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Isolation and Speciation. Macroevolution in action!. Formation of a new species… what is a “Species”?. Many definitions of species exist Morphological – based on finding physical/structural similarities Advantages: applies to both sexual/asexual organisms Disadvantage: subjective
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Isolation and Speciation Macroevolution in action!
Formation of a new species… what is a “Species”? • Many definitions of species exist • Morphological – based on finding physical/structural similarities • Advantages: applies to both sexual/asexual organisms • Disadvantage: subjective • Ecological – based on the niche of an organism (its role in ecosystem) • Phylogenetic – based on an animal’s ancestry/genetic history • Compare physical characteristics/molecular similarities • Paleontological – focus on morphologically-discrete species known only from the fossil record
Biologic Species concept • Defined as: • Population/group of populations that can successfully interbreed, producing viable, fertile offspring • Speciation often requires major genetic changes • Hinges on reproductive isolation – something that keeps two groups that would normally interbreed from doing so
Allopatric vs. Sympatric Speciation • Allopatric - “away from one’s fatherland” • Physical barrier divides 1 population into two • Mountains, channels, islands, rivers, lava flows, etc. • Leads to a divergence of the gene pool through mutations, selection, etc. • If enough time passes, will likely be unable to mate if reintroduced
Sympatric Speciation • Species evolves while alongside its fellow organisms. • How? • Polyploidy • Habitat differentiation • Sexual selection • Reminder: zygote = fertilized egg
Reproductive Isolation • Leads to speciation… • …By preventing gene flow among populations • Prezygotic Isolation – prevents fertilization • Mechanical • Habitat • Behavioral • Mating songs • Temporal • Gametic • Polyploidy (plants)
Post-Zygotic Isolation • Fertilization has occurred, but the hybrid isn’t viable, can’t reproduce • Reduced hybrid inviability – development/survival of hybrids is impaired • Reduced hybrid fertility – hybrids fail to produce functional gametes • Hybrid breakdown – offspring of hybrids are feeble/infertile
Some examples of hybrids that are infertile (sterile) Cool stuff! (Male partner listed first)
