Evolution3
-
Upload
jolie-yu -
Category
Technology
-
view
2.178 -
download
0
Transcript of Evolution3
![Page 1: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/1.jpg)
SpeciationThe Process of
Evolution
![Page 2: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/2.jpg)
Speciation• Formation of a new species• Species:
– a population that can breed freely and produce fertile offspring
• Speciation often occurs when part of the population is isolated from another part– Selective pressures of the environment in
one area may be different from pressures in another area
![Page 3: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/3.jpg)
What is a Species?• Definition :• Morphospecies - based on appearance• Biologic species - a population that can
breed freely and produce fertile offspring• The largest unit of population in which gene
flow is possible• Limitations:
– doesn’t work for asexual organisms– extinct life forms– populations that are geographically isolated -
sometimes call subspecies
• No clear answer; idea is arbitrary
![Page 4: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/4.jpg)
Patterns of Speciation
• Fossil record shows 2 patterns:• Anagenesis (phyletic evolution)
– the transformation of an unbranched lineage of organisms, sometimes creating an organism different enough to be a new species
• Cladogenesis – branching evolution; budding of one or
more new species from a parent species that continues to exist.
![Page 5: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/5.jpg)
Anagenesis vs. Cladogenesis
![Page 6: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/6.jpg)
Causes of Speciation• Speciation often occurs when part of
the population is isolated from another part
• Geographic Isolation – most common– a physical barrier develops (changing
course of a river; separation of an island)– Selective pressures in one area are
different from pressures in another area
• Reproductive Isolation– another form of isolation
![Page 7: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/7.jpg)
Isolation
![Page 8: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/8.jpg)
Geographic Isolation• Biogeography of Speciation • Classified according to geographic relationship
between new and old species• Sympatric
– population becomes reproductively isolated in the midst of the parent population
– ranges of new and old species overlap.
• Allopatric – species are physically separated– more likely in small populations
• Adaptive radiation is allopatric :– emergence of numerous species from a common
ancestor that spreads to several new environments.
![Page 9: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/9.jpg)
Allopatric vs. Sympatric
![Page 10: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/10.jpg)
Allopatric Barriers
![Page 11: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/11.jpg)
Geographic Isolation
![Page 12: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/12.jpg)
Reproductive Isolation
• Example: organisms breed at different times
• Reproductive barriers are of 2 types:• Prezygotic
– before the formation of fertilized eggs– impedes mating or fertilization
• Postzygotic – after
![Page 13: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/13.jpg)
Reproductive Isolation
![Page 14: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/14.jpg)
Prezygotic Isolation• Impedes mating or fertilization• Habitat isolation
– not geographically separated, but occupy different niches within an area, e.g. trees versus ground
• Temporal isolation – breed at different times
• Behavioral isolation– don’t produce appropriate courtship signals
• Mechanical isolation – anatomically incompatible
• Gametic isolation – mating occurs but gametes rarely fuse to form
zygotes
![Page 15: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/15.jpg)
Behavioral Isolation: Courtship Barrier
![Page 16: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/16.jpg)
Postzygotic Barriers
• Hybrid inviability – offspring don’t make it
• Hybrid sterility – e.g. mules
• Hybrid breakdown – F2 are sterile or weak
![Page 17: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/17.jpg)
Introgression
• Alleles pass a reproductive barrier when a fertile hybrid mates with a parent species
• Increases variation• Rare
– 2 species remain distinct
![Page 18: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/18.jpg)
Post Speciation Evolution• Divergent Evolution
– Process by which related organisms become less alike
– occurs after speciation– at first 2 new species are very similar, but
over time become more & more different.
• Adaptive radiation is a special type of divergent evolution– Many new species from a single parent
species
![Page 19: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/19.jpg)
Adaptive Radiation
![Page 20: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/20.jpg)
Timing of Evolution• Most scientists accept natural selection as the
process of evolution• The timing is controversial• Gradualism
– the traditional view– a slow, steady accumulation of changes, leads to
new species
• Punctuated Equilibrium– long periods of inactivity followed by big jumps
• Fossil record provides evidence that the pace of evolution varies– The same evidence is used to support different ideas– Could be some of both
![Page 21: Evolution3](https://reader036.fdocuments.in/reader036/viewer/2022062513/55500fa0b4c90535638b4955/html5/thumbnails/21.jpg)
Gradualism vs. Punctuated Equilibrium