User:Sw1277a@student.american.edu/Notebook/Biology 210 at AU
30th Jan Lab 1:
Biological Life at AU Lab 1 Bio210 Spring 2014 Bentley/Walters-Conte/Zeller
Objectives 1. To understand natural selection 2. To understand the biotic and abiotic characteristics of a niche Observing Evolution The interactions between organisms and their physical environments are the driving force for evolution via the process of natural selection. The conditions that have to be met for natural selection to occur are: 1. Variability – Charles Darwin noted that all species vary, that is, members of a species vary from other members of the same species. 2. Differential capacity for survival and reproduction - Darwin also observed that the environment and the conditions under which a species lives favor some varieties over others. 3. Heritability - the favored varieties have higher fitness values. If the traits leading to the higher fitness are heritable, they will appear more in succeeding generations because they will be selected based on survival. Selection is a little more complicated than simply having the best traits for survival. Certain traits can have a greater selective advantage for individuals in one environment, but may be disadvantageous in another. Some traits are neither helpful nor unhealthy and thus, are considered neutral. Neutral traits can remain in the population if they are not selected for or against. Sometimes the frequency of a trait in a population can just change due to random events and this is called genetic drift. A change in the frequency of neutral traits typically takes place in smaller populations or in founding populations. A founding population is a group that separates from the main population such as a small number of individuals that would reach an island. Also a bottleneck effect can affect the traits and this occurs when a significant part of a population disappears as with disease. Finally, genes or their regulatory factors can mutate into new or different traits. The best way to study how traits are changing in a population is to determine their frequencies over time. Changing traits in populations can be analyzed by looking at allele frequencies, phenotype frequencies, and genotype frequencies. Godfrey Hardy and Wilhelm Weinberg were some of the first scientists to actually measure how these frequencies were changing in populations so they could better understand natural selection and genetic drift. They extended Mendel’s work on inheritance and Darwin’s ideas about natural selection to develop the field of population genetics. The green algae, Chlorophyta, exhibits the greatest diversity among all protists, both in form and in reproductive patterns. Most of the approximately 9000 species are aquatic, but other habitats include the surface of snow, hot springs, trunks of tree, animals, and even as symbionts associated with lichens, protozoa, and hydra. The unicellular forms are considered the most primitive. Colonial forms probably originated as a unicellular alga that achieved complexity through cell divisions in different planes that remained attached. This morphology appears as groups of cells loosely coordinated into a colony or forming a stalk thallus. Sexual reproduction in Chlorophyta is defined by the types of gametes and/or reproductive cells involved. Isogamy is sexual reproduction that results in the fusion of gametes that are morphologically alike, and this is considered the most primitive. Oogamy is sexual reproduction where one of the gametes is larger and non motile, and is considered more advanced. Procedure I: The Volvicine Line
Today you will look at some samples of green algae. Think about what types of selective pressures have taken place?
• First observe an isogamous, single-celled, motile alga found in damp soil, lakes, and ditches called Chlamydomonas. In addition to asexual reproduction, Chlamydomonas has a primitive form of sexual reproduction in which two vegetative cells can function as isogametes. o Prepare a slide of living Chlamydomonas and examine it microscopically. o Adding protoslo will slow these very motile creatures down and make them easier to observe. o The cells are typically egg-shaped and have large cup-shaped chloroplasts containing a proteinaceous body, the pyrenoid, which functions in starch formation. o A stigma, or eyespot, is also present. o The nucleus is difficult to observe in a living cell. o Locate the conspicuous chloroplast and the pyrenoid. o The flagella, located at the anterior end of the cell, enable the organism to move through water. The flagella can be observed more easily by closing the iris diaphragm of the microscope to reduce the light and provide more contrast. Chlamydomonas is considered the origin of the Volvocine line of multicellular evolution. Evolutionary lines are related organisms that show a developmental progression of traits over millions of years, in this case, multicellularity. • Observe the living culture of Gonium on a slide. It is a progressively more complex species consisting of a colony of 4, 8, 16, or 32 cells. They are held together in a gelatinous matrix and each cell can form a new colony. • Volvox represents the peak of evolutionary complexity in this line of green algae. Observe the thousands of spiked cells making up a spherical Volvox colony. Most cells are vegetative and a few are selectively reproductive. The female gamete is larger than the male so Volvox is an example of oogamy. The fact that there are reproductive cells and also that the Volvox sphere has an anterior and posterior pole of cells indicates the very primitive beginnings of cell specialization.
Figure 1: Clamydomonas at 40X Figure 2: Volvox at 10X
Table 1 Evolutionary Specialization of Members of the Volvocine Line • Characteristic Chlamydomonas Gonium Volvox
Number of cells 1 (x40) 2 (x40) 50-1,000 (x40)
Colony size Small Small Large
Describe any functional Pyrenoid, Cells can form vegetative and reproductive specialization stigma a new colony cells, anterior and posterior poles of cells flagella in cells
Describe any reproductive specialization (isogamy vs oogamy) Isogamy Isogamy Oogamy
• What is the significance of cell specialization across these three genera? o The significance shows that evolution is occurring, as the chlamydomonas goes to gonium goes to volvox. The bacteria is growing and becoming more complex.
• Does evolution always move towards increased complexity? Provide an example to support your answer. o No, evolution does not necessarily move toward increased complexity, it can occur to better adapt to a specific environment dictated by necessity. If mice live on a white background then that breed of mouse may evolve to only produce white offspring, which does not imply greater complexity than black mice.
Procedure II: Defining a Niche at AU There are over a million different forms of life on earth and probably at least a million more that have not yet been identified. Each of these organisms has a specific set of requirements that collectively can be called their niche. Individuals that are genetically similar and can interbreed to produce viable progeny belong to a species. Usually there is more than one group of the same species (population) living in the same area or habitat, and a collection of species is a community. Larger communities are called an ecosystem with both the living organisms (biotic) and nonliving components (abiotic). The number and kinds of species (biodiversity) that live in an area affect the structure and characteristics of that ecosystem. Finally, Ecology is the scientific study of how different organisms and species interrelate with each other and the environment. The terms in the previous paragraph are important but what do they really mean? The first third of this course will provide you with an opportunity to understand the balance, complexities, and interactions that are typical of the community inhabiting an ecosystem. Each group of three students will analyze a 20 by 20 foot transect of land on the American University campus. This will be the ecosystem and you will study and write a report on the organisms inhabiting the area. You will study the protists, bacteria, plants, invertebrates and animals in the transect. You must keep detailed notes in a notebook!!! Each student will keep their own notes but students within each group will be sharing some data. From now on, any information required to be in the notebook will be highlighted in red. The notebook information will be regularly checked by the lab instructor. There are five transects and your group will be assigned one transect to study. Proceed to the transect with a 20 foot long string and your notebook. Each group will also be given a 50 ml sterile conical tube to collect a soil/surface plant (probably grass) sample. • Set the 20 by 20 feet dimensions of the transect (either 1, 2, 3, 4, or 5) with 4 popsicle sticks • Describe the general characteristics of the transect: location, topography, etc. o Located near civilization – the transect is near picnic tables and busy roads and a seminary. The area slopes downward, with two different types of ivy completely carpeting the ground, one kind near the top half the other on the bottom half. There are three trees within the transect – a holly, a sycamore, and a pine tree. There is also a layer of decomposing leaves, branches, and pine needles in the ground cover. The area is darker/more shaded because the trees block natural lighting. • List the abiotic and biotic components of the transect. o Abiotic components: tennis ball, park bench, dog poopbag, plastic, foil o Biotic components: holly tree, pine tree, sycamore tree, ivy, grass • Use the sterile 50 ml conical tube to take a soil and ground vegetation sample. Make sure it is representative of the ground and what is on the surface of the ground. • Do not leave the transect until your instructor has checked on your work. Back in the lab, make a hay infusion culture; • Weigh 10 to 12 grams of the soil/ground sample and place in the plastic jar with 500 mls of deerpark water. • Add 0.1 gms dried milk and gently mix it all up for about 10 seconds. • Then take the top off and place the jar in a safe place in the lab. • Make sure the jar is well labeled so the group can find it.
Next week you will use the hay infusion culture to observe protists and to inoculate agar petri plates for studying bacteria the following week.
Very good start. Don't need to rewrite all the instructions from protocol. Just describe what you did, why, the results and conclusions. See more instructions in TA notebook. SK