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Phylogenetics Notes

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Biological Sciences
BIOSC 0160
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4/8 Chapter 27: Phylogenetics What is Macroevolution? • The study of… o The evolution of complex adaptations o The origin of major groups of organisms o Patterns of diversity and extinction o The study of the history of life as revealed by the fossil record • Relation to microevolution and speciation o Natural selection occurs at the level of population o Ultimately, that is where microevolution takes place o But such adaptation yields long-term, major change o Speciation distributes such adaptations to daughter species o Extinction (sometimes massive) can alter diversity • Adaptation—the process o Via natural selection including sexual selection o Produces adaptations o Slow and gradual on the ecological time scale o Looks rapid in the fossil record • Adaptation—the products o Must be of utility o Produced via past selection within the context of utility o Pre-adaptations (exaptations) are excluded  E.g. feathers were originally developed for warmth, but then birds began using them for flight by happenstance 4/8 The Fossil Record • Documents microevolution Genetic Basis of the Origin of Adaptations • Modifications of development o Evolution:  Descent with modification  In which the modifications arise as novel phenotypes  Produced by heritable modifications of the development of the phenotype  With natural selection sorting heritable phenotypes  Such that phenotypes that confer higher fitness in an environment come to predominate in that environment o Van Valen: evolution is the control of development by ecology o Allometric Growth/Change in Shape  Different parts grow at different rates  Evolutionary change in rate results in different shape  E.g. humans’ brains grow much faster than chimps o Heterochrony  Evolutionary change in timing of development  E.g. Humans’ brains grow for a longer period of time than chimps’ do  E.g. paedomorphosis • Juvenillization compared to ancestor species • Salamanders o Some never change to the adult form o Look like a large juvenile tadpole forever o This is because the offset of development occurs earlier 4/8 • Domestic dogs o Less aggressive and more playful, juvenile characteristics o Pattern Formation- Hox genes  Developmental establishment of precise spatial relationships between parts  E.g. vertebrate limb • Lungfish have fin bones like the proximal elements of tetrapod limbs • Proximal zone of Hox gene expression • Tetrapods have extra zone of Hox gene expression that corresponds with the digital arch • Pattern formation is thus genetically altered to yield the evolutionary novelty of a limb Macroevolutionary Events • Adaptive radiation o Prolific diversification within a new adaptive contest o E.g. shells in mollusks  Happened rapidly  Occurred in a predator-free zone • Mass extinction o Drastic reduction in diversity over short periods of geological time o E.g. permian extinction wiped out 95% of all marine forms in only 5 million years (occurred 250 million years ago)  Occurred when continents merged
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