Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
What is Speciation? Speciation is the formation of new biological species, usually by the division of a single species into two or more genetically distinct one. Natural selection and chance events can change the relative frequencies of alleles in a population and lead to speciation. Speciation is the formation of new species. A species is a group of organisms that breed with one another and produce fertile offspring. KEY CONCEPT New species can arise when populations are isolated. Four Types of Isolating Mechanisms Reproductive Isolation Behavioral Isolation Temporal Isolation Geographic Isolation Reproductive Isolation Reproductive Isolation is the separation of a species or population so that they no longer interbreed and evolve into two separate species. Members of a certain species share a common gene pool. Over time, genes are shared by interbreeding. Reproductive Isolation Over time, isolated gene pools diverge into separate species. Behavioral Isolation Behavioral Isolation is a form of reproductive isolation in which two populations develop differences in courtship rituals or other behaviors that prevent them from breeding. Example: Eastern and Western Meadowlark The populations of the two subspecies overlap in the midwest. Behavioral Isolation Male birds sing a mating song that females like, East and West have different songs. Females only respond to their subspecies song. Behavioral isolation occurs when two populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior. Temporal Isolation a form of reproductive isolation in which two or more species reproduce at two separate times. Example: Northern Leopard Frog & North American Bullfrog Mates in April Mates in July Temporal isolation or seasonal isolation occurs when two or more species reproduce at different times of the year. Geographic Isolation Geographic Isolation is a form of reproductive isolation in which two populations are separated by geographic barriers such as rivers, mountains or bodies of water, leading to the foundation of two separate subspecies. Example: 10,000 years ago the Colorado River separated two squirrel populations. Geographic Isolation Kaibab Squirrel Albert Squirrel This resulted in a subspecies, but did not result in speciation because the two can still mate if brought together Geographic barriers do not guarantee the formation of new species. Speciation in Darwin's Finches Speciation of Galápagos finches occurred by: founding of a new population geographic isolation changes in new population's gene pool reproductive isolation ecological competition Speciation in Darwin's Finches Founders Arrive A few finches— species A—travel from South America to one of the Galápagos Islands. There, they survive and reproduce. Speciation in Darwin's Finches Geographic Isolation Some birds from species A cross to a second island. The two populations no longer share a gene pool. Speciation in Darwin's Finches Changes in the Gene Pool Seed sizes on the second island favor birds with large beaks. The population on the second island evolves into population B, with larger beaks. Speciation in Darwin's Finches Reproductive Isolation If population B birds cross back to the first island, they will not mate with birds from population A. Populations A and B have become separate species. Speciation in Darwin's Finches Ecological Competition As species A and B compete for available seeds on the first island, they continue to evolve in a way that increases the differences between them. A new species—C—may evolve. Speciation in Darwin's Finches Continued Evolution This process of isolation, genetic change, and reproductive isolation probably repeated itself often across the entire Galápagos island chain. Birds that are most different from each other have the highest fitness. More specialized birds have less competition for food. Over time, species evolve in a way that increases the differences between them, and new species may evolve (C, D, and E). When two species do not reproduce because of differences in mating rituals, the situation is referred to as A. B. C. D. temporal isolation. geographic isolation. behavioral isolation. reproductive isolation. All of the following played a role in speciation of Galápagos finches EXCEPT A. B. C. D. no changes in the gene pool. separation of populations. reproductive isolation. natural selection. Beak size in the various groups of Galápagos finches changed primarily in response to A. B. C. D. climate. mating preference. food source. availability of water. KEY CONCEPT Molecular clocks provide clues to evolutionary history. Molecular Clocks Uses mutation rates in DNA to estimate the time that two species have been evolving independently. Molecular clocks use mutations to estimate evolutionary time. Mutations add up at a constant rate in related species. This rate is the ticking of the molecular clock. As more time passes, there will be more mutations. Mutations add up at a fairly constant rate in the DNA of species that evolved from a common ancestor. DNA sequence from a hypothetical ancestor Ten million years later— one mutation in each lineage Another ten million years later— one more mutation in each lineage The DNA sequences from two descendant species show mutations that have accumulated (black). The mutation rate of this sequence equals one mutation per ten million years. Calibrating the Clock Genes accumulate mutations at different rates Compare the number of mutations in a particular gene in species whose age has been determined by other methods. Scientists estimate mutation rates by linking molecular data and real time. – an event known to separate species – the first appearance of a species in fossil record Hox Genes and Evolution Small changes in Hox gene activity during embryological development can produce large changes in adult animals. Change in a Hox Gene Mutation in a single Hox gene (Ubx) “turns off” the growth of some pairs of legs. Activity