Alexis

Question:

How Does Speciation Occur?

Initial Model

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Claim

Over time, a mutation in the population starts to become prominent in said population, and, having an "advantage" over the previous species' trait, becomes its own, only mating with other organisms with this new mutation of the population instead of those who do not have it.

Evidencegrassonmine.gif

1). The grass species Anthoxanthum odoratum lives in a continuous enviornment. However, some of the population live near mines where the soil contains heavy metals while others live in the uncontaminated soil. The plants around the mines have naturally selected a genotype that tolerates these metals, while the neighbor plants have not (they have no need to, for thier soil is uncontaminated by the metals). These two plants are a part of adjacent populations, so technically they can interbreed with one another. They do not, though, for otherwise the genotype for tolerance of heavy metals would mix with those who do not. Instead, the two plants have varying flowering times, therefore they only inbreed with those that share a similar genotype. These reflect the first steps of parapetric speciation, discussed in the final model.[1]

2). Darwin's Finches (Galapagos Islands Finches) consist of fourteen species of finches in which each have a different niche on their specific island (namely, the type of food they eat). It is thought that millions of years ago, a certain species of finch migrated to the Galapagos Islands from mainland South or Central America, later stemming to the fourteen species of finches found on the islands today. The original ancestor of the birds was thought to be a ground-dwelling, seed-eating finch, while today there are three species of ground-dwelling, seed-eating birds, three species of cactus-dwelling, seed-eating birds, one species of tree-dwelling, seed-eating bird, and seven species of tree-dwelling, insect-eating birds. The birds differ mainly by the size and shape of their beaks.[2] Since the Galapagos Islands are a chain, the population that moved into the orginal island from the mainland may have undergone extreme changes, and later migrations of the birds to the islands surrounding the main island may have resulted in further speciation (thus accounting for the fourteen species of finches the islands now home).[3]
Darwin_finches_dis2.jpg



3). Two hundred years ago, the ancestors of the present day apple magot flies only laid their eggs in hawthorne fruits; today, though, eggs are laid not only in hawthornes but also in domapplemaggotflies.jpgestic apples. When the apple maggot fly babies grew up, the females generally chose to lay eggs and males tended to look for mates in the fruit they were laid and raised in. Therefore, hawthorne flies ended up mating almost exclusively with other hawthorne flies and domestic apple flies ended up mating almost exclusively with other domestic apple flies. The flow of genes between the two populations thus became skewed so that flies only mated with those who grew up in the same fruit. Genetic differences have evolved in the two differing flies over the past two hundred years, which could eventually lead to a major species break. This is also an example of sympatric speciation.[4]


4). Speciation Video of California Salamanders-This is a description of how salamanders, decending from the same species, became very distict as they moved southward. These species have changed due to whether their enviornment calls for camoflage or copying the color and features of a posionous newt. They are on their way to becoming totally different species, for (as shown in the video) a hybrid baby has very little chance of blending in or standing out as a warning. David Wake of the University of California, Berkeley explains what has happened to cause the salamanders to change. This demonstrates allopatric speciation, where a break in the population (along the Sierra-Nevada and the other along the coastal mountains) causes the species to adapt to their enviornment, thus becoming distinct to the other species. This also demonstrates that, when the two meet back up, their offspring will be at a disadvantage (in this case, they will not blend or stand out dangerously). Eventually, because of this disadvantage, the two will refuse to breed with eachother, becoming new species.

Final Model

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Citations from final model:
~http://evolution.berkeley.edu/evosite/evo101/VSpeciation.shtml
~http://evolution.berkeley.edu/evosite/evo101/VADefiningSpecies.shtml
~http://evolution.berkeley.edu/evosite/evo101/VC1bAllopatric.shtml
~http://evolution.berkeley.edu/evosite/evo101/VC1eSympatric.shtml
~http://evolution.berkeley.edu/evosite/evo101/VC1cPeripatric.shtml
~http://evolution.berkeley.edu/evosite/evo101/VC1dParapatric.shtml
~http://www.uwyo.edu/dbmcd/molmark/lect2a.html
~http://www.biology-online.org/dictionary/Peripatric_speciation

Reasoning

The original claim is not completely correct. Mutations do not necessarily occur for a "fitter" species to become developed; a "fitter" species can occur, though, because the new species may be better adapted for the certain environment it lives in than the original species, which may later on become extinct due to weakness in competition. Instead, a shift in the population (whether it be a small scale migration, a large scale migration, an environmental change within a continous population, or just mutation within a population) can lead to a certain group becoming isolated from breeding with the original population of its species, causing a new species to develop. There are four ways in which a species can break off from an original ancestor: allopatric, sympatric, peripatric, and parapatric. Allopatric speciation occurs when a population is split and becomes geographically isolated, leading to inbreeding with each population ignoring the other. Sympatric speciation occurs when a genetic mutation causes a particular portion of the population to diverge from the other, eventually breaking into its own species. Peripatric Speciation occurs when a smaller group is isolated from the larger population, allowing for mutations to pass along faster due to the low starting population. Parapetric speciation occurs when a population refuses to mingle with that of an adjacent population; there are no barriers, but the organisms still choose to mate with those that are their geographic neighbors directly instead of slightly removed. These all allow for the creation of a new species, as illustrated above in the final model and again in the diagram of speciation below. In addition, the time frames in which these events occur can be extremely misleading. The species can diverge from the main group after a series of small changes over millions of years, which gradually change part of the original species into a new one (this is known as the gradualism model). The species can also diverge completely from the orginal species rather quickly, over thousands of years instead of millions; in this way, a "spurt of evolution" happens and stays virtually the same until equilibrium is reached in a new species (punctuated equilibrium). Though scientists are unsure which exactly is the "right" evolutionary tempo-or whether both do occur- these are both models for such occurances (based on fossil records).[5]
speciation.png




Monroe and Lydia


Question

How does speciation occur?

Initial Model

claim.jpg

Claim

Species continue to evolve, and can eventually evolve into other distinct species. Based on environment, species will change because they must adapt; they can lose and gain different traits. Species must also separate in order to survive. It will take a significant amount of time for speciation to occur, and it never really stops.

Evidence


Apple Maggot Fly

The Apple Maggot Fly that lives in Eastern North America used to only feed on the leaves of the Hawthorne. However, when apple trees were introduced to their environment, they began to lay eggs on them in addition to the Hawthorne. After a period of time, they began to also feed on the apples. Now, there are two clear groups of these flies. One still feeds on the leaves of the Hawthorne, while the other feeds on the apple trees. The two groups rarely interbreed, and have different feeding and mating times. This leaves hybrids at a disadvantage, because they cannot mate easily with either primary group of flies. This separates the groups effectively, giving evidence of one way that speciation occurs.
Diesel, Rudi. (2002) How Does Speciation Occur? from http://mygeologypage.ucdavis.edu/cowen/historyoflife/speciationmode.html accessed on December 1, 2011.

Maize

Speciation can occur in plants as well. Pasterniani selectively planted the next year's maize from white and yellow seeds, refusing hybrids with more and more vigor. After five years, the maize had a vastly increased percentage of white and yellow corn, with a drastically reduced percentage of hybrids. Since the white corn faced different selection than the yellow corn, their traits separated further than if they had both been left to interbreed.
Boxhorn, Joseph. (1995) Observed Instances of Speciation from http://www.talkorigins.org/faqs/faq-speciation.html accessed on December 1, 2011.



Final Model

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Reasoning

All species continually mutate. When division occurs, and the two groups of originally alike organisms face different environments, natural selection favors different traits in each group. Like the example of the introduction of the apple tree as a new food source, which produced two distinct groups of apple maggot flies, speciation separates organisms and changes them to the point that they cannot interbreed any longer.The separation can be an almost even division of the population (allopatric) or a division of a small group from the large population (peripatric.) At this point, a new species is formed. The last form of division is among different niches. The species is partially geographically divided, but the favoring of extremes of the spectrum of fitness for the different niches and a disadvantaged population of crosses eventually makes interbreeding genetically impossible. There is some evidence that suggests that the division can happen in the same geographical region (sympatric.) The original claim is correct; species form through division and adaptation to new environments. A new species forms when the adaptation renders the two groups unable to breed successfully.


McKenzie


Question


How does speciation occur?

Initial Model

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Claim


In a group, population, or niche that is mating exclusively amongst themselves, natural selection and genetic drift cause new traits to form in a gene pool, and other traits to dissapear completely from the gene pool. This cause great changes in that group, population, or niche overtime, and eventually these changes become so great that these organisms can no longer reproduce succesfully with individuals that are not part of their gropu, population, or niche.

Evidence


Allopatric Speciation
Two populations of the same species are separated geographically. The two populations experience genetic drift, different mutations occur, and the different pressures from each population’s environment cause different traits and mutations to be maintained. Over a long period of time, these differences become so drastic that the organisms from the two populations would not reproduce if they ever came in contact with one another.
Evidence
A population of snapping shrimp was separated by the closing of the Isthmus of Panama 3 million years ago. Today the separated populations are mostly identical, but when males are put with females from a different population, they choose to fight rather than mate, indicating that they have become different species.
There is a species of spotted owl that is found in the North American west. Two populations of this species have become isolated in different geographic areas—one population has settled on the Northwest coast, and the other has settled farther south, through Mexico. The Northern spotted owl has developed and adopted very different traits from the Mexican spotted owl. This illustrates the differences that arise from geographically separated populations, which can lead to its eventual change into a new species.

Peripatric speciation
Similar to Allopatric speciation, except that it is a very small population of a species that is isolated. The process is the same as Allopatric speciation, but because the population is smaller there is less chance of genetic variety so the traits that are passed to the next generation are less likely to be beneficial for survival.
Evidence
The London Underground Mosquito evolved from a small population of Culex Pipiens mosquitos that moved into the tunnels of the London Underground, isolating them from others of their species. The London Underground Mosquito has now developed genetic differences, behavioral differences, and difficulty mating with normal Culex Pipiens mosquitos. However, the genetic differences weren’t always favorable to surviving the underground environment, indicating that the lack of genetic variety in the small population increased the amount of genetic drift.

Parapatric
Two populations of a species are only partially separated.
Evidence
The organisms are simply more likely to mate with their neighbors than other organisms in the same species that live in a different part of their environment, reducing gene flow.
Two different populations of the leaf-litter lizard have been found to be genetically distinct, although both populations live in the same rain forest. However, one population lives in an open air part of the forest, while the other population lives under the rain forest’s canopy. Both populations tended to mate amongst themselves rather than travel to other parts of the forest to mate. The open air population eventually evolved different traits, such as shorter legs, that better protected it from flying predators.

Sympatric speciation
Two or more species evolve from the same population, without separating geographically. This usually happens because the population becomes dependent on different food sources, and evolves in ways that are favorable to attaining those food sources.
Evidence
Scientists have studied two different species of palm tree that are native to an Australian island, Howea forsteriana and H. belmoreana. They saw that the two species had the several identical nuclear mitochondrial DNA, indicating that they were the same species at some point. However, the island contains two different types of soil, acidic and calcareous, and the species adopted different traits— such as different periods of fertility—that were more favorable for surviving in the different types of soil. Therefore the ancestors of the Howea forsteriana, found in calcareous soil, developed differently than the organisms in the acidic soil, who evolved into the H. belmoreana, even though the two were a very short distance from one another. This shows that different species can evolve from a single species without having to be separated geographically.

Final Model


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Reasoning


The spotted owl and leaf litter lizard show how, to survive and best utilize the resources in an enviornment, two different groups of the same species can begin to evolve differently. The Australian pine trees show how this evolution can occur due to a reliance on different resources. The snapping shrimp show how this can occur due to a geographic seperation. The London Underground mosquitos show how this can occur dramatically in a small population because of genetic drift. All of the evidence points to a steady change that, over many generations, causes so many changes that a group can no longer reproduce with members of the species it used to be a part of, signalling total speciation.

http://classic.the-scientist.com/news/display/23103/
http://evolution.berkeley.edu/evosite/evo101/VC1dParapatric.shtml
http://www.biology-online.org/dictionary/Peripatric_speciation
http://evolution.berkeley.edu/evosite/evo101/VC1fEvidenceSpeciation.shtml
http://www.pbs.org/wgbh/evolution/library/05/2/l_052_03.html
  1. ^ http://evolution.berkeley.edu/evosite/evo101/VC1dParapatric.shtml discusses parapetric speciation and examples of
  2. ^ http://www.pbs.org/wgbh/evolution/library/01/6/l_016_02.html discusses Darwin's Finches and thier main purpose
  3. ^ Biology Concepts & Connections, Fifth Edition. Campbell, Reece, Taylor, and Simon. Pearson Education, Inc. 2006
  4. ^ http://evolution.berkeley.edu/evosite/evo101/VC1eSympatric.shtml describes sympatric speciation as well as the apple maggot fly example
  5. ^ Biology Concepts & Connections, Fifth Edition. Campbell, Reece, Taylor, and Simon. Pearson Education, Inc. 2006