Exam 2 Flashcards
Are discrete or continuous traits quantitative or qualitative?
- Continuous: quantitative
- Discrete: qualitative
Number of legs is an example of a ________ trait
discrete
Height is an example of a ________ trait
continuous
What are quantitative traits usually determined by?
Genotype at many loci and the environment
Do traits that have many genes involved in them (quantitative traits) follow the Mendelian model?
Yes, they can!
Define/describe broad sense heritability
The percent of the total phenotypic variation that is due to genetic variation
Define/describe narrow-sense heritability
Only considers additive genetic variation (not dominant genetic variation)
How do we estimate/measure heritable variation?
Cross fostering experiments
What does measuring heritable variation allow us to do?
Predict how a population will respond to selection
Any estimates of heritability are specific to…
A particular environment
Heritability includes both ______ and ______
V(G) and V(E)
What do heritability scores NOT tell us?
- Tell us nothing about how much the environment would contribute to variation in a different environment
- High heritability tells us nothing about the origin of differences between groups
- Heritability tell us nothing about the role of genes in determining traits that are shared by most members of a population
What would be the heritability score of number of eyes in humans? Why?
- Very low!
- Little to no phenotypic variation –> low score/low heritability
Why is it important to measure heritability?
Allows us to predict whether selection on the trait will cause a population to evolve and how quickly these changes will happen
Can influence of the environment be inherited?
Yes!
What is epigenetics?
The study of heritable changes in phenotype (appearance) or gene expression caused by mechanisms other than changes in the underlying DNA sequence
Are epigenetic changes heritable?
Yes!
What are selection differentials?
Difference in mean for selected and mean for entire population
What is the relationship between selection differentials and selection gradients?
The selection gradient (B) for trait t is equal to the selection differential (S) divided by the variance in the population
If the selection gradient tell us about the strength of selection, why do we need to know the selection differential?
Selection differential (S) is what we use to predict the strength of the response to selection
How/why is the selection gradient useful?
Often the easiest measure in the field
For predicting evolutionary response (R ) to selection, do you need to know heritability or selection differential?
Both!
What “defines” male and female across all animals?
A. Males are larger
B. Females provide more parental care
C. Males fight and females choose
D. Males produce smaller sex cells
E. You need all of the above to define males and females
D. Males produce smaller sex cells
What limits reproductive success?
- Resources
- Access to mates
What leads to different mating strategies?
- More selective of mates
- More competitive for mates
Define sexual selection
The advantage which certain individuals have over others of the same sex and species in exclusive relation to reproduction
Sexual selection is intensity measured. What does this mean?
A measure derived from a random measure; variance in mating success
Relative investment influences…
Variation in reproductive success
Differences in behavior is an example of a
component of sexual selection
What are the two main components of sexual selection? How are they different?
- Intra-sexual: competition for mates (when members of the same sex compete for mates)
- inter-sexual: choice of mates (when one sex chooses which members of the opposite sex to mate with)
Does social dominance always equal more mates?
No (Ex: baboons)
What maintains the smaller sneaker males?
- The sneaker males reach sexual maturity quicker, and are therefore able to achieve some level of reproductive success before the courter males
- The sneakers are able to semi-successfully reproduce longer than the courters
Define/describe infanticide
Competition that occurs beyond conception; the intentional killing of offspring
Why is infanticide used?
- Maintain resources
- Might kill offspring that are not their own
- Usher females back into breeding condition
Describe post mating competition and give some examples
- Preventing females from re-mating
^Examples: mate guarding, hormones in ejaculates,
barbs on penis of cats - Removal of other male’s sperm
- Polymorphism in sperm (ex: “killer sperm” that just takes up space, preventing a later fertilization event)
What are the three examples of direct selection in regards to an animal being “choosy” about their mate?
- Mate with the correct species
- Choose mate that provides resources
- Choose mate that has good genes
What are three characteristics that might indicate that an organism has “better” genes?
- The individual is older (has survived longer)
- Individuals that can do “extreme” behaviors
- Degree of bilateral symmetry
What are fluctuating asymmetries?
Random deviations from perfect bilateral symmetry
What drives the evolution of mate preferences?
- Selection
- Runaway (indirect selection)
Define/describe runaway
Genetic correlation between preference and trait, followed by selection on trait
Individuals with strong preferences mate with individuals with exaggerated traits is considered what type of selection?
Runaway sexual selection
Can the sexual selection theory be applied to humans?
Yes
What are criticisms of the sexual selection theory being applied to humans? Which criticism(s) have been proven false? True?
- No genes have been identified to code for behaviors (FALSE)
- Human choices not based on increasing fitness
- Not all human behavior is biologically adaptive (TRUE)
- Sociobiology maintains social injustice and inequality
In regards to humans, the sexual selection theory predicts
- Females are choosy, limited by resources
- Males are not choosy unless their investment is high
What were two results discovered about what men and women value in relationships?
- Women value resources and status of potential mates more than men (prefer older men)
- Men are more likely to prefer younger mates (young males prefer mates their own age, older males prefer mates that are 5-15 years younger)
Given greater variation in RS in females than males for seahorses, which of the following is likely to be true??
- Female reproductive success is limited by their access to males
- Males are more choosey about mates than females
- Females fight for access to males
- Males reproductive success is limited by resources
- All of the above
All of the above
If the alternative mating behaviors in the fish Xiphophorus multilineatus are an ESS, what maintains the small sneaker males?
- Not an ESS as the small males have lower mating success and therefore are just making the best of a bad situation and maintained by mutation/selection balance.
- Alternatives are a balance between mating success and survival, as small males are more likely to survive to mate.
- Small males get more mates when they get larger.
- Because there is a genetic basis to being a small sneaker male, any matings they get at all will help maintain this type of male.
Alternatives are a balance between mating success and survival, as small males are more likely to survive to mate.
Which of the following is true about sperm competition?
- It is most common in animals with external fertilization.
- Both males and females benefit by avoiding sperm competition.
- Males benefit by encouraging their mates to have multiple partners.
- Females will often choose to mate with additional males to promote sperm competition.
Females will often choose to mate with additional males to promote sperm competition.
Which of the following has been shown to be a reason why females choose to mate with one male over another?
- They were choosing the male of the right species.
- They were choosing a male that would provide parental care.
- The were choosing the most symmetrical male.
- They were choosing a male that provided them with food.
- All of the above have been demonstrated.
All of the above have been demonstrated.
What led to different sized gametes in males and females?
Divergent selection
The reproductive success of males is often limited by access to ________, while the reproductive success of females is often limited by access to ________
females, resources
T / F : the strength of sexual selection is often greater in males
T
In the case of seahorses, is sexual selection stronger in the males or females? Why?
- Females
- The females are competing for mates, the males are choosing mates
T / F : many traits are under selection by both components of sexual selection
T
When/why are alternative reproductive tactics used?
Alleviates strong selection on males that “lose” against others males (in terms of mating)
Describe the trade-off of sneaker vs courter male fish
1) Increased probability of surviving to mate (mature small)
2) Increased probability of mating once sexual maturity is reached (mature large)
Describe negative frequency dependent selection in terms of the sneaker/courter male fish
When sneaker male numbers go down, their success goes up
What is an example of indirect competition that we discussed?
- Sexual selection for male endurance
- Example: a male snake that is fast and is able to move around a lot will be able to encounter more females more often, having more reproductive fitness without any direct competition with other males
Cryptic female choice will only occur if…
the female mates with more than one male at a time
How is access to more resources an example/component of direct selection? What is an example of this?
- More resources = more offspring
- More resources = more time mating
- Ex: females that mate with larger bullfrogs that have larger territories produce more offspring
What two organisms discussed were found to prefer symmetrical males?
Female fruit flies and swordtail fishes
Do preferences become genetically correlated with traits?
Yes!
Can preferences evolve?
Yes!
Variation in eyestalks and preferences leading to assortative mating is an example of…
indirect selection
Assortative mating producing genetic correlation between sons and daughters within families is an example of…
indirect selection
According to indirect selection, should a selection on male eyestalks produce a response in female preference?
Yes
Do male or female humans have greater variation in reproductive success?
Males
When comparing degree of choosiness dependent on expected investment, what were the differences seen between men and women?
- Short term: women value intelligence of mate more so than men
- Long term: women and men value intelligence equally
Describe the significance of symmetry in humans
Both males and females find symmetrical faces more attractive
Studies have found that symmetrical males…
mate earlier and have more EPCs
Female preference for symmetrical males is strongest when…
most fertile
Describe the “traditional sex roles”
- Choosy and caring females
- Competitive and promiscuous males
____________ and __________ can influence one’s perception regarding sex differences in nature
Demographic traits, experiences
Reproduction usually involves…
a suite of traits
Are traditional sex roles always found?
No! There can be choosy males and females can have multiple mates
Describe some differences between sex and gender
- Biologically, sexes are well defined based on a physical difference (ex: gamete size)
- Sex is not fixed and influenced by both genes and environment
- Gender has multiple constructs in human societies
Why do life history traits involve trade-offs?
Limited amount of energy to invest in survival, maintenance and reproduction
How does natural selection optimize life history in light of trade-offs?
- Maximizes the number of offspring surviving to maturity
- Depends on the likelihood of survival to different age classes
Are life history strategies subject to evolution? If so, what types of life history strategies?
Yes! Strategies such as longevity and age of sexual maturity (ex: possum)
How did the life history of the female possum evolve?
- The variation in the timing of life events evolved, not the events themselves
- Changes in the allocation of energy to different time periods of life allowed for this evolution to occur
What did scientists determine to be the cause of the evolved life history in the possums?
- There was higher predation on the mainland, resulting in lower survival (longevity) and larger litters in the first year of sexual maturity
- There was greater muscle fiber degeneration for females on the mainland when compared to those on the island
- Aging faster, driving selection for larger litters
- Predation was main driving factor for the evolution to occur
Predation risk drives what two life history traits to evolve?
- Reach sexual maturity sooner
- Produce larger litters
What was the significance of the research done on the Brown Anolis lizards? What did the experiment entail?
- Showed a trade-off between reproduction and growth/survival
- The females that had their ovaries removed (were prevented from reproducing) were found to have both increased growth and survival rate when compared to the control group
Trade-offs arise when…
investment in one trait results in lower investment in another trait
Investment in reproduction is often at the expense of…
growth or maintenance
Selection may favor mutations that are…
beneficial early in life, even if they are deleterious later in life
Investment in early reproduction often reduces…
reproduction later in life
Changes in the environment can bring about…
rapid evolution of life history traits
Is male initial investment higher or lower? Why?
- Lower
- Sperm is much smaller than egg
Describe the significance of certainty of paternity and investment
- Certainty of paternity influences investment
- More uncertainty = lower investment
- Certainty for males is lower with internal fertilization, more likely to be equal with external fertilization
Biased OSR drives…
strong sexual selection
Define/describe the operational sex ratio (OSR)
The ratio of sexually competing males that are ready to mate to sexually competing females that are ready to mate
When does sexual selection become an important agent?
When members of one sex compete with each other to mate
Are there fewer or more of the sex that invests more in parental care?
Fewer/less available for mating
In what ways would/could an organism regulate the number of offspring to maximize fitness?
- Miscarriage
- Canabalism
When would cannibalism benefit an individual?
- In times of limited resources
- Cannibalize individual(s) least likely to survive
Organisms may also regulate the _______ of offspring to maximize fitness
sex ratio
When would having more offspring of one sex benefit an individual?
If the population is biased for one sex
Define/describe frequency-dependent selection
The production of each sex is favored when rare because the rare sex has more mating opportunities
How did the size of the clutch affect the sex ratio of fig wasp populations?
As the clutch size got larger, the sex ratio of males to females got lower
How are female fig wasps able to alter the sex ratios of their offspring?
- Sex ratio can be determined through fertilizing some eggs (male) and not others (female)
- Only a small number of males is needed to fertilize the females
Describe the Trivers-Willard hypothesis
Mothers alter sex ratio depending on conditions
- Produce females when in poor conditions; daughters will
likely have some offspring even if in poor condition
- Produce males when in good conditions; males likely to
benefit more from being large and will more readily
attract females
What did we learn about the blue-streak cleaner wrasse in relation to the Trivers-Willard hypothesis?
- Switches their sex in Trivers-Willard-predicted manner
- Begin life as females and breed as such when young and small, but switch to male when they are large given that larger males monopolize mating in harems
Describe the sex ratio adjustments observed in Seychelles warblers
- With high resources, females are favored (up to 3 “helping” daughters is beneficial to survival)
- With low resources, males are favored (males tend to disperse away from poor habitat)
T / F : females usually benefit from providing parental care more than males
T
Frequency-dependent selection maintains ________ within two populations and tells us about ________
variation, OSRs
The Trivers-Willard hypothesis predicts…
investment in females when mother is in poor condition and in males when mother is in good condition
Describe the strategies used by the male and female penduline tits to maximize offspring produced over a lifetime
- Males: move around and mate with new females
- Females: save energy for next brood
What behavior evolved from conflict in parental care in the female penduline tits?
The females were observed hiding their eggs from their male mates in order to keep them around as long as possible
Do siblings compete for parental investment?
Yes
What is siblicide? Is it adaptive? Why or why not?
- When a sibling kills another sibling
- Parents often watch and do nothing because it is ultimately adaptive
- Adaptive in times of limited resources
What example of siblicide did we discuss? Explain it
- Boobies
- Lay 2 eggs 2-10 days a part
- The older, larger masked booby chick almost always kills its younger, smaller sibling
- The boobies treat the second chick as a “backup” (the larger masked booby might die before it can commit siblicide)
How do the blue-footed booby parents react differently than the masked booby parents to siblicide?
While the masked booby parents rarely intervene, the blue-footed booby parents intervene more often as they have more access to enough food/resources
What is sexual conflict?
When the reproductive interests of males and females differ (not only in relation to parental care)
What is an example of sexual conflict?
Females may benefit from multiple mating (sperm competition) but males benefit from having multiple partners that do not mate with others
What were the findings of the antagonistic sexual adaptations experiment done on drosophila?
- After more than 30 generations of evolution without any sperm competition (forced monogamous mating), male semen became less toxic to females and females lost their defenses against seminal proteins
- When these females were later forced to mate with males reared in natural, competitive environments, they died much sooner than females that had evolved with the sexual conflict
What is genomic imprinting?
Gene expression silenced by methylation by one parent
What is the “parent of origin effect”?
When offspring express either maternal or paternal copy of a gene but not both (due to genomic imprinting)
What example of genomic imprinting did we talk about?
Mules and hinnies
Do mules and hinnies look the same? Why or why not?
- Although they are both hybrid offspring of horses and donkeys, they do not look the same
- Differences in appearances are due to the mother and father species being reversed, resulting in different genes being imprinted and ultimately, different appearances
Why is the paternal allele for growth factor II widely expressed in mice, while the maternal is hardly transcribed?
- The male is benefited by this but the female is not
- Male wants his offspring to grow faster and larger, but giving birth to offspring that are too big is detrimental to the mother
What is another piece of evidence for genomic imprinting in mice? Is this similar to anything in humans?
- The female type 2 receptor binds excess paternal hormone, while the male type 2 receptor does not bind the hormone
- Similar to gestational diabetes in humans
Parental care creates opportunities for many different kinds of conflicts. What are these conflicts?
Conflicts between parents, among siblings, between parents and offspring
Parental care is often rife with conflict. Give 3 examples
- Sexes may maximize fitness differently
- Males benefit when mother invests more in current offspring; females benefit by saving resources for future offspring
- Parental conflict can lead to battles of gene expression in offspring
What is senescence?
- Aging
- Decline in fertility and probability of surviving
What is the rate of living theory? What does it focus on?
- Focuses on proximate mechanism
- Describes aging as a function of metabolic rate
What two hypotheses were proposed to support the idea that aging is a function of metabolic rate? Did evidence support these hypotheses?
- Cell and tissue damage is caused in part by the by-products of metabolism - all organisms reach the limit of biologically possible repair
- Species should not be able to evolve longer life spans
Evidence did not support these hypotheses!
T / F : variation in metabolic rate is correlated with lifespan
F, it is NOT correlated with lifespan
How were scientists able to disprove the second hypothesis, that species should not be able to evolve longer life spans?
- Used artificial selection to increase life span of fruit flies
- Selected for fruit flies that were late in reproducing (these ones then lived longer to survive to reproduce)
What are the real mechanisms behind aging?
- Cells cannot divide an unlimited number of times
^ Shortening of telomeres!
In what cells do telomeres not shorten? Why?
Telomerase in germ line cells repairs the telomeres (germ line cells do not have a finite number of divisions)
What was the correlation between expected lifetime RS and dying young? Reproducing earlier?
- Expected lifetime RS goes down very little with dying younger
- BUT goes up a lot with reproducing earlier and dying even younger
Do late acting mutations accumulate faster or slower?
Faster
T / F : WHEN a mutation causes death is important
T
If late acting mutations accumulate at higher rates…
then severity of inbreeding depression should increase with age
Describe the experiment with house flies that was done in support for the mutation accumulation hypothesis
- House flies were only allowed to breed for 4-5 days
- Every six generations, some flies were allowed to live out their lives (to measure longevity)
- If late acting mutations accumulated (lack of selection), then life span should decrease
Were the results of the house fly/mutation accumulation experiment due to genetic drift? Why or why not?
No, because the results were the same with both small and large populations
According to the antagonistic pleiotropy hypothesis…
- There is selection for alleles with pleiotropic effects that are advantageous early in life and deleterious later in life
^ Genes put energy into reproduction and not repair - Widespread evidence for trade-off between reproduction early in life and survival later in life
Does/can aging evolve?
Yes!
Are the evolutionary mechanisms underlying aging different from those underlying most other phenotypes? If so, in what way?
- Yes
- Aging does not have a function or purpose and is not adaptive and because of trade-offs, you have to give to live longer
Does the power of natural selection decline later in life? Why or why not?
- Yes
- Because animals often die before reaching late life (disease, predation, accidents)
Describe the two mechanisms that are responsible for senescence
1) Deleterious mutations accumulate
2) When there are trade-offs between reproduction and maintenance (survival), selection favors early reproduction
Senescence results as a trade-off between what two things?
Trade-off between investing in reproduction early in life and investing in body maintenance for longevity
Do females live long post-reproductive lives?
Yes!
What is the mother hypothesis/what does it state?
The risk of reproduction at older age selects for reduced fertility
What is the grandmother hypothesis/what does it state?
The loss of fertility is associated with a shift in investment to grandchildren
The mother and grandmother hypotheses are adaptive explanations for _________
menopause
Did menopause evolve before or after humans split from apes?
After
The morphospecies concept is used by
paleontologists
What is the criterion for the biological species concept?
The inability to produce viable hybrids
What is the criterion for the phylogenetic species conept?
Monophyly
When does reproductive isolation occur?
When populations of organisms fail to hybridize regularly in nature or fail to produce fertile offspring when they do hybridize
Populations of organisms failing to hybridize regularly in nature is an example of
disruptive gene flow (geographic isolation)
Describe speciation in terms of the general lineage concept of species
The entire set of events that are known as species “criteria” (bounded by first and last event)
What are some examples of different subcategories of species?
- Reproductively isolated species
- Ecologically differentiated species
- Monophyletic species
T / F : determining if you have two species is similar to determining if you have two organisms
T
What were the two hypotheses in regards to X. cortezi and applying species criteria?
- X. malinche is a population of X. cortezi (not a separate species)
- More than one species of X. cortezi
What criteria can be used to demonstrate that X. malinche is an independently evolving lineage?
- Fixed differences
- Genetic vs geographic distances
What criteria cannot be used to demonstrate that X. malinche is an independently evolving lineage?
- Reproductive isolation criteria
- X. malinche and X. cortezi interbreed when in the same aquaria
Describe speciation (the classic model)
- The process by which one species becomes two species
- 3 steps/stages
- Gene flow is disrupted, and populations become genetically isolated (not exchanging genes anymore)
- Divergence in traits (such as mating system, habitat use)
- Secondary contact
What prevents gene flow?
Allopatric isolation, sympatric speciation
What drives divergence?
Random genetic drift versus natural selection
Describe allopatry
Gene flow is disrupted by physical isolation
Describe sympatric speciation
When two related species or populations live in the same region (are able to encounter each other) but do not interbreed
What two modes can allopatry occur by?
- Vicariance: existing range is split
- Dispersal: founder hypothesis
What is an example of sympatric speciation?
Mutation as a barrier to gene flow
What caused sympatric speciation in the fish Barbus? How many times was speciation initiated by this event?
- Polyploidy
- Polyploidization initiated speciation at least three times
In the case of the snapping shrimp, what mode of allopatry occurred?
Vicariance
In the case of Hawaiian fruit flies, what mode of allopatry occurred?
- Dispersal
- Closely related species found on neighboring islands
What three factors drive ecological divergence?
- Selection for different ecological traits can create reproductive barriers
- Populations may come into less contact, for example, and reduce their opportunity to mate
- Populations may evolve different traits depending on environment, leading to assortative mating
Describe/explain the divergent evolution of the cichlids in Lake Victoria
- Divergent evolution of the visual system coincides with divergence in male breeding coloration
- Male traits start to change depending on depth in water (red usually attracts females, but after a certain depth, the color cannot be seen and is no longer advantageous in attracting females)
What genes were changing in the pea aphids experiment?
- Host reference genes, which are pleiotropic
- These genes are closely linked to genes that influence fitness on two hosts
What happened if two diverging pea aphid populations came back into contact with one another?
The “mixed offspring” (transfers) don’t do well on either plant, leading to speciation
What are the possible outcomes of the third stage of speciation, secondary contact?
- Reinforcement and/or genetic incompatibility evolve
- Selection favors hybrids (new species!)
- Selection favors hybrids in transitional habitats (hybrid zone)
Reinforcement (of speciation) occurs if hybrids have…
reduced fitness
In some cases, hybridization can lead to the formation of…
a new species (higher fitness in a novel environment)
What are the hybrid zone forms?
- Hybrids equally fit: wide zone
- Hybrids less fit, strong selection: narrow zone
- Hybrids more fit: if in an environment outside parental range = new species, if at the edge of two ranges = “transitional zone”
What maintained the two species, X. cortezi and X. pygmaeus, in the field? In other words, what prevented hybridization, even though they created viable offspring in an experimental setting?
- When given only a visual cue (in experimental setting), the X. pygmaeus females chose the X. cortezi males
- When given odor and visual cues, however, X. pygmaeus females chose X. pygmaeus males
- In nature, they have both cues all the time, preventing hybridization!
What was interesting about the speciation of the three-spined sticklebacks?
- Six speciation events happened in the six lakes when hybridization occurred
- Found that the same sorts of variations would evolve
T / F : There is as much genetic variation within a species as across species
T
Reduced gene flow can arise due to…
- Allopatry
- Sympatry (if some groups do not interbreed)
- As a byproduct of ecological adaptations to different environments
Can species merge back together upon secondary contact?
Yes!
What is life?
- Some define life as populations capable of evolving by natural selection
- Others consider something alive if it has the ability to store and transmit information (genotype) and the ability to express that information (phenotype)
Why are viruses not considered alive, according to some definitions?
They need host machinery to replicate/cannot self-replicate
Until 1982, what was RNA considered to be?
The “relay” molecule for DNA
What evidence is there for RNA being ancient?
- Has catalytic properties
- Basic currency for biological energy is ribonucleoside triphosphates (ATP and GTP)
- Has genotype (primary sequence of nucleotides) AND a phenotype (a catalyst)
_______ are thought to be the RNA to DNA link
Viruses
_______ are the most abundant “denizens” of Earth, with at least 10 individual _____ particles for every cell
Virus (x2)
Where are viruses found?
Anywhere/everywhere their hosts can survive
What are the two functional modules of viruses?
Genome and capsid
What is the role of the capsid?
To protect replicators and enable the virus to attach to cells
Genome-replicating proteins lack any clear ________ among cellular life-forms
homologs
Why is it considered a problem to not call viruses “alive” because they cannot self-replicate?
Many cellular entities cannot replicate without their hosts (ex: Mycobacterium tuberculosis)
What are some hypotheses for the evolution of viruses?
- Genes that escaped from the genome of cellular organisms
- Descendants of cellular organisms that evolved reduced genomes due to parasitic lifestyle
- Remnants of earliest life in Earth (including RNA world)
The hypothesis that viruses are remnants of the earliest life on Earth is supported by what?
- The lack of homologs
- RNA to DNA (arms race between viruses and their hosts)
Describe the panspermia hypothesis
The idea that life did not necessarily originate here on Earth (astrobiology)
T / F : most researchers believe primordial form arose on another planet
False! Most still assume it arose on Earth
Evolving by __________ is a key concept of what makes something “living”
natural selection
What is the RNA world hypothesis?
The idea that catalytic RNA molecules were a transitional form between nonliving matter and the earliest cells
We know a lot about the origin of life on Earth, but it is limited by…
lack of knowledge of early Earth and the “pull” of the present
In the original 5 kingdom scheme, archaea had been grouped with _______
bacteria
Analysis of nucleotide sequences of small subunit rRNAs revealed three clades for the phylogeny of all living things. What are they?
- Bacteria
- Archaea
- Eukarya
Are archaea more closely related to eukarya or bacteria?
Eukarya
The cenancestor to bacteria, archaea and eukarya was…
not a single species, but a community!
How did organelles evolve? Specifically, mitochondria and chloroplasts
- Endosymbiont theory
- Both mitochondria and chloroplasts have their own chromosome that is a small circular DNA molecule, similar to bacteria’s
What is a fossil?
Any trace left by an organism that lived in the past
How do we get fossils?
- Compression and impression fossils
- Permineralized fossils
- Casts and molds
- Unaltered remains
Where would be a good place to look for fossils? Why?
- Somewhere dry, like a desert
- Often better preserved in dry areas
What are the weaknesses of the fossil record?
Sampling biases (geographic, taxonomic, temporal)
Some researchers say we should look to what to gather information or evidence of the earliest life on Earth?
Earth rocks on the moon
What are the oldest known fossils? How old are they? How do we know what the fossil is?
- Cyanobacteria
- 3.5 billion years old
- Fossil cyanobacteria look a lot like extant relatives
There are _____ major clades of living organisms
3
________ early on made it difficult at first to determine their (bacteria, archaea and eukarya) relationships
Gene swapping
What is the cosmic calendar?
A method to visualize the chronology of the universe, scaling its currently understood age of 13.8 billion years to a single year
For the first __________ years, all life was unicellular
3.2 billion
How long ago did the first animals appear?
560 million years ago
How long ago and over how long of a time period did most living phyla appear?
- 543 million years ago
- Over the course of 40 million years
What is special about the Cambrian explosion?
It only makes up 1% of Earth’s history, but includes relatively rapid appearance of many large and complex animals
__________ is considered to be one of the greatest events in the history of current life
The Cambrian explosion
Was the Cambrian explosion really an “explosion”?
- Conflicting evidence!
- Molecular and phylogenetic clock studies indicate that the animal kingdom arose about 750 million years ago, and bilaterians about 630 million years ago
- BUT the Cambrian “explosion” occurred long after animals had begun to diversify
What was the key to evolution of multicellularity and larger size during the Proterozoic era?
Increase in oxygen concentrations in seawater
Key to evolution of animals in the Cambrian era may have been…
- Increase in atmospheric oxygen, making large size and rapid movement possible
- Mass extinction of Ediacaran fauna, creating the opportunity for small deuterosomes and protosomes to evolve
Have living fossils not changed?
No! Just because there is not phenotypic variation doesn’t mean there hasn’t been any genetic variation and vice versa
Genetic variation is present even if ___________ is not
morphological variation
Living fossils remind us that…
morphological variation and genetic variation are not always correlated
The Paleozoic era is known as the
Ancient Life Era
The Mesozoic era is known as the
Age of Reptiles
The Cenozoic era is known as the
Age of Mammals
Divisions of time periods/eras is based on
fossils
What might make one time period smaller than another?
If there’s more to find (fossils) and more to talk about!
_______, _______, and _______ are the major groups of the Tetrapoda
Amphibians, reptiles, mammals
Describe the evolution of Theropods
- Feathers and flight evolved in early members of this group
- Convergent evolution with bats and pterosaurs
What are the three extant groups of mammals?
- Monotremes
- Placentals
- Marsupials
Has taxonomic diversity increased or decreased over time?
Increased!
What are the “Big Five” mass extinctions?
- Terminal Ordovician (440 Ma)
- Late-Devonian (356 Ma)
- End Permian (250 Ma)
- End Triassic (215 Ma)
- Cretaceous-Tertiary (K-T, 65 Ma)
The “big five” are responsible for around _____ of all extinctions during Phanerozoic. What is responsible for the rest?
4%, background extinction.
Describe the Ordovician extinction (440 Ma)
- Second largest mass extinction (57%), may never completely know why it happened
- Sudden bursts of gamma rays from nearby supernova (?)
Describe the Late-Devonian extinction (356 Ma)
- Series of pulses in decline of species, approximately 50% of living species went extinct
- Global cooling, drop in sea level, rise in oxygen-free water
What is background extinction?
Within a group of organisms, the likelihood of clades becoming extinct is constant and independent of how long the taxa have been in existence
Describe the End of Permian extinction (250 Ma)
- Largest mass extinction (83% of all life, 96% marine!)
- Reason is not for sure known (possibly due to formation of supercontinent Pangea)
Describe the End-Triassic extinction (215 Ma)
- 48% (all large amphibian, not as sudden)
- Base cause may have been increased volcanic activity (acid waters from the deep ocean to the shallows)
Describe the Cretaceous-Paleogene/K-Pg extinction (66 Ma)
- 75% of all plant and animal species on Earth died, including all non-avian dinosaurs
- Reason: asteroid hit off the coast of Mexico
Which mass extinction event do we know the most about?
K-Pg!
There are two hypotheses for the consequences of K-Pg. What are they?
- Hypothesis 1: acid rain (widespread wild fires, intense cooling, extensive darkness, enormous tsunami, subsequent ecological disruption)
- Hypothesis 2: global firestorm (vaporization of rock following the impact, condensed into sand-grain-sized spheres as they rose above the atmosphere, ejected material re-entered Earth’s atmosphere, etc.)
What are the three approaches to measuring current extinction rates according to Robert May?
- Satellite photos of number of species found per hectare
- Quantify the rate that well-known species are moving from threatened to endangered to extinction status in lists maintained by conservation groups
- Estimate the probability that all species currently listed as threatened or endangered will actually go extinct over the next 100-200 years
What were the results from using May’s three methods of measuring current extinction rates?
All three methods suggest current extinction rates are 100-1000x background extinction rates
Are we currently experiencing another mass extinction? Why or why not?
- Yes, some biologists fear that we have entered the sixth mass extinction
- A study of new vertebrate extinctions over the past few centuries revealed that the average vertebrate extinction rate is far above the background extinction rate
______ have become an endangered species largely because they have lost most of their historical habitat
Tigers
Only about _____ tigers survive in about ___% of their original habitat
3800, 7
Is extinction a common event in history? How is it documented?
- Yes
- Well documented by fossil record
While a single extinction may not have significant effects on an ecosystem…
we should still be very concerned about the cascading effects that may result from a sixth mass extinction
