Characteristics of Animal Reproduction

Some newborn animals hatch from eggs.

Many animals reproduce sexually in a process similar to human reproduction. However, the animal kingdom accommodates a wide range of variations on the cycle of conception, prenatal development and birth. For instance, humans take about 280 days to develop, while many birds take only 12 days, according to Your Veterinary Clinic, a veterinary center in the Netherlands. Some animals can even reproduce asexually.

Cell Division

All animals employ some form of cell division to reproduce. Dr. Michael Gregory, a science professor at Clinton Community College in Plattsburgh, New York, says many worms can reproduce asexually by dividing into two halves, with each half becoming a separate individual. Simple marine animals called cnidarians produce "buds," small polyps that break off to form new beings. Other animals, including humans, reproduce by causing an egg cell to divide over and over again until thousands of cells form an embryo.

Fertilization

In sexual reproduction, each animal contributes a specialized sex cell called a gamete to the process of conception, Gregory notes. A male gamete, or sperm cell, typically enters a female gamete called an egg cell. Each gamete contains half of the parent's genetic information. The sperm and egg combine their genetic data to create a new individual with traits from each parent. Asexual reproduction, by contrast, simply duplicates the genetic information of the parent without fertilization from a second gamete.

Reproductive Cycles

In many animals, the natural cycles of day and night help to time reproductive behaviors, Gregory says. Many creatures' brains have a pineal gland that produces the hormone melatonin during periods of darkness or night. Melatonin inhibits reproductive hormones, meaning that reduced melatonin levels during longer daylight hours correspond to breeding seasons.

Gestation

During a period called gestation, the newly created embryo inside an egg grows and develops into a creature capable of surviving outside the egg, continuing its growth as a hatchling or infant. Different animals require different gestation periods. Animals often gestate inside their mother's body, contained either in the egg or in a sac called the placenta. Other animals, such as birds and lizards, may develop inside eggs exposed to the external environment.

Birth

As gestation concludes, the fully formed animal emerges. Birds must peck their way out of hard protective eggshells. Animals that hold their developing young inside their bodies must push the live young out of a birth canal. Some animals enjoy the protection of the mother inside a nest or other safe habitat, but others must fight for survival on their own. Baby sea turtles, for instance, must crawl from sandy beaches into the ocean or die, according to Florida's Broward County Sea Turtle Preservation Program.

References

• Michael Gregory, Ph.D., Clinton Community College: Animal Reproduction
• Your Veterinary Clinic: Gestation Periods of Animals
• Broward County Sea Turtle Preservation Program: Hatchling Sea Turtles
• Michael Gregory, Ph.D., Clinton Community College: Sponges, Cnidarians
• Michael Gregory, Ph.D, Contact Page