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The Origin of Species The “mystery of mysteries” Macroevolution • Speciation=Evolution of new species – Source of biodiversity • Appearance of “evolutionary novelties” 2 patterns of evolutionary change • Anagenesis – Accumulation of heritable changes – micorevolution • Cladogenesis – Branching of species – macroevolution What makes a species? • Biological species concept – Population(s) that can interbreed to produce viable offspring • Reproductive isolation – Behavior – Geography – physiology Reproductive Isolation • Prezygotic Barriers-impede mating • Postzygotic Barriers-impede hybrid development Habitat Isolation • Occupy different habitats within the same area – Garter snakes – Anolis Temporal Isolation • Breeding seasons are asynchronous – Eastern and Western Skunks Behavioral Isolation • Courtship rituals that rely on unique traits Mechanical Isolation • Structural differences prevent cross mating – Differently shaped pollen – Different pollinators – Drastic differences in size Gametic Isolation • Zygotes don’t fuse – Sperm lack proper receptor proteins Reduced hybrid viability Hybrid Sterility • Hybrids are weaker than “pure-breds” • Hybrids are sterile – Mule – Liger Hybrid Breakdown • Hybrids are strong, their offspring are less viable – Coydog Speciation • Allopatric- population becomes geographically divided • Sympatric- Populations live in overlapping habitats, no geographical separation is necessary Allopatric Speciation • Individuals colonize new areas • Geologic changes (oxbow lakes, rivers, mountains) • Small, isolated populations are more likely to change • Isolated populations develop separately Sympatric Speciation • Chromosomal changes • Non-random mating that reduces gene flow – Polyploidy – Habitat differentiation – Sexual selection Adaptive Radiation • Evolution of many species from single common ancestor • Hawaiian islands – Colonizers arrive, diverge into different microhabitats Punctuated Equilibrium • Periods of stability, interrupted by periods of rapid evolution and change of species. • Fossil record isn’t exact, species can seem to just appear (could have taken 200,000 years to evolve into a unique form) • Transitional states aren’t always captured in fossil record Evolutionary Novelties • Complex structures evolve in increments from simpler versions • Thousands of “speciation events” take place as an evolutionary novelty is formed The Eye • Complex structures evolve from simpler structures Exaptations • Traits don’t evolve for future use, have to be beneficial in the present • Structures that evolved for one use can be used for other purposes – Ex. Feathers used for courtship or camouflage were also beneficial for flight Evolution of Development Genes • Depends on rate, timing and spatial patterns of changes • Heterochrony-change in rate or timing of developmental events Evolution is not goal oriented Species selection • Species that are around for the longest, and have the most successful offspring influence the direction of evolution • Species that are easily dispersed can give rise to many new species – Birds – Fish • Evolution is the interaction between organisms and their current environments • When conditions change, evolutionary trends change as well