Quinn 4 - Biology 1MO3 Jan. 25/2010 Species Concepts...

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Species Concepts Phylogenetic species concept --Bar coding –shortcomings? Biological Species Concept Reproductive Barriers Species Cohesion Breaking cohesion Speciation Speciation Allopatric -- vicariance Sympatric – genetic isolation ecological separation (food) Biology 1MO3 Jan. 25/2010 Chapter 26 NOTE: Study questions for my part of quiz 1 are now on ELM Some difficulties with the Bar Code of Life How much difference defines a species? -- within versus between species variation -- single species of copepod – 20% differences The CO1 type is based on a single molecule (mtDNA) Caution is necessary and other traits should be considered when establishing a phylogenetic species. However, in some cases, time to extinction is short! Biological Species Concept developed by Mayr for classifying species of sexual organisms. --Groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups. Note that the potential interbreeding may be untestable in some cases because some species do not occur together naturally . Unnatural settings can promote hybridization: In Zoos Tiger X Lion = Tigon Lion X Tiger = Liger
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Hybridizations in zoos show genetic similarities btwn tigers and lions PROBABLY DID NOT HYBRIDIZE IN NATURE currently not sympatric (overlapping ranges) No prior records – despite carefully kept hunting records kept in India during period of sympatry of lions and tigers Various mechanisms may prevent gene flow when separate species come together. Table 26.1 Reprod. Barriers Note errors in table (firefly example and sea urchin example) If all of these barriers are passed – successful reproduction occurs (pair are members of same species) Gene flow = species cohesion Key points: Species are maintained as cohesive units by gene flow Figure 25.7 selection for unbanded watersnakes on limestone islands and banded watersnakes on mainland – kept single species by gene flow! Speciation – requires cutting off genetic exchange (gene flow) --Spatial Separation --Temporal Separation --Genetic incompatability
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Other Fatherland Allopatric Speciation (geographic speciation) Define Allopatry – living apart geographically Two populations separated by barrier --Natural selection &/or genetic drift cause divergence --With sufficient divergence, interbreeding becomes unlikely, and/or offspring survive poorly Figs 26.5 a and b Founder populations diverging from ancestral pop’n; vicariance. Conditions Favoring Allopatric Speciation --small isolate (founder) population --at frontier of parent population’s geographic range WHY? 1) Small peripheral isolate will differ from parental population (Founder effect) 2) until peripheral isolate grows to large pop’n, genetic drift will cause further genetic and phenotypic divergence 3) Frontier environment is likely to differ from much of the parent population’s environment, therefore Natural Selection will increase divergence. MAIN FEATURE OF IMPORTANCE—PHYSICAL BARRIER TO GENE FLOW….
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Quinn 4 - Biology 1MO3 Jan. 25/2010 Species Concepts...

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