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
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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
ex. chchlid fishes and sympatry
• Species flocks of cichlid fishes in African Great Lakes Lake Tanganyika ~140 - 300 species Lake Victoria >200 - 600 species Lake Malawi ~800 - 1,000 species Feeding regimes
sympatry new species in plants v animals?
- In animals, it may result from gene-based shifts in habitat, feeding, or mate preference
- In plants, sympatric speciation can result from accidents during cell division that result in extra sets of chromosomes, a mutant condition known as polyploidy
define autopolyploidy
• Autopolyploidy
○ An individual or strain with multiple sets of chromosomes that are derived from the same species
define allopolyploidy
○ An individual or strain with multiple sets of chromosomes that are derived from different species
describe autopolyploidy mutation
• An individual can have more than two sets of chromosomes from a single species if a failure in meiosis results in atetraploid (4n) individual
• This autopolyploid mutant can reproduce with itself (self-pollination) or with
other tetraploids
• It cannot mate with diploids from the original population, because of
abnormal meiosis by the triploid hybrids
speciation by autopolyploidy ex
- in the early 1900s, botanist Hugo de Vries produced a new primrose species, the tetraploid Oenotheria gigas,from the diploid Oenothera lamarckiana
- This plant could not interbreed with the diploid species
describe alloployploidy. hybrid fertilitiy?
• Another mechanism of producing polyploid
individuals occurs when individuals are
produced by the mating of two different
species, an allopolyploid
○ While the hybrids are usually sterile, they may be quite vigorous and propagate asexually
○ Various mechanisms can transform a sterile hybrid into a fertile polyploid
○ These polyploid hybrids are fertile with eachother but cannot interbreed with either parent species
allopolyploidy cross polination?
• One mechanism for allopolyploid speciation in plants involves several cross-pollination events between two species of their offspring and perhaps a failure of meiotic disjunction to a viable fertile hybrid whose chromosome number is the sum of the chromosomes in the two parent
species
how does origin of allopolyploid species occur? ex?
• Origin of polypoid species is common and rapid enough that scientists have documented several such speciation in historical times • For example, two new species of plants, called goatsbeard (Tragopodon), appeared in Idaho and Washington • They are the results of allopolyploidy events between pairs of introduced European Tragopodon Species
sucker ex of allopoly?
• Hybrid species displaying hybrid vigour (= increase in level of production due to crossing) • Sucker family Catostomidae: all species are tetraploid suckers grow faster than minnows - likely origin from minnow /carp family tetraploid hybrids
how is polyploid speciation used by humans
• Many plants important for agriculture are
the products of polyploidy
• For example, oats, cotton, potatoes, tobacco, and wheat are polyploid
• Plant geneticists now hybridize plants and use chemicals that induce meiotic and mitotic errors to create new polyploids with special qualities
• Example: artificial hybrids combine the high yield of wheat with the ability of rye to resist disease
sympatric vs polyploid in animals
• While polyploid speciation does occur in
animals, other mechanisms also contribute
to sympatric speciation in animals
• Sympatric speciation can result when genetic factors cause individuals to be fixed on resources not used by the parent
• These may include genetic switches from one breeding habitat to another or that produce different mate preferences
look at overview chart for help
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