Study Guide

Animal Reproduction In the Real World

  • Research

    Zebrafish to Study Embryo Development

    A model organism is a living thing which scientists study to learn more about biological processes. Then, they can apply this knowledge to humans (and other animals). When studying reproduction and embryo development it is much better to use a model organism because of ethical concerns. Plus, humans take a really long time to reproduce, they are expensive to feed, their embryos are inside their mother at all times, and it is hard to keep them in a small lab space.

    This is why scientists turned to the zebrafish, or Danio rerio. In fact, it has contributed more to scientific research than most scientists. Zebrafish gained popularity in the 1980's as a research tool.

    Zebrafish are inexpensive and easy to maintain in a small lab space. They are primarily used as a model organism in developmental biology because they are vertebrates with a quick reproduction time. Many organs begin to develop within 24 hours. After three days they are already hatched and swimming. At five days, most cells types have differentiated.


    A zebrafish showing off his stripes.

    Best of all, the embryo develops externally and it is transparent. This means that scientists can look at different cells and see which cells become brain cells and which cells become muscle cells, etc. During embryo development, different types of cells move and travel to special zones inside the embryo. It is almost like a gene inside the embryo calls out, "All future brain cells over here pronto."

    Scientists use zebrafish to learn which genes are in charge of organizing the cells. They look at fish with mutations in certain genes. Then, they look to see if those mutations caused disorder in the embryo. If mutating the gene caused developmental problems then they know the gene must normally be important.

    Zebrafish have been helpful in understanding the genetic control of embryo development. They can be just as helpful in understanding many other types of health problems as well such as cancer and heart defects. If you ever wander into a laboratory and something fishy is going on…it is probably a good thing.

  • Agriculture

    Animal Husbandry: Anything but Natural

    Raising animals is big business. For this reason, those who work in the agriculture industry try to streamline the process as much as possible. Instead of leaving animal reproduction to nature, they have engineered several technologies and techniques to produce as many animals as possible.

    One major technique is artificial insemination. This is when semen is taken from the male and implanted in a female. There are farmers, ranchers, or scientists who decide which animals will make the perfect match. They strive to create better and better animals through carefully arranged matings. The process of helping and encouraging animals to breed is called animal husbandry.

    In order for artificial insemination to work we need three things: a female animal in estrus, some primo semen, and a gun (an insemination gun). We will go over the basics of this process using cows and horses as examples.

    Selecting a Female Cow in Estrus

    Bull-pen Method: An infertile male, called a gomer bull, gets a pen (yep, a basic writing utensil) strapped to his chin. When the gomer bull tries to mount a female, the pen draws a line on her. So, basically, the gomer bull is just a big walking estrus detector/marking device.

    Painted Lady Method: Paint or chalk is put on the female cow's tail ahead of time. When it gets rubbed off, it shows that males have been trying to mount her.

    Fancy Shmancy Method: "Kamar heatmount detector" is a fancy version of the paint/chalk. It can be glued to rump of a female cow. It will change color due to pressure if a male mounts the female. This is more accurate since the bull has to mount it for several seconds. Therefore, it eliminates false positives from rubbing or other short non-estrus mountings.

    Semen Collection

    Manual Masturbation: A person physically arouses the animal.

    Tease-mare: Used in horses, they bring a female horse and a male horse near a device containing an artificial vagina. The male is brought to full arousal by the real female, but then they pull the switcheroo and he deposits his sperm into the artificial female instead.

    Penile Vibratory Stimulation: The animal’s penis is vibrated for stimulation.

    Electroejaculation: An electrical current is sent through the rectum into the prostate (this is only done with the animal unconscious under anesthesia) or directly through a syringe inserted into the testicles.

    When the goods are collected through any of these methods, they can be stored in liquid nitrogen (which is cold enough to turn a banana into a hammer instantly) until they are ready to be used.

    Insemination Process

    Now that we have the bullets, we can get out the insemination gun. One hand is inserted into the rectum (cattle, horses, and sheep prefer you to have small hands) to locate the cervix (entrance into the uterus). Next, the gun holding the sperm is inserted into the vagina and then the semen is deposited. Voilà. If we've done it correctly, the male of our choosing will impregnate the animal we want to be pregnant.

  • Environment

    Breeding Ground Destruction: Endangered Species

    Reproduction is important for species survival. What would happen if an animal's breeding ground were destroyed? Yep, you guessed it. No breeding grounds means no reproduction, which means no new animals.

    This is exactly what is happening to many species because of climate change. Increasing temperatures are changing the landscape of this planet. Places that have stood unchanged for thousands of years are quickly transforming into new types of environments or disappearing completely.

    In Australia, loggerhead turtles have to lay their eggs in sand that is a particular temperature for egg development. Cooler temperatures produce male eggs and warmer temperatures produce female eggs. Until now, the turtles have been using the same beaches every year without trouble. In other words, they have been producing a lovely number of male and female turtles. Now, however, the sand at these beaches is becoming too hot. More and more female turtles are being born. Without more male turtles, there will be no reproduction. As we learned at the beginning of the chapter, reproduction is necessary for a species to continue, and now loggerhead turtle numbers have dipped.

    A loggerhead sea turtle doing jumping jacks in his aquarium.

    The ferocious wolverine is also at risk from increasing temperatures. Wolverines live in cold northern climates. They can only reproduce in a climate with heavy snowfall because they dig their dens under the snow. The winter snow must be deep enough to last until May since it protects the developing offspring. Increasing temperatures in the wolverine's habitat are causing decreased snowfall. The area that provides sufficient snow cover is shrinking. If a wolverine digs a den that melts before the pups are ready they are at risk. Wolverines will have to adapt to decreased snowfall or they will be soon be endangered. If you thought wolverine was just a name of and X-man, then check out this video for some more info about these deadly cuddly creatures.

    Increasing temperatures are also putting Emperor penguins at risk. They rely on Antarctic ice for their breeding grounds. Climate change is causing the ice to melt and break apart at faster and faster rates. If this continues, they will have no place to meet their partners and raise their chicks. Some breeding grounds have already become abandoned. If all the ice disappears, there will be no more penguins with happy feet.

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