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Lecture 3 - BILD 3 Organismic and Evolutionary Biology...

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BILD 3 – Organismic and Evolutionary Biology Lecture 3 What is a species? - Species : The smallest evolutionarily independent unit o Mutation, natural selection, gene flow, and drift operate separately in different species Biological Species Concept - Definition of a species by Ernst Mayr: A population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring - The Biological Species Concept focuses the study of speciation on the study of the evolution of reproductive isolation o Reproductive Isolation: The existence of biological factors that prevent members of two species from producing viable, fertile hybrids Confirms the lack of gene flow - Limitations of the Biological Species Concept: o The biological species concept cannot be applied to: Asexual organisms Fossils Organisms about which little is known regarding their reproduction o An example: Different species of lizard in California, should we classify them as two species or not? What about the hybrid? Morphological Species (Morphospecies) Concept - Characterizes a species in terms of its body shape, size, and other structural features - Used to define fossils - Limitations: o Similarity between different species o Diversity within a species(different race among humans) o Cryptic Species: Species that are morphologically identical but genetically distinct The Phylogenetic Species Concept - The smallest group of organisms with an independent, unique genetic history - Can use molecular data instead of behavioral data to infer a lack of gene flow - Applies to all organisms, including asexual organisms and fossils - Disadvantages of the PSC: o Good phylogenies are not available for most organisms o Expensive and time consuming The Best Option: Allopatric, Sympatric and Parapatric Speciation - Allopatric("Other Country") Speciation
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o Gene flow is interrupted or reduced when a population is divided into two or more geographically isolated subpopulations o The predominant of speciation in sexually reproducing animals o Example: Chain of islands in Hawaii, older islands --> older species, youngest island --> youngest species o Divergence and Speciation is caused by: Genetic Drift - Bottlenecks/Founder Natural Selection - Different environment can lead to different adaptations, behavior and sexual preference - Sympatric("Same Country") Speciation o Divergence and speciation take place without geographic isolation o
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