Bio 201B
Terms
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Species or higher-order group of organisms
- Taxon
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Goal of phylogenetics
- Inform taxonomy
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Taxa at the end of branches
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Terminal taxa
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Split in a phylogenetic tree where a common ancestor was
- Node
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Branches between nodes
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Terminal taxa
- <>Lead to terminal taxa
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Peripheral branches
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Evolution without speciation; as opposed to...
- Anagenesis; Cladogenesis
- Species on the outside least related to ones in subsequent branches
- Outgroup
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Group including an ancestor and all of its descendants
- Monophyly
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At least one descendant is excluded in this phylogenetic group
- Paraphyly
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at least one excluded member of a phylogenetic group is ancestral to some of the others
- Polyphyly
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Features which are homologous among taxa and are thought to vary independently of other features; alternative condition thereof
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Characters; character state
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Derived, with or without modification, from a common ancestor
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Homologous (e.g. vertebrate limb bones)
- Character is changed from an ancestral state
- Derived
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Shared and derived character
- Synapomorphy
- Tree with the fewest evolutionary changes is the most likely
- Parsimony
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Similarity not inherited from a common ancestor; cause
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Homoplasy; convergent evolution, parallel evolution, evolutionary reversals (frog teeth)
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independently evolved features that are similar but arose from different developmental pathways
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Convergent evolution (vertebrate and cephalopod eyes)
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independent evolutionof similar features from similar developmental pathway, generally between closely related organisms
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Parallel evolution (Lepidoptera wing patterns)
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Use of comparisons of sets of species to test hypotheses about evolution
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Comparative method (sticklebacks - rituals follow aggression)
- Implications of phylogenetic thought
- Heierarchy, paraphyly
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Species that look the same, but come form different lineages and don't interbreed
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Cryptic species
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Species are groups of potentially or actually interbreeding populations which are reproductively isolated from other such groups
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Biological Species Concept; used by those studying speciation
- a species is a single linage (ancestral-descendant sequence) of populations or organisms that maintains its identity from other such lineages and which has its own evolutionary tenden
- Evolutionary species concept
- an irreducible (basal) cluster of organisms that is diagnosably distinct from other such clusters, and within which there is a parental pattern of ancestry and descent
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phylogenetic species; used by those describing species
- a hybrids don’t survive at all or have low fitness [viability or fercundity] (between adults and mating)
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Postzygotic isolation
- some genetic problem with the genes of the two different species being mixed
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Intrinsic (genetic) postzygotic isolation
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One species is fixed for AABB
Covers all mechanisms that reduce the number of viable hybrids that come out of a cross between mating and zygote pro
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Postmating, prezygotic isolation
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Prevent mating in the first place
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Premating isolation
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types of premating isolationg
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- temporal isolation (crickets)
- habitat choice (aphids)
- mate choice (morphic male hummingbirds)
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a development of isolation mechanisms when the subspecies (incipient species) are geographically separat
- Allopatric speciation; vicariance, peripheral isolation
- one large population breaks into two subpopulations (due to, say, a river or mountain range), gradual changes are accumulated, and the two can’t interbreed
- Vicariance; Panamanian crustaceans
- a large population colonizes a new area, and the colony evolves on its own until it can’t interbreed with the parent population
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Peripheral isolation; Hawaiian Drosophila
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A widespread species has populations that diverge because of adaptations to different environments
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Parapatric speciation
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Speciation in the same location – complete geographic interdispersal
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Sympatric speciation; cichlids in Africa?
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The evolution of premating isolation after secondary contact to prevent the formation of unfit hybrids
- Reinforcement
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Mechanism of reinforcement' examples
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·Individuals choosing to mate with individuals of the same population have the trait spread becau
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evolutionary divergence of members of a single phylogenetic line into a variety of different adaptive forms
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Adaptive radiation (see Darwin's finches, Carribean anoles)
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Fossil record: best/worst for...
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Challenges in the fossil record
- Most organisms eaten or decomposed
- Sediments form episodically
- Fossils must persist for millions of years
- Rock must be accessible to paleontologists
Archaean era
- earliest eukaryotes
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proteozoic era
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marine animals diversify; 1st appearance of most animal phyla and many modern classes, all within 40 My; beginning of Paleozoic
- Cambrian period (543 Mya)
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Why the Cambrian explosion?
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- Rise in O2 concentration allows larger forms, more metabolism (faster movement)
- Homeotic genes - hox loci duplicated
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Lay out 3-D body plan
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Homeotic genes
- divergence of bony fishes; origin of amphibians
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Devonian period
- dinosaurs and other reptiles diversify; 1st birds
- Jurrasic Period, Mesozoic era
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Mammalian evolution
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- temperal fenestra
- Hammer, anvil, stirrup
- differentiated teeth
- Secondary palate
- Enlarged braincase
- new joint in lower jaw
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Evolution of limbs
- Eusthenopteron-Panderichthys-Tiktaalic-Acanthostega-Icthyostega
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Evolution of whales
- Elomeryx-Ambulocetus-Rodhocetus-Dorudon-Phocoena
- body sizes tend to increase
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Cope's Law (horses)
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Dinosaur extinction
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K/T Boundary
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Iridium layer characteristics
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- Iridium
- Microtektites
- Shocked quartz
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How humans cause mass extinction
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- Hunting
- Invasive Species
- Habitat loss
- little stasis; steady, constant evolution
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phyletic gradualism (formaniferans)
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Faces flatten, braincases grow, teeth shrink, jaws strengthen, sexual de-dimorphicism; timeline
- Gracile Australopithecines and Ardipithecus, Robust Australopithecines, early Homo, late Homo
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Human history
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- 8 Mya: origin in forests
- 6 Mya: grasslands replace forests
- 4.5 Mya: bipedalism in A. anamensis
- 3.5 Mya: fossilized bipedal footprints of A. afarensis
- 2 Mya: Homo habilis
- 1.8--1.5 Mya: H. erectus
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Human timeline, late
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- 1.5 Mya: H. erectus out of Africa
- 150 kya: H. neanderthalensis
- 100 kya: H. sapiens in Africa
- 35 kya: H. sapiens reaches Europe
- 18 kya: H. floresiensis
- H. Erectus, which evolved in Africa, migrated 1Mya to Europe and Asia; continual migration led to archaic Homo sapiens; further migration led to modern H. sapiens
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Multi-regional model
- H. Erectus migrates 1 Mya into Asia and Europe; archaic H. sapiens evolved from H. erectus in Africa and migrated 166 - 250 Kya to Asia and Europe and displaced H. erectus
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out-of-Africa migration
- a decline, with age, in reproductive performance, physiological function, or probability of survival
- senescence
- Mutations that cause death really late in life are only mildly deleterious and do not really factor into selection; these mutations are accumulated as a result of weak natural selecti
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Late-Acting Deleterious Mutations Theory (Huntingotn's disease)
- Maybe there is pleiotropy working in different directions with regard to fitness at different points in life; the genes give you an advantage early on, but a disadvantage later
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Antagonistic Pleiotropy theory (Drosophila:birth rate and death rates)
- asexuals reproduce twice as fast, since female offspring production is limited (put most of the energy into rearing young)
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Two-fold cost of sex
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Why sex?
- Meiosis and crossing over + mating between unrelated individuals --> recombination + alleles on new genetic backgrounds
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Loss of rare alleles/gain of bad alleles to drift in asexual populations, but not in asexual populations
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Muller's Ratchet
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In a large haploid population where A, B, and C are better than a, b, and c, the mutational appearance o
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Fixation of Rare Beneficial Mutations