Animal Fertilization

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•  Fertilization in animals can be internal or external

External Fertilization

  • External fertilization involves the fusion of gametes (egg and sperm) outside of the body of a parent
  • It is most common in aquatic animals, where the water acts as a medium via which the gametes can travel
  • This method of fertilization is susceptible to environmental influences, such as predators and pH changes
  • Consequently, species that reproduce this way usually release large quantities of gametes to compensate for losses
  • The process of releasing gametes into the water is called spawning

External Fertilization – Mass Spawning by Coral

 Video caption from Jonathan Bird’s Blue World ( 

Internal Fertilisation

  • Internal fertilization involves the fusion of gametes (egg and sperm) inside of the body of a parent
  • This requires a method by which the gamete of one parent can be introduced inside the body of another (e.g. copulation)
  • Terrestrial animals typically use internal fertilization so as to prevent exposure and desiccation of gametes or embryos
  • Internal fertilization offers more protection to the gametes and embryos, but at a potential survival cost to the parent 

Internal Fertilisation – Fusion of an Egg and Sperm