Lecture 10-13 Flashcards
What is a taxonomic rank?
The most specific unit of taxonomic classification (ex. Homo sapiens)
What is a biological classification?
A way we try to classify individuals based on a set of characters
What is speciation? What does it depend on?
The creation of new species
Dependant on limited or absent gene flow between populations
- If gene flow does occur between populations, they will remain genetically similar therefore they cannot become different species if they share the same genes
What are the mechanisms of speciation?
Change in gene flow due to something cuasing a pop. to seperate
- can be caused by physical barriers or geographic conditions (mountains, rivers, deserts)
- physically isolated pop. rarely interbreed and are therefore characterized by the lack of gene flow
- since different courtship behaviours, different breeding seasons, different periods of activity (diurnal vs. nocturnal)
Mutation, genetic drift, natural selection (or a combination) act separately on each isolated pop.
Leads to different isolated populations
Where did the variation that natural selection acts on come from?
Natural selection may select for different variations in traits (alleles) between populations that
- already existed when they separated
- newly arose from chance mutations
What is a mutation?
Random change that happens when DNA is replicated
Most are NOT adaptive, but some create new characters (most mutations are bad, but occasionally good)
What is genetic drift?
Based on probability, the frequency of different genes in a population can change over time, even when not under selection pressure
- since at each generation, each allele is passed on randomly
Occurs in small populations by change
Whole alleles (traits) may even be lost
The allele is not under strong envr. pressure
What is the morphological species concept?
Two populations that have distinguishable phenotypic characteristics (e.g., physical appearance, internal anatomy) are classified as different species by this concept
In other words, things that look similar and of similar size, shape, function, likely to be more related to each other
What is the use of the morphological species concept?
Examining the fossil record, especially when fossils are the only data available
What are the limitations of the morphological species concept?
Oldest species concept –> sorting species by appearance is a very coarse-grained way of differentiating groups
Does not take modern genetics into account (e.g. how genes and other microevolutionary differences affect what individuals look like)
It is much more accurate to use ecological and molecular evidence to determine whether individuals are the same species
What is the biological species concept?
Defines a species as members of populations that actually or potentially interbreed (mate with each other) in nature and produce offspring that are fertile (can also reproduce)
What are the issues with the biological species concept?
Assumes sexual reproduction, but not all species reproduce sexually
- does not work for asexual species (including animals and plants)
Cannot be used in all scenarios where we would like to distinguish between species
We cannot test the ability to mate between every pair of species (not practical/ethical)
What is the phylogenetic species concept?
Species are groups of individuals that share a unique common ancestor
Determined by showing that individuals share traits (e.g. morphological, now usually genetic) unique to that species
Causes them to cluster distinctly from other groups
Branching out is due to speciation events
When no subset share a unique common ancestor, or there are no distinct clusters of individuals –> conclude that pop. are members of the same species as they share one common ancestor
What is allopatric speciation?
Speciated caused by geographic isolation of two different populations
Low gene flow can occur between populations but must be rare
Caused by barriers such as mountains, canyons, movement of plate tectonics (panama), oceans, etc.
This type of speciation is believed to be the primary speciation which takes place on island
What is parapatric speciation?
Speciation when the ranges of two speciating populations are actually overlapping but gene flow is reduced
A contentious theory, not all evolutionary biologists believe that parapatric speciation can occur
What are ways for parapatric speciation to occur?
New niches open
- population moves into new niche
- niche causes evolution in the new pop.
- eventually, enough different to speciate
Environment differs across a large range
- environmental differences –> differences in evolution
- pop. at the far edges become very different since not exchanging genes
- eventually, individuals in the middle either disappear or become one of the two populations
What is sympatric speciation?
A species arises from within a range of overlapping with its origin species
How is gene flow restricted to a sub-population from within a larger population in the context of sympatric speciation?
Reproductive isolation
- reproductive methods are incompatible
- restricting gene flow, even in completely overlapping populations
Could be due to different rituals, reproductive structures, chromosome duplications in plants
– often arise from mutations
- infertile hybrid offspring
What are hybrids?
Organisms that we consider to be different species can interbreed, hybridize
Offspring are often sterile
However, some interbreeding can create a viable offspring which can survive and mature (hybrid speciation)
What is the exception to the rarety of hydrid speciation?
Plants
Often hybrid offpsring are fertile, even if not many plants can propagate themselves
- Hybrids can spread without sexual reproduction
What is despeciation?
When two species become one
Hybridization can cause distinct lineages to collapse into a single lineage with an admized mosaic genome
relatively rare
Gene flow between two different species can eliminate the distinction between those two species
What are the two scales that characterize evolution?
Macroevolution: evoluation over geological time, mainly observed through fossils
Microevolution: evolution we can observe within a human generation, mainly observed through genomic work
What is a trait?
Observable feature in the phenotype of an organism
Generally physical or physiological characteristics, but can also be considered behavioural in some instances
Examples: organ presence, body size, colour, live birth, migration, etc.
How does trait evolution work?
Traits are generally linked to the genome (genes of the organism)
Randome mutation can create new or altered genes
Some will be expressed as new phenotypes
Natural selection acts on the phenotype
What is the likelihood of a mutation?
Severe mutations adding completely novel traits are extremely unlikely
Most evolutionary changes are slight modifications on existing traits
But genes can be duplicated or repurposed
What does gene duplication have to do with mutation?
Can have duplication of genes or large sections of a chromosome
Duplicate copy mutates and acquires new function
Major source of raw material for genes to evolve
What is specialization?
A species losing generalized traits to become better adapted to a very specific habitat/niche
How have orchids evolved into a specialized group?
Seeds have lost the ability to germinate by themselves
- little to no stored energy
Need to form a symbiosis with a mycorrhizal fungi to germinate and grow
Saves energy for the orchid since little energy investment required for seeds
Mycorrhizae likely only found in optimal habitats for orchid growth
- way to ensure seeds are germinated in the best habitat
Can a species regain a trait if it is lost through evolution?
Poor evidence for this in the fossil record, but we do find examples such as the viviparous lizard
- some lay eggs some have live births
- not all genes present in the genome are expressed, they are regulated –> expression can be turned on and off
What is irreducible complexity?
Trait(s) whose function(s) have become so essential to life, losing them through evolution seems impossible
example: mitochondria
Why was the evolution of seeds in plants a key innovation?
First land plants reproduced mainly by spores
Development of seeds allowed plants to reproduce away from water and experience dormancy
Allowed greater provisioning and dispersal
Vast majority of plants now reproduce by seed
What is the island rule (or fosters rule?)
Species that evolved on islands typically get either larger or smaller than their mainland counterparts (trait evolution of body size)
What is insular dwarfism?
Animals which are large on the mainland become smaller on an island
Because islands have limited resources, smaller animals need less food
Herbivores
- larger size deters predators
- few to no predators on island
- larger size no longer selected for
Carnivores
- prey tends to be smaller on islands
- larger size no longer needed
What is insular gigantism?
Species which are small on the mainland tend to become large on islands
Carnivores
- often lack large carnivores on islands
- new carnivores species can become larger to fill the niche of apex predator
Herbivores
- small herbivores stay small to escpae predation
- if there are no efffective predators, they will become larger (selective pressure gone)
How can we date evolution?
Molecular clock
The background rate of mutation, often of “invisible) mutations (e.g. ones that don’t change the phenotype)
Compare the number of changes
- more similar = recent divergence
- more different = less recent
What is gradual speciation?
Species arise slowly over time
Many morphological intermediates
- evolutionary steps between an ancestral species or trait and a species or trait seen today
- example: there is evidence for gradual evolution of the eye
Traits change slowly and gradually
- example: creeps
What are the issues with gradual speciation?
If intermediate forms are adaptive, why does evolution continue?
Why doesn’t evolution move towards stabilizing selection instead of changing traits over time?
What is punctuated equilibrium?
Species diverge quickly
After quick divergence, remain unchanged over long periods of time
- stabilizing selection
Single of very few mutations must occur in a short period of time (new mutations in offspring)
Mutations must be severe enough to cause noticeable changes in the phenotype
- but not so severe that the fitness of the organism is negatively impacted
Less common than gradual speciation
Must be reproductive or geographic isolation between the ancestral species and new species
What can impact our evaluation of gradual speciation vs. punctuated equilibrium?
May be biased by an incomplete fossil record (missing many intermediate forms in the fossil record)
Generally what conditions lead species to not change?
If habitats remain stable over time, species tend to remain stable (assuming genetic drift is not significant)
What is adaptive radiation?
Rapid speciation event into a multitude of new forms
Adaptive:
- evolutionary changes shape traits allowing organisms to adapt to their envr and convey fitness advantages
- when natural selection meets a particular ecological opportunity
- often these species vary in their microhabitat or food sources
Radiation:
- seems to correlate with a sudden abundance of open niches
What is an ecological niche?
The specific place a species holds in its biotic and abiotic envr.
E..g. the physical space where it feeds/reproduces, etc. the role it plays in the food chain of its community and its interactions with other organisms
No two species can hold exactly the same niche in the same envr. One outcompetes the other
What are some aspects that define the niche of an organism?
Predators, elevation, ecosystem type, competitors, food source, nesting season
What might cause an abundance of unfilled niches?
When old niches are cleared out
- dispersal to new envr (island, lake)
- extinction events
When new features open up new niches
- hard bodies
- angiosperms
When new niches are engineered/created
What is an example of the emptying of niches?
End-Cretaceous Extinction
Loss of dinosaurs = abundace of empty niches
Led to incredible adaptive radation in mammal species
Resulted in the domination of mammal species today
Why did mammals recover and dinosaurs did not?
Small size –> fast reproduction rate
Generalist habit –> could survive on a diverse range of foods
Lead to mammal radiation
What is an example of a new feature creating new niches?
Rapid emergence of new traits such as hard bodies, predation, eyes
- Massive radiation of new animals during the Cambrian (Cambrian explosion)
Adaptive radiation in Angiosperms
Why did angiosperms experience extreme adaptive radiation and increase at the expense of all other plant groups (conifers)?
Coevolved with pollinators
- flowers attracted pollinators
- pollinators greatly improved pollen transmission
- an insect can travel much farther than wind-dispersed pollen
There was therefore the major diversification of angiosperm pollinators along with angiosperms
- new pollination niches
Decline in pollinators associated with other plant groups (such as conifers)
- some switched to angiosperms
Where did the first angiosperms arise?
In forests dominated by conifers
However, angiosperms grow more rapidly than conifers
- moreover, angiosperm litter neutralizes the soil and favours the envr that they grow better in (compared to conifers that like more acidic soil)
Once dominant, angiosperms had changed the abiotic and biotic landscape to favour their own growth
Conifers today are largely limited to colder areas where angiosperms cannot thrive due to short growing seasons
What is convergent evolution?
Independent evolution of analogous traits (structures, functions, behaviours) in two or more lineages
The trait in question is NOT present in the last common ancestor of both groups
Evolved similarly because they occupy the same evolutionary niche
What are examples of convergent evolution?
Flight has evolved in very diverse lineages (arthropods, birds, mammals, pterosuars)
Venom injection arose separately in cobras and vipers, and in platupi hornets and scorpions
What are examples of convergent evolution?
Flight has evolved in very diverse lineages (arthropods, birds, mammals, pterosuars)
Venom injection arose separately in cobras and vipers, and in platupi hornets and scorpions
Phylogeny of seed plants shows that alternative photosynthesis paths evolved independently many times in diverse lineages
Carcinization definition
The urge to become a crab
A crab like body-plan has arisen independtly 5+ times
How do check the evidence for convergent evolution?
Map a trait onto a phylogeny
Look for present of train in fossil ancestor
- if trait is present in ancestors –> not convergent (however traits can be lost, do not need to be in all decedents)
What is mimicry and is it an example of convergent evolution?
phenomenon characterized by the superficial resemblance of two or more organisms that are not closely related taxonomically
- can evolved to look like smt noxious
Yes, it is an example of convergent evolution
For example, a non-toxic species evolving to resemble an unrelated toxic/dangerous one to deter predation
What is parellel evolution?
Similar development of a trait in distcint species that are not closely related, but share a similar originial trait, in response to similar evolutionary pressure
- expanded in similar niches
Different from convergent in that ancestors shared the trait
Example: placental mammals and marsupials (with pouches) –> each lineage developed similar forms on different continents after they diverged to fill similar niches
What does the founder effect do to the founder population of an island?
Smaller than source population
Contains only a subset of the genetics of the original population
May also have harmful recessive founder mutations
Why does the founder effect lead to faster evolution?
Due to small populations, there are fewer individuals and fewer genes overall in the gene pool
Therefore, each individual gene counts for more of the overall gene frequency
Mutations spread much more rapidly because a new mutation in a small gene pool makes a larger overall contribution to genetic diversity compared to a large population
The greater the frequency of a gene in the gene pool, the greater chance it will be passed on in the pop.
Also relates to genetic drift leading to bottleeck effect
Where do we find the highest human genetic diversity in the world?
Africa
- a greater proportion of rare allele in African populations (rare alleles are likely to be lost in founder population unless they become dominant)
Europe is lower
- greater proportion of deleterious mutations in European populations
South America is the lowest
What is sexual selection?
differential fitness that is not related to envr but to sexual process, example behaviour trait (such as a call) that attracts mate –> that trait will be under sexual selection
The mate preferences of one, or both, sexes drives evolution
In sexual selection, these maladapted traits may not be beneficial for the survival aspects of fitness
- but seem to directly impact the reproduction of individuals
What are primary sexual characteristics?
Characters required for reproduction such as ovaries
Differences in the biological sexes directly related to reproduction (e.g. genitalia)
What is secondary sexual characteristics?
Traits which are used in sexual selection, but are not required for sexual reproduction
Can be for direct competition, or attractiveness, not behaviour though
Examples: horns, pretty feathers
What is sexual dimorphism?
Difference in appearance between males and females of the same speices
What are the two types of sexual selection?
Intrasexual selection: within the same sex
Epigamic (intersexual) selection: between sexes
What is intrasexual selection?
Direct competition between two members of the same sex for the opposite sex
Particularly strong in polygynous species (one male many females)
Most often seen as male to male competition for female
- female competing tends to not be for access to mates (rather territory, food)
Female has limited (or no) choice in mate selection
Males generally to not help care for offspring
Examples: crabs, lions, gorillas
What are common sexual dimorphism patterns in intrasexual selection?
Larger males than females
Males have sexual ornaments used primarly for fighting other males (antlers, fighting spurs)
Males similar colour to females
What is epigamic (intersexual) selection?
Selective pressure from the member of one sex having complete choice over a mate of the opposite sex
- display or other courtship to attract members of the opposite sex
Most common type of sexual selection in species where both individuals help raise the offspring (but not required)
- also “monogamous” pairs
Most common type of epigamic seleciton is female of the species having primary choice in mates
- male choice does exist, but much rarer
What are common sexual dimorphism patterns in epigamic (intersexual) selection where males do not stay to help raise the offspring?
Males are often much more colourful than females (extreme sexual ornamentation)
Females are often larger than males, or of a similar size
What are common sexual dimorphism patterns in epigamic (intersexual) selection where males help raise the offspring?
Both sexes are often the same colour and size
Why is female choice much more common?
Females invest more energy and resources –> bear the cost of reproduction
- eggs are high energy investment, fixed number
- pregnancy is energy intensive
- reproductive success comes from breeding with the best male (helps ensure offspring are as fit as possible)
- costly to choose poor mate
Males
- sperm: low input, high output
- reproduction success comes from mating with as many females as possible
- many mates = the male can afford to select a suboptimal mate
What is the Bateman’s Principle?
The sex which invests the most in producing offspring will become a limiting resource over which the other sex competes
Implies the male can be the sex which invests the most
Is male competition in epigamic selection possible?
Yes, though any system where mate choice exists is considered primarily epigamic
Does the development of extreme sexual dimorphism impact fitness?
Yes, math models have shown that is actually decreases overall fitness
Trade-off with survival for the male
What are the 4 aspects of the Fisherian Runaway Selection Hypothesis?
Female prefer a secondary sexual characteristic
Female selects that mate, then passes that secondary character to her male offspring
She also passes on a genetic trait in her daughters to desire that secondary sexual characteristic
Creates a positive feedback, increases the desirability and extreme nature of the character over generations
What is the Sexy Son Hypothesis?
Females choose attractive mates because it means that their own male offspring will be better able to attract mates
What is the handicap hypothesis?
Extreme secondary sexual characteristics
- indicate to the opposite sex that the individual can afford to waste resources on developing the secondary sexual characteristic
Effectively, the individual can “handicap” itself, and ye still survive
- therefore it is a good choice for a mate
What leads to reproductive isolation?
More elaborate sexual practices and structures
Taxonomic groups with the greatest amount of sexual dimorphism generally also have the largest species diversity (presumably from more speciation)
What is coevolution
Also known as reciprocal evolution
Where two or more species impact each other’s evolution
What is the difference between natural selection vs. coevolution?
Natural selection refers to the broad changes in phenotypes in response to envr conditions (abiotic and biotic)
On the other hand, coevolution refers to when a small number of traits/genes in one species directly impact the evolution of a second suite of traits/genes in another species
What is symmetrical arms race?
Selection pressures are identical on two species
Two species whose interactions result in them co-evolving the same trait
Ex. Only the tallest trees receive full sunlight in a mature forest
- Sunlight: symmetrical selection pressure on all tree species
- Different trees evolving the same trait: increased height
- A tree is only tall because the next tree threatens to overshadow it
What is asymmetrical arms race?
Contrasting selection pressures
Both species are co-evolving, however the selection pressure acting on the two species is different
Ex. cheetah and gazelle
- cheetah runs faster but can only maintain for a short distance (evolved traits for hunting: speed and stealth)
- gazelle runs less fast but can run longer due to blood being cooled before reaching the brain (gazelle evolved DIFFERENT traits for evading capture: endurance and evasion)
–> coevolution
Symbiosis definition
A close and prolonged interaction between organisms of different species
Can be beneficial to both partners, neutral to one partner or harmful to one partner
What is mutualism
Interactions between two different species mutually benefit each other
Two types:
1) Obligate mutualism:
- two species must co-operate in order for both to survive
- the survival of one species depends on the survival of the other
- Ex. fig and wasp, corals
2) Facultative mutualism:
- both species derive benefit from each other, but one would survive if the other went extinct
- Ex. tarantula-frog
What is the current hypothesis for the tarantula-frog facultative mutualism?
Tarantula protects frog from other predators
Frog protects the tarantula eggs since it is specialized in eating ants (ants are the primary predator of tarantula eggs)
What are the pros and cons of obligate mutualism?
Pros: outsourcing protection, food, energy, etc.
Cons: extra vulnerability of relying on another species
What is parasitism?
Interaction between two different species where one benefits at the expense of the other
Highly destructive, since the parasite is living at the expense of the other species
Generally very finely tuned to preserve the life of the host or at least conserve the host species
- the parasite needs the host to survive since it depends on the host to complete its lifecycle
What happens when a parasite kills large numbers of the host?
Usually a novel mutation is found in the parasite which throws off the careful host/parasite balance
Often after time, the host will evolve a better defense to the new mutation, and equilibrium will be restored –> the parasite may even evolve to be less virulent
Myxomatosis
Myxomatosis virus killed 99.8% of rabbits in Australia
Within several years, the virus became less virulent
There was a strong selection for rabbit immunity –> selection for strains that didn’t kill all and quikcly
Therefore, rabbits survived longer and disease transmission was enhanced
Brood parasites cuckoos
Obligate brood parasite (cuckoo) doesn’t raise own offspring, relies on birds of other species to raise its offspring
Will find nests of other bird species, and lay its own eggs in the nest
When the cuckoo eggs hatch, the babies will push the other eggs out of the nest
- ensures that only cuckoo offspring is raised
The host can sometimes identify the cuckoo egg before it hatches
- will push the cuckoo egg out of the nest
There is a continuous evolutionary arms race betweem the cuckoo finch and its host
- Cuckoo eggs closely resembling the host
the host evolves a diversity of egg patterns to try to distinguish its eggs from the cuckoo
- if either species were to succeed completely, the other would become extinct
