Ecology

Geology/Geography/Oceanography/Atmospheric Sciences

Quiz 8 :

Social Relations

Quiz 8 :

Social Relations

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Contrast the approaches of Charles Darwin and Gregor Mendel to the study of populations. What were Darwin's main discoveries? What were Mendel's main discoveries? How did the studies of Darwin and Mendel prepare the way for the later studies reviewed in chapter 8?
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Charles Darwin was a naturalist who spent his life studying plants and animals. He sought to understand their variations, similarities, reasons for being and the basic forces that cause them to change. Darwin observed the variations as caused due to phenotypical changes.
Gregor Johann Mendel was a scientist who was later known as the father of genetics. This was based on his extensive experimental observations and conclusions which are based on genetics. Mendel proved the variations as the result of the genetic changes.
Both Darwin and Mendel are known for their contributions to science which. However, their approach towards their discoveries was entirely different.
Darwin's Approach
• Darwin's studies were completely based on his long-term observations of geographical areas.
• He added onto the extensive studies of other scientists. However, his conclusions were unique and based on his own ideas.
• He did not use mathematical methodology in his works.
Mendel's Approach
• Mendel preferred experimentation and observation in all of his works.
• His approach involved physical sciences, like mathematics, which enabled him to convert the data gathered by him into a more approachable form.
• He worked with plants, such as garden peas, which were easy to cultivate and maintain under normal conditions.
• He had more segregated and recorded work, which made it easier for him to present his results.
Darwin's Main Discoveries
1) The theory of natural selection is considered a milestone in to the study of evolution. It states that evolution is a natural process by which a population acquires biological traits on the base of differential reproduction to survive and adapt.
2) The theory of compelling evolution explains natural selection as the basic mechanism for evolution.
3) The majority of his work and discoveries were based on his work on plants and animals of different geographical areas. Some of his major works are published in the following books;
• Origin of Species
• Descendants of Man
• Selection in Relation to Sex
• The Expression of Evolution in Man and Animals
Darwin spent a long tenure of his life observing populations, and he understood the differences between successive generations on the basis of characters. With his observations and guidance from the works of Thomas Malthus, he was able to develop the theories mentioned above.
Mendel's Main Discoveries
1) The principle of segregation states that alleles account for variations in inherited characters.
2) The principle of independent assortment states that a random assortment of homologous chromosomes leads to a variety of allele recombinations in gamete cells. These chromosomes are independent from the distribution of alleles of other chromosomes during gamete formation.
Mendel explained the reasoning behing genetic inheritance using terms such as alleles, homozygotes, dominant trait, recessive trait, and variation. Once he developed a complete set of data collected via experiments and observation, he mathematically converted the patterns to a more reliable and reproducible form.
The studies of Darwin helped ecologists and scientists to understand the trends of nature. It led to further research on population studies.
Mendel's work helped to generate a foundation of genetics.
Mendel and Darwin complement each other's work, and the correlation of their postulates has led to major scientific findings. A few of these discoveries are are as follows:
• Genetic variation and its impact on population and evolution
• The Hardy Weinberg equilibrium law
• Variation-based population changes in large and small populations.
• Reasons for and consequences of genetic drifts
• Production of captive breeding techniques on the basis of genetic variation

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Review the historical studies of genetic and phenotypic variation among populations of plants using transplant experiments. How did the studies of Clausen, Keck, and Hiesey complement these earlier studies?
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The studies of Clausen, Keck and Hiesey demonstrated that different populations of the same species may not only differ genetically but also be clearly adapted to the local environments in which they grow naturally. The studies of Hansen, Elven, and Brochmann demonstrate how combining morphological and genetic information can be used to distinguish variation within species versus variation between species.

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How did the studies of Scott Carroll and his colleagues demonstrate rapid evolutionary adaptation to introduced soapberry plants? What advantages do a group of organisms, such as soapberry bugs, offer to researchers studying natural selection compared to larger organisms such as Chihuahua spruce and chuckwalla lizards?
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Carroll and his colleagues worked specifically on the adaptation of the beak length of soapberry bugs in response to the introduction of new species of soapberry plants into their habitat. Let us study their work and conclusions in detail.
Soapberry bugs in their natural habitat :
Soapberry bugs are insects with slender, long beaks due to their requirement of feeding on the seeds of soapberry plants. Their natural habitat had plants of the Sapindaceae family like Sapindus saponaria , Serjania brachycarpa , and Cardiospermum corindum. These plants have very hard seeds with thick seed coats. The process of feeding on them was as follows:
Piercing the seed surface
Piercing the seed coat
Interjecting digestive enzymes or fluids in the seed
Sucking the digested matter
The beak length in soapberry bugs was a requirement to survive in the vegetation as shown above.
Soapberry bugs in the modified habitat:
As a part of the experimentation, two different types of soapberry plants, which had different seed sizes, were introduced into the two different areas of the habitat of the soapberry bugs.
• In the southern United States, plants like K. paniculata were introduced. They had a larger radius of seed when compared to the native host plants.
• In the central United States and Florida, plants like K. elegans were introduced. They had a smaller radius of seed when compared to the native host plants.
The following adaptations were seen of the soapberry bugs who fed in the newly introduced vegetation in respective areas of their habitat.
• Soapberry bugs in the southern U.S developed a larger beak length in order to adapt to the new vegetation.
• Soapberry bugs of central U.S and Florida developed a smaller beak length in order to adapt to the newly introduced vegetation.
Furthermore, Carroll and his colleagues went on rearing the new generations of the soapberry bugs to observe the beak length correlation to the plant seed type. They observed and interpreted that the genotypes were maintained in the new generations, which showed that the adaption was a genetic change.
Conclusions by Carroll and his colleagues:
Their work on the introduction of the new soapberry plants into the natural habitat of soapberry bugs had the following conclusions:
• The adaptation of the beak length of the soapberry bugs as per the available vegetation was a rapid evolutionary change.
• The adaptation was a genetic change, as it was inherited by the next generation of soapberry bugs, and this showed natural selection.
• The probability of the adaptation being a phenotypic plasticity was ruled out.
Thus, we can say that they went on to experiment, study, and prove the above mentioned facts, which were not confirmed by earlier studies.
A group of organisms, like soapberry bugs, offers the following advantages over larger species like the Chihuahua species to researchers working on natural selection:
• Soapberry bugs were found in very large populations, whereas Chihuahuas were found in very small populations. The larger population helps the researchers to conduct experiments based on the various parameters, such as temperature, climate and feeding habits which come under the predictable forces for natural selection.
Whereas the smaller populations are more prone to genetic drifts, which not only reduces the genetic diversity, but also leads to unpredictable natural selection, which is difficult to be studied for evidence.
• A very practical difficulty to experiment with an isolated population of Chihuahua species was their very confined restrictions for proper conditions of survival. They couldn't survive well with other climates, other than their microclimates, which makes it a compulsion to study them in confined area.
On the other hand, species like soapberry bugs can survive in a broader range of climatic and vegetative conditions. This enables researchers to design experiments on a larger scale.
• Although the larger animal, like a Chihuahua, can have many phenotypic traits to study, a smaller insect like soapberry bug can demonstrate the adaption in a lesser amount of time. This not only reduces the time for any experiment, but also leads to extensions of the experiment. For example, after studying the beak length, the researchers worked on collecting evidence to prove whether the adaptation is genetic or not.
• A smaller animal has very distinct change, which can be visible and easily recorded. On the other hand, a larger animal may or may not express the change in an extent that can be observed. Apart from this, the rearing of smaller insects, like soapberry bugs, is far easier than larger animals.

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How do classical approaches to genetic studies, such as common garden experiments, and modern molecular techniques, such as DNA sequencing, complement each other? What are the advantages and disadvantages of each?
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What is the Hardy-Weinberg principle? What is Hardy-Weinberg equilibrium? What conditions are required for Hardy-Weinberg equilibrium?
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What is genetic drift? Under what circumstances do you expect genetic drift to occur? Under what circumstances is genetic drift unlikely to be important? Does genetic drift increase or decrease genetic variation in populations.
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Review the Hardy-Weinberg equilibrium equation. What parts of the equation represent gene frequencies? What elements represent genotype frequencies and phenotype frequencies? Are genotype and phenotype frequencies always the same? Use a hypothetical population to specify alleles and allelic frequencies as you develop your presentation.
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Suppose you are a director of a captive breeding program for a rare species of animal, such as Siberian tigers, which are found in many zoos around the world but are increasingly rare in the wild. Design a breeding program that will reduce the possibility of genetic drift in captive populations.
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What environmental variable did Ted Case determine to be the best predictor of variation in body size among populations of chuckwallas? Did Case's studies of chuckwallas demonstrate genetic differences among his study populations? What did the more recent studies by Christopher Tracy add to our understanding of variation among chuckwalla populations?
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What are the evoluationary implications of the patterns shown in figure 1? img Figure 1 Regression analyses indicating degree of heritability of body length in three hypothetical populations of water lily leaf beetles.
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Jonathan Losos, Kenneth Warheit, and Thomas Schoener's studies of Anolis populations demonstrated significant morphological change following introduction of the lizards to various islands differing in vegetative structure. Design an experiment to determine whether the morphological changes in the study populations were based on genetic changes. Can you adapt the methods of Christopher Tracy to this project?
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