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Unit 3 biology.doc

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University of Guelph
BIOL 2060
Joyce Buck

Unit 3- Populations 3.1-Testing for Plasticity and Adaptation Chapter 4 pages 90–93, 98–100 Key Terms Phenotype: is a product of the interaction between an organism’s genes; organism's observable characteristics or traits: such as its morphology or development Genotype: genetic makeup of a cell, an organism, or an individual common garden study: representatives from different populations that had distinctive growth forms, which he called ecotypes, were grown under the same environmental conditions in a common location. If plasticity was the only cause of the variation in morphology in a species, then you would expect that plants grown in a common garden would look the same ecotypes: genetically distinct geographic variety, population or race within species (or among closely related), which is adapted to specific environmental conditions. genetic drift: change in gene frequencies in a population due to chance or random events local adaptation: a population survives best in its home environment. If the genetic differences are the result of adaptation, then the growth of each plant in its home environment should be better than in the other environments. reciprocal transplant experiment: used to determine if genetically differentiated populations are adapted to their home environments. Heritability: the proportion of total phenotypic variation in a trait attributable to genetic variation; determines the potential for evolutionary change in a trait homozygous: having identical alleles at a given locus heterozygotes: having different alleles at a given locus Phenotypic Variation in a Desert Lizard - Ted Case (1976) explored variation in body size among Sauromalus (lizard known at Chuckwalla which lives in hot, dry places) populations at twelve sites distributed across its geographic range, and found that average summer temperatures at his desert study sites ranged from 23.8 C to 35 C, while average annual rainfall varied from approx. 35 to 194 mm. Because the environments in which Sauromalus lives vary greatly across its range, we might expect that selection have favored different characteristic in different parts of the species’ range. Prefers to eat herbaceous plants and the amount of winter rainfall largely determines the amount of plant growth in these desert environments therefore higher rainfall means more available food. - Variation in rainfall translates into variations in food availability. Lizards at lower elevations on average have access to less food and the amount available on any given year is unpredictable. - This case found that lizards from the food-rich higher elevations are approximately 25% longer than those from lower elevations therefore different body mass. Therefore the best predictor of body length with these lizards is average winter rainfall. - Christopher Tracy (1999) collected 12 to 15 juvenile Chuckwallas from 6 populations in Arizona, California, and Nevada, living at elevations ranging from 200 to 890m. He then raised these lizards under identical environmental conditions in a laboratory to determine the contributions of environmental versus genetic factors to size differences among this population. He concluded that lizards from higher elevations grew to a larger size, approximating in a lab common garden for lizards the pattern of variation in body size found in the field. Genetic Variation and Heritability - i2 an equation variability can be defined as: h =V GV Pwhich is genetic variance and phenotypic variance - sub dividing V gPves an equation of: h =V G(V +G ) E - Peter Boag and Peter Grant (1978) the latter formerly a professor at Mcgill, estimated bill width in the Galapagos finch (geospiza fortis) to have a heritability of 0.95. By comparison they estimated that bill length in the species has a heritability of 0.62. Calculating Gene Frequencies - Chia-Chen Tan (1946), Chia-Chen Tan and Ju-Chi Li (1934), and Theodosius Dobzhansky (1937) determined that the variation in colour patterns shown by Harmonia (Asian lady beetles) is due to the effects of more than a dozen alternative alleles for colour pattern - Hardy-Weinberg Principle states that in a population mating at random in the absence of evolutionary forces, allele frequencies will remain constant. To maintain constant allele frequencies in a population: • Random mating • No mutations • Large population size • No immigration • All genotypes have equal fitness Disruptive Selection - A form of natural selection that favours twos or more extreme phenotypes over the average phenotype in a population. Acclimation/plasticity or adaptation/evolution? • Organisms can optimize their performance three key ways: (1) acclimation or developmental plasticity, (2) dispersal or range shifts, and (3) evolution (adaptation) or extinction. • The first and third ways involve expressing a new phenotype to suit a new environment. • Two things to keep in mind are that acclimation and plasticity represent the capacity of an individual to adjust to environmental change within their own lifetime, and it occurs very quickly, whereas adaptation is an evolutionary response of a population that occurs from generation to generation and therefore takes more time. Testing for developmental plasticity 1) Phenotype = Genotype × Environment • One genotype (or clone) can be grown in different environments. If phenotypic differences are observed between environments then plasticity can be implicated as the cause of that phenotypic variation. 2) P = G × E ↑ Held constant • French botanist, Gaston Bonnier, observed in his early studies on variability in plant populations in Europe (Bonnier 1890). On his travels in various mountain ranges he observed that many species of plants grew over a wide range of elevations, and differed dramatically in their form in different locations. These observations prompted him to conduct transplant experiments on the effects of climate on plant morphology. • Bonnier was able to produce genetically identical clones of a single plant, and transplant one into a lowland site and the other into an alpine site. He then made measurements and drawings comparing each pair of plants. These results show that the phenotypic differences between these plants were caused by developmental plasticity; a single genotype was able to produce morphologically different phenotypes in response to the environment. Testing for genetic variability among populations • Gote Turesson (1925) extended this type of research farther and looked for evidence for genetic variability among populations. He used a common garden study in which representatives from different populations that had distinctive growth forms, which he called ecotypes, were grown under the same environmental conditions in a common location. If the morphological differences persisted when grown in the same environment, this would be evidence for genetic differences among populations. 1) P = G × E ↑ Held constant • It is important to realize that change in gene frequencies in a population can be due to chance or random events (i.e., genetic drift) and mutation, or it can be the product of natural selection and therefore adaptive. Testing for adaptation • To demonstrate adaptation, you would have to show that: (1) phenotypic differences among populations are based on genetic differences, using a common garden study. (2) each population survives best in its home environment (local adaptation) when compared to others derived from other environments. A reciprocal transplant experiment can be used to determine if genetically differentiated populations are adapted to their home environments. (1) Common garden comparison: If plasticity was the only cause of the variation in morphology in a species, then you would expect that plants grown in a common garden would look the same (2) Local adaptation (reciprocal transplant) comparison: If the genetic differences are the result of adaptation, then the growth of each plant in its home environment should be better than in the other environments. “Unintentional” experiments to test for adaptation • An unintentional experiment occurred when three new species of plants in the Sapindaceae family were brought to the United States in the 1950s and were planted farther north than the existing species’ range. Soapberry bugs (Jadera haemotaloma) feed exclusively on plants in this family. They have piercing mouthparts (beaks) that they insert into the fruits to feed, and the length of the beak must be a certain length to reach the seeds within the fruit. • Scott Carroll and Christin Boyd (1992) seized the opportunity to ask whether the soapberry bugs were able to adapt to these new food sources and expand their range. They first collected eggs from each population of soapberry bug and grew them in a common garden. Differences in beak length among populations were maintained in the common garden, suggesting that beak length is genetically determined • The researchers also found a positive correlation between beak length and the radius of fruits each population used, suggesting that each soapberry bug population had adapted to its plant host. But this was only observational evidence. • Scott Carroll, Stephen Klassen, and Hugh Dingle (1998) continued the study. They asked whether soapberry bug populations were ecotypes, and answered this question by doing a reciprocal transplant study and measuring juvenile survivorship of each population on different plant hosts. 3.2- Speciation Chapter 4 pages 103–107 Key Terms Inbreeding: mating between close relatives; more likely in small populations microsatellite DNA: short repeating units of DNA that can be used identity relatedness among individuals. Biological species concept: a group of actually or potentially interbreeding populations, which are reproductively isolated from other such groups Isolating Mechanisms: some process that prevents the production of a viable offspring between two individuals. Isolating mechanisms are critical to the species integrity Allpatric Speciation: speciation that occurs when isolating mechanisms evolve among geographically separated populations Parapatric speciation: speciation that occurs when a population expands into a new habitat-type within the pre-existing range of the parent species Sympatric speciation: speciation that occurs when isolation mechanisms evolve among populations with overlapping geographic ranges Assorative mating: mating among phenotypically similar (positive assortative mating), or dissimilar (negative assortative mating), individuals Parallel Evolution: the independent evolution of similar traits in geographically separated species Genetic Diversity and Butterfly Extinctions - Richard Frankham and Katherine Ralls (1998) point out that one of the contributors to higher extinction rats in small populations may be inbreeding. Combining already low genetic variations in small populations with a high rate of inbreeding has several negative impacts on populations, including reduced fecundity, lower juvenile survival, shortened life span and it further accelerates the loss of genetic diversity especially in Plantago lanceolata and Veronica spicata that act as hosts for the Glanville fritillary butterfly, Malitaea cinxia. - Ilik Saccheri and colleagues (1998) reported one of the first studies giving direct evidence that inbreeding contributes to extinctions in wild populations. Studied dry meadows. Documented an average of 200 extinctions and 114 colonization’s. Conducted genetic studies on populations of Melitaea in 42 meadows estimating heterozygosity and indicator of genetic variability with respect to seven enzyme systems and one locus of nuclear microsatellite DNA. Results of the study indicated that influence of inbreeding on the probability of extinction was very significant. High inbreeding=probability of extinction. Speciation: what is a species? -Ernst Mayr (1942) defined species as “groups of actually or potentially interbreeding populations, which are reproductively isolated from other such groups.” Based upon a real ecological concept: reproductive isolation Speciation: what is reproductive isolation? - isolating mechanisms can be categorized into two groups, pre and postzygotic. Prezygotic isolating mechanisms are processes which prevent two individuals from forming a zygote. Postzygotic isolating mechanisms are equally efficient at maintaining species integrity, but they occur after a zygote has been formed. Speciation: what causes speciation? - in both allopatric and parapatric speciation, the evolution of reproductive isolation could occur through drift or natural selection. Since genetic drift is random, fluctuations in allele freguencies in subpopulations will be independent, and thus loss of genetic diversity through drift could lead to reproductive isolation Reproductive Isolation and Ecological Divergence - Dan Funk and colleagues (2006) decided to conduct a broad test of this prediction that increased ecological divergence will be associated with increased reproductive isolation. Using both parametric and nonparametric tests for relations they found that the more different the habitats were the more reproductively isolated the pairs of related species were. - Mckinnon and colleagues (2004) wanted to know to what extent ecological difergence plays in the early stages of speciation. What they did was collected fish from marine and stream populations and placed them in an experiemental aquarium to see which individuals would and would not mate. Concluded that reproductive isolation occurred based upon ecological differentiation and not primarily geographic isolation. 3.3 Distribution and Abundance of Populations and Species Chapter 10 pages 255–256, 259–267, 269–274 Distribution Limits - G. Caughley and his colleagues (1987) found a close relationship between climate and the distribution of the three largest kangaroos in Australia. One in the eastern third of the continent of Australia that includes several biomes (temperate forest grows in the southeast and tropical forests in the north, and mountains with their varied climates. Another in the southern and western regions of Australia (temperate woodland and shrubland biome). Third in the savanna and desert. These limited distributions may not be determined by climate directly but suggest that climate often influences species distributions through factors such as food production, water supply and habitat. - Also studied was the tiger beetle (Cicindela longilabris) that lives at higher latitudes and high elevations that just any other species of tiger beetle in north America. Thomas Schultz, Michael Quinlan, and Neil Hadley (1992) set out to study the environmental physiology of widely separated populations of the species. Found that metabolic rates are higher and its preferred temperatures lower than those of most other tiger beetle species that have been studied. None of their measurements differed significantly among populations. Distribution Patterns -There are three distributions of patterns: 1. Random Distribution: an individual has an equal probability of occurring anywhere in an area. Neutral interactions between individuals and local environment 2. Regular Distribution: individuals are uniformly spaced through the environment. Antagonistic interactions between individuals or local depletion of resources 3. Clumped Distribution: individuals live in areas of high local abundance which are separated by areas of low abundance Organism Size and Popul
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