Speciation

• Species is defined by Ernst Mayr (Evolutionary Biologist). It is a population whose members can interbreed and produce viable, fertile offspring.
• Reproductive Isolating Mechanisms

  1. Pre-zygotic Barriers - various forms of isolation
  2. Post-zygotic Barriers - generally related to fertility and viability of offspring
• pre-reproduction barriers - there is an obstacle to mating or to fertilization if mating occurs.
• pre-reproduction barriers

  1. geographic isolation
  2. ecological isolation
  3. temporal isolation
  4. behavioral isolation
  5. mechanical isolation
  6. gametic isolation
• geographic isolation

  •New species occur in different areas

  •physical barrier separated ancestor species
• ecological isolation

  •Species occur in same region, but occupy different habitats so they rarely encounter each other
• temporal "time" isolation

  •Species that breed during different times of day, different seasons, or different years cannot mix gametes.
• behavioral isolation

  •Unique behavioral patterns & rituals isolate species

  •identifies members of species

  •attract mates of same species

  •courtship rituals, mating calls
• mechanical isolation

  •Morphological differences can prevent  successful mating
• gametic isolation

  •Sperm of one species may not be able to fertilize the eggs of another species

  •biochemical barrier

  -sperm cannot penetrate the egg

  -receptor recognition: lock & key between egg & sperm

  •chemical incompatibility

  -sperm cannot survive in the female reproductive tract
• post-reproduction barriers

  •Prevent hybrid offspring from developing into a viable, fertile adult
• Reduced hybrid viability

  •Genes of different parent species may interact & impair the hybrid’s development
• reduced hybrid fertility

  •Even if hybrids are vigorous they may be sterile

  •chromosomes of parents may differ in number or structure & meiosis in hybrids may fail to produce normal gametes
• hybrid breakdown

  •a mechanism that reduces the viability or reproductive capacity of hybrid offspring.
• Hybrid zygote abnormality

  • is a type of postzygotic barrier in which hybrid zygotes fail to mature normally.
• gradualism

  • Gradual divergence over long spans of time•assume that big changes occur as the accumulation of many small ones
• punctuated equilibrium

  •Rate of speciation is not constant

  •rapid bursts of change

  •long periods of little or no change

  •species undergo rapid change when they 1st  bud from parent population
• Mode of speciation

  1. allopatric
  2. parapatric
  3. sympatric
• role of speciation

  1. gradualism
  2. punctuated equilibrium
• being reproductively compatible

  • key component of species
• reproductive isolating mechanisms

  • prevents nascent species from interbreeding