Its my second time posting these, please I need them answered ASAP! Please answe
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Its my second time posting these, please I need them answered ASAP!
Please answer the parts that doesnt needs the figure. thank you
show the work, if necessary please, Thanks in advance.
Biology 202 S18 Problem Set 10 Speciation
Note: You are responsible for the information in any sections of Campbell assigned in the questions below. You are also responsible for any information presented in the PowerPoint slides shown in lecture.
1. What are subspecies of a species? As we discussed in lecture, House Sparrow populations occur throughout the U.S. Various subspecies of house sparrow are recognized (ex. individuals in pops in the NE are larger and darker in color than in the SW where they are smaller and lighter in color) . Note that subspecies differ phenotypically and genetically to some degree. By the Biological Species Concept, why aren’t phenotypically distinct subspecies classified as different species? In general, how do different subspecies form in a species that exhibits population structure?
Discuss the geographic variation observed among altitudinal populations of Achillea, and explain the experiments that indicate that the observed phenotypic differences have some genetic basis and suggest that the differences are the result of adaptation to different environmental conditions. In your discussion include answers to the following:
a) Why have populations of this single species found at different altitudes been classified by plant taxonomists as different subspecies?
b) What are the possible reasons why individuals growing at different altitudes differ in phenotype in the field (field=natural conditions)?
c) When seeds collected from different populations were grown in a greenhouse under the same conditions, what was observed and why did this observation indicate that the populations of plants from different altitudes differed genetically? What do you think would have been observed in the greenhouse experiment if the different populations were genetically identical?
d) Describe in general terms how the “transplant experiment” was done to determine whether there was evidence that the phenotypic (and genotypic) differences observed among the different population represented adaptations to the different environmental conditions found at different altitudes (the result of natural selection)? What observations suggested that the phenotypic differences were adaptive (see lecture slides)?
2. a) Explain the allopatric model of speciation (allo= different or other, patric=homeland). In this model what prevents gene flow (migration) between populations of a species? What evolutionary forces can cause allopatric populations of a species to diverge genetically over time?
b) Explain the distinction between the two modes of allopatric speciation, Vicariance and Dispersalthat we discussed.
3. Recall that under the Biological Species Concept in order to be considered different species individuals must be reproductively isolated. Speciation can be viewed as the evolution of reproductive isolationbetween two subpopulations that previously belonged to the same species. We discussed in lecture that reproductive isolating mechanisms arise as a result of genetic divergence while the two subpopulations are isolated (allopatric). The test of whether speciation has occurred is when the two isolated populations come back into secondary contact after a barrier has been removed or another dispersal event brings them together in the same area. Examin Fig. 24.3 in Campbell. Some prezygotic isolating mechanisms may evolve as a result of the two populations adapting to different conditions (habitat and temporal) while they were separated. Other isolating mechanisms arise by chance as changes in mating behaviors or morphological changes occur in the two populations (behavioral and mechanical isolation). Postzygotic isolating mechanisms arise as genetic changes that affect development occur in the different populations.Explain the different types of prezygotic reproductive isolating mechanisms we discussed in class and that are shown in Campbell in Fig. 24.3. Mechanical isolation can prevent two species from mating. The genitalia of males and females in many insect species show a precise “lock and key” relationship. Changes in the structure of genitalia could prevent mating, another example of mechanical isolation. Sea urchins release their sperm and eggs into the ocean. The sperm of even closely related species of sea urchins in the same area cannot fuse with the egg of the other species. This is an example of gametic isolation. What are some examples of postzygotic isolating mechanisms. Ultimately, prezygotic and postzygotic isolating mechanisms arise as a result of the genetic divergence of populations due to selection (adaptation to different conditions), genetic drift, and random mutations that arise when populations are separated.
4. As we discussed in lecture, when secondary contact occurs between two populations that had be isolated for an extended period of time, individuals of the different populations may be reproductively isolated (due to any of the mechanisms discussed in the previous question). The speciation process would be complete in such cases. In some cases, individuals from the two populations might mate and produce hybrid offspring, forming a hybrid zone where the populations initially come into contact. We discussed three possible scenarios of what might happen to this hybrid zone over time (see Lec. notes and slides, and Campbell section on Hybrid Zones pp. 514-518 and Figure 24.14):
a) Explain the conditions that could lead to the expansion of the hybrid zone and the fusion of the two populations into one species b) Explain how the process of reinforcement could occur if the hybrid offspring have low fitness c) the hybrid zone may remain stable (at least over observable time spans).
5. a) What do we mean when we say that a pair of species are sister-species? Examin the figure of the snapping shrimp species shown in lecture (and your textbook Fig. 24.8 - also read the section Evidence of Allopatric Speciation starting on p. 510) explain the evidence that a number of species of snapping shrimp underwent allopatric speciation via a vicariance event (what was the event?).
b) In lecture we discussed Darwin’s finches as an example of allopatric speciation via dispersal and adaptive radiation. See class notes and read the section on Adaptive Radiation in Campbell (pp. 540-542). Examine the phylogeny of the 14 species of Galapagos finches shown in lecture (see Campbell Fig. 1.20). Note the varied beak morphologies of the different finch species. It appears that different beak sizes and shapes are adaptations associated with different food resources. It is fairly simple to understand how an isolated founder population of finches on the Galapagos could diverge from the main population of the species on the South American mainland. In the context of the allopatric speciation model, discuss how the largely uninhabited Galapagos Islands offered the geographic conditions and ecological opportunityfor the adaptive radiation (the evolution of many diversely adapted species from a common ancestor) of finches there.
d) Mammals underwent a major adaptive radiation about 65 million years ago after the extinction of the dinosaurs, the dominant group of vertebrates at the time. Before this adaptive radiation mammals were a relatively minor group. In what way might the extinction of the dinosaurs be linked to the adaptive radiation of mammals? S18: We did not cover this in lecture this year, but think about the possible connection between dinosaur extinction and the mammalian adaptive radiation. One of the requirements for an adaptive radiation is the availability of open ecological niches. We will discuss the idea of the ecological niche in ecology soon. For now, think of it as the absence of competitors feeding on a particular type of food resource. Mammals first appear in the fossil record in the Jurassic period (199.6 – 145.5 MYBP = million years before the present), but remained a relatively minor group until the dinosaurs went extinct around 65 MYBP. Dinosaurs were the dominant group of terrestrial vertebrates, and occupied most of the available ecological niches. Their extinction provided tremendous ecological opportunity for mammals, which underwent a rapid adaptive radiation in a relatively short time span (about 7-10 MY). All of the major groups of mammals evolved during this period, including whales.
6. It is essential that the reproductive isolation of species be tested in nature rather than in zoos or the laboratory. Which reproductive isolating mechanisms are more likely to break down in captivity? Some isolating mechanisms are closely associated with the natural environment such as habitat isolation and seasonal isolation. The mating behaviors of organisms are also likely to be altered by an artificial zoo or lab environment. For example, among cichlid fish species from Lake Victoria in Africa many of the species are reproductively isolated in nature by ecological or behavioral isolation and hybrids are not observed in nature. When some pairs of species are placed in a fish tank in the lab they will mate and produce viable fertile offspring.
Explanation / Answer
1. Subspecies are the geographically separated race or group of organisms of the same species. Ddifferent subspecies of organisms of the same species only look different from one to each other, but they can breed among each other. So different subspecies of organisms are not considered as separate species.
Different subspecies of organisms have separate phenotypes as their surroundings are different. Phenotype is the resultant expression of a genotype in accordance to the environment. So same genotypic organisms do have different phenotypes in different environments.
a) taxonomists classified them as different subspecies, as they are growing at different altitudes. Environmental conditions at different altitudes will be different. So, populations of this single species found at different altitudes have been classified as separate subspecies.
b) Individuals growing in different regions are exposed to different environmental conditions, So they have altered phenotypes from one to each other. So they do have different phenotype in field conditions.
c) seeds collected from different populations will have different genotypes, but when they are grown under the same roof of one green house, they exhibit similarities in characters due to their convergence at the same place, though they are genetically not identical.
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