in class
- Euarchontoglires: primates, rabbits, hares, rodents
» All share 18 AA deletion in gene encoding stem cell antigen-1 protein - Laurasiatheria: carnivores, ungulates, whales, dolphins and bats
Do parasites exert natural selection on their hosts?
Yes, parasites have strong negative effects on host survival and reproduction
Examples
- Squirrelpox virus in red squirrels in UK
- MYXV in rabbits in Australia
- Bd (fungus) reduced abundance of amphibian species
Fruit flies and parasitoids wasps
- Wasps lay eggs inside the fruit fly larva. Eggs hatch and the emerging wasp larva usually kill fruit fly larva
- Some Fruit flies (~5%) have developed ability to mount an encapsulation response that kills the wasp eggs
Increased host resistance fruit flies
- Selected fruit flies with a stronger encapsulation response over 8 generations
- Exposed fruit fly larva to high densities of parasitoid wasps allowing natural selection to take place. The best will survive.
»Survivors were allowed to reproduce
» Led to protective immune response fruit flies increasing from 5% to 60%
**The resistance was due to genetic variation. Showed that this variation can rapidly increase protection against parasites
Fruit fly resistance trade-off
Flies that had better resistance/immunity actually showed worse growth during times when parasite was absent.
House finches and mycoplasmosis
- House finches are native to western N. America but they were released in the east and are now widespread in eastern N. America
- Found that eastern N. American finches had mycoplasmosis from Mycoplasma gallisepticum which is typically a pathogen of poultry
»Led to 60% decline in finch population
