Speciation & Macroevolution Flashcards
Speciation
Creation of a new species
Macroevolution
Evolutionary change above the species level (i.e. the evolutionary components of speciation)
Microevolution
Change in allele frequency in a local population in time
Biological species concept
Individuals are members of the same species if they are capable of interbreeding and producing fertile offspring (does not work in all cases, but works in most)
Reproductive isolation
The existence of biological factors (reproductive barriers) that prevent 2 individuals from interbreeding and producing fertile offspring
- key concept of biological species concept
- a single behavior may not give rise to complete reproductive isolation
- many factors can act in concert to create reproductive isolation
Reproductive barriers
- pre-zygotic
2. post-zygotic
Zygote
Fusion of sperm and egg
Pre-zygotic barriers
- prevent mating
2. prevent fertilization of egg
Post-zygotic barriers
- prevent survival
2. prevent reproduction of offspring
Pre-zygotic isolations: (5 isolations)
- temporal isolation: timing is off
- habitat isolation: habitat is off
- behavior isolation: behavior is off
- mechanical isolation: mating may be attempted, but prevented by morphological differences (his dick don’t fit)
- gametic isolation: sperm of 1 species may not be able to fertilize eggs of another species
Post-zygotic consequences : (3 consequences)
Fertilization occurs but…
- reduced hybrid viability (i.e. hybrids do not survive well)
- reduced hybrid fertility (i.e. hybrids cannot reproduce)
- hybrid breakdown (i.e. hybrids are non-viable or sterile in subsequent generations)
2 ways speciation can occur:
- Allopatric speciation
2. Sympatic speciation
Allopatric speciation
Geographic separation of populations
- divergence
- greatly reduced gene flow
- genetic drift (founder effect)
- natural selection (differences in environment between populations)
- new species can only form when geographic isolation is followed by reproductive isolation
Sympatric speciation
Speciation without geographic isolation
-most common mechanism = polyploidy (“many chromosomes”)
Polyploidy
Error during meiosis changes the number of chromosomes in gametes -> offspring (may be viable and self-fertile)
- most common in plants
- can occur in animals (much less common)
Allopatric vs. sympatric speciation
Allopatric speciation:
-geographic isolation restricts gene flow between populations
-reproductive isolation may then arise via (genetic) drift
-natural selection (sexual selection in the isolated populations)
Sympatic speciation:
-a reproductive barrier still isolates subset of population without geographic isolation
-can result in polyploidy and natural selection (sexual selection)
How much genetic change is required for speciation?
Impossible to generalize
How quickly does speciation occur?
Patterns can often be inferred from fossil record, morphological, or molecular data
- the interval between speciation events can range from 4,000 - 40,000,000 years
- average = 6,500,000 years
Punctuated equilibrium
Periods of little change interrupted by short periods of rapid change
Gradualism
Big differences between species accumulated through slow, steady change
