Adpatation Flashcards
adaptation (2)
- a trait, or integrated suite of traits, that enables (or enhances the probability of) an organism to survive and reproduce
- outcome of evolution by natural selection
how do you begin testing adaptive hypotheses? (3)
- state your question(s) clearly
- state your hypotheses
- design a study that allows you to discriminate among your hypotheses
what kind of studies can be conducted? (3)
- manipulative experiments
- observational studies
- comparative studies (the “comparative method”)
examples of manipulative experiments (2)
- lizard fever study
- tephritid fly mimicry
tephritid fly mimicry
- question: what is the function of the wing markings and wing-waving display of the tephritid fly Zonosemata?
- based on this question, what are the three hypotheses?
- tephritid flies don’t mimic jumping spiders. Patterns and behaviours are just coincidental.
- tephritid flies mimic jumping spiders, but to deter other nonspider predators.
- tephritid flies mimic jumping spiders to avoid predation by jumping spiders.
what are the controls for the tephritid fly experiment? (3)
- tephritid fly untreated
- tephritid fly with wings cut and glued back on
- house fly untreated
what are the experimental groups for the tephritid fly experiment? (2)
- tephritid fly with house fly wings
- house fly with tephritid fly wings
under hypothesis 1: tephritid flies don’t mimic jumping spiders. Patterns and behaviours are just coincidental, what is expected to be seen?
- all flies are attacked by both the jumping spiders and other predators
under hypothesis 2: tephritid flies mimic jumping spiders, but to deter other nonspider predators, what is expected to be seen? (2)
- other predators will retreat from the tephritid fly untreated and the tetraphid fly with its wing cut and glued back on
- jumping spiders will attack all groups and other predators will attack all other groups
under hypothesis 3: tephritid flies mimic jumping spiders to avoid predation by jumping spiders, what is expected to be seen? (2)
- jumping spiders will retreat from untreated tephritid flies and tephritid flies with their wings cut and glued back on
- jumping spiders will attack all other groups and other predators will attack all groups
what components are necessary for manipulative experiments? (4)
- control
- replicate
- randomize
- perform experiments “blind” to avoid biases and subjectivity
examples of observational studies (2)
- Grant’s Galapagos finches study
- Garter snake thermoregulation
Garter snake thermoregulation experiment
- question: do Garter snakes make adaptive choices when choosing a night-retreat
- what are the 2 hypotheses based on this question?
- Garter snakes choose medium-sized rocks that allow optimal thermoregulation
- (null) Garter snakes take whatever rock is available
Garter snake thermoregulation experiment
- If under the Hypothesis 1: Garter snakes choose medium-sized rocks that allow optimal thermoregulation and ~30% of all rock types available, what are the expected results? (3)
- <33% choose thin rocks
- > > > > 33% choose medium rocks
- <33% choose large rocks
Garter snake thermoregulation experiment
- If under the Hypothesis 2: (null) Garter snakes take whatever rock is available and ~30% of all rock types available, what are the expected results? (3)
- ~33% choose small rocks
- ~33% choose medium rocks
- ~33% choose large rocks
what are the potential drawbacks of observational studies? (2)
- many confounding variables
- cannot conclude causation, only correlation
confounding variable
- variable that influence both independent and dependent variable, causing an association
what are the potential drawbacks of the finches observational study? (2)
- correlation between larger size of the birds and better territories (inflate heritability)
- offspring sired by males other than social partner (deflate heritability)
examples of comparative studies (3)
- nematode virulence study
- testes size in fruit bats; sleep study
- flu evolution at the molecular level
what is the goal of comparative studies
- test for correlation between state of trait and variable proposed to be responsible for the pattern (ie. environmental condition, state of another trait, etc) by comparing across species (ie. using nature’s experiments)
potential problem of comparative studies (2)
- related species may share same combination of traits due to common ancestry
- phylogenetic non-independence
what the solution for the problem of comparative studies?
- correct for phylogeny to obtain species pairs that can be treated as phylogenetically independent
phylogenetic trees (3)
- hypotheses of how species/individuals are related to one another
- consist of terminal nodes connected by branches to internal nodes, which represent inferred ancestors
- can be built using morphological characters, amino acids or nucleotide suquences
phylogenetic non-independence problem
- species at all terminal nodes cannot be taken as independent data points
how to correct for phylogenetic non-independence (4)
- find internal nodes
- graph the internal nodes by taking the descendant species and plotting them on a graph connected by a line
- move smaller x- value point on each line to the origin
- only keep the point where the larger x-value point was
testes size in fruit bats experiment
- question: why do some bat species have bigger testes, for their body size?
- what is the hypothesis for this question
- larger testes may be an adaptation for sperm competition
how are fruit bats affects by sperm competition? (2)
- group size varies from few to tens of thousands across species
- greater opportunity for sperm competition in larger groups
testes size in fruit bats experiment prediction based on the hypothesis: larger testes may be an adaptation for sperm competition
- species roosting in larger groups should have males with larger testes relative to their body size
how can correction for phylogenetic non-independence affect results of an experiment?
- may remove or reveal a correlation
how can molecular phylogenetic trees be used? (2)
- obtain evidence of selection
- non-synonymous or synonymous mutations can be used to infer neutral drift, positive selection, or purifying selection
neutral drift (basic)
- NS/S = 3/3
positive selection (basic)
- NS/S = 6/0
purifying selection (basic)
- NS/S = 0/6
non-synonymous mutation (NS)
- a nucleotide mutation that alters the amino acid sequence of a protein
synonymous mutation
- do not alter amino acid sequences, sometimes silent mutations
what ratio is used to correct phylogenetic tree ratios for what is expected by chance? (2)
- NSexp : Sexp = ~3:1
- due to the degenerate nature of the genetic code, ~25% of possible sequence changes are expected to be synonymous
what formulas are used to correct for phylogenetic tree ration for what is expected by chance? (2)
- K(A) = NSobs/NSexp
- K(S) = Sobs/Sexp
neutral drift (2)
- K(A)/K(S) = 1
- K(A) = K(S)
positive selection (2)
- K(A)/K(S) > 1
- K(A)»_space; K(S)
purifying selection (2)
- K(A)/K(S) < 1
- K(A) «_space;K(S)
other evidence of purifying selection
- emerging strong deleterious variants are quickly purged from the population so that all alleles are non-deleterious after selection
other evidence of positive selection (2)
- classic hard sweep
- new advantageous variant emerges and quickly purges all other alleles after selection occurs
other evidence of balancing selection
- heterozygote advantage
