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Types of Speciation: a Review Sympatric Speciation Sympatric Speciation: Polyploidy

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Types of Speciation: a Review Sympatric Speciation Sympatric Speciation: Polyploidy Macroevolution Part III Sympatric Seciation STUDENT HANDOUTS Types of Speciation: A Review Sympatric Speciation Sympatric Speciation & Habitat Differentiation • Allopatric speciation is the evolution of geographically isolated • Sympatric Speciation occurs • Suppose that a certain populations into distinct species. There is no gene flow, which without geographic isolation, species feeds on a tends to keep populations genetically similar. thus it occurs at a local level. particular host and only • Parapatric speciation is the evolution of geographically adjacent that host. populations into distinct species. Divergence occurs despite There is something within • • Next, suppose a mutation limited interbreeding where the two diverging groups come into the environment that keeps a occurs that allows it to contact. single species separated into feed upon a different • Sympatric speciation has no geographic constraint to two or more distinct groups. • Eventually,host. the species is divided into interbreeding. Macroevolution: two groups that are separated from one another. • These categories are special cases of a continuum from zero • The end result is that the two Given enough time, speciation can occur. Part III Sympatric Speciation (sympatric) to complete (allopatric) spatial or geographic groups evolve into separate segregation of diverging groups. species. • The species of treehoppers pictured above are host specific. The first lives on bittersweet while the second lives on butternut. The Physics of Light & Speciation The Physics of Light & Speciation The Physics of Light & Speciation The Physics of Light & Speciation • There are three primary colors of light: red, green and • However, everything changes when the water is • The physics of light affects not just how blue water • In fact, biologists recently demonstrated that the light blue (sorted by frequency which corresponds to energy). clouded by particles. looks to us, but how the animals living in the world's penetrating to different depths of Africa's Lake Victoria • Water molecules tend to absorb reddish light, leaving • Just picture a silt-clogged river or lake. oceans, lakes, and rivers are able to find food and each seems to have played a role in promoting a massive other — and this, in turn, can impact their evolution. evolutionary radiation. the blue light to travel towards the depths of large • Such sediment particles are particularly good at bodies of water. absorbing bluish light — the opposite of water • Because of this, deep ocean waters look blue. molecules. • Many fish species, for example, have evolved vision • More than 500 species of often brightly colored cichlid that is specifically tuned to see well in the sort of light fish have evolved there in just a few hundred thousand • So when the sun shines on cloudy waters, blue light is present near the surface, but just a few meters down, available where they live. years! most of the blue light will have been absorbed and mainly red light will penetrate. • But even beyond simple adaptation, the physics of • WHY?? light can lead to speciation. The Physics of Light & Speciation The Physics of Light & Speciation The Physics of Light & Speciation The Physics of Light & Speciation Like all populations, the fish have genetic variation, • Picture a lake with slightly cloudy water. Near the surface, blue • • Because of the differential penetration of light into the light dominates the visual environment, but in deeper waters, individual fish have different versions of genes. lake, fish sensitized to blue light have an advantage in • By itself, natural selection acting on light sensitivity red light does. • Some of this genetic variation affects the fishes' color shallower waters because they can better find food can cause something of a rift in the population, but • A fish population lives along the lake's shore where it slopes vision. and spot predators there, while fish tuned to red light when sexual selection is considered as well, the from very shallow water to deeper water — so some of the fish have an advantage in deeper waters. divergence is amplified. spend more of their time in blue light and some spend more of • Some fish have genes that enable them to see blue their time in red light. light better, while other fish have a red light advantage. • Male fish have some variation in color. • So in different parts of the fishes' habitat, different • Some males have genes for blue coloration, some color-sensitivity genes are favored by natural selection. have genes for red coloration. • This matters because female fish are choosy about their mates and tend to pick brightly colored males to father their offspring. The Physics of Light & Speciation The Physics of Light & Speciation Sympatric Speciation: Habitat Differentiation and Sympatric Speciation: Polyploidy Sexual Selection In this scenario, blue males • Over many generations of • Polyploidy refers to instant living in deep waters would sexual selection acting in this speciation which occurs in most have trouble finding mates for way, the two parts of the often in plants. two reasons: population may diverge. • Polyploid cells and organisms are (1) there is little blue light those containing more than two around, so they look more dull • Though they live right next paired (homologous) sets of than red males, and door to one another, the fish chromosomes. will evolve to prefer to mate (2) the females living in deep with other fish that share • Polyploidy may occur due to waters tend to be less sensitive their coloration, light- abnormal cell division, either to blue light than they are to sensitivity, and habitat. during mitosis, or commonly red. during metaphase I in meiosis. Macroevolution Part III Sympatric Seciation STUDENT HANDOUTS Sympatric Speciation: Polyploidy Sympatric Speciation: Polyploidy Sympatric Speciation: Autopolyploidy Sympatric Speciation: Allopolyploidy • Autopolyploidy refers to the occurrence in which the • The normal primrose is number of chromosomes double in the offspring due to diploid with 14 total non-disjunction during meiosis. chromosomes. 2N = 14 • This was discovered by Hugo deVries when studying • In this species there was primroses. a total nondisjunction event resulting in • He noticed some of primroses that are them were larger and tetraploid. 4N = 28 • Allopolyploids are polyploids with chromosomes very hardy. This is the mechanism for autopolyploidy. A diploid plant becomes a tetraploid plant. The offspring look very much like the derived from different species. • These primroses cannot diploid plant but may be a little larger and more vigorous. • Precisely, it is the result of multiplying the successfully mate with chromosome number in an F1 hybrid. the diploid species. Sympatric Speciation: Chromosomal Rearrangements Sympatric Speciation: Chromosomal Rearrangements Tempo of Evolution: Gradualism Tempo of Evolution: Gradualism Humans started synthesizing new species of plants in the In the 1960's Australian biologist • Gradualism or phyletic • When speciation laboratories of Sweden and Scotland during the 19th century. M.J.D. White was studying two gradualism is a model of occurred or is Triticale was among the first synthetic plants. As a rule, triticale neighboring flightless grasshoppers. evolution which theorizes They appeared to be identical in completed usually combines the high yield potential and good grain quality of that most speciation is slow, wheat with the disease and environmental tolerance (including form but showed clear differences in cannot be determined uniform and gradual. soil conditions) of rye. the configuration of their with respect to chromosomes. • Evolution works on large gradualism. populations over an expanse Time • The seasonal isolating of time. mechanism is a good It appeared that there had been a random change in the • The population slowly example. chromosome structure that did not result in a lethal zygote. Those accumulate changes and grasshoppers possessing it were more fit for certain areas of the evolves. grasshoppers' range. These are now two different species of the genera Vandiemenella. Tempo of Evolution: Punctuated Equilibrium Tempo of Evolution: Punctuated Equilibrium Gradualism vs. Punctuated Equilibrium • Punctuated equilibrium was • Punctuated equilibrium occurs first proposed by Stephen Jay after some crisis in the Gould and Niles Eldredge in environment. It may also be 1972. accompanied by a reduction in Created by: population size. • Most species will exhibit little Carol Leibl Time Science Content Director net evolutionary change for Time • Once natural selection occurs National Math and Science most of their geological and the population evolves, the history, remaining in an population may stay static for extended state called stasis. long periods of time once again. • The fossil record supports both of these tempo types. .
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