The Origin of Species

The origin of new taxonomic groups called speciation. Macroevolution The origin of new taxonomic groups called speciation. 1- Anagenesis (phyletic evolution): accumulation of heritable changes completely replacing one species with another 2- Cladogenesis (branching evolution): budding of new species from a parent species that continues to exist (basis of biological diversity)

What is a species? A population or group of populations whose members have the potential to interbreed and produce viable, fertile offspring Genetic exchange is possible and they are genetically isolated from other populations When populations no longer interbreed they are thought to be separate species

Modes of speciation (based on how gene flow is interrupted) Barriers to gene flow between pop.’s isolate them, leading to new and separate species. Two ways Speciation can occur: Allopatric Sympatric

Allopatric Speciation Is when a physical barrier separates a species and doesn’t allow any further contact. Mountains, glacial movement, river boundary movement, the ocean, plate tectonics, etc. Populations diverge when gene flow between them is restricted resulting in adaptive radiation. Adaptive radiation is the evolution of many diversely adapted species from a common ancestor. Geographic isolation is often the first step in allopatric speciation.

Examples: Darwin’s finches isolated by being on different islands. Grand Canyon squirrels that at one time were an interbreeding population but over time were separated by the GC. The Ensatina salamanders in California

Sympatric Speciation Speciation occurring in organisms living within the same habitat. It’s when members of a population develop some genetic difference that prevents them from reproducing with the parent type. Wild specimen of the butterfly species, Heliconius heurippa. Researchers recently demonstrated that this species is a naturally-occurring hybrid between H. cydno and H. melpomene.

Sympatric Continued Seen more often in plants Autopolyploid an organism has more than two chromosome sets. Due to nondisjunction in either mitosis or meiosis or self-fertilization. Allopolyploid a polyploid hybrid resulting from contributions by two different species. More common than autopolyploidy. Usually sterile hybrids, but can reproduce asexually.

Reproductive Isolating Mechanisms Either a structural, functional, or behavioral characteristic that prevents successful reproduction. Divided into premating (prezygotic) and postmating (postzygotic) types. http://www.pbs.org/wgbh/evolution/library/05/2/l_052_04.html

Prezygotic barriers Impede mating between species or hinder the fertilization of the ova Habitat Behavioral Temporal Mechanical Gametic http://www.pbs.org/wgbh/evolution/library/01/6/l_016_07.html

Habitat isolation When two species occupy different habitats, even within the same geographic range, so they’re less likely to meet and to attempt to reproduce.

http://www.dnatube.com/video/12171/The-Moonwalking-Bird-Redcapped-Manakin Behavioral isolation Is when there are differences in mating behaviors. Fireflies mate signaling Frogs singing for a mate http://birdcinema.com/view_video.php?viewkey=df0e43641f1dc52d810b http://dsc.discovery.com/videos/is-it-possible-polly-want-a-chainsaw.html

Temporal isolation When two species live in the same location, but reproduce at different times of the year, preventing successful mating.

Mechanical isolation Is the differences between two species in reproductive structures or other body parts, so mating is prevented.

Gamete isolation Is the physical or chemical incompatibility of gametes of two different species. If the gametes lack receptors to facilitate fusion, they can’t form a zygote. An egg may have receptors only for the sperm of its own species.

Reproductive Isolation Postzygotic barriers: fertilization occurs, but the hybrid zygote does not develop into a viable, fertile adult Reduced hybrid viability (frogs; zygotes fail to develop or reach sexual maturity) Reduced hybrid fertility (mule; horse x donkey; cannot backbreed) Hybrid breakdown (cotton; 2nd generation hybrids are sterile)

Patterns of Evolution

Divergent evolution Occurs when a species finds a new and different way of using the environments resources. When a species finds their “niche” in the environment.

Adaptive radiation Is a form of divergent evolution. When a species finds itself in a new territory and adapts to better suit the environment ultimately forming a new species. Example would be in Hawaiian honeycreepers . http://www.pbs.org/wgbh/evolution/library/01/1/l_011_03.html

Convergent evolution Is when geographically isolated species develop similar characteristics due to the needs of their environments. Due to different species needing to adapt to similar types of environments. Best example would be geographically isolated marsupials of Australia, and Placental mammals of North America. (the marsupial mouse, marsupial mole, and Tasmanian wolf)

Coevolution Is when two species somehow influence one another’s evolutionary direction. Most common in predator-prey relationships. If a predator becomes better at catching its prey, the prey will be forced to adapt and get better at getting away. http://www.pbs.org/wgbh/evolution/library/01/3/l_013_01.html

The Pace of Evolution Two views on the Tempo of speciation: Gradualism http://www.pbs.org/wgbh/evolution/library/11/2/e_s_3.html Two views on the Tempo of speciation: Gradualism Punctuated Equilibrium

Gradualism The traditional, or Darwinian, view of evolution was that it was a very slow process, resulting from the gradual accumulation of small differences.

Punctuated equilibrium According to another model based on the fossil record, speciation occurs rapidly over a short time, followed by a long period of little or no change. "Short" means thousands or hundreds of thousands of years. https://www.23andme.com/gen101/prehistory/prologue/