Week 11 Microevolution Individuals do not evolve, they just live or die. Populations evolve over time as the traits in the population change. Change in traits is reflected in a change in the frequency of alleles. E.g. as the number of dark-colored moths in the peppered moth population increased over generations there was also an increase in the frequency of dark alleles in the gene pool. Over a shorter amount of time 50 to 100 years. Population as a gene pool E.g. different color patterns of snails correspond to different allele in the gene pool. Ways that allele frequencies can change other than by natural selection Mutation- one allele is changed and is now a different allele. Important source of variation for selection to work on. Rare event; by itself mutation can?t really change allele frequencies. Gene flow- alleles move from one population to another as individuals migrate between populations. Tends to keep separated populations from becoming genetically different. Paint can analogy. Prevents speciation (see later). Genetic drift Random changes in allele frequencies that happen in small populations. Occasionally small populations. Bottlenecks, Founder effect. Chronically small populations. Consequences of Genetic Drift Random change in allele frequencies. Most noticeable in small population. May have high frequency of otherwise rare alleles. E.g. Old Order Amish. Dwarfism and Polydactyly in Old Order Amish. Marry within their group. Lancaster, Pennsylvania. Some alleles may disappear. Loss of genetic diversity. E.g. Northern Elephant Seal and Cheetah. Adaptation Product of evolution by natural selection. An adaptation is a trait that increases the fitness of an organism in its environment. Adaptation to the Abiotic Environment Selection may occur because of features of the abiotic environment (physical factors such as temperature). E.g. in a cold environment animals with long fur are selected for this (survive better). We say that long fur is an adaptation to a cold environment. Adaptation to the Biotic Environment Selection may occur because of feature of the biotic environment. Other species, e.g. competitors, predators, (e.g. birds eat peppered moth), mutualists (plants and pollinators). E.g. camouflage is an adaptation to avoid being eaten by a predator. Members of your own species. E.g. Antlers on male deer (bucks) are an adaptation for fighting other males so as to win mates. Biotic Environment: Other Species The abiotic environment is fixed but the biotic environment is changing. Coevolution: change in one species selects for change in the other species. E.g. prey evolve to be faster, then predators evolve to be faster. Biotic Environment: Our Species Sexual selection: selection on features associated with acquiring mates. Sexual selection: Ornaments When females choose male to mate with. Adaptation: males have ornaments, e.g. brightly colored feathers of a male peacock. Sexual selection: Armaments When males fight each other for access to females. Adaptation: Males have armaments, e.g. large body size, protruding canine teeth and ?trunk? of male elephant seals. Sexual Dimorphism Result of sexual selection. Males and females look different. Convergent evolution Similar environments produce similar adaptations in unrelated species. E.g. body shape and fins of sharks, dolphins and penguins. E.g. plants in African deserts (Euphorbia) that look like the cacti of American deserts. Nature of Adaptations Adaptations are more like contraptions built from what is available rather than elegantly designed devices. E.g. middle ear bones of mammals. Adaptations are compromises Can?t be good at everything. E.g. tail length in male birds. Scissor-tailed flycatcher male. Scissor-tailed flycatcher female. Exaptation Some adaptations may originally have evolved for one purpose then been co-opted for another. E.g. feathers of birds may originally have evolved to keep reptiles warm then found a new role for flight. Origin of Evolutionary Novelty How do new features come about? Changes in many genes or a few genes? Sometimes mutations in a few genes are important in development (regulatory genes) can produce large morphological changes. E.g. changes in human skull from ape skull could be the result of a few changes in rate of development. Micro and Macroevolution Microevolution: change in species over short term, years to thousands of years. E.g. peppered moth. Macroevolution: change over long time, thousands to millions of years, origin of species, extinction, trends in evolution.
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