Exam 2 Flashcards
____________ is the only known explanation for adaptation.
Natural Selection
Why can drift not be an adaptation?
Drift is random
What are three examples of adaptations?
Feeding Specializations, Crypsis, and Mate Attraction or competition
What is crypsis?
Camoflauge/ adaptations to blend in
What are the two qualifications for a trait to be an adaptation?
- It must improve the fitness so that the organism with the trait has higher fitness than those without
- There must be a correlation between the presence of the feature and the hypothesized selection pressure (greater selection = greater presence of feature)
What results from differences in fitness?
Differential reproductive success and survival
How does adaptation occur: gradually or rapidly?
Adaptation occurs through gradual, directional selection over several generations
What is are analogous structures?
Structures that are functionally similar, but structurally and historically different (Independent evolutionary origins, such as the vertabrate eye and octupus eye)
What are analogous structures a product of ?
Convergent Evolution
What is convergent evolution?
Organisms that are not closely related independently evolve similar traits as a result of having to adapt to similar environments or ecological niches
What are homologous structures?
Structurally similar structures, but can be functionally different
What are homologous structures a product of?
Divergent Evolution
What is Divergent Evolution?
The accumulation of differences between groups which can lead to the formation of new species
_________ is evidence for natural selection.
Poor Design (panda’s thumb is not a “perfect” thumb, it is a makeshift adaptation for stripping bamboo)
What are Vestigial Structures?
Structures with little or no current function, retained due to common ancestry
What is a pre-adaptation?
An existing structure modified to serve a new function
Bird feathers were originally intended for thermoregulation, but they now also facilitate the evolution of flight. What is this an example of?
Exaptation
What is an exaptation?
An adaptation that has arisen via preadaptation
What is the genetic constraint on adaptation?
Heterozygotes have the advantage of the highest fitness, but they cant “breed true”
What is the morphological constraint on adaptation?
Certain morphologies may be impossible due to some uknown developmental constraint
What is allometry?
Something is allometric if it scales with size. When the Irish Elk got bigger, its antlers got significantly bigger, decreasing the geometric similarity. It became extinct because any more increase in size would cause such a large increase in antler size that the elk could not support its antlers.
What is the trade-off constraint on adaptation?
When adaptation for one function may compromise another function (the cheetahe h adapted longer legs for greater speed, but that came with higher chance of breaking a limb)
Why is large population size important for Hardy-Weinberg theorem?
In genetic drift, the passing on of A and a alleles may not be equal in a small population. In a large population, it will be close to 1:1
What is the result of genetic drift over time?
The population will eventually drift to homozygosity
What can be used as a standard measure of genetic variation per locus in a population?
Heterozygosity (gene diversity)
What is the equation for heterozygosity?
H = 1- (p^2 + q^2)
H is the chance of drawing two different alleles
What is the equation for homozygosity?
f = (p^2 + q^2) or f = 1- H
Drift tends to ________ heterozygosity.
reduce
Mutation tends to _________ heterozygosity
Increase
What is the establishment of a new population by a smaller group of a larger population that onl carry a small fraction of the total genetic variation of the parental population?
Founder Effect
If the founder event occurs but genetic variation of the new population is the same, then there is no ____ ____ via founder effect
Genetic Drift
Genes in low frequency in the original population become _________ in the founder population.
Common
True of False: Founder evens are likely to produce homozygosity
False, they are not likely to produce homozygosity
What is a population bottleneck?
Environmental or other catastrophe decreases the size of the population. The population rebounds, but the genetic diversity is very low
________ ________ is a type of bottleneck.
Founder Effect
What does a present low level of genetic diversity indicate?
A past bottleneck
True or False: Founder Effect results in genetic drift because a non-representative sample of the population produces more gametes
True
_________ populations may be more vulnerable to random events such as genetic drift because it is easier to draw a non-representative sample from them.
Small
Given enough time, drift will end in fixation for ________ alleles.
Neutral
What are neutral alleles?
Those with no selective advandage/disadvantage
Small populations are more sensitive to _____ _____, but the _______ _______ ______ through genetic drift is independent of population size.
random events, rate of evolution
The rate of neutral evolution depends entirely on ______ _______.
mutation rate
If drift occurs, will the population become homozygous?
No, mutation balances drift to produce equilibrial heterzygosity
When the population is small and mutations are infrequent, is drift more or less powerful?
More powerful
Why do females determine the reproductive output of a population?
Any individual female typically has a higher mating success than any individual male
What is a gonochoric population?
Separation of sexes in different individuals (opposite of hermaphrodite).
What are the two advantages for asexual reproduction?
- Most members of the population can reproduce
2. The reproductive output is higher since more individuals can reproduce
What evidence is there that sex is good from an evolutionary standpoint?
- It is seen in most eukaryotes (ubiquity)
2. Longevity of sexual lineages compared to asexual lineages
Why is sex advantageous?
Because recombination is advantageous and results in more variability
What is Muller’s Rachet?
The process by which deleterious mutations accumulate in an asexual population over time. Used to explain the evolution of sex.
What are the two consequences of Muller’s Ratchet?
- The proportion of the population made up of low-fitness genotypes increases
- The size of the population decreases
How does migration violate Hardy-Weinberg?
- By introducing/removing alleles
2. Maintains genetic diversity in the face of natural selection or genetic drift
What is microevolutionary change?
change in gene frequencies across generations
What are the four mechanisms for microevolutionary change and which ones are random?
- Mutation (random)
- Genetic drift (random)
- migration/ gene flow (random)
- Natural Selection
What is the biological species concept?
Species are groups of that can interbreed and reproduce
What three observations led to the Biological Species Concept?
- Variation within populations
- Geographic variations between populations
- Sibling (cryptic) species that are reproductively different but look alike
What is a cryptic species?
Morpholigically identical but cannot interbreed, so they are different species
What are four limits to the biological species concept?
- Organisms that do not reproduce sexually
- Hybrid zones (populations were geographically isolated, became distinct, then came back together and mated and reproduced)
- Extinct species cannot be studied
- Geographically separated species cannot be studied to see if they can reproduce
What is the morphological species concept?
Species are defined by physical features (morphology)
What is the phylogenetic species concept?
an irreducible group whose members are descended from a common ancestor and who all possess a combination of certain defining traits
What is a synapomorphy?
Shared, derived (homologous) features
What is a monophyly?
A group of species characterized by synapomorphy
What is a clade?
A monophyletic group made up of all the descendants of a common ancestor
What is paraphyletic?
An ancestral group but not all descendants are included
What are three commonalities between all species concepts?
- Species are populations linked by history
- Species are characterized by shared, derived characters
- Genetic and morphological continuity is maintained by interbreeding
What is speciation?
The mechanisms by which populations attain reproductive isolation
What do isolating mechanisms do?
Prevent gene flow between populations or members of the same population
What are two prezygotic barriers that are isolating mechanisms?
- prevention of mating between populations
2. positive assortative mating (non-random mating based on phenotype or genotype)
How is a lack of contact or time an isolating mechanism, and what is this isolation mechanism called?
- Incipient (cryptic) species may be in the same place but mate at different times of the year or day
- An organism may be isolated by its habitat so it spends its whole life in the same place so it doesn’t come into contact with the incipient species
- Temporal Isolation
Why is lack of interest an isolating mechanism?
The male may not engage the female, or the female does not respond to the male
What is ethological isolation?
Behavioral isolation. For example, male lacewings have a mating call to attract females. The females show preference for certain mating calls.
What are two post-mating, prezygotic isolation mechanism?
- Mating occurs, but zygotes are not formed. May be due to the lock and key hypothesis, where the parts don’t fit so no sperm is transferred.
- Gamete isolation occurs in which the eggs may not recognize the sperm due to incompatible receptors. Common in plants.
What is a postzygotic isolating mechanism?
Fertilization takes place but does not result in a successful offspring
__________ are the outcome of reproductive isolation.
Species
What are three things that can happen in hybrid species?
- Embryo dies shortly after morality
- Hybrid offspring develop then die
- Hybrids are viable but are not fertile
What causes aneuploid gametes?
Chromosomes have different genes or morphologies so they don’t separate properly
What is allopatric speciation?
A population is subdivided, and during the separation mutations arise in each population so that they are different from the original population. These differences are able to maintain distinctiveness even after the physical barrier is removed
_______ is the most important mod of speciation in animals.
Allopatric
What is the difference between dispersal and vicariance, and what type of speciation are these?
Dispersal is the movement of a species into a new area. Vicariance is the separation of a species by a geographical barrier. These are allopatric speciation.
What is Allopatry?
Speciation in adjacent areas across which gene flow is restricted
What is parapatric speciation?
physical distance prevents gene flow
what is sympatric speciation?
Speciation without physical or spatial barriers. Different groups of the population specialize on a particular resource (niche) and speciate.
__________ are features which enhance relative fitness and lead to greater reproductive success
Adaptations
What is sexual selection?
Selection arising from differences in mating success
What are two basic kinds of reproductive modes?
- Spawning
2. Copulation
What are advantages and disadvantages to copulation?
Advantage: the ability to choose ones mate
Disadvantage: Requires time and energy searching for mates
What three things does spawning require?
- Coordination of timing of spawning
- Concentration and density of gametes appropriate to environment
- Gamete recognition mechanisms
What is polyandry?
Multiple smaller males compete for access to largest and oldest female
What is polygyny?
The oldest and largest individual is male and he fertilizes a group of females
________ selection is between members of one sex to gain access or opportunity to mate
Intrasexual
What is preference by one sex for certain phenotypes in mates?
Intersexual Selecion
How does Sexual Selection violate Hardy-Weinberg?
No random mating
________ mating is when there is an equal chance of mating between every male/female pair.
Random
What is positive assortative mating?
Preference for similar phenotypes
What is negative assortative mating?
Preference for different phenotypes
What are the six components of reproductive fitness?
- Viability- probability the individual will survive
- Mating success- number and quality of mates
- Fecundity- number of gametes per individual
- Segregation advantage- alleles have a greater chance of showing up in the gametes
- Gamete viability- longevity/quality of the egg or sperm
- Fertilization Success- fertilization will take place
Why do females typically pick their mates?
- produce the “expensive” gametes
- May have post-mating responsibilities
- Focus on getting the best mate so her investment in eggs has the greatest genetic dividend
What do females look for in males?
- Signs of health and capability in feeding
- Features that emphasize the distinction between males and females
- Novelties that suggest they are from another population
What does Zahavi’s handicap hypothesis say?
Males that have a handicap, such as a peacock’s large, heavy feathers, prove to have superior genes since they are surviving with their handicap. This is why females mate with them. Survival despite the handicap demonstrates fitness.
Why do the offspring of choosy females have higher average fitness?
If male quality correlates with male fitness, choosy females have an increased frequency of mating with higher fitness males.
What is runaway sexual selection?
When female choosiness for a certain male appearance does not necessarily mean the males have greater fitness
