topic 10 - modes of speciation Flashcards
5 modes of speciation
- Allopatric
- Peripatric
- Parapatric
- Sympatric
- Polyploidy
describe allopatric. evolution fast or slow?
• Divergence of two large populations • Gene pool large • Environments initially Similar • Evolution likely slow, but speciation inevitable given enough time
what processes can fragment a population
• Several geological processes can fragment a population into two or more isolated populations
○ Mountain ranges, glaciers, land bridges, or splintering of lakes may divide one population into isolated groups
○ Alternatively, some individuals may colonize a new, geographically remote area and become isolated from the parent population
○ For example, mainland organisms that colonized the Galapagos Islands were isolated from mainland populations
what does the significance of a barrier to limit gene exchange depend on? ex?
• How significant a barrier must be to limit gene exchange depends on the ability of organisms to move about
○ A geological feature that is only a minor hindrance to one species may be an impassible barrier to another
○ Valley of the Grand Canyon
§ Significant barrier for ground squirrels which have speciated on opposite sides, but birds which can move freely have no barrier
when is allopatric speciation likely? is it common?
• Likelihood of allopatric speciation increases
when a population is both small and isolated
○ A small, isolated population is more likely to have its gene pool changed substantially by genetic drift and natural selection
• However, very few small, isolated populations will develop into new species; most will simply perish in their new environment
describe itsthmus of panama
• A narrow strip of land between Caribbean Sea & Pacific Ocean linking North & South America • Until ~3mya, two waterbodies joined by Atrato Seaway • Some recent study even suggested that the connection might be there for ~10 my
look at shrimp and salamander exs at isthmus
ok
example of genetic divergence in isolation?
• Many kinds of fishes have distinct eastern and western populations as shown by MtDNA sequences • Reduced gene flow in the past -> evidence of past geographic Isolation
what is peripatric speciation. fast or slow evolution?
• Peripheral isolation • Divergence of a small population from a widely distributed ancestral forms • Dispersal • Founder effects; small subset of gene pool • Extreme environment? • Rapid evolution more Likely bc small pop
ex of peripatric speciation
paradise king fishers - varies little in new guniea large island but several distinct forms in smaller costal islands
describe parapatric speciation. what might it lead to
• Of two species or populations, having contiguous (= sharing a common border; touching) but non- overlapping geographic distributions • Neighbouring populations • Modest (low) gene flow between them • Evolution of reproductive isolation • Subsequent range expansion can lead to sympatry
what is common in areas of sympatry?
• Character displacement common in areas of sympatry ○ Sympatric species possess many different characters although the same species in allopatry were sometimes indistinguishable
example of parapatric
Character displacement in closely related species of fruit flies • Traits are more distinct in sympatry than they are in allopatry • Caused by strong selection against Interbreeding
describe sympatric. is it common?
• Initially, a single randomly mating population • Evolution of reproductive barriers within the same geographic area • Still debated as to how common this is - probably not very common
how do new species arise in sympatric
• In sympatric speciation, new species arise
within the range of the parent populations
• Reproductive barriers must evolve between sympatric populations
• In animals, it may result from gene-based
shifts in habitat, feeding, or mate preference
