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Biology LibreTexts

43.1A: Methods of Reproducing

  • Page ID
    14115
  • Animal reproduction is essential to the survival of a species; it can occur through either asexual or sexual means.

    LEARNING OBJECTIVES

    Describe reproduction in animals

    KEY TAKEAWAYS

    Key Points

    • Reproduction (or procreation) is the biological process by which new “offspring” are produced from their “parents”.
    • Asexual reproduction yields genetically-identical organisms because an individual reproduces without another.
    • In sexual reproduction, the genetic material of two individuals from the same species combines to produce genetically-different offspring; this ensures mixing of the gene pool of the species.
    • Organisms that reproduce through asexual reproduction tend to grow exponentially and rely on mutations for DNA variation, while those that reproduce sexually yield a smaller number of offspring, but have larger genetic variation.

    Key Terms

    • reproduction: the act of producing new individuals biologically
    • clone: a living organism produced asexually from a single ancestor, to which it is genetically identical

    Animal Reproduction

    Reproduction (or procreation) is the biological process by which new “offspring” (individual organisms) are produced from their “parents. ” It is a fundamental feature of all known life that each individual organism exists as the result of reproduction. Most importantly, reproduction is necessary for the survival of a species. The known methods of reproduction are broadly grouped into two main types: sexual and asexual.

    In asexual reproduction, an individual can reproduce without involvement with another individual of that species. The division of a bacterial cell into two daughter cells is an example of asexual reproduction. This type of reproduction produces genetically-identical organisms (clones), whereas in sexual reproduction, the genetic material of two individuals combines to produce offspring that are genetically different from their parents.

    During sexual reproduction, the male gamete (sperm) may be placed inside the female’s body for internal fertilization, or the sperm and eggs may be released into the environment for external fertilization. Humans provide an example of the former, while seahorses provide an example of the latter. Following a mating dance, the female seahorse lays eggs in the male seahorse’s abdominal brood pouch where they are fertilized. The eggs hatch and the offspring develop in the pouch for several weeks.

    image

    Sexual reproduction in seahorses: Female seahorses produce eggs for reproduction that are then fertilized by the male. Unlike almost all other animals, the male seahorse then gestates the young until birth.

    Asexual versus Sexual Reproduction

    Organisms that reproduce through asexual reproduction tend to grow in number exponentially. However, because they rely on mutation for variations in their DNA, all members of the species have similar vulnerabilities. Organisms that reproduce sexually yield a smaller number of offspring, but the large amount of variation in their genes makes them less susceptible to disease.

    Many organisms can reproduce sexually as well as asexually. Aphids, slime molds, sea anemones, and some species of starfish are examples of animal species with this ability. When environmental factors are favorable, asexual reproduction is employed to exploit suitable conditions for survival, such as an abundant food supply, adequate shelter, favorable climate, disease, optimum pH, or a proper mix of other lifestyle requirements. Populations of these organisms increase exponentially via asexual reproductive strategies to take full advantage of the rich supply resources. When food sources have been depleted, the climate becomes hostile, or individual survival is jeopardized by some other adverse change in living conditions, these organisms switch to sexual forms of reproduction.

    Sexual reproduction ensures a mixing of the gene pool of the species. The variations found in offspring of sexual reproduction allow some individuals to be better suited for survival and provide a mechanism for selective adaptation to occur. In addition, sexual reproduction usually results in the formation of a life stage that is able to endure the conditions that threaten the offspring of an asexual parent. Thus, seeds, spores, eggs, pupae, cysts, or other “over-wintering” stages of sexual reproduction ensure the survival during unfavorable times as the organism can “wait out” adverse situations until a swing back to suitability occurs.