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Evolution Chapter 8


Evolution Chapter 8 BIOL 3303


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Evolution Chapter 8
Dr. John Wise
Class Notes
evolution, Dr. Wise, John Wise, Wise, Chapter 8
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This 22 page Class Notes was uploaded by an elite notetaker on Tuesday March 29, 2016. The Class Notes belongs to BIOL 3303 at Southern Methodist University taught by Dr. John Wise in Winter 2016. Since its upload, it has received 25 views. For similar materials see Evolution in Biology at Southern Methodist University.


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Date Created: 03/29/16
Chapter 8 Natural selection: empirical studies in the wild Evolution by Natural Selection Definitions: Darwinian fitness: The ability of an individual to survive and reproduce in its environment. The offspring of fit individuals make up a greater percentage in the next generation. Adaptation: A trait or characteristic of an individual organism that increases its fitness relative to individuals without the trait. 2 Evolution by Natural Selection The Four postulates (review): (1) Individuals within populations are variable. (2) The variation among individuals can at least in part be passed from parent to offspring. (3) In every generation, some individuals are more successful at surviving and reproducing than others. (4) The survival and reproduction of individuals are not random. Survival and reproduction are tied to the variation among the individuals. Those individuals with the most favorable variations for survival and reproduction are naturally selected. 3 Reproductive Potential - In every population studied, more offspring are produced than survive to breed. Also known as biotic potential or fecundity. The number of progeny an organism or pair can produce under optimal conditions assuming no deaths in the offspring. In every population looked at, some individuals are more successful at mating and producing offspring than others. A sbreeding survivor is produced.wth and no decline) an average of 1 offspring per Postulate 3 - Individuals vary in survival and reproduction is universal4y true. 2 Does Natural Selection Work in Nature? Beak shape in Galápogos Finches – Originally studied by Darwin . – Since 1973 by Grant & Grant • Total of 15 species – All similar in size and color. • Size and shape of beaks shows much variation. – Variation reflects the diversity of foods utilized. Crushers biters probers 5 Medium Ground Finches on Isla Daphne Major Grant and Grant have studied these finches for over 30 years. Few finches move into or off the island. Population is small enough to be studied completely. By 1980 marked 100% of the population. Life span ~ 16 yrs.; generation time 4.5 yrs. Seed eaters Crack by grasping at base of bill and applying force. Correlation by beak size and seed size observed by many. 6 3 Medium ground finch • Variation in beak size influences efficiency at eating different types of seeds Beak size evolution 1. Beak size is variable 2. Beak size is heritable 3. Large beaked birds survived better in 1977 4. Survival and reproduction appears tied to favorable variation • Drought resulted in more hard, woody seeds – Favored larger beaked birds Natural selection is variable over time • Often selection is not constant Natural Selection is not Forward-Looking Selection never looks ahead to predict the (environmental) changes that will occur in the next generation. Evolution is always a generation behind any changes in the environment. Each generation is the product of selections that occurred in the previous generation. In this sense evolution is not a real-time system. It operates on a one-generation delay. 10 Variation in beak size: How does it work? Embryonic growth factors should control growth • G. magnirostris expresses BMP4 at 26 weeks – BMP4 = bone morphogenic protein 4 (a bone growth factor – detected by mRNA probes in embryo cross-sections). • Others express it much later. Chapter 10 p. 304-307 11 The Nature of Natural Selection Difficult to comprehend because the result is statistical. Changes in trait distributions in populations. 12 6 The Nature of Natural Selection • Natural selection acts on individuals but its consequences are on populations. – HIV selected for AZT- resistance – Finch selected for seed utilization No individual is changed. – Cheetah selected for Each individual either lives to sprint speed reproduce or does not survive to reproduce. 13 Evolution by Natural Selection Hummingbird Diversity Video \Pbs_Videos_1\Evolution of Diversity\Evolving Ideas How Does Evolution Really Work_e_s_4_7 minov Darwin’s Dangerous Idea Chapter 3 (20:00-32:57) 14 7 Coat color variation affects fitness • Oldfield mice on mainland or white sands • Differential predation rates Light coat color evolved independently in different populations • Different mutations responsible for light color in different populations • Geographic separation • Independent adaptations Evolution by Natural Selection The Four postulates (again!): (1) Individuals within populations are variable. (2) The variation among individuals can at least in part be passed from parent to offspring. (3) In every generation, some individuals are more successful at surviving and reproducing than others. (4) The survival and reproduction of individuals are not random. Survival and reproduction are tied to the variation among the individuals. Those individuals with the most favorable variations for survival and reproduction are naturally selected. 17 Natural selection can be variable across space • Gene flow can bring alleles to new locations – Alleles may increase or decrease fitness Aposematism (warning coloration) favored only in areas where coral snakes co-occur • Predators wary of coral snake venom • Mimics protected in overlapping geographies only • Geography plays a role in fitness Gall flies induce plants to produce galls Opposing selective forces • Gallflies lay eggs in the goldenrod and induce a gall to form (feeds the larvae) • Gall size is heritable trait of the fly • Bird predation – prefers large galls • Wasp predation – prefers small galls to lay eggs • Stabilizing selection for intermediate galls Key Concepts • Stabilizing selection results when agents of selection act in opposing directions Eda involved in production of lateral plates in stickleback Marine ancestral Eda form (ectodysplastin) Freshwater alleles control number of plates derived form • Common ancestor was marine (3 spines and armor plates protect from predation) • Some populations trapped in fresh water lakes after last ice age (2 spines, less plates) Low Eda allele favored in freshwater populations • Production of armor energetically costly – Little predation pressure to counterbalance • Low Eda allele present at low frequency in marine environment – Favored when introduced to freshwater Shift in dorsal spine length recorded in fossil record • Cost of armor is high • 110,000 years of fossils from the same lake beds • Shows influx of spines and then loss • COST is important! Ability to digest lactose as adults found in certain populations - For some humans, Lactase expression persists into adulthood - Correlates with domestication of cattle Frequency of Lactase persistence gene Pattern of genetic linkage indicates history of selective sweep • Hitchhiking effect – strong selection will sweep neighboring alleles as well as selected allele to high frequencies Strong evidence for positive selection on lactase persistence alleles • Hitchhiking effects in Africans (A) and Europeans (B) are large • Green and Orange shows lactose tolerance alleles neighboring regions are very large Artificial selection in crop production • First chapter of “Origins of Species” devoted to artificial selection • Selection performed by humans Domesticated Brassica Explained Suddith et al. sequenced the CAULIFLOWER (inflorescence) genes from a variety of Brassicas. They found loss of function in mutations in: – 2 of 11 alleles in wild cabbage – 3 of 7 alleles in kale – 8 of 9 alleles in broccoli – 10 of 10 alleles in cauliflower. It is likely that ancient farmers selected the larger and larger inflorescence traits caused by the loss of function alleles in CAULIFLOWER. Eventually, these alleles became very common in the populations. 29 Artificial selection in crop production 15 Gradual increase in cob size documented by archaeologists All from one site in Mexico – three main loci involved Teosinte Oldest ---- to ------ Youngest Co-evolution of humans and plants • Are the plants manipulating the humans so that the humans reproduce the plant? 32 Domestic dog diversity created in last 15,000 years Pesticides and herbicides act as agents of selection Resistance to pesticides in houseflies Rapid evolution of herbicide resistance Alteration in EPSPS enzyme leads to Roundup resistance Monsanto Roundup (glyphosphate) • Blocks EPSPS enzyme (amino acid biosynthesis) • Ryegrass (A) and goosegrass (B) point mutation in EPSPS creates resistance • Palmer amaranth (C) – gene duplication / up-regulation of EPSPS creates resistance Two mechanisms of resistance Creation of refuges can slow the evolution of resistance • Bt crops select for resistance in pests – Comes at a cost when Bt is not present • Creation of Bt-free refuges favors Bt- susceptible insects – resistanceution of • required by law – 20% for corn – 50% for cotton Evolution of shorter male horns due to “Trophy” hunting Cod fishing has influenced life-history evolution • Atlantic cod reach sexual maturity at a much smaller size (and younger age) than before industrial fishing with nets Important Concepts • The speed of evolution depends on amount of genetic variation and strength of selection – Leads to rapid resistance in pest populations • An understanding of evolutionary biology can lead to novel management practices Big Misconception Natural selection acts on individuals and the individuals do not do things for the good of the species. Nothing is ever done for the "good" of the species. If an allele existed that was truly altruistic, it would be strongly selected against. – Altruism: a behavior that reduced the fitness of the bearer and increased the fitness of others. – Bearer would have less offspring (altruistic allele frequency would decrease in the population). – Others would have more offspring (higher percentage would not have the allele). 42 Lions can be Anti-Altruistic • Competing males that defeat other males and take over a pride will immediately kill all infant cubs (infanticide). • This increases the winning males fitness because non- nursing females will become fertile much sooner than nursing females. • The winner will have offspring sooner. Infanticide is widespread among animals. • Clearly not for the good of the species. 43 Anti-altruism in humans? The graphs show the rate at which parents kill their children (biological parents compared with step-parents by age of child). Data shown was collected in Canada,1974 – 1983. (Canada is a relatively normal country in terms of its total homicide rate.) Is it the same infanticide seen in lions? Is this evidence that we hold our genes more carefully than those of others? Does it reflect some other social factors? Or is it some combination of biological and social factors? 44 22


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