APS11006 Principles of Evolution- Freckleton Lectures Flashcards
Ancestral form of pigeons
Rock pigeon
Artificial selection
Variation in species generated by human-driven selection e.g. domesticated animals. Breeding and producing viable offspring with ‘ideal’ characteristics.
Evidence for evolution
- Fossil record
- Artificial selection
- Variation in space
- Homology
- Experimental evolution
- Observable evolution
Examples of animals that have been artificially selected
- Pigeons
- Dogs
Examples of crops that have been artificially selected
- Einkorn to ‘heritage’ wheat to ‘modern’ wheat
- Beta vulgaris and Beta maritima bred to become beetroot, chard and sugar beet
What sort of characteristics are bred for in crops?
- Easily grown
- Nutritious
Primula kewensis
- Hybrid between two existing, naturally occuring species (Primula verticillata and Primula floribunda)
- Realised through an accident
- Speciation through allopolyploidy
- Diploid 2n=36, while parents are 2n=18
- Therefore it cannot interbreed with either parent species
- Leads to ‘instant speciation’
Allopolyploidy
- Polyploidy is a condition in which an organism has more than two complete sets of chromosomes in every cell (>diploid)
- Allopolyploidy occurs when a polyploid offspring is derived from two distinct parental species
- (Primula kewensis is 4n compared to parents)
‘Instant speciation’
- Sympatric speciation which occurs by polyploidy
- Offspring is reproductively isolated and independent
What % of plant species are polyploids?
-40-70%
Sympatric speciation
Divergence of species by isolation within the same geographical location without a physical barrier
Spatial variation
- Variation in environment leads to variation in species
- Temperature change, predation and prey change etc lead to selection pressures
Biogeographical ‘rules’
- Bergmann’s rule
- Allen’s rule
- Lack’s rule
- Rensch’s rule
Bergmann’s rule
- Animals get larger further north
- SA:V is minimised, heat is lost at a lower rate
Allen’s rule
- Animals in colder climates have thicker limbs (and smaller appendages such as ears and tails)
- Small appendages reduces SA:V and thus heat loss
Lack’s rule
- The clutch size of each species has evolved to an evolutionary optimum
- May vary spatially
Rensch’s rule
Sexual dimorphism increases with average body size
Sexual dimorphism
Systematic difference in form between individuals of different sex in the same species
How do foxes in the US follow the biogeographical rules?
- Red foxes in north are larger, with thicker limbs and fur and smaller ears
- Red foxes in south have larger ears, thinner body, less fur
- Bergmann’s and Allen’s rules
Lepus arcticus vs Lepus californicus
- Arctic hares have small, fur-covered ears
- Desert hares have large ears
- Different coat colours
Ring species
- Situation in which two populations that do not interbreed are living in the same region and connected by a geographic ring of populations that can interbreed
- E.g. herring and lesser black-backed gulls
- Different characteristics for each species
How does fossil evidence exist?
- Fossils are contained within layers of sedimentary rock
- Older layers are covered by newer ones
- Also preserved animals e.g. in permafrost
What is Archaeopteryx an example of?
- Transitional form (birds and reptiles)
- Discovered through fossil records
Vestigial characters
- Structures that have no apparent function
- Serve as evidence of evolutionary relationships
- Whales possess pelvic bones, linking them to terrestrial mammals
Types of selection
- Natural selection
- Sexual selection
Natural selection
Descent with modification, driven by adaption to the local environment (change in organisms through time with inheritance of traits)
Basis for natural selection
- Variation
- Heritability
- Competition and fitness
Types of variation
- Discrete e.g. colour morphs in Biston betularia moths
- Continuous e.g. range of variation in banding intensity oh shells of cepaea nemoralis
Non-genetic variation
Over last 20 years, its recognised that there’s a form of non-genetic variation involving the modification of DNA throughout lifetime in response to environment which is inheritable. Epigenetics.
Is variation completely random?
No, has a deterministic genetic basis
Problem with Mendelian inheritance
- Does not produce a directional change in gene frequency, parental generation, F1 and F2 all have same proportion of gene frequency
- End up with equilibrium of genotypes in population unless traits offer advantage
- No evolution occurring
Biston betularia as an example of natural selection
- Peppered moth (common in UK) comes in light and dark morphs (colour effective in determining camouflage)
- Started off with colour variation which is heritable
- Far more eggs are laid than the habitat’s carrying capacity allows, leading to ecological competition
- In habitat with light background, lighter morphs are more difficult to see
- Genotype for dark morphs less successful and passed down less, lower fitness
Ecological competition
- Consequence of limited resources
- Include food, water, shelter, space or mates
- Direct relationship between amount of resource captured and fitness
Fitness
- Measure of reproductive success of individual, including its chance of survival
- If an individual passes on 100& of genes, fitness = 1.0
Types of natural selection
- Directional selection
- Stabilising selection
- Disruptive selection
Directional selection
A shift towards one phenotype, away from the mean
Stabilising selection
- Optimum phenotype around the mean
- Values that are particularly high or low will be disadvantaged
- Extremes are selected against
- Creates a narrower range of trait values
Disruptive selection
- Two different ways of exploiting environment, either of which is equally fit
- Selection favours one or other, leading to a distribution with two peaks of optimum trait values (multimodal distribution)
Altruism
- Behaviour of an animal that benefits another at its own expense
- E.g. Belding’s ground squirrels
- Give alarm calls when predator approaches (seems counterintuitive)
- Studied by Sherman and colleagues
- Likelihood of alarm call related to whether or not group contains relatives
- Tested empirically
Second example of altruistic behaviour
- In most birds, fledglings leave nest when they are able to fly
- Florida scrub jay young sacrifice their own reproduction to help their parents raise more broods
How have altruistic genes evolved through natural selection?
- Kin selection
- If one individual possesses a gene, it is highly likely their kin does too
- Altruistic genes increase the rate of spread of themselves (genetics) via relatives
- Altruistic action will be favoured if it benefits kin
- A focal individual with a given gene calling an alarm can help protect that gene in itself and also its kin, so lots of copies remain in population
How do altruistic actions evolve?
If: r x b > c
- Where r is relatedness of target individual
- B is benefit to target
- C is cost to giver (likelihood of being eaten after alarm)
- I.e., benefit (increased fitness with respect to relation) must be bigger than cost
What is relatedness?
Relatedness is the proportion of genes shared because of common ancestry.
Parent-offspring = 0.5, sibling-sibling = 0.5, grandparent-grandchild = 0.25, cousin-cousin = 0.125
Multiplies down branches (0.5x0.5…)
What is B (Benefit to target)?
B is the number of extra copies of the gene the act yields (benefit in terms of generating copies of gene in future)
Green beard gene hypothesis
- Altruism gene is linked to an obvious phenotype
- These two genes are genetically linked, next to each other in genome so get passed between generations together
Examples of green beard hypothesis
- Red fire ants, reproductive females are Bb, workers kill BB queens using odours to distinguish BB from Bb, genotype is linked to a behaviour
- Unrelated lizards from partnerships to protect, these have blue throats. One male may have no offspring and spends whole time defending territory of other. Genes for throat colour and cooperation are linked.
Intrasexual selection
Competition between members of the same sex
Intersexual selection
Interactions between members of different sexes
Fecundity vs fertility
- Fecundity is the physiological maximum potential reproductive output
- Fertility is the current (actual) reproductive performance
Sexual dimorphism
- Differences in appearance between sexes of the same species
- Driven by sexual selection
Mating system
The way that organisms form mating pairs and the way they look after offspring and behave in terms of subsequent mating
Type of mating systems
- Monogamy, 1 male and 1 female
- Polygamy, male and female have multiple partners throughout lifetime
- Polyandry, female has multiple partners
- Polygyny, male has multiple partners
Sexual selection in monogamy
- Very little sexual selection
- No sexual dimorphism seen
Extra-pair paternity
- Offspring not sired by both parents in pair
- Monogamous mating systems thought to be extremely stable until 1990s, with genetic fingerprinting
- Looked at parents and offspring of monogamous birds
- Surprisingly high rates of extra-pair paternity in supposedly monogamous species
Rates of extra-pair paternity in different bird species
- Chaffinch, 17%
- Blue tit, 10-15%
- Dunnock, 0-36%
- Tree swallow, 38-76
- Superb fairy wren, 75-85%
Types if intrasexual competition
- Male-male competition
- Mate guarding
- Sperm competition
- Lek competition
Male-male competition
- Fighting, beetles physically fight
- Dunnocks, floating male is competing with resident male
- Sexual selection leads to these behaviours
Mate guarding
- Organism holds onto mate to prevent other males from mating with her
- Bigger males could outcompete this male, change in ownership
- Gamerus sp. (water shrimp), pre-copulatory
- Scatophaga stercoraria (fly), post-copulatory
Sperm competition
- E.g., damselflies and dragonflies
- Females mate with several males, then contains sperm of multiple males
- Behavioural and physiological changes have evolved as a consequence
Lek competition
- Gathering of males compete together
- Display and fight, females observe
- Females choose ‘best males’
- Lekking is costly for males
Lekking species
- Paper wasp
- Fruit flies
- Manakins
- Red grouse
- Capercaillie
Epigamic selection
- Competition between members of the low investment sex for features that are attractive to the high investment sex
- As with intrasexual selection, low investment sex is usually male
What do females gain by choosing males?
- Access to resources
- Access to good genes, utilitarian (disease resistance etc) and attractiveness (for future mates)
Well-known example of rapid microevolution
- Biston betularia
- Before industrial revolution, individuals were light, allowing them to camouflage
- Post-industrial, blackening of buildings so camouflage no longer useful
- In 1848, dark forms were noticed
- By 20th century, 90% are dark
What does selection act on?
- Replicators, individual units that replicate themselves such as a gene
- More copies left, most successful
- Therefore, species are not the units of selection
Causes of rapid evolutionary changes
- Competition
- Exploitation
- Climate change
- Parasites
Competition
- Ecological process
- Two species have similar requirements cannot co-exist at same time with same requirements
- One species must outcompete other, or one must evolve alternate requirement
Adaptive radiation
-The diversification of a group of organisms into forms filling different ecological niches
Evolutionary changes in bill size of Geospiza fortis
- Looked at by Peter and Rosemary Grant
- Island of Daphne Major originally inhabited by Geospiza fortis but invaded by Geospiza magnirostris (big beak)
- Both eat seeds
- 1978 drought and selection for new food sources caused increase in beak size
- 1983 magnirostris begin to breed, causes decrease of fortis beak size as there is selection for them to eat small seeds
Exploitation
Species are exploited by humans in some way e.g. fishing or hunting
Human impacts leading to rapid evolution of bighorn sheep
- Hunted for horns as trophies
- Large rams biggest target (evolutionary pressure)
- Selectively removes individuals with genes for large horns and body size
- More small individuals can now survive and reproduce, but eventually this cannot be sustained by the population
Phenology
The study of periodic events in biological life cycles and how these are influenced by seasonal and interannual variations in climate and by climate change
Example of climate change impacting life history
- In a good environment, it pays for plants to spend time growing and taking advantage of good conditions as long as possible, and then reproduce
- In a poor environment, it makes sense to reproduce as early as possible and not take risk of dying before reproduction
Experimental evolution
Using fast-reproducing organisms, it is possible to demonstrate evolution and control it under lab conditions – taking advantage of bacteria, fast reproducing plants, etc. can show us how they respond to different environments and how evolution develops
How do human activities change the environment?
- Habitat loss
- Climate change, patterns of rainfall, temperature
- Pollution, chemicals can be toxic to organisms, making habitats more difficult to reside in
- Invasive species, such as rabbits introduced to Australia
Examples of animals that have become extinct due to human interactions
- Dodos, hunting
- Great Auk, combination of egg collecting and specimens for museums
- Chinese river dolphin
What is the main current driver of extinction?
Habitat loss- conversion of natural habitats to agriculture, clearance of tropical forest, land use change
