Animal Reproduction: Asexual Reproduction

• Animal reproduction encompasses more than just male and female mating.
• Reproduction is the process by which new individuals are created from existing ones, ensuring the survival of a population.

Modes of Reproduction

• Reproduction, also known as procreation or breeding, is the biological process through which new organisms ("offspring") are produced from their parents.
• In the animal kingdom, reproduction occurs through either asexual or sexual means.

Asexual Reproduction

• Asexual reproduction allows an organism to reproduce without another organism.
• Results in new individuals without the fusion of egg and sperm.
• This form of reproduction is not limited to single-celled organisms.
• Cloning (of eukaryotes or prokaryotes) is a type of asexual reproduction.
• Offspring are genetically similar or identical to the parent
• Relies only on mitotic cell division.

Mechanisms of Asexual Reproduction

• Simple forms of asexual reproduction include:
  • Budding
  • Fission
  • Fragmentation and regeneration
  • Parthenogenesis

Budding

• Budding involves new individuals arising from the outgrowths of existing ones.
• Stony corals reproduce through budding.

Fission

• Splitting and separation of a parent organism into two roughly equal individuals.
  • Single-celled organisms like amoeba, paramecium, and stentor reproduce via fission.
  • Multicellular organisms like flatworms, hydra, and corals also reproduce via fission.
  • Microorganisms: Bacteria, archaea, yeast

Fragmentation and Regeneration

• The body breaks into several pieces, followed by regeneration of lost body parts or the creation of a new organism.
• Annelid worms, corals, sponges, cnidarians, and tunicates reproduce through fragmentation and regeneration.

Parthenogenesis

• Parthenogenesis happens when an egg develops into an embryo without fertilization.
• More common among invertebrates but also occurs in vertebrates.
• Bees, wasps, and ants reproduce through parthenogenesis.

Parthenogenesis Among Vertebrates

• Parthenogenesis in vertebrates is documented as a rare response to low population density.
• Komodo dragons and hammerhead sharks can produce offspring asexually when females are isolated from males.
• DNA analysis has found evidence of vertebrate parthenogenesis in the wild, such as genetically identical female sawfish.

Types of Parthenogenesis

• Complete (obligate) parthenogenesis
• Incomplete (cyclic) parthenogenesis
• Paedogenetic parthenogenesis

Sexual Reproduction

• Requires the fusion of gametes (specialized reproductive cells).
• Gametes are haploid, containing half the number of chromosomes found in normal (diploid) cells, and are formed during meiosis.
• Involves a male gamete (sperm) fertilizing a female gamete (egg) of the same species to create a diploid zygote.
• Offspring inherit genetic characteristics from both parents.

Gametes

• The female gamete (egg) is large and non-motile.
• The male gamete (sperm) is generally much smaller and motile.

Variations in Patterns of Sexual Reproduction

• Sexual reproduction requires the mating of a female and a male.
• Finding a mate can be challenging for some animals, leading to adaptations that blur the distinction between male and female.
• Hermaphroditism is a common adaptation among sessile animals like barnacles, burrowing animals like clams, and some parasites like tapeworms.
• These animals have limited mating opportunities.

Hermaphroditism

• Each individual has both male and female reproductive systems
• Hermaphrodites can mate with any other individual, with each donating and receiving sperm.
  • Sea slugs are an example
• Some hermaphrodites can self-fertilize, enabling sexual reproduction without a partner.
  • Corals are an example