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This 7 page Class Notes was uploaded by Beatrice Deckow I on Monday September 28, 2015. The Class Notes belongs to BIOL 303 at George Mason University taught by Staff in Fall. Since its upload, it has received 11 views. For similar materials see /class/215109/biol-303-george-mason-university in Biology at George Mason University.
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Date Created: 09/28/15
Other mechanisms of evolution Sexual selection recognized by Darwin Several gures not in book but see 2315 p 482 what about obviously silly characteristics like colors in birds silly behaviors e g humans etc Characteristics selected by opposite sex eg females like longer trunk brighter tails etc There is often a trade off between sexual selection and natural selection if character becomes too bizarre natural selection may put a halt to it why does sexual selection exist because if you have silly characteristics and can still survive this indicates you re doing pretty good Speciation formation of new species So now that we understand evolution a little bit how do new species arise Two possibilities from evolution Fig not in book A single species changes A single species gives rise to several species origin of diversity generally more interesting First definition of a species A group of organisms that can interbreed but who cannot produce viable offspring with a different species Even this definition is breaking down in some areas wolf dog Plants are horrid examples This is the only objective category that we have What prevents different species from producing viable offspring Prezygotic barriers before fertilized egg Habitat living in areas where there is no mixing of species Behavioral behave differently so that opposite sex is not attracted Temporal reproductively active at di erent times of the dayyear etc Mechanical simply can t consummate reproductive act Gametic the gametes of male may not survive inside female or may not be recognized by female Postzygotic barriers after fertilized egg Reduced hybrid viabilityfertility hybrids don t do as well Hybrid breakdown offspring of hybrids are affected Hybrid sterility hybrids are sterile e g mules Summary Fig 244 p 490 Modes of speciation Generally involves geographical barriers eg Fig 245 p 493 allopatric living in di erent areas sympatric living in the same area so allopatric speciation is generally caused by reproductive isolation organisms on each side of barrier evolve in their own direction Nice example in book Fig 246 p 493 Grand Canyon Birds are the same on both sides of canyon but rodents which can t easily cross are different but still similar Adaptive radiation amp island chains Fig not in book A burst of speciation from one or a small number of original species Especially good case can be made in island groups Each island has a slightly di erent species adapted for local conditions Darwin s finches Galapagos tortoises Fig not in book Also note that many groups are missing in islands Only successful survivors make it onto islands Often this means that groups that do reach the islands are much more diverse than mainland relatives because they can fill areas usually occupied by other species back home A real example Fig not in book though this is a little simpler than what was presented above Taxonomy Your text makes a real mess of this Use these notes as a guide through the book Study of classifying and naming organisms Founded by Linnaeus If done properly is based on evolutionary relationships at least to some extent If based on ancestrally derived similarities then often this is automatic Kingdom gt Phylum gt Class gt Order gt Family gt Genus gt species These categories may be supplemented with Super Sub Infra below sub etc A few other categories also exist Domain above Kingdom Tribe between family and genus So how does it work Complete classi cation of Humans Kingdom Animalia grouped with all animals Phylum Chordata grouped with mostly vertebrates Class Mammalia grouped with Mammals fur milk Order Primates grouped with Monkeys Family Hominidae grouped with Humans fossils incl Genus Homo grouped with very similar humans e g Homo erectus species sapiens only humans Note that fossil species are classified the same way Another example Fig 263 p 537 note that one can use this classification to make a phylogenetic tree there s a lab exercise that will let you do this Fig 264 p 538 Note that the only objective category is species although the species concept has problems we can test to see if organisms belong to a particular species or not we have no such test for the other categories Instead we need to decide what goes where based on what we think which isn39t really objective much argument about the other categories About writing scienti c names Always include Genus and species Genus always capitalized species always lower case few very rare exceptions in botany Both underlined or italicized Favorite quizexam question More on phylogenetic trees Taxon a group of animals eg a family a class etc Fig 2610 p 542 Monophyletic best Each group includes ancestor and all immediate descendent species Eg cats Polyphyletic pretty bad Organisms with different ancestors are grouped together E g grouping humans and jelly fish together in the same Genus an obviously silly example Paraphyletic not good but okay depending on who you talk to Ancestor is grouped with some but not all descendents Birds and dinosaurs Birds are in their own class as are dinosaurs Comments on the text The text makes a big deal about a lot of this including why paraphyletic is really bad note that to get rid of paraphyletic groups we39d need to reclassify birds as dinosaurs or reptiles this may re ect a true evolutionary relationship but it s nonsense for most people I refuse to make a big deal out of this We ll stick with the traditional system of classifying animals even if some scientists want to turn everything upside down The text also makes a big deal about clades and such We will ignore this almost entirely But before we do let39s at least explain just a little of the fuss there are many ways of coming up with classi cation trees we need a way to build our trees for example how do we decide to group big cats together and separate them from smaller cats At what point do we put cats in one family and dogs in another What about bears which are related to both there are three main ways of coming up with classi cations traditional cladistic amp phenetic traditional uses expert knowledge often based on shapemorphology but can also use DNA and other methods cladistics uses computers to make decisions based on the input of characters eg size color shape by experts Cladistics also insists on monophyletic trees and single branching points phenetics isn39t used much anymore since it arbitrarily lets computers do everything Cladidistics seems to have won out recently It39s hailed as a more objective way of nding relationships But it does have problems who decides what characters to use and is directly responsible for the mess that taxonomy is in e g birds are reptiles and other silliness until this is straightened out I suggest ignoring this Finally don t worry about some of the concepts in chapter 26 such as PhyloCode which promises to make taxonomy a nightmare for the average person outgroups ingroups etc Finally what are animals They belong the the Kingdom Animalia Incidentally your book puts them into the Domain Eukarya If you39ve had cell biology you should remember eukaryotes But domains are in ux and though your book tries to be reasonable here domains are changing so much that it s hard to know what will be happening a few years from now Animal origins Probably the group most closely related to animals are the choano agellates Fig 323 p 656 Belong to the protists a name for sometimes unrelated eukaryotes protists include such things as ameobas algae paramecium slime molds etc They frequently form large colonies They bear a remarkable similarity to the choanocytes found in sponges Characteristics of animals multicellular this should be obvious heterotrophic means they get their energy by consuming other organisms they can not generate their energy like a plant from sunlight plants are autotrophs eukaryotic we don39t have the time to go into details here but the essence of being a eukaryote means having membrane bound organelles like a nucleus or endoplasmic reticulum Fig 66 p 98 amp 69 p 100 Animal development Before starting our survey of the animal kingdom we need to know a little bit about how animals develop For example how do we go from a single cell to a human being how does an individual cell give rise to heart muscles nerves etc we will not go into a lot of detail here In general we ll follow the development of a zygote Fig 322 p 655 division occurs until a hollow ball blastulaforms one side of ball folds in like poking a tennis ball we now have two cavities the original and a new one with an opening to the outside go through parts also note that now we have two cell layers inside endoderm outside ectoderm if a middle layer forms mesoderm this can happen in one of two ways Fig 329 p 661 mesoderm forms from outpocketings of endoderm archenteron mesoderm forms from cells at the sides of the opening blastopore of the archenteron depending on which happens one gets either protostome blastopore forms mouth anus is formed through another opening that is eventually made deuterostome second opening forms mouth anus is formed from blastopore most animals are protostomes but echinoderms and chordates are deuterostomes one reason that chordates and echinoderms are thought to be closely related Some other di erences between protostomes and deuterostomes include the type of cleavage and determinate vs indeterminate cleavage Protostomes spiral and determinate spiral oblique determinate each cell s fate is determined early on Deuterostomes radial and indeterminate radial parallel or perpendicular indeterminate each cell can still form an entire individual until late The three layers eventually form all the structures within the organism Fig 4714 p 1032
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