Macroevolution
Evolutionary change above the species level
What is a species?
Biological species concept: A population or group whose members have the potential to breed in nature and produce viable, fertile offspring.
Prezygotic Barriers (mating)
Habit isolation: won’t find each other in nature
Temporal isolation: Breed at different times of the year
Behavioral isolation: Female will only mate with a male with a certain courtship ritual.
Prezygotic barriers (fertilization)
Mechanical isolation: genital openings not aligned
Gametic isolation: sperm will not fertilize egg of another species
Postzygotic barriers (impede hybrid offspring)
Reduced hybrid viability: Zygote formed, individual formed but doesn’t survive until adulthood.
Reduced hybrid fertility: Survives but cannot reproduce, ex. Mule is robust but sterile
Hybrid breakdown: Gets weaker with every generation, F2 generation feeble and sterile
Allopatric speciation
Geographic separation of populations restricts gene flow:
1. different selective pressures
2. mutations arise
3. genetic drift alters allele frequencies
Sympatric speciation
Occurs in geographically overlapping populations when biological factors, such as chromosomal changes and nonrandom mating reduce gene flow:
- change in ecology (habitat isolation, sexual selection)
Gradual evolution
Slow change over time
Punctuated evolution
history of a species has long periods of stasis (no evolutionary change) interrupted by short (1000s of years) periods of rapid speciation
What is a phylogenetic tree?
A diagram that represents evolutionary relationships among organisms (based on morphology and DNA)
Parts of a phylogenetic tree
Sister taxa: organisms that share a common ancestor that is not shared by any other group
Basal taxon: a lineage that evolved early and remains unbranched
Branch point: where lineages diverge
Ancestral lineage: Common ancestor
What is a clade?
A clade or monophyletic group is a group of organisms that includes a single ancestor and all of its descendants
