Sex. Copulation. Coitus. Intercourse. All are synonyms for the act that delivers sperm, the male sex cell, into the body of a female. This, however, is only one strategy used by organisms to reproduce. Reproduction is one of the most fundamental characteristics of life and the mechanisms used for reproduction are as varied as the organisms themselves. Organisms are driven by the innate, instinctual urge to propagate their species. Two basic strategies exist in nature: asexual and sexual reproduction.
Asexual reproduction is nature’s cloning. Offspring created by asexual reproduction are genetically identical to each other and to the parent. This form of reproduction is fast and efficient but provides no genetic diversity for the species, therefore it is seen primarily in very stable environments. A wide variety of asexual mechanisms exist. It can be as simple as a cell dividing. For example, binary fission provides the major mechanism used by bacteria for reproduction. Other unicellular organisms such as amoebas, paramecia, and many forms of algae can reproduce in this manner.
More complex forms of asexual reproduction occur in multicellular organisms. Plants undergo vegetative propagation as seen when a potato sprouts. In animals, mechanisms include the formation of gemmules in sponges, budding as seen in many cnidarians, fission followed by regeneration, and parthenogenesis. Budding involves an offspring growing out of the body of the parent as with the formation of a colony of coral. Fission involves the splitting of the body of the adult and then is followed by the regeneration of the missing parts. An example of an organism that uses this process includes flatworms called planaria. The most unusual asexual mechanism in animals is parthenogenesis. This involves the development of an unfertilized egg into an adult. (1) Examples of organisms that use this process are honeybees and some other insects, rotifers, and whiptail lizards to name just a few.
Sexual reproduction creates offspring with a unique genetic makeup. Two parents contribute to this genetic compliment via the union of sex cells called gametes sperm and egg. The mechanisms utilized by sexually reproducing organisms are also varied. Two main forms of fertilization are practiced: external and internal fertilization. Many species utilize external fertilization. Species such as coral synchronize the release of millions of sperm and eggs into the surrounding environment in an event known as spawning. Some species of fish, amphibians such as frogs, and many other aquatic species also spawn.
Internal fertilization involves the union of sperm and egg inside the body of the female. However, even this form of reproduction does not always involve “sex”. Some species utilize specialized sperm cases known as spermatophores. These sperm packages are either placed into the environment or placed into the body of the female. For example, some species of scorpion carry out a complex mating dance wherein, the spermatophore is placed on the ground and the female is then positioned to receive it. (2) Squid, octopi, and some species of insects also utilize spermatophores.
Whether organisms are created in the good old fashion way, sex, or by such unique mechanisms as parthenogenesis, reproduction is a fundamental life process. With the diversity of life that exists on Earth, it is natural that a myriad of reproductive mechanisms have evolved to populate it.
1)Campbell, Neil and Reece, Jane. Biology, 7th edition. Benjamin Cummings, San Francisco, 2005.