15: Animal Life Cycles
  • Introduction
  • Asexual Reproduction
    • Polyembryony and budding in parasitic flatworms
    • Budding and splitting in Cnidarians
      • Alternation of polyp and medusa forms
      • Repication and colony formation by budding
    • Parthenogenesis in aphids
  • Sexual life cycles
    • Simple life cycles
    • Complex life cycles
      • Examples
  • Oviviparity, Ovovivparity, and Viviparity
Additional Resources

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 Vocabulary List

Image Index for this Lab
Introduction
The life cycles of many familiar animals, like mammals and birds, appear less intricate than the life cycles of plants and fungi. As you will see, the life cycles of most animals are more complex than those of birds and mammals, but animals in general still lack some complications seen in other groups. The main simplifying factor is the lack of any alternation of diploid and haploid generations, at least of the type seen in plants. All animals have gametic meiosis, meaning that meiosis leads directly to the production of gametes. There is no independent haploid stage in the life cycle. Successful gametes unite to form a diploid zygote, which develops into an embryo and then into a functional organism. If this organism is lucky enough to survive, it may grow to maturity and produce gametes of its own. Finally, the cycle ends with the death of the individual (although death could have occurred at any step along the way). The processes of fertilization, development, growth, maturation, reproduction, and senescence occur in nearly all multicellular organisms, so some general principles apply to the life cycles of fungi, algae, plants and animals alike. However, each of these groups has its peculiarities, and even within each group special circumstances contribute to differences in life cycles.

The purpose of this laboratory is to survey some features of animal life cycles. You will note differences between the life cycles of animals and those of other multicellular organisms, and describe some of the variety of life cycles found in animals. You will be introduced to several groups of animals in this laboratory. Don't be alarmed, you will see many of these groups again.

Throughout the lab, keep in mind that an individual's alleles will disappear from the population if it does not produce at least one successful, reproductive offspring during its life. We'll see that there are many ways of reaching this end, some of which are constrained by fundamental features of the morphology and ecology of the animal.