Species, A group of organisms that can naturally interbreed and produce fertile offspring—offspring that can reproduce., Biological species concept, Defines species by their ability to reproduce with one another and their reproductive isolation from other groups. Associated with Ernst Mayr., Speciation, The formation of new species as populations become genetically different and reproductively isolated., How can environmental changes affect species?, Changes can cause some populations to increase, contribute to the formation of new species, or cause extinction., Extinction, The disappearance of an entire species when its last member dies., Allele, A version of a gene. Different alleles can contribute to differences in inherited traits., Gene flow, The movement of alleles between populations through reproduction., How does isolation contribute to speciation?, Isolation reduces or stops gene flow. Separated populations can accumulate genetic differences over generations and eventually become different species., Allopatric speciation, New species form after populations become separated by a geographic barrier, such as a river, mountain, or canyon., Geographic isolation, Physical separation that prevents populations from regularly mating and exchanging alleles., Steps in allopatric speciation, Population separates → gene flow decreases → genetic differences accumulate → reproductive isolation develops., Why might separated populations become different?, Different environments can favor different inherited traits. Mutations and genetic drift can also cause differences to accumulate., Squirrel example from the slides, Abert’s and Kaibab squirrels illustrate geographic isolation associated with the Grand Canyon. Physical separation limits gene flow; separation alone does not automatically establish that populations are different species., Sympatric speciation, New species form while populations live in the same geographic area, without a physical barrier separating them., Reproductive isolation, Barriers prevent populations from successfully interbreeding and producing viable, fertile offspring. It can develop during either allopatric or sympatric speciation., Prezygotic isolation, A reproductive barrier that acts before fertilization. It may prevent mating or prevent fertilization even if mating occurs., Behavioral isolation, Differences in courtship behaviors, such as songs, dances, or displays, prevent organisms from mating. Example: Females respond only to their own species’ courtship signals., Temporal isolation, Populations reproduce at different times, such as different seasons or times of day. Example: Two frog populations breed in different months., Postzygotic isolation, A barrier that acts after fertilization. Hybrid offspring may fail to develop, survive poorly, or be unable to reproduce., Genomic incompatibility, Genetic or chromosomal differences between parents interfere with a hybrid’s development or ability to reproduce., Hybrid, Offspring produced by parents from different species or genetically distinct populations., Sterile, Unable to reproduce., Horse + donkey = mule, A mule is a hybrid that is usually sterile. This illustrates postzygotic isolation because fertilization and development occur, but the offspring generally cannot reproduce., Peacock spider courtship, A male uses visual displays and movements to attract a female. Courtship signals help females recognize and choose mates., Bird-of-paradise courtship, A male uses elaborate feathers and a courtship display to attract a female., Sexual selection, A form of natural selection in which inherited traits become more common because they improve mating success., How can courtship contribute to behavioral isolation?, If populations develop different displays or mate preferences, they may stop mating with one another even when they live in the same area., Does a courtship display automatically prove speciation?, No. It illustrates mate choice. It contributes to reproductive isolation only when differences in signals or preferences prevent interbreeding., Natural selection, Individuals with certain inherited traits leave more offspring than others in a particular environment. Those traits can become more common over generations., Evolution, A change in the inherited characteristics, or allele frequencies, of a population over generations., How are natural selection and evolution related?, Natural selection is one mechanism of evolution. Mutation, genetic drift, and gene flow can also change populations., Do individuals evolve?, No. Populations evolve over generations. Individuals survive and reproduce with different levels of success., Does evolution always happen slowly?, No. Evolution can occur rapidly or gradually, depending on generation time and other conditions., Coevolution, Two interacting species evolve in response to one another. Each creates selection pressures affecting the other., Coevolution example: flowers and pollinators, Flower shapes and pollinator feeding structures can evolve in response to one another. Pollinators obtain food while helping plants reproduce., Does coevolution always benefit both species?, No. It also occurs between predators and prey or parasites and hosts., Antibiotic resistance clarification, Antibiotic resistance is a clear example of natural selection. By itself, it does not demonstrate two species evolving in response to one another, so it is not the clearest example of coevolution., Convergent evolution, Different evolutionary lineages independently develop similar traits because they face similar selection pressures., Convergent evolution examples, Sharks and dolphins independently evolved streamlined bodies for swimming. Birds and insects independently evolved wings for flight., Analogous structures, Structures with similar functions that evolved independently, rather than being inherited as that feature from a common ancestor. Example: Bird wings and insect wings., Common ancestry and convergence, Convergent organisms still share distant ancestors. The key is that their similar adaptation evolved independently., Divergent evolution, Related populations or species become increasingly different as they evolve from a common ancestor., Divergent evolution example, Mammalian forelimbs evolved for different functions: grasping in monkeys, swimming in whales, and walking in pigs., Homologous structures, Structures with the same underlying evolutionary origin that may perform different functions. Example: The similar bone arrangement in mammalian forelimbs., Homologous vs. analogous, Homologous = shared origin. Analogous = similar function that evolved independently.

Evolution & Speciation

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