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SPECIATION

SPECIATION. formation of a new species BIOLOGICAL SPECIES CONCEPT population or group of populations whose members have the potential to interbreed with one another to produce viable, fertile offspring, but who cannot produce viable, fertile offspring with members of other species.

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SPECIATION

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  1. SPECIATION • formation of a new species BIOLOGICAL SPECIES CONCEPT • population or group of populations whose members have the potential to interbreed with one another to produce viable, fertile offspring, but who cannot produce viable, fertile offspring with members of other species

  2. REPRODUCTIVE BARRIERS • impede 2 species from producing viable, fertile hybrids PREZYGOTIC • impede mating or hinder fertilization of egg • HABITAT --different  rare  no chance habitats encounters to mate • BEHAVIORAL --signals and unique behaviors used to attract mates --Ex. fireflies --Ex. meadowlarks

  3. PREZYGOTIC (cont.) • TEMPORAL --breed during different times of day, seasons, or years • MECHANICAL --anatomically incompatible --Ex. Flowering plants pollinated by insects or other animals • GAMETIC --gametes don’t fuse to form zygote --sperm may not be able to survive in female internal environment or specific molecules on coat of egg may prevent fusion

  4. POSTZYGOTIC • successful fertilization, but hybrid zygote doesn’t develop into a viable, fertile adult • REDUCED HYBRID VARIABILITY --developing zygote may abort at some embryonic stage • REDUCED HYBRID FERTILITY --sterile offspring; meiosis doesn’t produce gametes --Ex. horse + donkey  mule • HYBRID BREAKDOWN --1st generation hybrids are viable and fertile, but successive generations are sterile or feeble

  5. MODES OF SPECIATION • ALLOPATRIC --allos = other --patria = homeland --speciation takes place in populations with geographically separate ranges --gene flow is interrupted due to this separation

  6. MODES OF SPECIATION • SYMPATRIC --sym = together --patria = homeland --speciation takes place in geographically overlapping populations 1. polyploid plants = result from accident in cell division 2. allopolyploid = contribution of 2 different species to polyploid hybrid 3. animals = best example is L. Victoria ciclids --fish have exploited food sources and other resources differently --nonrandom mating

  7. Limitations of the BSC • no way to check interbreeding of extinct species • like fossils, which use morphological characteristics to distinguish species, existing species are classified based primarily on their appearance • cannot be applied to organisms that reproduce asexually

  8. OTHER SPECIES CONCEPTS MORPHOLOGICAL • appearance ECOLOGICAL • based on ecological niche (set of resources used by a species) • Ex. parasite defined by adaptations to host PLURALISTIC • factors important to identifying species vary GENEALOGICAL • species is set of organisms with unique genetic history (DNA, RNA, protein sequencing is basis)

  9. islands are living laboratories for the study of speciation --flurries of allopatric speciation occur when groups stray • adaptive radiation = evolution of many diversely adapted species from a common ancestor

  10. Gradualism • traditional evolutionary trees have gradual branching pattern --big changes occur by the accumulation of many small ones --however, gradual transitions are rarely seen in fossil forms --new forms appear suddenly --lack of connecting fossils confused Darwin • gaps can be partially explained by applying the allopatric model of speciation

  11. Punctuated equilibrium • species diverge in spurts of rapid change (long periods of stasis punctuated by episodes of speciation) • “sudden” may be thousands of years in evolutionary time • paleontologists base theories almost entirely on external anatomy and skeletons (changes in internal anatomy, physiology, and behavior cannot be observed)

  12. Speciation • exists on the boundary between microevolution (change in allele frequency) and macroevolution (cumulative change over millions of speciation events)

  13. Most evolutionary novelties are modified versions of older structures • examples of complex structures evolving in increments • complex eyes of various types evolved from simpler ones • exaptation = feature evolves in one context, but becomes co-opted for another function Ex. light, honey-combed bones of birds

  14. “Evolution is like modifying a machine while it’s running.”Karl Liem • interface between evolutionary biology and how organisms develop is termed “evo-devo” • many examples of slight genetic divergences leading to major morphological differences

  15. Growth & development • allometric growth = progression of proportions through development • heterochrony = evolutionary change in the rate or timing of developmental events • paedomorphosis = reproductive development accelerates compared to somatic development, resulting in the mature stage of the organism retaining body features that were juvenile structures • homeotic genes = control placement and spatial organization of body parts

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