Chapter 27-28 - Speciation and Phylogenetics (Test 3) Flashcards
Define phylogeny of all organisms
Genealogical relationships between species
How many domains are they, and what are they?
3: Bacteria, Archaea, Eukarya
Characterize the three domains in terms of their nuclei and their # of cells
Most bacteria and archaea are prokaryotic; eukaryotes are the others.
Most bacteria and archaea are single-celled; some eukaryotes are multicellular
Who is responsible for the three-domain classification system?
Woese – thanks to his experiements tracing ribosomal RNA (rRNA) to construct the tree.
Describe the evolutionary relatoinships of the three domaiB
Eukaryotes and Archaea share a common ancestor, which shares a common ancestor with Bacteria.
Are prokaryotic organisms monophyletic?
No; prokaryotes can be bacteria or archaea. But archaea have a common ancestor with eukaroytes before they have one with bacteria.
What is taxonomy?
The effort to name and classify organisms.
what is anamed group of organisms called re: taxonomy?)
a taxon. (plural: taxa)
What is a phylum?
a major grouping within each domain
Describe the system for scientific (latin) names and who came up with it.
Linnaeus.
Two-part name: Genus (closely related group of species)
Species
Capitalize genus but not species. Italicize or underline separately if handwritten.
What causes speciation?
genetic isolation and genetic divergence
What is speciation?
A splitting event that creates two or more distinct species from a single acnestral species.
Define species.
An evolutionarily independent population or group of populations.
What are three common criteria used to develop species?
Biological species concept
Morphospecies concept
phylogenetic species concept
Define the biological species concept
The main criterion for identifying species is reproductive isolation.
What are the two types of reproductive isolation
prezygotic isolation - prevents individuals of different species from mating.
postzygotic isolation, in which the offspring of different species do not survive or reproduce.
Disadvantages of the biological species concept?
- Can’t be evaluated in fossils or asexual species
- Difficult to apply when populations do not overlap geographically
Define the morphospecies concept
Identify evolutionarily independent lineages by size, shape, or other morphological species. Logic: distinguishing features likely to arise if populations are independent and isolated from gene flow.
What are the pros and cons of the morphospecies concept?
- good: Useful when there is little other data
- bad: can lead to the naming of 2+ species when there is only one polymorphic species with differing phenotypes (jaguars with different spots)
- bad: Cannot ID cryptic species, which differ in traits other than morphology, like meadowlarks
- morphological features used to distinguish species are subjective
What are the five mechanisms of prezygotic isolation?
- Temporal – lived at different time
- habitat – lived in different habitats
- behavioral – courtship displays differ
- gametic – eggs and sperm are incompatible
- mechanical – male and female reproductiv structures are incompatible
What are the three mechanisms of postzygotic reproductive isolation?
- hybrid viability – hybrid offspring do not develop normally and die as embryos
- hybrid sterility – hybrid offspring mature but are sterile as adults
- hybrid breakdown
Define the phylogenetic species concept
Species are the smallest monophyletic groups on the tree of life
define monophyletic group
a clade or lineage. an ancestral population, all of its descendants, and only those descendants.
How do we identify monophyletic groups?
synapmorphies
What is a synapmorphy?
a trait found in certain groups of organisms and their common ancestors but is missing in more distanct ancestors
What are the advantages and disadvantages of the phylogenetic species concept?
Pro:
- can be applied to any population.
- logical because different species have different synapmorphies only if they are isolated from gene flow and have evolved independently
con:
- carefully estimated phylogenies are available only for a small subset of populations.
2.
What begins speciation?
the reduction or elimination of gene flow between species, causing genetic isolation
What is allopatry?
the state of being geographically separated – (“different homeland”) – species that are separated.
Speciation that begins with geographic isolation is allpatric speciation.
How does geographic isolation occur?
- dispersal
- vicariance, the physical splitting of a habitat
Give an example of allopatric speciation by dispersal
Finches colonizing a new island. Genetic drift (founder effect) and natural selection led to a new population with larger average beak size
Define allopatric speciation by vicariance
If a new physical barrier – a mountain range or river splits the geographic range of a species, vicariance has taken place. This interrupts gene flow.
Define living in sympatry
“together homeland.” populations living close enough to one another to make interbreeding possible live in sympatry.
Define sympatric speciation
speciation that occurs even though populations live in sympatry
What types of events can initiate sympatric speciation?
- external events like disruptive selection for extreme phenotypes
- internal events like chromosomal mutations
Give an example of sympatric speciation by disruptive selection
apple maggots and hawthorne maggots live in geographical proximity but experience prezygotic reproductive isolation because they evolved specificity for particular fruit environments.
Define polyploidy
When an error in meiosis or mitosis results in a doubling of the chromosome number
what are the two types of polyploids?
autopolyploids
allopolyploids
define autopolyploid
individuals produced when a mutation results in a doubling of chromosome number and the chromosomes all come from the same species
define allopolyploidy
individuals who are created when parents that belong to different species mate and produce an offspring with two different sets of chromosomes
Describe what happens if 2n individual can make 4n offspring through mutation
The 4n offspring produce 2n gametes (unlike 2n individuals that make n gametes) and so even if they are able to mate, the resultant 3n (2n + n) offspring are sterile. 4n individuals could mate properly with other 4n individuals. Speciation happened in one generation!
Describe the formation of an allopolyploid
2n parents with different numbers of chromosomes (say, 2n = 6 and 2n = 4) produce n gametes (3 and 2); they form hybrid offspring that is effectively n = 5 and is sterile. Then an error in mitosis happens before meiosis, doubling the chromosome number and creating offspring 2n = 10. Now meiosis can take place because each chromosome has a homolog.
Why are polyploids so successful and why is polyploidy so common among plants?
Polploids have more heterozygosity
Polyploids can tolerate higher levels of self-fertilization because they are not as affected by inbreeding depression
genes on duplicated chromosomes can diverge independently, increasing genetic variation
What happens when isolated populations come into contact and there is no prezygotic isolation?
Populations can fuse and gene flow erases distinctions over time
reinforcement
hybrid zones
speciation by hybridization
extinction of one population
What is reinforcement
Reinforcement is when formerly isolated populations have difficulty interbreeding because of postzygotic barriers
What is adaptive radiation?
many species evolving rapidly from a common ancestor due to environmental conditions in isolation
What is convergent evolution?
similar characteristics evolving in unrelated species via adaptations to similar conditions. (marsupials + flying squirrels)
Define homology
similarity in organisms due to common ancestry
define homoplasy
similarity in organisms due to reasons other than common ancestry
What are the two mechanisms that trigger adaptive radiations?
new resources - ecological opportunity
new ways to exploit resources - morphological innovation
What are the five characteristics of life?
Composed of cells
reproduce using DNA
acquire energy from environment
grow and develop
maintain homeostasis
who first observed cells?
Hooke and Leeuwenhoek
define Spontaneous generation
Life on earth was believed to have developed from nonliving matter that became ordered in molecular aggregates that could self-replicate and metabolize
describe All cells from cells
All organisms are made of cells (pattern) and all cells come from preexisting cells (process)
How might chemical/physical processes on earth have produced very simple cells?
- abiotic synthesis of small organic molecules
- joining of small organic molecules into macromols
- packaging molecules into protobionts
- origin of self-replicating molecules
What was earth’s early atmosphere like?
Reducing – not much oxygen. Miller-Urey may have replicated biogenesis conditions
what experimental evidence shows how monomers could be joined into macromols?
dripping monomers onto hot rock can cause them to form polymers. Waves could have washed monomers onto hot rocks and then back into th esea.
What are protobionts?
aggregates of abiotically produced molecules surrounded by a membrane that can maintain an internal chemical environment. can repdocue and do simple metabolism.
Give an example of a protobiont
liposomes
What was likely the first genetic material?
RNA molecules called ribozymes, not DNA
What was Linnaeus’s classification system for life?
Two kingdoms: Animalia and Plantae
What was Whittaker’s classification of life?
Five kingdoms:
Prokaryotes (Monera)
Eukaryotes (protista, plantae, fungi, animalia)
What was Wose’s classification system for life?
Three domains: bacteria and archaea (prokaryotes)
eukarya (eukaryotes)
Descirbe the characteristics of archaea
- Many prokaryotic characteristics:
- no nuclear envelope or organelles
- small genome
- circular chromosome
- Some similarities with eukaryotes
- histones with DNA
- characteristics of DNA synthesis and transcription/translation
- ribosomal size
Describe the characteristcs of the three domains
All three have metabolism (ATP), genetic code, and ribosomes
Bacteria are simple
Archaea and Eukarya have histones
