10-ch14-species - Chapter Chapter 14 The Origin of Species

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Unformatted text preview: Chapter Chapter 14 The Origin of Species http://www.trollart.com http://www.trollart.com The origin of species is the source of biological diversity (macro)evolution – (1) all changes that have transformed life on earth from its beginnings to its current diversity, resulting from (2) any change in the genetic makeup of a population across generations generations species – group (of organisms) whose members possess similar characteristics and have the ability to interbreed th taxonomy – branch of biology concerned with naming and classifying biological diversity - identify new species new species - establish relatedness among species - chronicle evolutionary history; “tree of life” evolutionary history; tree of life Macroeveolution Macroeveolution sometimes leads to speciation reproductive barrier different selection pressures lead to different adapations different adapations Phenotypic variation & genetic diversity occur both among & within species. Where do we draw the line between species? “allo” “allo” = other “patria” = country (place) Speciation often involves geographic separation. allopatric speciation – ancestral population segregated by geographic barrier (divided into two or more geographically isolated populations) isolated populations) Continental drift has influenced evolution… earth crust divided into tectonic plates; geologic events occur at boundaries Pangaea – supercontinent formed near end of Paleozoic era (250 mya) when plate movements brought all landmasses together Lungfish distribution: a result of continental drift Fossil lungfishes Fossil lungfishes from six continents appear to be closely related... ...because lungfish evolved when Pangea was still intact! sympatric speciation – radical change in genome of subpopulation reproductively isolates it from the parent population population Cope’s gray treefrog Hyla chrysoscelis diploid (24 chromosomes) Common gray treefrog Hyla versicolor tetraploid (48 chromosomes) Where our ranges overlap, males can be distinguished (only) by the speed of their calls. “sym” = together; same “patria” = country (place) Some Some plant species (and a few animals) have their origins in accidents of cell division polyploidy – mutational change that results in new species with multiple sets of chromosomes (meiotic error diploid gametes) Thus, polyploidy is one mechanism for sympatric speciation. “poly” = many Polyploid Polyploid plants clothe and feed us oats, potatoes, bananas, peanuts, barley, plums, apples, sugarcane, coffee, pp cotton, tobacco... wheat: 20 species wheat: 20 species, including bread wheat Selecting Selecting for the traits that allow for domestication is easier in some species than in others, and it turns out that our Big Three—wheat, rice, and corn, which together provide more than half of all calories consumed in the modern world—are particularly suitable for selective breeding. All of them them are what is known as polyploid, which means their genomes have been duplicated—the chromosome number literally doubled at some point in the past few million years, in some cases more than once. Many plants are polyploid, and genome duplication seems to have happened quite often during plant evolution It as if you photocopied the entire genome and inserted that quite often during plant evolution. It's as if you photocopied the entire genome and inserted that spare spare copy into the nucleus of the cell. This has some pretty interesting consequences for what you can do to the plant with selective breeding. When you have spare copy of something, you can take more risks than if you had only one. It When you have a spare copy of something, you can take more risks than if you had only one. It's kind kind of like the "lives you have in a video game—you can make poor choices and still keep playing. This holds true at the genetic level as well, since having a duplicate allows you to tinker with one of the copies while retaining an unaltered version. It gives you a backup, in other words, in case something goes wrong in your tinkering. Duplicate copies can open up new ti opportunities for evolutionary change without risking the loss of vital functions—and can sometimes lead to more rapid evolution. This idea was first championed by Susumu Ohno, a aneseEvolution Japanese-American population geneticist, who wrote a classic book entitled Evolution by Gene Duplication in 1970. In this book... he also coined the term "junk DNA," This is the ultimate fate of gene duplicates that suffer a fatal mutation and become nonfunctional. But the working copy of the gene keeps the organism alive. Almost all cancerous tumors duplicate their DNA, becoming polyploid as they develop Geneticists believe this duplication of key genes gives them becoming polyploid as they develop. Geneticists believe this duplication of key genes gives them more more plasticity—more options to develop in ways that normal cells never would. Spencer Wells, Pandora’s Seed: the unforeseen cost of civilization Pandora adaptive radiation – emergence of numerous species from a common ancestor introduced to a new & diverse environment these closely related Hawaiian plant species have very species have very different different adapatations! Let’s Let’s dissect the mechanism for adaptive radiation... 1) founder population (species A) arrives from mainland 2) “A” evolves new adaptations in this different environment, becoming “B” “B” may sooner or later end up on another island 3) “B” evolves new adaptations on the new island, becoming “C” “C” may sooner or later end up on other islands including the original “B” & “C” are now distinct species, too different to interbreed! 4) On one new island, “C” evolved into “D,” then recolonizes original islands On one new island evolved into then recolonizes original islands 5) “D” is now distinct from “C” (and “B”), so they coexist without interbreeding Prezygotic Prezygotic barriers are evolutionary adaptations that prevent hybridization prevent hybridization before fertilization Postzygotic barriers are biological accidents that can result in decreased can result in decreased or zero fitness different different habitats minimize contact active at different active at different times times of day, year, or breeding season distinct body color and courtship courtship display can prevent hybridization (many birds, frogs, insects) structural structural differences in genitalia may prevent accidental sperm transfer (many plants, insects, spiders) X hybrid offspring does hybrid offspring does y y s s e e not develop properly not develop properly o o o o (most organisms) (most organisms) m m a a inability of inability sperm to fuse with ovum of other species (e.g., chemical barrier as in barrier as in sea sea urchins) hybrid hybrid F1 offspring may be healthy but cannot reproduce as easily as their parents (or at all) future generations are less viable (some ornamental garden flowers, crops: cotton, rice) X My diploid karyotype diploid karyotype is 62 chromosomes. Can’t take half of sixty-three... sixtythere’ll be no meiosis for me! Mine is 64. Prezygotic Prezygotic barriers in wolf spiders… silk dragline (chemical pheromones) male courtship display (visual cues + vibrations) differences in shape of genitalia Pardosa lapidicina mother with offspring Prezygotic Prezygotic barriers in wolf spiders… http://bugguide.net P. lapidicina female epigynum http://bugguide.net P. lapidicina male pedipalp Prezygotic Prezygotic barriers in frogs… green frog Rana clamitans American bullfrog Rana catesbeiana closely related, both native to Eastern North America similar habitat, diet, etc. (sometimes mate in the same ponds) overlap in breeding season females can tell males apart easily by their calls When When prezygotic barriers fail... male mallards are conspicuously different speculum (wing ornament) is blue for mallards & purple for black duck purple for black duck American Mallard American Black Duck (occasional hybrid accidents are a waste of genes) homology (homologous structures) – features in different species are similar because of common ancestry analogy (convergent evolution) – adaptations in different species are similar only due to similar selective pressures (marsupial) Do we share a common ancestor… (rodent) …who explains our remarkable likeness? Tasmanian wolf American coyote American coyote http://www.youtube.com/watch?v=6vqCCI1ZF7o Standard poodle Asiatic jackal One of these things is not like the other things... Marsupial Marsupial distribution: a result of continental drift The pattern of continental mergings and separations solves pa co sepa so many puzzles, including Australia’s great diversity of marsupials, which probably originated in North America and spread southward while the continents were still joined. The The subsequent breakup of continents set Australia “afloat” like a great ark of marsupials. historical distribution(s) current distribution http://evolution.berkeley.edu/evosite/lines/IIIBgeography.shtml Evolution Evolution of the genes that control development homeotic genes – control changes in the timing and rate changes in the timing and rate of growth (i.e., switch growth factor chemicals on / off neoteny – retention of juvenile characteristics in a mature organism (evolution toward youthful appearance) Can something as complex as the camera-type eye evolve from a series of random mutations? A range of structural complexity among mollusk eyes… range http://www.pbs.org/wgbh/evolution/library/01/1/l_011_01.html The The neural pathways which process vision are evolving too... NOVA Secrets of the Mind V.S. Ramachandran (neuropsychologist) Scene 2: Blind Sight (8 minutes) ...
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