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Speciation

Speciation. Species . One or more populations of individuals that can inter breed under natural conditions and produce fertile offspring. Different species may arise from genetic divergence between populations. Genetic Divergence.

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Speciation

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  1. Speciation

  2. Species • One or more populations of individuals that can inter breed under natural conditions and produce fertile offspring. Different species may arise from genetic divergence between populations

  3. Genetic Divergence • Genetic divergence is the process whereby local units of a population become reproductively isolated from other units and thus experience changes in gene frequencies between the groups • If the environments are different between isolated units then natural selection, mutations, and genetic drift will work independently on each. This will speed up genetic divergence and speciation.

  4. Isolating mechanisms • Mechanisms that lead to, or cause genetic divergence by preventing interbreeding between two groups. • As long as two groups do not interbreed their gene pools will continue to drift further and further apart. • The longer two species are genetically isolated from each other the more different they become from each other.

  5. Isolating mechanisms • Isolating mechanisms can be divide into two different types. • Isolating mechanisms that occur before fertilization are called Prezygotic mechanisms • Isolating mechanisms that occur after fertilization are called postzygotic mechanisms

  6. Types of Prezygotic Isolating mechanisms • Behavioral isolation: Potential mates meet but cannot figure out what to do about it because patterns of courtship may be altered to the extent that sexual union is not achieved • Temporal isolation: (Time) Different groups overlap in range but may not be reproductively mature in the same season. • Mechanical isolation: Potential mates attempt engagement but sperm cannot be successfully transferred . This may be due to differences in reproductive organs.

  7. Types of Prezygotic Isolating mechanisms cont. • Gametic isolation: Sperm is transferred but sperm and egg are incompatible. • Ecological isolation: potential mates never meet because they live in different habitats

  8. Types of Postzygotic isolating mechanisms • Zygotic mortality: Egg is fertilized but zygote does not develop properly dies before birth because parents are genetically incompatible. • Hybrid inviability: Hybrid very weak and can’t live outside the uterus. • Hybrid offspring: Hybrid is sterile.

  9. Speciation • Speciation occurs when a species gives rise to one or more different species. • There are three main speciation patterns • Allopatric speciation • Sympatric speciation • Parapatric speciation

  10. Allopatric • Allopatric (Allo= different, Patric=homeland) Population are separated due to geographical barriers • Rivers, earthquakes, continental drift, glaciation, archipelagos cause allopatric speciation. • Examples: • Cave fish, • Darwin’s finches • Antelope squirrels of the Grand Canyon • Isthmus of Panama

  11. Sympatric speciation • Sympatric (Sym = same, Patric=homeland) speciation occurs in the same geographical region without physical isolation. • A new species can arise in a single generation if a genetic change produces a reproductive barrier between mutants and the parent population. • Example: Accidents during cell division that result in extra sets of chromosomes (Polyploidy). Self-fertilization can give rise to new individuals that are unable to mate and form fertile off-spring with the parent species.

  12. Parapatric Speciation • Parapatric (Para = near, Patric=homeland) neighboring populations become distinct species while maintaining contact through Hybrid zones • If hybrid zone is removed through increased natural selection, natural disasters or some other means the extremes of a population fail to mate. • Examples 1 Toad population along the north rim of the Grand Canyon. 2 Dogs

  13. Branching and unbranched evolution • Cladogenesis: Branched evolution. Occurs as populations split and become reproductively isolated from each other. • Anagenesis: Unbranched evolution. Occurs as changes in allele frequency and morphology accumulate over long periods of time. New species do not live within the same time period B B A C C B A Related species are only seen in the fossil record

  14. Transitional Forms • Species which are intermediate in body form between two groups of organisms. • Species that are intermediate in time in the fossil record. Archaeopteryx

  15. ArchaeopteryxIntermediate between birds and dinosaurse • Archaeopteryx lived after the development of dinosaurs but before that advent of birds. • Archaeopteryx contains features that are both characteristic of reptilian dinosaurs as well as modern birds. Some features are half way inbetween.

  16. The tempo of speciation • Phyletic gradualism: New species develop slowly and gradually as an entire species changes over time. This idea was asserted by Darwin. • Punctuated equilibrium: This theory states that new species arise suddenly and rapidly as small subpopulations of a species split from the populations of which they were a part.

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