Natural Selection (2) Flashcards
Natural selection?
= process by which favourable heritable traits become more common in successive generations of a population of reproducing organisms & unfavourable heritable traits become less common.
Explain natural selection.
Natural selection enables/cause populations to evolve through traits within those populations being favourable to their environment/fit to survive the environment and is more likely to be passed on to subsequent generations through reproduction.
Thing to consider about favourable?
That it may change.
Who/What does natural selection act on?
Individuals.
NS attributes? (5)
• Differential reproduction of genotypes.
• Non-random process, but no “intent”.
• Acts on mutations (random).
• Acts on the genotype through the phenotype.
• Occurs at different stages of a life cycle.
3 selection types we’ll be focusing on from the adult section of the life cycle?
• Variable selection.
• Sexual selection.
• Survival selection.
NS principles? (4)
• Acts on individuals.
• Not progressive/linear.
• Can’t predict the future.
• Populations evolve, not individuals.
What do we mean when we say that NS is not progressive/linear?
We mean that in NS things change often if not all the time & is unpredictable (not straight to the point).
Results of NS? (2)
• Increase in no. of individuals in subsequent generations that possess potentially adaptive characteristics.
• Adaptations to local environment (local adaptation).
Give an eg of how NS can’t predict the future & explain it?
Darwin’s finches
• how they responded to seed availability where beak size depended on the types of seeds that where available.
Conditions for NS to occur? (3)
• Variation in individual traits.
• Heritable traits/Heritability.
• Difference in fitness (reproduction).
Eg of the 1st NS condition?
Beak depth in Darwin’s finches.
What does fitness involve? (4)
• Variability.
• Fecundity.
• Longevity.
• Mating success.
Viability?
= the probability that an organism is able to survive & pass down their traits to the next generation.
Fecundity?
= where an individual is able to produce fertile/healthy gametes to increase the chances of them transferring their traits to the next generation.
Longevity?
= the lifespan of individuals before & after mating & whether they will be able to mate successfully before their ultimate deaths.
Mating success?
= whether an individual is able to transfer their genetic traits to the next generation & in subsequent generations.
Fitness types? (2)
• Absolute fitness.
• Relative fitness (w).
Absolute fitness?
= the average no. of offspring produced for genotypes.
Relative fitness?
= an individual’s/genotype’s fitness relative to the fitness of other individuals/genotypes in the population.
Main selection types that act on a character that is continuously distributed? (3)
• Directional selection.
• Disruptive selection.
• Stabilizing selection.
Eg of Directional NS & explain?
Pterosaurs body size.
- As birds emerged, pterosaurs got bigger.
Eg of Disruptive NS?
False Wanderer (butterfly).
Eg for Stabilizing NS & explain?
Baby birth weight
- where average (middle) weight is favoured/healthy.
Results of Disruptive/Diversifying NS? (2)
• Increase in extreme traits in population.
• Increase in trait diversity.
Result of Stabilizing NS?
Decrease in variation/diversify.
How do we distinguish Stabilizing NS & No selection? (2)
• Compare Expected change (random) & Observed change (chi² test).
• If calculated change < expected change = Stabilizing selection is occurring.
What are the applications of evolution? Where can we apply the evolution theory? (4)
• Phylogenetics (viruses).
• Genetic counseling (zebra fish).
• Pharmaceuticals (medicinal purposes).
• Artificial selection (wild mustard= provides kale, cabbage, broccoli).
Genetic drift?
= the random change in allele frequency.
Frequency-dependent selection (FDS)?
= selection that depends on how many morphs/morphologies are present in a population.
FDS types? (2)
• Positive FDS (+).
• Negative FDS (-).
+ FDS?
= selection where the common morph is favoured.
– FDS?
= selection where the rare morph is favoured.
+ FDS attributes? (3)
• Eliminates polymorphisms.
• Higher fitness when common.
• Predators avoid common morph & select the rare form.
What does + FDS result in regarding risk?
It results in a shared risk among common individuals.
What do we mean by shared risk when talking about + FDS?
We mean that if you look like everyone else, there’s a lower risk of getting eaten by prey.
Egs of + FDS? (2)
• Aposematism.
• Language.
What does - FDS result in?
It results in genotypes (common + rare) reaching an intermediate frequency.
– FDS attributes? (2)
• Maintains polymorphisms.
• Results in genotypes reaching an intermediate frequency.
How does -FDS maintain polymorphisms?
By producing stable polymorphisms in a population.
Egs of -FDS? (2)
• Side-blotched lizards.
• Scale-eating cichlids.
+ FDS in terms of FDS & Mimicry?
= selection common mimics survive.
– FDS in terms of FDS & Mimicry?
= selection where the rare mimics survive if the common is poisonous.
To better understand FDS & Mimicry refer to what paper?
Chouteau et al. 2016.
Things to note for FDS & Mimicry according to Chouteau et al. 2016? (3)
• Warning colouration frequency/Common frequency is dependent on predator avoidance knowledge.
• + FDS.
• Tested using Heliconius butterflies.
Mimicry types? (2)
• Müllerian mimicry.
• Batesian mimicry.
Müllerian mimicry?
= mimicry that involves aposematism/warning colouration.
Müllerian mimicry attributes? (2)
• Honest signaling.
• Both groups are toxic/harmful.
What do we mean by “Honest signaling”?
= signaling where organisms bravely show predators that they’re poisonous.
Batesian mimicry?
= mimicry where the edible/harmless species resembles the toxic/harmful species.
Batesisn mimicry attribute?
Deceptive signaling.
Eg of Müllerian mimicry?
Heliconius species mimicking each other (H. erato & H. melpomene).
Egs of Batesian mimicry? (2)
• King snakes mimicking coral snakes.
• Barnyard grass mimics rice.
Outcomes of NS (2)?
• Mimicry.
• Adaptations.
Adaptation?
= any change in form/function/behaviour that promotes the likelihoods of a species’ existence.
Adaptation attributes? (2)
• Increases the ability of a species to survive in an environment & more likely to reproduce.
• Has a genetic basis (except for learned behaviour).
Why does Barnyard grass mimic rice?
To prevent being weeded out of the rice paddy garden.
What is adaptation based on?
Genetics.
What does adaptation exclude?
Learned behaviour.
How do we identify traits that are adaptations? What questions do we need to ask to identify adaptations? (4)
● Is it heritable?
● Is it functional?
● Does it increase fitness?
● How did the trait first evolve?
Egs of animal adaptations? (3)
• Loose bone attachment in snakes (wide mouth opening).
• Camouflage.
• Finches on Galapagos islands.
Camouflage types? (2)
• Visual camouflage.
• Chemical camouflage.
Visual camouflage?
= camouflage that aimed to blend in with the environment.
Eg of visual camouflage?
Chameleons.
Chemical camouflage?
= camouflage that aimed to remove scent.
Eg of chemical camouflage?
Female puff adders when they don’t feel like mating with male puff adders.
Eg of plant adaptation?
Flowers mimic the form & scent of pollinator mates (orchids mimicking female wasps).
If a trait is not an adaptation, then what/where did it arise from? (4)
• Chance result of evolutionary history (long term).
• By product of another trait.
• Outdated adaptation (vestigial structure).
• Result of genetic drift (short term).
Exaptation?
= a trait that acquires a function that it was not originally selected for.
Egs of an exaptation? (2)
• Feathers.
• Penguin’s wing.
Explain the exaptation eg?
They were meant for sexual selection & insulation but developed to be adapted for flight.
Eg of where these conflicting selection pressures are seen & explain?
Guppies.
- where when a predator is present they are basic/simple fish (to avoid getting eaten).
- when a predator is absent they are colourful fish (to attract female guppies for mating).
Directional selection?
= where the extreme phenotype/trait is favoured.
Egs of directional selection? (3)
• Pink salmon size and net size.
• Pterosaurs body size in Mesozoic period.
• Change in finch beak size over time.
Stabilizing selection?
= where the trait mean is selected for (average trait is favoured).
Stabilizing selection attributes? (2)
• Traits in tail of distribution are selected against.
• Decrease in variation.
Egs of Stabilizing selection? (2)
• Baby birth weight.
• Sickle cell anaemia (heterozygous).
Fitness?
= number of offspring produced.
Generational fitness?
= fitness that depends on an organism’s offspring having offspring and so on to perpetuate the gametes.
Important thing to note with fitness?
Fitness is key to NS.
What is relative fitness (w) used for?
To evaluate NS as selection occurs through differences among individuals in the population.
Disruptive selection is AKA?
Diversifying selection.
Things to be mindful of with selection types? (2)
• Trait distribution in the original population.
• How that changes to identify the type of selection.
Directional selection attributes? (3)
• Occurs due to competition, migration, human interference, etc.
• Distribution moves in one direction or the other.
• Variation is constant.
Disruptive selection?
= where the trait mean is selected against.
Disruptive selection attributes? (2)
• Leads to increase in extreme traits in the population.
• Leads to increase in diversity of traits (increase in variation).
Extreme?
= tails of the distribution (increase in frequency).
Explain the eg for Disruptive selection? (2)
• Extreme phenotypes mimic Butterflies not normally predated on because they’re morphologically similar to 2 other toxic species.
• Frequency of alleles in the population changed due to selection for extreme phenotypes.
Things to consider for Diversifying selection? (2)
• Mean (x bar) = trait predated on.
• Increased frequency of tail phenotypes.
Stabilizing selection attributes? (2)
• Traits in tail of distribution are selected against.
• Leads to decrease in variation.
Why does sickle cell anaemia persist in a population?
Because of the heterozygous state which enables detrimental traits to remain in a population.
Compare Directional selection; Disruptive selection & Stabilizing selection in terms of variation? (3)
● Directional selection = variation is constant.
● Disruptive selection = increase in variation.
● Stabilizing selection = decrease in variation.
What do we mean when we say “traits must be heritable”?
Offspring should resemble their parents more than organisms within the same environment.
Body size in terms of trait types?
Continuous trait.
Selection types use what type of traits?
Continuous traits.
Distribution associated with continuous traist?
Normal distribution.
Why is variation important in a population?
It gives natural selection something to acton and ensures the reproductive fitness/success of varying organisms within population.
Aposematism?
= where the warning colouration indicates that an organism is poisonous to predators, thus predators avoid eating the common & there’s higher fitness for the common.
Explain Eg 1 of -FDS?
Touches on sperm frequency being the main factor in determining mating success.
Side-blotched lizards male types & their description? (3)
• Blue = single females.
• Orange = harems.
• Yellow = sneaker male.
Yellow male Side-blotched lizard attributes? (4)
• Sneaker male.
• Imitates females.
• Don’t defend territories.
• Rare morph.
What are the conflicting selection pressures? (2)
• SS.
• NS.
Eg of + FDS in terms of FDS & Mimicry?
Heliconius butterflies.
Eg of – FDS in terms of FDS & Mimicry?
Monarch & Viceroy butterflies.
Arabidopsis thaliana?
= small plant from the mustard family important for genetic research.
Arabidopsis thaliana attributes? (3)
• Selection = trait changes.
• Gave biologists a window to genotypes.
• Helps biologists underpin genotypes & how traits change.
Other evolutionary process that affects trait change?
Hybridization.
Explain graph of butterflies? (4)
• Warning colours in butterflies.
• Common morph is favoured.
• Chouteau et al. 2016.
• + FDS.
Selection types for continuous traits? (3)
• Directional selection.
• Disruptive selection.
• Stabilizing selection.
Selection types for discrete traits? (2)
• + FDS.
• – FDS.
How do you know that a butterfly isn’t part of the population or is a mimic of another butterfly species?
The difference in the morphs is in the details.
Why is it beneficial to be honest in Müllerian mimicry/Benefit of Müllerian mimicry?
Increases their chances of being recognized by predators & being left alone.
Why is it beneficial to be deceptive in Batesian mimicry/Benefit of Batesian mimicry?
Organism mimic gains protection as predators mistake it for the toxic organism & leave it alone.
Can adaptations evolve by chance alone?
No.
Difference between learned behaviour & Inherited behaviour?
● Learned behaviour = develops during an organism’s lifetime.
● Inherited behaviour = behaviour that an organism is born with.
If trait is not an adaptation or even not explained by the other 4 reasons, then what is it?
Exaptation.
What does selection alter/change? (3)
• Frequencies.
• Alleles.
• Genotypes.
What do we mean by “Is it heritable”?
We mean that traits need to be genetically encoded.
What do we mean by “Is it functional”?
We mean that the trait needs to perform that task it was shaped to do.
What do we mean by “Does it increase fitness”?
We mean that the trait must help produce more offspring/enable longer lifespan.
What kind of question is “How did the trait first evolve”?
Pattern question.
What kind of question is “Did form & function arise simultaneously”?
Process question.
Did form & function arise simultaneously?
Unlikely.
Arabidopsis thaliana common name?
Thale cress.
Learned behaviour?
= behaviour that develops during an organism’s lifetime.
Inherited behaviour?
= behaviour that an animal is born with.
