Lecture Notes: Macroevolution Flashcards
Mechanisms of Reproductive Isolation
Pre zygotic & post-zygotic
Prezygotic
- habitat isolation
- behavioral
- temporal
- mechanical
- gametic
Postzygotic
- reduced hybrid viability
- reduced hybrid fertility
- hybrid breakdown
populations are constantly evolving so:
- population today is a “snap shot” of that group
2. difficulty in identifying the characteristics that indicate common ancestry
Modes of Speciation
allopatric & sympatric speciation
Allopatric speciation
a. populations speciate as a result of segregation by geographical barriers
Allopatric speciation favored by:
- small population size
- differences in the environments of the isolated habitats
- Peripheral isolation
Sympatric Speciation
new species arise within the same geographical range of the parental species
Mechanism to sympatric speciation
polyploidy, resource partitioning, and assortative mating
Polyploidy
common in plants
autopolyploidy and allopolyploidy
autopolyploidy
chromosomes derived from the same parental species
cannot produce viable gametes
may be able to mate with itself or another tetraploid (reproductive isolation)
Allopolyploidy
chromosomes derived from two hybridizing parental species
often fertile because chromosomes can pair during meiosis
Resource partioning
limited resources partionined at different levels among individuals
assortative-selective mating
segregation of individuals into isolated “morphs” based on selection of mates
ex: cichlids of Lake Victoria
shifts in adaptive peaks
- populations occur in both valley and peaks
- several peaks are available within a population, but natural selection maintains population at a single peak
- to shift peaks must go through valleys of low fitness: achieved by genetic drift, non-adaptive radiation
- once peak is reached, NS will leads towards reaching equilibrium
- adaptive landscape can change as the environment changes.
What does an adaptive peak represent?
optimal gene pool for success in a particular enviornment
Hybrid Zones
a region where two populations interbreed
can change in width over time
typically shown in cline
Gradualism
a. microevolutionary changes lead to macrogradualism
b. gradual changes in allele frequency through time lead to divergence and eventually speciation.
punctuated equilibrium
fossil record shows long periods of statis punctuated by short periods of rapid change
fossil
- preserved remnants or impressions of an organism
- typically found in sedimentary rock
- mineralization of tissues leads to petrification
- some retain organic material
- casts, molds, impressions
- trace fossils
- more complete specimens found in acid bogs, amber, ice, caves, etc
Fossilization:
a. a chance event
b. requires rapid burial under the right conditions that slow down decay
c. requires escaping geological forces
d. in order for fossil to be exposed you need weathering
e. hard body parts have a higher chance of fossilization
Fossil records
- a catalogue of evolution of life on earth
- incomplete
- biased towards species that: existed longer, more abundant, widespread, had hard parts
Relative dating of fossils
strata: sedimentary layers
younger strata above older ones ( rule of superposition)
-igneous rock are younger than the rocks through they cross
-correlate strata in one location with strata in other location.
-Index Fossils: widespread with good record that can be used or correlating strata
Absolute dating of fossils
- determines a specific age with error bars
- radiometric dating and racemization
Radiometric Dating
measures content of isotopic elements
each element has a specific rate of decay, which is temperature and pressure insensitive
Molecular Clocks
- use of amino acid or nucleotide substitutions to determine time of divergence among two groups
- calibrate the clock with the fossil record: know date of divergence for closely related groups
- Assume constant rate of substitution
- ok for closely related groups
- differences in generation time, metabolism are sources of error for non-closely related groups
Geological time scale
- geological history of the earth divided into eras, periods, epochs
- boundaries determined by radiations and mass extinctions
- durations of stages not comparable
