speciation Flashcards
phylogenetic species concept
species = one or more populations that share a trait derived from a common ancestor which sets them apart from other organisms
can be physically separate populations
biological species concept
a species includes only individuals that could potentially produce fertile offspring in nature and are isolated from others (can’t/don’t reproduce with others).
Speciation requires
1) Reproductive Isolation of some type
2) Genetic divergence(evolution) due to different selective pressures or genetic drift
3) Evolution of differences that prevent interbreeding even if reintroduced to original home land
Speciation occurs when 2 populations become reproductively isolated by
geographic barriers
prezygotic mechanisms= before zygote forms
Postzygotic mechanisms= after zygote forms
PREzygotic mechanisms of reproductive isolation
mechanical temporal behavioral ecological/habitat gametic
Mechanical Isolation
parts don’t fit snail shells twist in different directions
Temporal Isolation
mate at dif. times seasons, years, nocturnal vs diurnal
Behavioral Isolation
courtship/recognition
Ecological/habitat Isolation
field vs forest
Gametic Isolation
sperm fail to survive or penetrate egg
what type of reproductive isolation:
Song birds change their mating song
behavioral isolation & sexual selection
what type of reproductive isolation:
Female fish select mates that are most similar in color to themselves
sexual selection
what type of reproductive isolation:
One group of fish feed at the top of the lake the other feeds at the bottom. They seldom encounter each other and do not mate.
ecological isolation also called Habitat isol
what type of reproductive isolation:
One population of flowers blooms earlier than another
temporal isolation
Postzygotic mechanisms …zygote forms and then
Embryo mortality
Death before maturity
Reduced hybrid fertility
Hybrid breakdown:
Hybrid breakdown:
offspring of hybrid weak or sterile
Polyploidy
Plants can be 3n or 4n or more
B) Polyploid individuals no longer interbreed with the 2n population = reproductive isolation = new species.
Autopolyploidy
just keep two full sets of your own chromosomes (4n can self pollinate)
Allopolyploidy
hybridize with other species
Patterns of Evolution defined by
rates of change
(gradual or punctuated equilibrium model)
number of species formed
punctuated equilibrium model
no change for long time then rapid change for ‘short’ time (10,000 – 100,00 years
anagenesis =
single line of descent
cladogenesis =
branching line of descent
1) lineage splits
2) adaptive radiation
3) graphical models
cladogenesis lineage splits due to
reproductive isolation and genetic divergence (evolution)
cladogenesis graphical models
Cladograms and Phylogenetic Trees
1) mathematical models - computer generated
2) based on morphological homologies and molecular data (amino acid/DNA sequence)
3) show when traits are derived or lost
cladogenesis: Each branch point shows an
extinct common ancestor of the organisms further down the branch
Outgroup =
group at base
One that branched off first
Most different
Used as comparison
cladogenesis: lines that do not reach the top of the page show
lineages that went extinct
cladogenesis: Lines crossing the cladogram show
when derived traits showed up.
All organisms further along the branch will have those traits unless they were lost due to natural selection
Types of cladistic grouping
Monophyletic group
Paraphyletic group
Polyphyletic group
Monophyletic group
All the descendants of a common ancestor in one group
Paraphyletic group
All members of group share a common ancestor but not all descendants included in the group
Polyphyletic group
includes descendants from more than one common ancestor
Molecular Clock Theory
A) Attempts to measure absolute time of evolutionary change
B) # nucleotide substitutions proportional to time since divergence
C) Assumes constant rate of evolution of genes
D) Δ rates depend on importance of gene/mutation
