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Time of Day Time of Year. Flowers Snails. Bullfrog x Leopard Frog. Courtship Sounds/Songs. Plants Broadcast Spawners. Horse (2n=64) x Donkey (2n=62)  Mule (2n=63). Fig. 24.3. Reproductive Isolation Limitations of Biological Species Concept

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slide1

Time of Day

Time of Year

Flowers

Snails

Bullfrog x

Leopard Frog

Courtship

Sounds/Songs

Plants

Broadcast Spawners

Horse (2n=64) x

Donkey (2n=62) 

Mule (2n=63)

Fig. 24.3

slide2
Reproductive Isolation
    • Limitations of Biological Species Concept
      • Mayr’s definition emphasizes reproductive isolation; may not work in all situations
        • Ex: Classifying fossil organisms
        • Ex: Species that reproduce asexually [prokaryotes, some protists, fungi, plants (e.g. bananas), animals (e.g. fishes, lizards)]
        • Ex: Multiple species are inter-fertile but remain distinct (e.g. orchids)
slide3
Speciation
    • Occurs when a population becomes reproductively isolated from rest of species
    • May be allopatric or sympatric
    • Allopatric Speciation
      • Population becomes geographically separated
      • Over time, mutation, genetic drift, natural selection  genetic divergence
      • Thought to be responsible for development of most new animal species
      • How do populations become isolated?
slide5
Speciation
    • Allopatric Speciation
      • Geographical barriers
        • Land bridges form, separating aquatic populations (e.g. Isthmus of Panama)
        • Land masses separate or split off from continents (e.g. South America & Africa)
        • Mountain ranges form
        • Water levels in water bodies become lower, creating multiple smaller pools
        • Rivers change course (Ex: oxbow lakes)
        • Glaciation occurs
        • Islands form and are colonized (e.g. Galàpagos, Hawaii, Madagascar)
        • Note: Geographic barriers for some species aren’t barriers for others
          • Ex: Birds and many insects can fly between isolated patches of habitat
          • Ex: Some fishes can swim long distances
          • Ex: Airborne pollen and drifting gametes in the ocean can be transported long distances
slide6
Speciation
    • Allopatric Speciation
      • Conditions Favoring Allopatric Speciation
        • Typically occurs at edges of parent population’s range
        • Splinter population (peripheral isolate) may be good candidate for speciation because:
        • Gene pool different from parent population
          • Likely to represent extreme of genotypic range
          • Speciation more likely if founder population small
          • Ex: Harris’ and white-tailed antelope squirrels on rims of Grand Canyon
        • Genetic drift within peripheral isolate
          • Can lead to rapid divergence from parent population
        • Natural selection
          • Diversifying or directional selection under conditions at extremes tolerated by parent population

Fig. 24.6

slide8
Speciation
    • Sympatric Speciation
      • Population becomes reproductively isolated without geographic separation
      • May be common in plants; importance in animals less clear
      • Plants
        • Autopolyploidy
          • Results from error in mitosis
slide10
Speciation
    • Sympatric Speciation
      • Plants
        • Autopolyploidy
          • Results from error in mitosis
        • Allopolyploidy
          • Error in meiosis + hybridization
slide12
Speciation
    • Sympatric Speciation
      • Plants
        • Allopolyploidy
          • Allopolyploids typically can’t produce fertile offspring with either parent (incompatible chromosome numbers)
          • If population of allopolyploids becomes established, typically one of three outcomes:
          • New species unable to compete successfully; goes extinct
          • New species competes successfully; coexists with parent species
          • New species competes very successfully; causes extinction of one or both parent species
slide13
Speciation
    • Sympatric Speciation
      • Plants
        • Allopolyploidy
          • May be very common in plants
          • Up to 80% of flowering plant species are polyploid
          • May account for 25-50% of plant species
          • Mechanism for very rapid speciation (single generation)
          • May account for rapid radiation of plants in fossil record and high diversity of flowering plants (>290,000 species)
slide14
Speciation
    • Sympatric Speciation
      • Animals
        • Mechanisms of sympatric speciation less well understood than in plants
        • Polyploidy usually lethal
        • Habitat differentiation
        • Ex:North American apple maggot fly (article)
        • Mutation  short-term isolation reinforced by non-random mating (sexual selection)
        • Ex: African cichlids
slide16
Speciation
    • Allopatric vs. Sympatric Speciation
      • Animals (usu. allopatric)
        • Isolating mechanisms?
      • Plants (usu. sympatric)
        • Isolating mechanisms?
slide17

Time of Day

Time of Year

Flowers

Snails

Bullfrog x

Leopard Frog

Courtship

Sounds/Songs

Plants

Broadcast Spawners

Horse (2n=64) x

Donkey (2n=62) 

Mule (2n=63)

Fig. 24.3

slide18
Speciation
    • Adaptive Radiation
      • Evolution of many diversely adapted species from common ancestor
      • Island chains offer unutilized habitat and open ecological niches
        • Ex: Colonization of Hawaii by honeycreepers
        • Ex: Silversword alliance in Hawaii
slide21
Speciation
    • Adaptive Radiation
      • Occurs when niche space is available
        • Ex: Radiation of mammals after K/T extinction
      • Radiation events often are associated with the appearance of novel features
        • Why?
        • Ex: Shells & skeletons first appeared at beginning of Paleozoic (may have facilitated radiation)