1
Q
What was Darwin’s main idea?
A
There is variation between breeding groups that are heritable, and this variation is related to fitness
2
Q
Define: Darwinian fitness
A
Individual’s ability to survive and reproduce relative to other members of a population
3
Q
Define: population
A
Individuals of one species in a geographic area sharing the same gene pool
4
Q
Define: community
A
Group of species that live together and interact in a given area
5
Q
Define: ecosystem
A
Interactive system composed of one or more communities and their environment
6
Q
Define: biosphere
A
All of Earth’s ecosystems together
7
Q
What were the 6 main assumptions of the theory of evolution by natural selection?
A
- Variation in phenotype
- High reproductive potential = constant increase
- Individuals compete for limited resources
- More fit individuals more likely to survive + reproduce
- Natural selection acts on phenotypes within generations, but evolution acts between generations
- Complex adaptations require accumulation over long periods of time
8
Q
What are the main evidences for evolution
A
- Fossil Record
- fossil intermediates = evolution of whales - Biogeography
- Selective Breeding
- Convergent Evolution
- homoplastic/analogous features: similar function in distantly related organisms (common solutions_
- e.g. anteater and aardvark show similar feeding methods - Homologies
- derived from same structure in common ancestor
- anatomical: vestigial structures (e.g. goosebumps in humans)
- developmental: reveals ancestral structures no longer in adults (gills in human embryo)
- molecular: homoeotic genes show underlying “universal blood plan” in all animals (HOX gene for segmentation)
9
Q
What’s the difference between proximate and ultimate explanations?
A
- proximate = immediate observation, mechanistic
- ultimate = involves evolutionary perspective
10
Q
What frequencies should you look at when detecting evolution?
A
- phenotypes (physical expression of genotypes)
- genotypes (combination of alleles at a given locus)
- alleles (variants of DNA sequence at given locus)
11
Q
What maintains genetic variation?
A
- mutations (needs to occur in gametes)
- sexual reproduction (recombination via crossing over in meiosis)
12
Q
What are 2 ways to measure genetic variation?
A
- avg. heterozygosity = # of loci in genome that have 2 diff. alleles
- allelic richness = avg. # of diff. alleles/loci
13
Q
What is phenotypic plasticity?
A
Same genotype can result in diff. phenotype depending on the environment
14
Q
What are synapmorphies?
A
Cladistic methods group organisms by shared derived characteristics (e.g. all birds have feathers)
- characters can be genetic or phenotypic
- “clades” = all descendants of the common ancestor bearing the synapmorphies that define that group (e.g. birds are reptiles - descended from dinosaurs)
15
Q
What is the main source of variation in microbes/parasites?
A
- mutation: leads to adaptation
- asexual organisms are small, have short generations, huge populations, and few repair mechanisms
- big chance of beneficial mutation (causes rapid evolution)
16
Q
What maintains genetic polymorphism?
A
- Balanced Polymorphisms
- heterozygotes are advantaged over homozygotes (e.g. sickle cell and malaria) - Spatial/Temporal Environmental Variation
- phenotypic plasticity (e.g. Endler’s guppies) - Trade-Offs
- improvement of 1 character can cause loss in the other - Frequency Dependent Selection
- evolutionary process by which the fitness of a phenotype depends on its frequency relative to other phenotypes in a given population
17
Q
What is the best way to estimate variance in fitness?
A
of grand offspring (offspring that reach sexual maturity)
18
Q
What are clines?
A
- evidence for environmentally-mediated maintenance of genetic variation (e.g. wing size)
- mutations can be beneficial: e.g. when a double stranded break occurs, repair mechanisms occasionally cause a flip
- this stops cross over: can form “super genes”
- evidence of local adaptation
19
Q
Why is sex a “double-edged sword”?
A
- recombination mixes up gene freqs. within and between: allows for new alleles + large assortment of gene combinations
- good if environment is unpredictable/you hold a “bad hand”
- bad if you are well adapted
- NS builds good genes, recomb. breaks them up
20
Q
What were some early problems with blending?
A
- complete blending = no variance
- dominance = eventually no recessive
21
Q
Define…
a) polymorphism
b) polymorphic gene
A
a) variation of traits
b) gene that exists as 2 or more alleles
22
Q
Define…
a) allele freq.
b) genotype freq.
A
a) (#copies of allele)/(total #alleles in that gene)
b) (# individals w/ specific genotype)/(total # individuals)
23
Q
What is the Hardy-Weinberg Equation?
A
- relates allele and genotype freq. in a population
- if allele freqs. can predict genotype freqs., the population is in equilibrium
p = freq. of allele A
q = freq. of allele a
p + q = 1
AA = p^2
Aa = 2pq
aa = q^2
p^2 + 2pq + q^2 = 1
24
Q
What are some forces of non-equilibrium?
A
- genetic drift: smaller population = sampling error
- non-random mating: mate choice/inbreeding
- gene flow: immigration
- fitness difference: natural selection
25
What can H-W equation be used for?
If at equilibrium...
- to approximate allele freqs. of interest
- determine if the population is at equilibrium
If not at equilibrium...
- count allele/gene freqs.
- calculate expected genotype freqs.
- compare observed number w/ expected number
26
What are the tenets of Neo-Darwinism?
1. Evolution can be explained using genetic mechanisms/observations
2. Adaptation occurs via graded/gradual change in genetic freqs./phenotypes
3. Natural selection upon phenotypes = major driving source for adaptation
4. There must be variation among individuals for evolution
5. Microevolution processes are sufficient to explain macroevolution
27
What is heritability?
- amount of which a trait depends on genetic influence
- correlation between parents and offspring estimates heritability
- don't follow Mendelian genetics (blending)
28
What is genetic drift?
- populations are finite in size, meaning that gene freqs. can change from pure "sampling error"
- drift most profoundly affects small populations
29
What is founder effect?
- when a new population is established by a small # of colonists, it can skew genetic freqs.
30
What is bottleneck effect?
- large populations subject to dramatic decrease in size, remaining individuals repopulate but lower genetic variation than before
31
What are the 4 patterns of natural selection?
1. Directional selection: favours 1 of the 2 extreme phenotypes
2. Stabilizing selection: favours intermediate phenotype
3. Disruptive selection: favours extreme phenotype
4. Balancing selection: maintains genetic diversity
32
Define...
a) intersexual selection
b) intrasexual selection
a) males compete with each other
| b) females actively select the best mate
33
What is the extinction vortex?
Inbreeding → Small Population Size → Exposes Deletrious Recessives → Fitness Reduced
34
Explain monogamous mating systems
- male and females are paired for at least one reproductive cycle
- can be explained by...
- male guarding: prevent females from being fertilized by another male
- male assistance: help to rear offspring
- female-enforced monogamy: females make males stay
35
Explain polygamous mating systems
- one male mates with many females
- resource based polygyny: some males dominate resources and mate with visiting females
- communal courting: males all congregate and perform mating displays, then females choose
36
Explain polyandrous mating systems
- one female mates with many males
| - only limited by the amount of males she can find to incubate her eggs
37
Explain the vole experiment/phenomenon
- meadow voles are promiscuous + don't parent
- prairie voles are monogamous and co-parent
- attributed to vasopressin and oxytocin
- prairie voles have more receptors for these hormones
38
What can reproductive isolation lead to?
- formation of a new species
| - no gene flow can lead to divergence and evolutionary adaptations
39
What is sexual selection?
- when certain characteristics are favoured by evolution due to their appeal to the opposite sex
- sometimes seems to contradict NS (e.g male peacock feathers make it hard to escape predators)
- based on the idea not every male will get to "sow his seed"
- leads to sexual dimorphisms
40
What is negative frequency-dependent selection?
The fitness of a phenotype decreases as it becomes more common
41
What is positive frequency-dependent selection?
The fitness of a phenotype increases as it becomes more common
42
What is paedomorphosis?
The retention of juvenile traits in adults
43
What is positive allometry?
Something grows rapidly/more in comparison to the rest of the body
44
What is negative allometry?
Something grows slowly/less in comparison to the rest of the body
45
What is allopatric speciation?
Geographic barriers isolate a population into 2+ groups, which over time may develop to become a separate species
- genetic drift and adaptation to local environment may perpetuate this divergence
46
What is sympatric speciation?
Differentiation that occurs in a population without geographic isolation
- caused by major genetic changes that quickly create reproductive isolations
- e.g. change in the number of chromosome
47
What is adaptive radiation?
Differentiation of a single species into a multitude of different species
- often due to new environmental or physiological feature
- multiple species radiating from one common ancestor
48
What is the order of classification for animals?
domain→ kingdom → phylum → class → order → family → genus → species
49
What is evolutionary phylogeny?
- tracks the differentiation of species from a common ancestor
- done using homologies (common structure/genetic similarity)
- e.g. phylogenetic trees
50
What is ecology?
The study of the interactions between organisms and their respective environment
51
What is population ecology?
The study of changes in the number of organisms within a population over time and space
52
What is population density?
A form of quantitative characterization of a population over space
- # of individuals/unit space
53
What is population dispersion?
A form of qualitative characterization of a population over space
- distribution of a population within an allotted space
54
What are the 3 forms of population dispersion?
1. Clumped
- e.g. pack animals (wolves)
2. Uniform
- e.g. penguin nests are spread out evenly
3. Random
- e.g. plants
55
What is population growth affected by?
1. Natality/birth rate (b)
2. Mortality/death rate (d)
3. Immigration (i)
4. Emigration (e)
56
What is growth rate (r)?
The rate at which a population increases per capita
- growth rate = birth rate - death rate
- r = (b-d) + (i-e)
57
What is anisogamy?
In most sexual species, one mating type produces large, nitrified gametes, whilst the other makes small gametes virtually devoid of cytoplasm
58
CASE STUDY: Explain the evolution of virus in terms of the seasonal flu
- Flu virus type A, B or C
- Type A = most mutable
- Antigenic drift = caused by mutation leading to changing proteins on surface
- Antigenic shift = caused by recombination between strains
- Both shift and drift make vaccines problematic/imperfect (must be based off of probabilistic estimations)
59
CASE STUDY: Explain the evolution of virus in terms of influenza
* ** Pybus et al. 2015
- used phylogenetic methods to assess relatedness, shows how seasonal flus evolved over a 6 year period
- the colours of the branches reflect the match of DNA sequence to regional frequency: the virus diverges evolutionarily as it spreads globally.
- Flu usually comes from Asia
- the main trunk of phylogenetic tree that carries the virus along over time is predominantly Asian, reflecting the epicentre of seasonal flu ancestry.
60
CASE STUDY: Discuss the Zika Pandemic
- First identified in Zika forest in Uganda at virus research centre
- Arbovirus (arthopod borne virus)
- Zika virus is spreading rapidly out from a narrow equatorial band
- Has been linked to microcephaly (small brain) in child development and Guillain-Barré syndrome
- Involves as many as 8 recessive genes affecting brain growth
61
CASE STUDY: Discuss the Spanish flu
- 1918/1919 pandemic flu (characterized by seasonal waves)
- Kills estimated 50-100 million people, sometimes within hours of infection
- Mortality rate of 15-34 year olds 20x higher than any flu epidemic known
- Killed itself off (ran its course)
- Age distribution of mortality differs between highly virulent pandemic strains of flu and seasonal flu
- This is partially due to evolving nature of immune response through our lives with age
- Risk (for pandemic strains) tends to grow with increasing intensity of immune response (unlike seasonal flu).
62
CASE STUDY: Discuss the bird flu
- H1N1 (avian flu) = strain of influenza virus A
- Negative sense, single-stranded, segmented RNA virus
- Limited human-human transmission (no evidence of recombination with human strains)
- Also limited human resistance and widespread endemic population in birds in Asia
- High rate of mortality
- Huge threat if it mutates
63
CASE STUDY: How did Carrol's soapbug study contribute to the evidence of evolution
- Bugs feeding apparatus changed when the bugs transitioned from balloon vine fruit to flat-podded golden rain fruit
- When the bugs were taken to the lab, the change persisted.
- This means the change was an adaptation and not phenotypic plasticity
- Also evidence of rapid evolution
64
CASE STUDY: How did Endler's Greenhouse experiment contribute to evidence of phenotypic plasticity?
- Field caught guppies were brought into artificial streams in the greenhouse
- Measured male spots (number, size, colour) according to experiment treatment
- Male spot number: increased in control/low predator treatments, decreased in high predator treatment
- Most visible colours (blue & iridescent) went down sharply in the high predator treatment
- Spot size/colour also shifted towards matching gravel under high predation
65
CASE STUDY: How did Endler's Field experiment contribute to evidence of phenotypic plasticity?
- Endler found a part of a tributary where guppies were absent above a barrier waterfall
- General conditions were similar to a lower location containing predators
- He caught and moved a sample of 200 guppies upstream
- Guppies got sexier (more spots, more colour) after about 15 generations
66
CASE STUDY: What did Lenski's E.coli experiment contibute?
- 12 clone populations
- New beneficial mutations occurred randomly in all 12 lines
- Fitness increased over the first 20 000 generations:
the E. coli had “tried out” every point mutation possible
- A number of lines became mutators and had elevated
rates of spontaneous mutations (new adaptation occurred in occasional jumps
- After generation 33,000 population A3 exhibited a sudden increase in fitness
- A key innovation had arisen
- Conclusion: E. coli were unable to aerobically metabolize citrate but with one mutation they were able to
- Mutations can be beneficial and lead to evolution/adaptation
67
How much change occurs in the episode of selection depends on which 2 factors?
1. Strength of Selection
- did a small or large proportion of individuals reproduce?
2. Heritability of Variation
- small/large fraction of variation seen underpinned by genes whose effects will be expressed in the phenotype of the offspring
68
CASE STUDY: What did the Red Queen Hypothesis discuss?
- Showed that fossil record shows a consistent rate of extinction at species and family levels of organization; past success does not predict future survival.
- Proposed that pressure from evolving competitors and enemies (parasites, predators) means that no organism is ever completely “adapted”.
- Much of evolution is an "arms race" with other evolving organisms
- Sexual snails are only found in the shallow waters of lakes where parasites are abundant due to the presence of their primary host: ducks
- The trematode larvae grow in the snail gonads, sterilizing the host, but sexual snails are different enough that the parasite won’t kill them all
- Where sexual and asexual forms of the same organism coexist, asexuals harbour more parasites
- Genetic change in a population is necessary to maintain the status quo
- Frequencies of asexual hosts increase (hills) and decrease (valleys) in response to parasite adaptation, while sexual hosts can avoid these coevolutionary ups and downs.
69
CASE STUDY: Describe the consequences of Dutch Afrikaaners arriving in S. Africa all on one ship
* * founder effect
- 50% of current 2.5 million population have 20 names traceable to that ship
- 1/3 white south Africans from 40 founders
- Huntington’s disease is abnormally high
70
CASE STUDY: Discuss the conservation of the Greater Prairie Chicken
- Population was not genetically diverse and approaching extinction
- Strategies used to recovery habitat were largely unsuccessful
- Importation of stock from neighbouring states led to dramatic reversal
- Gene flow can go a long way
- Conservation also need to be cognizant of the breeding system and effective population size
71
CASE STUDY: Discuss sexual conflict in Drosophila (Wolfner)
- Promiscuous species that typically exist in large populations
- Male fruit flies exert a harming effect upon females through (persistent harassment, mechanical wounding, and chemical properties of the seminal fluid)
- Monogamy reduced sexual conflict
- Seminal Fluid Proteins: diverse antimicrobial functions, stimulate egg production, increase oviposition rate, decrease sexual receptivity, decrease female attractiveness, help transport and store sperm, release rival sperm from storage, form mating plug, reduce female longevity
72
CASE STUDY: Discuss sexual conflict in Drosophila (Rice)
- Rice showed that when males were allowed to adapt to courting and mating with a certain type of female that could not change (fixed genotype):
- Male fitness increased through greater mating success and higher success rate in sperm competition.
- Females kept with these males died much more rapidly from toxic side effects of the seminal fluid.
73
CASE STUDY: Describe sexual conflict in Silene
- Dioecious and sexually dimorphic
- Females have few, larger flowers
- Males have many, smaller flowers
- High levels of additive genetic variation for flower number and size
74
CASE STUDY: Describe intralocus sexual conflict over human height
- Over 10,000 people who graduated from Wisconsin high schools were tracker over 50 years
- Looked at brother sister pairs
- Shorter woman had more kids than taller woman
- Average height men had the most offspring
75
CASE STUDY: Discuss homosexuals and fecundity
- Female relative of gay men have higher fertility than female relatives of straight men
- Fitness costs of homosexuality recovered opposite sex relatives
- Effect matrilineal, implying X-chromosome linkage
- The results were replicated including gay woman in reverse
76
CASE STUDY: Discuss homosexuals and fecundity
- Female relative of gay men have higher fertility than female relatives of straight men
- Fitness costs of homosexuality recovered opposite sex relatives
- Effect matrilineal, implying X-chromosome linkage
- The results were replicated including gay woman in reverse
77
CASE STUDY: Discuss sexual selection in drosophila
- Measured relationship between # of mating and reproductive success in drosophila
- Finding: The variance in male fitness is higher than the variance in female fitness
- Males show undiscriminating eagerness
- Females show discriminating passivity
- Explanation: Sperm is cheap to produce therefore males can mate with many females
- Female offspring is limited so they have to invest more energy
78
CASE STUDY: Discuss sexual selection (role reversal) in shorebirds
- When females tend the offspring, males tend to be showier and perform aerobatic displays
- When males tend the offspring, the females tend to be larger, more colourful and more aggressive
- If males are going to care for the offspring and males are limited, a female may need to convince several males to accept her eggs
- Males will be choosey
- He wants to make sure he is the father of the kin his is rearing
- Investing energy in rearing another male’s kin is worse than not mating at all
79
CASE STUDY: Discuss sexual selection (mate preference) in grey tree frogs
- Female grey tree frogs prefer males that have longer and more complex calls
- Females respond to male calls doing more complex calls
- Complex signal: puts the male in danger, costs them to make it
80
CASE STUDY: Discuss sexual selection (mate preference) in Trinidadian guppies
- Some studies show that female guppies prefer male with strong orange colouration
- Good genes: If the bright colouration signals ability evade predators to find rare carotenoid pigments in the diet or is difficult to produce it could be an indicator of genetic quality
- Sensory exploitation: Females seek orange food items and they are tuned to be finding orange fruit so orange guppies stand out
- Negative frequency dependence (rare male advantage) helps avoid inbreeding
- Guppy males have at least two distinctive mating strategies:
1. Colourful Displays
2. Sneak copulation is an alternative mating strategy maintained by negative frequency dependence (If a male can thrust his gonopodium into a females gonopore then he may be able to latch on and inseminate)
81
CASE STUDY: Discuss sexual selection in side-blotched lizards
- Three colour morphs correspond to genetically mediated behavioural mating strategies
- Orange: Ultra dominant, polygynous, territorial
- Blue: Monogamous, territorial
- Yellow: sneaker drifter
- Orange beats Blue , Blue beats Yellow, Yellow beats Orange
- A cycle is created where the least common morph of one breeding season often has the largest number of mature living offspring in the next year (frequency dependant selection)
82
CASE STUDY: Describe Nancy Burley’s Zebra Finches experiment
- Male finches artificially ornamented with leg band jewelry had higher pairing success.
- Females that pair with them have lower rates of extra pair copulation and provide more nest care for young.
- Ornamented males reduce nest care and solicit EPCs.
- Females mated to ornamented males invest more energy and testosterone in male eggs, and bias their clutches towards sons
83
CASE STUDY: Discuss the dung fly experiment
- Opened awareness of post-copulatory sexual selection
- Early models saw sperm competition as a numbers game
- Relative testis size is a good predictor of the intensity of sperm competition
- Analysis of the reproductive systems of a number of organisms has revealed enormous complexity
- Models have had to accommodate this extraordinary potential for extended male-male and female-male interactions after mating
84
CASE STUDY: Discuss the impact of giant sperm
- Back swimming beetles, some ostracods, the painters frog an Australian land snail known for really big sperm
- Record help by drosophila bifurca
- 58mm sperm are over 20x male body length
slow maturation (17d), incredibly low number transferred
85
CASE STUDY: Discuss hybridization in terms of the Greenish Warbler
- Ring Species: Greenish Warblers
- Pattern points to southerly origin, and have evolved to move northern
- Southern range: at a higher elevation
- Species does not hybridize (breed with each other) = prezygotic isolation
- As birds expanded range, their songs are very complex
- Females don’t like the males’ songs from the other group
- Continuous variation around the plateau
86
CASE STUDY: Discuss cichlid speciosity
– territorial
– adaptable, particularly in mouthparts (pharyngeal jaws (extra set of crushing plates in throat)
– strong mate choice (strong chromatic ornamentation allows both mate choice and species discrimination)
– many reproductive strategies
• cooperative breeders (nesters, moothbrooders)
• free spawners
• many strategies in between
87
CASE STUDY: Discuss sympatric speciation in Lake Malawi
- Bathymetrically fragmented: deep and anoxic below 250m (west and east side are very separated b/c of the deep lake and they don’t move a lot
- Habitat fragmented: cobble, boulder, sandy habitats may be interspersed by small coves
88
CASE STUDY: Discuss adaptive radiation in volcano lake
- Salticid spider found widely in the American SW (desertification has fragmented range leading isolated populations living at high altitudes
- Males on these sky islands vary markedly in ornamentation, drumming song and other courtship behaviours
- Females look the same and DNA shows little evidence of divergence between populations
- Suggests little naturally selected divergence or drift but very rapid divergence in sexual signals
89
CASE STUDY: Describe habitat differentiation in rhagoletis
- Major crop pest (have made a host shift from native hawthorn fruit to introduced apple fruit
- Strongly differentiated at marker loci by electrophoresis
- Mate on the fruit, suggesting that host-specialization reinforces reproductive isolation
- Display strong host-specificity when offered a choice
- Gene flow still easily possible (host plants coexist in close proximity, flues fly) but most hybrids probably die)
- Prezygotic isolating mechanisms will reinforce postzygotic isolation
- Hawthord fruit ripen in fall, apples ripen early
- If a fly pupates too early it may wake up before winter and perish; too late it isn’t ready
- Flies on hawthorn must develop rapidly to pupate and diapause before the frost
- Flies on apple develop slowly so they can time diapause to winter
- Hybrids don’t do well because the system goes from warm to cold weather
- Hawthorns blood later than apples but rhagoletis needs to dispose at a specific time
- But if it gets into the apple it will have a slower developmental program
- But if it goes into an hawthorn it will have to mature to fast
- If you have hybrid then you will dispose to early in apple and to late in hawthorn because the time period is in between the two
90
CASE STUDY: Discuss paedomorphic salamanders
- Heterochronic changes provides a potential mechanism for rapid evolution of whole body forms via growth allometry
- Provides mechanism for some views of rapid/punctuated evolutionary change
- Associated with leaps in evolution that skips over gradual change
- We retain many of the juvenile stages from our parents
91
CASE STUDY: Discuss paedomorphy in humans
- Chimp cranial development deviates from human cranial development by: strong negative allometry of brain case, strong positive allometry of the jaws and brow ridges
- Strong positive allometry for relative brain size: selection on intelligence or byproduct of neotony
- MYH16: Inactivation results in smaller jaw muscles, may have facilitated evolution of language, related to food manipulation and cooking??
92
CASE STUDY: Discuss the bithorax complex in Drosophila
- The bithorax complex includes Ubx, a gene which, if mutated, can specify an extra set of wings in a dipteran fly
- Used mutagenesis to study segmental development in flies
- Work would lead to the discovery of the Hox complex
- Suggests deep homologies eg. Complex protostome/deuterostome common ancestor
93
CASE STUDY: Discuss the fruit fly vs. royal albatross
- Royal Albatross:
- Raises a small amount of offspring
- More expensive
- Fruit Fly
- Very quick reproductive cycle
- Explosive reproductive output
- Output is huge but success may be low
- Two animals are using different life history strategies:
- The fly (r-selected) is adapted to exploit available resources with explosive reproductive output; mortality rates are very high with few surviving to reproduce
- The albatross (k-selected) is adapted to reproduce slowly, with a high rate of survival
- Life history strategies are constrained by trade-offs:
Investing energy into reproduction may lead to reduction in survival probability
- Tradeoffs occur in individual lives but are also characteristic of species
- Virgin female flies may live 20% longer but they don’t live forver
94
CASE STUDY: Discuss the different energy allocation strategies
- Because there is a cost to reproduction, organisms employ widely varied energy allocation strategies.
- semelparous (reproduce once) organisms like salmon or Antechinus (small marsupials) invest in a terminal reproductive strategy.
- iteroparous (reproduce many times) organisms like the eider duck (above) breed over over multiple rounds.
95
CASE STUDY: Discuss the terminal reproductive strategy
- Employ a terminal investment strategy with male living just one year
- Reallocation of resources to sperm and semen production, mate guarding via extreme copulation duration and female hyperpolyandry lead to massive physiological collapse
96
CASE STUDY: Discuss hare cycling
- Hare cycling is a classic example in population dynamics:
- As hare populations expand, their predators (fox, wolf, lynx) grow too → this drives down the hare populations with predators collapsing slightly out of phase
- Most of the change is due to predation directly but other changes possible → hare females get stressed out by the presence of predators and produce fewer offspring/more still born offspring
97
CASE STUDY: Discuss predator evasion in frogs
- One from is cryptic whereas the other is aposematic
- Aposematic species pack a potent deterrent such as a toxin
- Palatable Batesian mimics use aposematic colours but lack the actual defences: their fitness will be negatively frequency dependant, too common and the predator does not learn avoidance
- Mullerian mimicry where model and mimic are dangerous is a form of convergent evolution where there may be positive frequency dependence
- Cryptic = camouflage
98
CASE STUDY: Describe predator avoidance in plants
- Plants may not be able to run, but they can protect themselves
- Spines and thorns, thick bark offer some physical protection
- Chemical defences are also common, including numerous poisons, insecticides and distasteful compounds
- Many herbs and spices are flavourful because of plant defence compounds
- Fruit are difference: many are sweet and delicious because they want to be eaten
99
CASE STUDY: Discuss chillies and fusarium
- The capsaicin that makes a pepper hot is a chemical protectant
- The number one cause of seed death is a fungus called fusarium
- Fusarium enters the fruit through wounds caused by insect herbivores
- Capsaicin kills microbes and deters insects as well as mammals
- Birds don’t have receptors for capsaicin and eat the ripe chili fruit dispersing the seeds
- But capsaicin is complex and expensive to produce
- A trade off between seed quality and protection is apparent:
- Pepper plants are polymorphic for pungency
- Where the insect wounding/fungus is uncommon, peppers tend to be mild
- Mild peppers are larger and have thicker, studier seeds
100
CASE STUDY: Discuss mutualistic experiments
- The ants lack invertase expression
- The tree provides the enzyme in nectar
- The tree also produces chitinases that permanently disable invertase
BIOL103
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