Lecture 2 - Phylogenies and Speciation Flashcards
3 Steps to Develop New Trait
- Priming (makes it possible)
- Actualization of the trait (makes it manifest)
- Refinement (makes it effective)
Priming
Step 1: Mutation becomes possible
- Earlier mutations develop a genetic background on which the desired function is accessible
- Primed generations are more likely to develop the mutation
ex: mutation that results in upregulation of Kreb’s cycle so that citrate may be used more effectively
Actualization
Step 2: Trait manifests
- Mutation occurs that allows trait to actually occur
- Small but significant competitive advantage
Refinement
Step 3: Makes mutation effective
- Population with the trait begins to thrive
- Small mutation makes the trait more efective
Evolution of the Eye
Evolution of a complex trait
- known to have evolved independently 50-100 times
Stages of Evolution of the Eye
- Priming:
- development of light detecting pigments in common ancestor
- other proteins that were already present for other functions were co-opted to function in the eye - Actualization
- now ready to evolve into a basic eye over and over - Refinement
- refined in each lineage to develop complexities such as color, lens, focusing
Evolutionary Constraints (5)
- evolution can’t produce any trait we want
1. Environment is constantly changing
2. Dependent on a mutation randomly arising
3. Evolution is limited to physical constraints
4. Adaptations are Compromises
5. Evolutions is limited by historical constraints
Environment is Constantly Changing (Evolutionary constraint)
- Environment influences what traits would be favored if evolving
Dependent on a Mutation Arising (Evolutionary constraint)
- Dependent on a mutation randomly arising (if an allele for a given trait does not exist , the trait cannot evolve even if it would be favorable)
Limit of Physical Constraints (Evolutionary Constraint)
- Evolution is limited to physical constraints
ex: limit to how light but strong birds wing bones can be
Adaptations are often compromises (Evolutionary constraints)
examples
- horses: thinner legs are lighter and faster but more prone to breaking
- snakes that are resistant to newt toxin are also slower…
Historical Constraints (Evolutionary Constraints)
Examples
- Modifications of PREVIOUSLY existing structures
- Build up what existed before in small steps
- Not going to start over from scratch
Examples
- Appendix is vestigial organ - don’t need to ruminate grass anymore
- hernias arise because we are built to be quadrupeds and it strains our spine to walk upright
- Hiccups are a reflex to make our now non-existent gills begin working when we are low in oxygen - gills are no longer there but still have the reflex
Laryngeal Nerve Example
Ex: Historical Constraint
- Path: brain, down the neck, loops through arteries in chest, then up neck to larynx
- Indirect –> not logical
- the way it existed originally was in fish with no necks
- As evolution occurred and animals developed neck, the nerve kept the same path
- resulted in a loop
Phylogeny
The evolutionary history of relationships among organisms or their genes
Phylogenic Tree
and features
Diagram used to portray phylogenies
- Based on similarities and differences in physical or genetic characteristics
- Lineages joined together in tree have descended from common ancestor
Node (Phylogenic Tree)
- split that represents point at which lineages diverged
Root (Phylogenic Tree)
- The common ancestor of all organisms in a tree
Taxon
- A group of species designated/named
- ex: humans, primates, vertebtrates
Clade
- Taxon that consists of all the evolutionary descendents of a common tree
- Are subsets fo larger clades
Taxon vs Clade
- Taxon is ANY group of species we designate or name
- A clade is a taxon that consists of all evolutionary descendents of a root
- Track clade back to the branch point, everything from that point on is included in the clade
- Clade is a taxon, but a taxon is not always a clade
Reptiles = Taxon but not clade
Clade would also include birds
Mammals = Clade
Tree of Life
- Phylogenic tree that represents the complete evolutionary history of life
- Describes relationships of all life on earth in an evolutionary context
Three main “branches” in tree of life
- Bacteria
- Eukarya
- Archaea
Homologous Traits
Any feature shared by two or more species that have been inherited from a common ancestor
ex: whale fin, human arm, lizard leg, bird wing
Ancestral Trait
A current trait that was present in the ancestor of its current group
Derived Trait
A trait found in a descendant that differs from the ancestral trait
Synapomorphies
- Shared derived traits
- Shared through a clade
- A newly derived homology
Ancestral vs Derived Traits
Depends on point of reference
Ex: Feathers
Ancestral
- Considered ancestral for any group of modern birds
- Homologous but not a synamopomorphy
- In phylogeny of all living vertebrates, feathers are considered derived
- synamopomorphy
Continuity of Evolution
- All species are constantly evolving
- Doesn’t make sense to say some are more highly evolved
Convergent Traits/Evolution
- Independently evolved traits subjected to similar selection pressures may become superficially similar
- Similar traits in unrelated organisms
Homoplasies
Similar traits generated by convergent evolution
Ingroup
Focus of phylogenic tree
How are phylogenic trees constructed?
- Can focus on any trait that is genetically determined, and therefore heritable
Sources of data for phylogenic trees (5)
Sources of data:
- morphology
- development
- behavior
- paleontology
- molecular data
Morphology
Q: Do they look similar?
- presence, size, shape and other attributes of body parts
- Limitations: 1. some diverse species look similar (leopard frogs), 2. hard to compare very distant species (earthworms and humans)
Development
Q: Do they have similar traits early in life?
- Similarities in developmental patterns
- Ex: frog larva and seq squirt larva look similar
Behavior
Q: Do they behave similarly?
Ex: Flight animals
Paleontology
- Fossils provide information about where organisms lived and what they looked like
- Help determine derived ancestral traits and when lineages diverged
- Information on extinct species is often critical to understanding the large divergences among surviving species
Limitations: fossil record is fragmentary and missing for some groups
Molecular Data
- Heritable variation is encoded in DNA
- most widely used data for constructing phylogenic trees
- also use mitochondrial, chloroplast and nuclear DNA
- mathematical models to describe how DNA sequences change over time
How did self-fertilizing flowers arise?
- Convergent evolution
- NOT members of the same species
- ability arose independently three different times
How is the “molecular clock” used to date divergent species?
- Use average rate at which mutations accumulate in a given gene or protein to gauge the timing of divergences
Significance of HIV and evolution
- molecular clock can be used to datetransmission of HIV-1 from chimps
- Data suggests the virus was transmitted from chimps to the original human around 1930
Binomial Nomenclature
two name system
genus + species
Hierarchical Classification (acronym…)
Kingdom Phylum Class Order Family Genus Species
“King Phillip came over for great spaghetti”
“Species”
Typically groups of organisms that mate with one another and produce fertile offspring
(not always clear cut)
Species Concepts (3)
- Morphological
- Lineage
- Biological
Morphological
- Individuals that look alike
limitation:
- not all members of a species look alike (males, females, juveniles)
- cryptic species morphologically indistinguishable but do not interbreed
Lineage
- Species is considered a branch on the tree of life
- speciation is process by which one species splits into two or more daughter species that evolve as distinct lineages
- each lineage starts as a speciation even and ends in extinction or another speciation event
- concept of a species over evolutionary time
Biological
Species are groups of inter-breeding natural populations that are reproductively isolated from other groups
Reproductive isolation
2 populations no longer exchange genes
Polar Bear vs. Brown Bear
- considered to be two different species within genus Ursus
- diverged 4-5 million years ago (lineage concept)
- Can interbreed, produce fertile offspring, have intermittently mated during warming periods (biological concept)
- Cannot survive long in each others climates, have different morphologies, metabolism, social and feeding behaviors (morphological concept)
- most brown bears have 2% polar bear DNA, up to 5/10%
Dog vs. Wolf
- dogs were domesticated from the grey wolf (lineage concept)
- both in genus “Canus”
- all breeds of dogs considered same species (biological, not-reproductively isolated = can mate)
- dogs and wolves can also interbreed
- husky looks more like a wolf than a chihuahua but WERE not considered same species
- NOW considered a sub-species of the grey wolf
How do new species arise?
- Reproductive isolation
- Allopatric Speciation
- Sympatric speciation
Reproductive Isolation
- Requires evolution of reproductive isolation within a species whose members formerly exchanged genes
- As they diverge genetically, they become more reproductively isolated
- May take millions of years or only generations for isolation to develop
Allopatric Speciation
- PHYSICAL, aka geographical speciation
- Results when a population is divided by a physical barrier
- Evolve differences because environments are different
- Barrier can form
- Species can cross barrier (founder effect)
Prezygotic Reproductive Barriers (5)
- Act BEFORE fertilization to prevent individuals of different species from mating
- Habitat Isolation
- Temporal Isolation
- Mechanical Isolation
- Behavioral Isolation
- Gametic Isolation
Harry Took My Big Gun
Postzygotic reproductive barriers (3)
- Act AFTER fertilization to prevent development of viable offspring or reduce the offspring’s fertility
- low hybrid zygote viability
- low hybrid adult viability
- hybrid infertility
Habitat Isolation
- Different species have evolved genetic preferences for different habitats to live or mate in
- Never come into contact during mating periods
Temporal Isolation
- Different species have distinct mating seasons
- Different times of year or times of day
Mechanical Isolation
- Different sizes and shapes of reproductive organs prevent fertilization
(tiger and house cat…)
Behavioral Isolation
- Reject or fail to recognize individuals of other species as potential breeding partners
ex:
- different mating cals
- pollination by specific insect or bird that is not drawn to other types of flowers
Gametic Isolation
- sperm of one species does not attach to eggs of another
- chemically incompatible: attractive signals from egg or ability of sperm to penetrate egg
low hybrid zygote viability
- zygote fails to mature normally
- develops abnormalities
- most do not survive birth
low hybrid adult viability
- hybrid offspring have lower survivor-ship than purebred offspring
- some different species of salamanders can mate with one another but the hybrid offspring are frail
(ligers?)
hybrid infertility
- hybrids may mature normally but are infertile
ex: mules - healthy but sterile
Outcomes in “hybrid zones”
- Gene pools re-mix and combine into one species
- Reinforcement
- Formation of narrow hybrid zones
gene pools re-mix and combine
- if hybrids are as fit as individuals of each species
- hybrids will mate with individuals of both parental species
- gene pools will gradually become mixed, resulting in one species
reinforcement
- Post-zygotic reproductive barriers reinforce pre-zygotic barriers
- hybrid offspring are less fit –> leads to reproductive isolation
- natural selection favors evolution of pre-zygotic
formation of narrow hybrid zones
- hybrid offspring are less fit but reinforcement is not complete
- does not expand because of selective pressure against hybrids
- continues to exist because the two parent species continue to move into it
adaptive radiation
- rapid proliferation of species from a single ancestor to fill a variety of ecological niches in a new habitat
- resulting species differ in the characteristics they use to exploit those environments
ex: Hawaiin Islands
- 10,000 species of insects from about 400 immigrant species
- 100 species of birds from 7 immigrant species
- 28 species of silversword plant
Sympatric Speciation
- without physical isolation
- species have a preference for certain microhabitats where mating takes place
ex: apple maggot fly
- historically deposited eggs on hawthorn fruits
- 150 yrs ago apple trees introduced, some flies began depositing eggs there
- flies began mating with other flies that preferred apples
ex: Horseshoe bats
- different echolocation call frequencies isolate bats
Allopatric vs Sympatric Speciation
Allopatric - species physically cannot get to each other
Sympatric - species, for some reason, choose not to mate with one another
Hybrid Zones
- when reproductive isolation is incomplete
- reproductive barriers do not completely prevent individuals from mating
- closely related species may form hybrids in areas where ranges overlap
Example of Adaptive Radiation
ex: Hawaiin Islands
- 10,000 species of insects from about 400 immigrant species
- 100 species of birds from 7 immigrant species
- 28 species of silversword plant
Rate of Speciation
- occurs at different rates
- the more specialized a species is, the higher the rate of speciation
- subtle differences lead to isolated groups diverging from original
- higher in groups with poorer dispersal abilities
Synapomorphies vs Homoplasies
Synapomorphy
- is synonymous with homologous trait
- shared derived trait
Homoplasy
- Traits generated by convergent evolution
- similar environmental pressures allow similar traits to arise in different, unrelated animals
- ex wings in bats and birds - very different structures actually
