Animal Reproduction and Development Quiz

Sexual Reproduction in Animals

• Learning Objectives:
  • Differentiate between internal and external fertilization
  • Differentiate the three types of embryos' development (oviparity, viviparity, ovoviviparity)

Fertilization

• External Fertilization:

  • Sperm and egg unite outside the female's body
  • Often occurs in aquatic environments
  • High number of gametes released
  • Massive zygotes produced
  • Often lack parental care
  • Environmental cues (temperature, pheromones) are important for synchronizing release of gametes.

• Internal Fertilization:

  • Sperm are deposited in or near the female's reproductive tract
  • Union takes place within the female's body.
  • Low number of gametes released.
  • Fewer zygotes produced
  • Often involves parental care
  • Requires complementary mating behavior and reproductive organs between the two sexes

Embryonic Development

• Oviparity:

  • Eggs are laid externally
  • Internal or external fertilization
  • Yolk in the egg provides nutrients for the embryo's development
  • Examples: frogs, snakes, lizards, birds, fish

• Viviparity:

  • Development of the embryos takes place within the female's body
  • Live birth
  • Internal fertilization
  • Nutrients & oxygen are obtained from the female via placenta
  • Mostly in mammals, but rare in fish, reptiles, and amphibians

• Ovoviviparity:

  • Embryos develop inside eggs retained within the mother's body
  • Live birth
  • Internal fertilization
  • No nutrition is provided except the egg's yolk itself
  • Examples: snakes, stingrays, seahorses, frogs

Animal Examples

• Cnidaria (e.g., Hydra):

  • Reproduction involves both sexual and asexual reproduction (budding)
  • Some Hydra species are hermaphroditic (possessing both male and female reproductive organs).
  • Asexual reproduction: Interstitial cells of the ectoderm divide to form swellings that become testes and ovaries.
  • Sexual reproduction: Ovum remains in the ovary, gets fertilized by sperm from the matured testes, developing into a mature Hydra in favorable conditions.

• Annelida (e.g., Earthworms):

  • Worms are hermaphroditic
  • Reproduce sexually by exchanging sperm during copulation via spermatheca
  • Clitellum secretes a mucous cocoon that slides off the worm, collects eggs from oviduct and sperms from spermatheca.
  • Fertilization takes place within the cocoon, which then slips into the soil, where eggs hatch later after a few weeks.

• Arthropoda (e.g., Insects):

  • Most insects reproduce sexually.
  • Reproductive adaptations include internal fertilization and oviparity (laying eggs).
  • Some insects exhibit viviparity (live birth).
  • Mating: Female produces chemical cues (pheromones) to attract males; males flap their wings and probe the females' abdomens when they sense the pheromones; during mating, the tips of the abdomens are held together; sperm package is inserted into the vagina.
  • Ootheca: Fertilized eggs are carried in a sac.

• Osteichthyes (e.g., Seahorses):

  • Ovoviviparous
  • Male incubates fertilized eggs within its pouch.

• Amphibia (e.g., Frogs):

  • Separate sexes
  • External fertilization
  • Amplexus: Male mounts female, sheds sperm on eggs being laid by the female in the water
  • Spawning is the releasing of sperm and eggs into the water.
  • Parental care exists in some species (incubating eggs on their back or in mouth/stomach)

• Reptilia (e.g., Snakes and Lizards):

  • Internal fertilization
  • Courtship behaviour & production of amniotic eggs are observed
  • Mostly oviparous or viviparous
  • Hemipenes: paired copulatory organs

• Aves (e.g., Birds):

  • Internal fertilization
  • 90% of bird species are monogamous
  • Courtship rituals
  • Singing, flamboyant plumage, and offering food all part of attracting mates.
  • Cloacal kiss: copulation involves a kiss with the male on the female's back & twisting his tail under the female

• Mammalia:

  • Internal fertilization
  • Monotremes (lay eggs)
  • Marsupials (give birth to immature young, which continue to develop in a pouch)
  • Eutherians (placental mammals, where embryo gets nutrients from mother)