* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download 34 speciation
Survey
Document related concepts
Unilineal evolution wikipedia , lookup
The Selfish Gene wikipedia , lookup
Evolving digital ecological networks wikipedia , lookup
Catholic Church and evolution wikipedia , lookup
Evolutionary landscape wikipedia , lookup
Sexual selection wikipedia , lookup
Hybrid (biology) wikipedia , lookup
Hologenome theory of evolution wikipedia , lookup
Population genetics wikipedia , lookup
Theistic evolution wikipedia , lookup
Reproductive isolation wikipedia , lookup
Natural selection wikipedia , lookup
Evidence of common descent wikipedia , lookup
Transcript
Speciation - Polymorphism - Patterns of natural selection - Mechanisms of isolation - Rates of evolution Refer to chapter 17 in text http://supplementalscience.files.wordpress.com/2007/07/rbc.jpg http://www.cdc.gov/Malaria/images/microscopy/gam_rings_arrowed.jpg http://www.healthsystem.virginia.edu/internet/hematology/HessImages/Sickle-Cell-100x-website-arrow.jpg - Polymorphism Within a population there is a range of forms (morphs) for a variety of traits: phenotypic polymorphism: two or more conspicuous forms. genetic polymorphism: multiple genes affecting a form, like height. This is the variety acted on by natural selection. Why isn’t it better to have one trait, or the other? Balanced polymorphism: Two (or more) alleles cooperating is better than either one alone. e.g. HsHs → sickle-cell anemia HHs → OK (heterozygous advantage) HH → more susceptible to malaria Note: this is microevolution, not speciation, but provides a testable example of natural selection. http://www.genetologisch-onderzoek.nl/index.php/92/biologie/ Transient polymorphism: One version is favored sometimes, the other at other times. e.g. industrial melanism and peppered moth - Patterns of natural selection stabilizing selection: The central-most morph is most successful, and distal forms are reduced. Results in fine-tuned, but potentially fragile species. disruptive selection: The central form is less adaptive, and the population splits into two. Due to competition, loss of original resource... Easy step to speciation. directional selection: One extreme is favored over the other. Generally leads to speciation only if two populations are already separated. divergent evolution: The result of divergent selection, in which one species faces selective pressure for two different niches: Recognized by presence of homologous structures. e.g. Australian apple maggot fly: originated from the Australian hawthorn maggot fly, but when apples were brought in, the new food source was optimized... Now two distinct species exist. adaptive radiation is a specific case of divergent evolution, in which many niches are available for exploitation e.g. the post-Mesozoic explosion of mammals after mass extinction of dinosaurs Adaptive radiation also happens when organisms colonize a new island grouping… This resembles the process of the finches in the Galapagos islands. convergent evolution: A specific type of directional selection, in which two species are long separated, but selected towards a common adaptation: Often recognized by the presence of analogous structures. The C4 pathway has cropped up at least 40 separate times. http://cas.bellarmine.edu/tietjen/Evolution/Charley/Converge36.gif - Mechanisms of isolation In order for actual speciation to occur, there has to be some sort of boundary preventing the mixing of genes… Reproductive isolation… self explanatory. - prevention of successful interbreeding, ….somehow. Two main groupings: 1. Allopatric – (“other country”) Organisms are physically separated. This could be across an ocean, or a stream, or a spit of land, or adjacent puddles. 2. Sympatric – (“same country”) Various mechanisms that isolate neighbors… Sympatric mechanisms prezygotic (no zygote formed) habitat isolation: different local habitat. e.g. water v land garter snakes behavioral isolation: courtship, communication boobies, Pacific killer whales, bower birds.... temporal isolation: time of day, year, cycles… NA E spotted skunk (winter) v W (summer) mechanical isolation: structural incompatibility… 2 monkey flowers attract different pollinators gametic isolation: repro. tract or gamete surface sea urchins postzygotic (no reliably fertile offspring) reduced hybrid viability: don’t survive to repro. Ensatina salamanders (‘zygote mortality’ in Mader) reduced hybrid fertility: hybrids live, but can’t repro. horse + donkey = mule hybrid breakdown: hybrids can’t survive over multiple generations (‘F2 fitness’ in Mader) rice strains This is the blurry path to speciation. These work for solely sexually reproducing organisms. What other factors contribute to speciation? Polyploidy e.g. autoploidy, mostly in plants, due to nondisjunction in meiosis, leads to speciation in one generation. (It can’t breed with a diploid anymore, but can self-pollinate until there is a population of tetraploids.) alonefarmer.blogfa.com/post-1851.aspx There are various invertebrates that can do this, too, and a mouse line was made tetraploid in a lab… Cross 2n w haploid gamete → triploid (seedless) Hybridize 2 w different 2n, then nondisjunction = alloploidy - Rates of evolution Microevolution by selection or genetic drift can happen in the course of a few generations. Speciation by polyploidy happens in a single generation. More commonly, the accumulation of adaptive mutations can be very slow (thousands of years? tens of thousands?), and if an organism is well adapted, there may be little change in allelic frequency over millions of years. HOWEVER, after a disruption, there is generally astonishingly rapid evolution as newly freed or created niches are filled, depending on existent mutations. - Punctuated equilibrium Contrast allopatric and sympatric speciation Explain the role of morphic variability in natural selection. phenotypic polymorphism allopatric genetic polymorphism sympatric balanced polymorphism prezygotic heterozygous advantage habitat isolation transient polymorphism behavioral isolation stabilizing selection temporal isolation disruptive selection mechanical isolation directional selection gametic isolation divergent evolution postzygotic adaptive radiation reduced hybrid viability convergent evolution polyploidy reduced hybrid fertility reproductive isolation hybrid breakdown punctuated equilibrium