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Unformatted text preview: Offspr ing wi th Gamet esdpr oduced by may be viable and fer t ile – a new bi ological species. t et r aploi kar yot ypes f lower s on t his br anch will be di pl oid. Speciation Speciation is the process by which daughter species evolve from a parent species Outline: 1. Key concepts 2. Biological species 3. Reproductive Isolating Mechanisms 4. Other concepts of species 5. Allopatric speciation 6. Sympatric speciation 7. Adaptive radiation 8. Key Terms 9. Conclusions Key concepts • A species consists of one or more populations of individuals that can interbreed and produce offspring • Populations of a species have a shared genetic history • Speciation is the process by which daughter species evolve from a parent species • There are many different mechanisms to isolate species • Geographic barriers can start the process of speciation o Allopatric speciation • With sympatric speciation, a species can form within the range of a parent species Biological Species Concept Defines a species as a population or group of populations whose members have the potential to i nterbreed in nature and produce viable, fertile offspring by are unable to produce viable fertile offspring with members of other population Same species or not: (a) Similarity between different species. The eastern meadowlark (Stumella magna) and the western meadowlark (Stumella neglecta) have similar body shapes and colorations. Nevertheless, they are distinct biological species because their songs and other behaviors a re different enough to prevent interbreeding should they meet in the wild. (b) Diversity within a species – As diverse as we may be in appearance, all humans belong to a single biological species (Homo sapiens), defined by our capacity to interbreed. Prezygotic and postzygotic barr iers Prezygotic bar riers impede mating or hinder fertilization if mating does occur L imitations of the Biological Species Concept The biological species concept cannot be applied to: • Asexual organisms • Fossils • Organisms about which li t t le is known regarding their reproduction Other definitions of Species • • • • The m orphological species concept o o o o Characterizes a species in terms of i ts body shape, size, and other structural features Focuses on morphologically discrete species known only from the fossil record Views a species in terms of i ts ecological niche Defines a species as a set of organisms with a unique genetic history The p aleontological species concept The ecological species concept The p hylogenetic species concept Speciation can occur in two ways: • Allopatric speciation • Sympatric speciation Allopatric Speciation • Speciation in geographically isolated populations • Probably most common mechanism • Some sort of bar rier arises and prevents gene f low • Effectiveness of barrier varies with species Extensive Divergence Prevents Inbreeding • Species separated by geographic bar riers will diverge genetically • If divergence is great enough it will prevent inbreeding even if the barrier later disappears Speciation without a Bar r ier Sympatric speciation • Species forms within the home range of the parent species • Speciation takes place in geographically overlapping populations Polyploidy • • Is the presence of extra sets of chromosomes in cells due to accidents during cell division Has caused the evolution of some plant species An Autopolyploid: • Is an individual that has more than two chromosome sets, all derived from a single species
Failure of cell division in a cell of a growing diploid plant after chromosome duplication gives r ise to a tetraploid branch or other tissue • 4n = 12 4n An autopolyploid is a species with multiple sets of chromosomes derived from different species An example of natural selection: Darwin’s finches Showed relatively rapid evolution: • Ancestral finches from mainland reached islands, underwent adaptive radiation and populated many diverse habitats • Ancestral species became groups of closely related yet diverse population Hawaiian Islands • Volcanic origins, variety of habitats • Adaptive radiations: o Honeycreepers – in absence of other bird species, they radiated to fill numerous niches o Fruit f l ies (Drosophila) – 40% of frui t f lies species are found in Hawaii Key Terms: Speciation Biological Species Prezygotic reproductive barriers Postzygotic reproductive barriers Allopatric speciation Sympatric speciation Polyploidization Adaptive radiation In Conclusion: • A species consists of individuals in a population or populations • Populations of a species share genetic history • Speciation is the process by which species form from a population of a parent species • Genetic divergence is a buildup of differences in allele frequencies between populations • M icroevolutionary processes can give r ise to reproductive isolating mechanisms • Speciation occurs gradually by genetic divergence • Pre-zygotive and post-zygotic isolating mechanisms contribute to speciation • There are two models of speciation: Allopatric speciation and Sympatric speciation ...
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- Spring '08