Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Evolution for Ecology
Document related concepts
Transcript
Evolution for Ecology The Importance of Evolution in Ecology Ecologists questions: study proximate or “how” How nutrients flow through ecosystems Evolutionary biologists study ultimate or “why” questions: Why does a stickleback fish have armor in one lake but not another? The Importance of Evolution in Ecology Evolutionary processes can work surprisingly fast. This is increasingly important in agriculture and medicine. Pink Bollworms Farmers consistently had to spray their crops with insecticides to control the pests. Pink Bollworms Transgenic cotton incorporates a gene from a bacterium that causes the caterpillars to die when they eat the plant. Few applications of insecticide needed. Resistance The problem with pesticides is that pests evolve resistance to them and they become less effective over time. Would this happen with transgenic cotton? Pink Bollworm Experiment Did the Pink Bollworms evolve resistance to the Bt toxin in the transgenic cotton? Pink Bollworm Experiment Yes, in just one generation! Evolution can be fast! So, is transgenic cotton useful? How can we prevent resistance from becoming established? Rapid Evolution in Sticklebacks Armor plates protect the fish from predators. But there is a cost to plates – slower growth, breed later, and have lower winter survival rates. Rapid Evolution in Sticklebacks Cutthroat trout are predators of sticklebacks. Use vision to find prey – easiest to find sticklebacks in clear water. Rapid Evolution in Sticklebacks So, if a murky lake is cleaned up and is now clear, what would you expect to happen to the plate count on the fish? Plate count will increase? Plate count will decrease? Plate count will stay the same? Rapid Evolution in Sticklebacks As the lake cleared, predation became more of a problem and plate number increased. Rapid Evolution of Invasive Species The snowy campion is native to Europe, introduced to North America 200 years ago. No enemies Smut (fungus) Hadena bicruris caterpillars Now a common agricultural weed. Rapid Evolution of Invasive Species Two possible ways to allocate resources. Which is best will depend on levels of predation, infection etc. Rapid Evolution of Invasive Species Europe – more enemies so bigger investment in defense. North America – fewer enemies so more invested in reproduction & growth. The Logic of Evolution by Natural Selection Sticklebacks Plating in sticklebacks is determined genetically. Set at birth & can’t change. Natural Selection Variation occur. is essential for natural selection to Populations of sticklebacks contain a variety of plate counts. Natural Selection Heredity is also essential for natural selection to occur. Traits are passed genetically from parents to offspring. Natural Selection Survival and reproduction are selective In a lake with high predation, sticklebacks with more plates survive better & reproduce more. Natural Selection in the Medium Ground Finch Daphne Major – Galapagos No fresh water source – rely on short spring rains. Medium ground finches eat seeds. Natural Selection in the Medium Ground Finch The finch population contains: Variation Heritibility Natural Selection in the Medium Ground Finch 1977 drought – birds had to rely on seeds from previous year. Small soft seeds eaten first, larger tougher seeds left. Many birds starved. After drought, average beak size was larger. Natural Selection in the Medium Ground Finch When the survivors reproduced, their offspring also had larger beaks. Genetics and Evolution Some terms Assertions: 1. Populations vary in their phenotype What they look like 2. Differences in the phenotype are due at least in part to difference in genotype. Which alleles are present Alleles 3. are different versions of a gene Some phenotypes and thus some genotypes survive better & reproduce more. Some terms Consequence: The beneficial trait will spread through the population. The alleles for the beneficial trait will increase in the population. Alleles associated with failure will disappear. Total reproductive contribution is an individual’s fitness. Evolution involves changes in the frequencies of alleles in the population. Genetics of Plating in Sticklebacks Plating is controlled by a gene called Eda. There are two versions, or alleles c for complete plating l for light or low plating Codiminant Genetics of Plating in Sticklebacks Tradeoff between fast growth & overwinter survival vs protection from predators. Different phenotypes (& therefore genotypes) will be selected for in different situations. Different environmental pressures. Genetics of Plating in Sticklebacks You can see here how the population varied over time as the lake cleared. Adaptation Over time, natural selection leads to adaptation to the environment. Traits beneficial in a particular environment have accumulated in the population. Move the organisms to a different habitat and the tight fit may be gone. Genetic Drift Genetic drift is another mechanism of evolution. Does NOT result in adaptation. Due to random chance. Does result in a change in the frequency of alleles in the population. Migration can also change the frequency of alleles in the population. Managing the Evolution of Resistance Pink Bollworms Recall that pink bollworms can evolve resistance to the Bt toxin in the transgenic cotton. Resistance is recessive. rr are resistant sr and ss are susceptible There are several different resistance alleles Pink Bollworms Tradeoff: Susceptible worms grow faster and mature sooner, but are killed by Bt toxin. Pink Bollworms Resistant worms have a much higher fitness on transgenic (Bollgard) cotton, while susceptible worms have a somewhat higher fitness on normal cotton. The latter means that resistance alleles will be rare where Bollgard has never been used. Goal: delay evolution of resistance Integrated Pest Management IPM involves the use of a variety of techniques to battle pests. Use two different types of Bt toxin. Parasitic nematodes – more lethal to resistant bollworms. Managing a Bollworm Infestation High dose / refuge strategy Part of a field planted with Bollgard cotton, part with normal cotton. The refuge (normal cotton) allows some of the susceptible worms to survive which decreases the fitness advantages associated with resistance.
