Hybrid Animals LEVELED BOOK • Z A Reading A–Z Level Z Leveled Book Word Count: 1,647 Connections Hybrid Animals Writing Write an informative article for a local paper on the science of hybrid animals. Include the benefits and challenges so readers are fully informed. Math Research five different hybrid animals not included in the text. Describe how the hybrids compare to their two parent species. Use glossary words in your description. 2 1 •Z Z•Z Written by Cheryl Reifsnyder Visit www.readinga-z.com for thousands of books and materials. www.readinga-z.com Words to Know adapt offspring Hybrid Animals DNA reproduce fertilize species genetic sterile hybrids test tube interbreeding transgenic Photo Credits: Front cover, back cover: © Tom Reed/AP Images; title page: courtesy of Holly Steinkraus/University of Wyoming; page 3: © Jeff Pawloski/Barcroft Media/ Landov; page 4: © Funwayillustration/Dreamstime.com; page 5: © Yva Momatiuk & John Eastcott/Minden Pictures; page 7: © Bettmann/Corbis; page 8: © Splash News/Corbis; page 9: © Eriklam/iStock/Thinkstock; page 10: © Chris Mattison/ NPL/Minden Pictures; page 13: © Steven Kazlowski/NPL/Minden Pictures Cover: A four-day-old zedonk—a rare cross between a zebra and a donkey— stands near her mom. Title page: You can’t tell by looking, but twin kid goats Armstrong (left) and Sweet Pea (right) contain DNA from spiders! Page 3: This wolphin is a cross between a bottlenose dolphin and a false killer whale. Even her teeth show that she is a hybrid: bottlenose dolphins have eighty-eight, false killer whales have forty-four, and she has sixty-six. Written by Cheryl Reifsnyder www.readinga-z.com Hybrid Animals Focus Question Level Z Leveled Book Correlation © Learning A–Z LEVEL Z Written by Cheryl Reifsnyder What are the pros and cons of interbreeding Fountas & Pinnell U–V different species? All rights reserved. Reading Recovery N/A www.readinga-z.com DRA 50 What Is a Hybrid Animal? The ancient Greeks imagined creatures that were half one animal and half another—centaurs and minotaurs, griffons and manticores. These creatures may not exist, but animal hybrids do. They combine the traits of different species—and they are more common than most people realize. A hybrid is an animal that has parents of two different species. For instance, horses and donkeys are different species, but they are similar enough Table of Contents in appearance and behavior that they can mate What Is a Hybrid Animal? .................. 4 with one another. If the mother is a horse, the baby is called a mule, and if the mother is a Human-Made Hybrids ...................... 6 donkey, the baby is called a hinny. Natural Hybrids and the If different species mate, they don’t always give Tricky Definition of Species ................. 9 birth to hybrid young. Parent species that are too When Species Overlap ..................... 11 different may not have live offspring, or their young may be weak or unhealthy. When two Whats the Big Deal? ....................... 13 species do produce healthy offspring, though, the Creatures by Design ....................... 14 young usually have a combination of the parent species’ characteristics. The more closely related Animal Hybrids: Problem or Solution? ....... 15 the parent species are, the more likely they are to Glossary ................................. 16 have healthy hybrid offspring. Hybrid Animals • Level Z 3 4 Similar, but Not the Same Horse and donkey DNA carry much of the Female Parent Male Parent Offspring same information, which is why mules can Horse × Donkey = Mule survive. Even though their cells don’t have a full Donkey × Horse = Hinny set of horse DNA or donkey DNA, they still have all the information they need to function. Hybrid animals often have different names However, information is arranged differently depending on which on horse and donkey DNA. When the mule’s body species acted as which parent. That’s because tries to make reproductive cells, the mismatched the characteristics of the DNA molecules throw a wrench in the gears. hybrid animal are often determined by which Two species have to be closely related to species was the mother. produce hybrid offspring when they mate, but In the case of donkey- they have to be really closely related for their horse hybrids, mules offspring to make healthy reproductive cells. are generally larger and Mule hardier than hinnies. Human-Made Hybrids People have bred hybrid animals, such as Most of the time, hybrid animals can’t mules, since ancient times. Mules are hardier and reproduce. That’s because reproductive cells— more sure-footed than horses. They are also less eggs and sperm—are trickier to make than sensitive to heat and less prone to injury. regular body cells. Zebra hybrids, sometimes called zebroids, are Take the mule: every cell in its body gets half a more recent hybrid. Wild zebras are extremely its DNA from Mom (a horse) and half from Dad difficult to train but are resistant to many diseases (a donkey). DNA molecules carry instructions for that affect horses and donkeys. Zebroids inherit a how cells operate—instructions for everything gentler personality from their domesticated parent from hair color to ear shape. They encode the and resistance to disease from their wild parent. information that makes a horse a horse and makes a donkey a donkey. Hybrid Animals • Level Z 5 6 Ligers never occur naturally since lions and tigers live in different habitats. Accredited zoos avoid interbreeding the big cats, A zebra-donkey hybrid shows traits of both. but independent breeders sometimes Another recent hybrid, the beefalo, combines the Hercules, the world’s biggest cat, poses raise big cat hybrids traits of bison (buffalo) and domesticated cattle. with little brother Aries. Both are ligers. as curiosities. Bison are much hardier than cattle and produce Other big cat hybrids include leopons (leopard × meat lower in fat than standard beef. However, lion), jaguleps (jaguar × leopard), and lijaguleps like many wild animals, bison are difficult—even (lion × jagulep). dangerous—to handle. Until recently, people could only obtain Beefalo hybrids are as easy to handle as hybrids between species similar enough to mate ordinary cattle but have bison’s hardiness and with each other. Some species, while somewhat independence. Like bison, beefalo are able to similar, can’t—or won’t—mate, so their hybrids withstand both hot and cold temperature extremes. didn’t exist. For instance, even if given the They produce meat that is low in fat and the bad opportunity, camels and llamas would rarely mate. type of cholesterol, with more protein than beef. When modern medicine provided a way to A liger is a hybrid of a male lion and a female fertilize eggs in a test tube, a camel-llama hybrid tiger. Ligers grow about twice as large as either became possible. Scientists hope this hybrid, parent species; the largest known healthy male called a cama, will couple the camel’s strength and weighs nearly 1,200 pounds (544 kg)! They are hardiness with the llama’s sweeter disposition. usually tawny colored, like lions, with pale bellies and faint stripes, like tigers. Hybrid Animals • Level Z 7 8 Natural Hybrids and the Ring species provide a great example of how Tricky Definition of Species it can be difficult to determine the line between Hybrid animals can arise whenever related hybrids and distinct species. To understand ring species interbreed—which can occur whenever species, imagine a group of preschoolers sitting they live in the same environment. Identifying in a circle. Each child represents a separate species hybrids can be surprisingly difficult, though, sitting within arm’s reach of two others. because it’s surprisingly difficult to define when animals are separate species. Scientists often define a species as a group of picta individuals with two important characteristics. (PIK-tuh) oregonensis (or-e-guh-NEN-sis) platensis 1. They have the potential to interbreed in nature. San Joaquin Valley (plah-TEN-sis) 2. If they do interbreed, they produce healthy, fertile offspring—that is, offspring that are able to reproduce. xanthoptica croceater (zan-THOP-ti-kuh) (KROH-see-ay-tur) Same or Different Species? Great Dane It can be difficult to tell whether two animals are the same species based on appearance alone. These two dog breeds look quite different from eschscholtzii klauberi (es-SHOHLT-zee-y) (KLOU-bur-y) one another, but they are considered the same species—Canis lupus familiaris. Two fruit flies may look like twins but Chihuahua actually be different species. Hybrid Animals • Level Z 9 10 Now imagine them playing a game of Sometimes two species that were isolated from telephone: the first child whispers to the second, one another are brought together abruptly. In this who whispers to the next, and so on. When the situation, hybrids can cause problems for their last child gets the message, it’s usually completely parent species by competing for food, territory, different from the starting words! or other resources. They may compete for mates, potentially changing the genetic makeup of the The changes in the whispered message are original species. similar to the changes seen around a circle of ring species. Each species is similar to those on either Over the past decades, changing side—similar enough that they can interbreed— environmental conditions due to climate change until you get back to the starting point. The have brought together many previously separated starting and ending species are the most different species. Climate change has had its greatest effects from one in the Arctic, where some native species are another changing their natural ranges in response to and cannot rising temperatures and melting sea ice. Animals interbreed. from farther south that might have previously found northern regions too cold are extending their ranges northward.