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Hybrid Animals LEVELED BOOK • Z a Reading A–Z Level Z2 Leveled Book Word Count: 2,335

Hybrid Animals LEVELED BOOK • Z a Reading A–Z Level Z2 Leveled Book Word Count: 2,335

2 LEVELED BOOK • Z A Reading A–Z Level Z2 Leveled Book Word Count: 2,335

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 . 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 interbreeding Hybrid Animals meiosis diverged offspring DNA reproduce embryos species expediting sterile fertilize susceptible genetic test tube hybrids transgenic

Photo Credits: Front cover, back cover: © Tom Reed/AP Images; title page: © Todd Pusser/ NPL/Minden Pictures; page 3: © Bettmann/Corbis; page 4: © Funwayillustration/ Dreamstime.com; page 5: © Yva Momatiuk & John Eastcott/Minden Pictures; page 9: © Splash News/Corbis; page 12: © Eriklam/iStock/Thinkstock; page 13 (top): © Olga Filatova/iStock/Thinkstock; page 13 (bottom): © Flip Nicklin/Minden Pictures; page 17: © Steven Kazlowski/NPL/Minden Pictures; page 20: © FLPA/ Rex/REX USA; page 21: courtesy of Steinkraus/University of Wyoming

Cover: A four-day-old zedonk—a rare cross between a and a — stands near her mom.

Title page: This wolphin is a cross between a and a false . Even her teeth show that she is a hybrid: bottlenose dolphins have Written by Cheryl Reifsnyder eighty-eight, false killer whales have forty-four, and she has sixty-six. Page 3: This is a zebra-donkey hybrid. www.readinga-z.com

Hybrid Animals Focus Question Level Z2 Leveled Book Correlation © Learning A–Z LEVEL Z2 Written by Cheryl Reifsnyder What are the pros and cons of interbreeding Fountas & Pinnell Y–Z different species? All rights reserved. Reading Recovery N/A www.readinga-z.com DRA 70+ What Is a Hybrid ? 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 of two different species . For instance, and donkeys are different species, but they are similar enough in appearance and behavior that they can mate with one another . If the mother is a , the Table of Contents baby is called a ; if the mother is a donkey, What Is a Hybrid Animal? ...... 4 the baby is called a .

Human-Made Hybrids ...... 7 When different species mate, they don’t always create a hybrid . Parent species that are too Natural Hybrids and the different may not have live offspring or, if they do, Tricky Definition of Species ...... 11 the young may be weak or unhealthy . When two When Species Overlap ...... 16 different species do produce healthy offspring, though—as in the case of the mule and hinny— What’s the Big Deal? ...... 18 the young usually have a combination of the Creatures by Design ...... 20 parent species’ characteristics . The more closely the parent species are related, the more likely it Animal Hybrids: Problem or Solution? . . . . 22 is that they will be able to have healthy hybrid Glossary ...... 23 offspring .

Hybrid Animals • Level Z2 3 4 Similar, but Not the Same By contrast, non-hybrid animals end up with a Female Parent Male Parent Offspring matched set of chromosomes . For instance, a horse Horse × Donkey = Mule receives one set of thirty-two chromosomes from Donkey × Horse = Hinny Mom and another set of thirty-two from Dad, making two copies of every in each Hybrid animals of the horse’s cells . A donkey receives thirty-one often have different names depending on from each parent, also ending up with two copies which species acted of every chromosome in each of its cells . as which parent. That’s because the In a hybrid animal, though, Mom’s characteristics of the chromosomes are different from Dad’s . A mule hybrid animal are doesn’t have two copies of anything—just a often determined by jumble of sixty-three chromosomes, none of which which species was have matches . the mother. In the case of donkey-horse The mule’s chromosomes don’t need to hybrids, are matched pairs for normal cell : the generally larger and hardier than . mule chromosomes simply form copies of themselves and sort one copy into each of the new cells . However, when the mule tries to make reproductive cells, those unmatched chromosomes Like many hybrid animals, mules and hinnies cause problems . are sterile—unable to make sperm or eggs to produce offspring . This situation stems from the Unlike most cells, sperm and egg cells have fact that different species of animals often have only one copy of each chromosome . Getting different numbers of chromosomes . Mules and to that one-copy state requires a process called hinnies receive nonmatching genetic information meiosis, which requires each chromosome to line from their horse and donkey parents: thirty-two up with its match so one member of each pair can horse chromosomes from one parent and thirty- be sorted into separate cells . one donkey chromosomes from the other .

Hybrid Animals • Level Z2 5 6 Since the horse and donkey chromosomes and produce lower in fat than standard beef . don’t look very much like one another, they can’t However, buffalo are difficult to handle and can form nice pairs . The dividing cell has a hard time sometimes be dangerous . sorting the right chromosomes into the right are as easy to handle as ordinary places; some offspring cells receive too many but are much hardier and easier to care for . They chromosomes and others receive too few . These have an efficient digestive system, which allows cells rarely survive . them to eat and bushes as well as grass . -Made Hybrids Unlike cattle, they are able to withstand both Sometimes people hybrids intentionally, hot and cold temperature extremes . Like buffalo, hoping to produce a hybrid that has the best their meat is low in fat, with more protein than qualities of both parent animals . Mules have been standard beef . Unlike or mules, beefalo deliberately bred since ancient times because they are able to reproduce, as long as breeders are are hardier and more sure-footed than horses . mindful of their math . It turns out that the ratio Mules are also easier to care for than horses—less of three-eighths bison to five-eighths cow is ideal . likely to overeat, less susceptible to heat, and less As long as the proportion of bison is kept at or prone to leg injuries . below the three-eighths level, there are few—if any—reproductive problems . Zebra hybrids, sometimes called zebroids, are a more recent of hybrid . are A , which is a hybrid of a male and wild animals that are difficult to train for riding a female , looks like a supersized lion with or carrying packs, but they aren’t susceptible faded tiger stripes . grow about twice as to the same diseases as domesticated equines . large as either parent species, with Hercules, the Zebroids inherit a gentler personality from their world’s biggest male liger, weighing in at nearly domesticated parent as well as resistance to 1,200 pounds (544 kg)! They are usually tawny disease from their wild parent . colored, like , but with pale bellies, like . A similar hybrid, the , is created by breeding Beefalo, another recent hybrid, were created the opposite genders of parents—a female lion to combine the traits of buffalo (bison) and and a male tiger . domesticated cattle . Buffalo are hardier than cattle

Hybrid Animals • Level Z2 7 8 Hybrid Parent Species (Female, Male) Characteristics

• Size and strength of a horse Hercules, the Mule Horse × Donkey • Endurance, hardiness, and sure- world’s biggest footedness of a donkey , poses with his little brother • Like a mule, but smaller and Hinny Donkey × Horse Aries. Both less hardy are ligers. • Cattle-like temperament • Buffalo-like in that they are Beefalo* Bison × Bovine hardier, have a more efficient digestive system, and yield lower-fat meat * Ideal ratio: 3/8 bison and 5/8 cow

Zedonk Zebra × Donkey Ligers never occur naturally since lions and • Disease resistance of a zebra tigers live in different . However, these • Temperament midway between a zebra’s and a domestic animal’s strange mixes can draw a crowd, and although Zorse Zebra × Horse • Striking appearance that is accredited avoid interbreeding the big , a combination of the parent both independent breeders and exotic animal species’ look Zony Zebra × preserves have tried their at making money

from them . Breeders have created other • Tawny coat like a lion, partial hybrids as well: ( × lion), jaguleps Liger Tiger × Lion stripes, on some males ( × leopard), and lijaguleps (lion × jagulep) . • Larger than either parent

The males of these hybrids are usually sterile, but • Tiger-sized, appearance midway Tigon Lion Tiger the females are usually able to offspring . × between a tiger and lion

Until recently, people could only obtain • Larger than domestic house cat, Savannah Domestic African × long legs, -like fur pattern hybrids of similar species that might be willing Cat house cat serval • More -like in their behavior to mate with each other . Other species, while somewhat similar, were unwilling . For instance, • Strong, but smaller than a even when given the opportunity, and × Camel • Better temper and easier to handle than a camel would rarely mate . However, modern

Hybrid Animals • Level Z2 9 10 medicine provided a way to fertilize eggs in a test tube instead of inside an animal . As a result, Great Dane the first camel-llama hybrid—the cama—was born . Scientists hope the cama will couple the camel’s hardiness and strength with the llama’s calmer disposition .

Natural Hybrids and the Tricky Definition of Species You might have the impression that hybrids Chihuahua only occur when breed them intentionally, but that’s not the case . Hybrids can arise whenever related animal species interbreed—which can happen any time they live and interact in the same environment .

It can be surprisingly difficult to identify which animals are hybrids, though, because it can Same or Different Species? be surprisingly difficult to define what constitutes It can be difficult to tell whether two animals are the same separate species . species based on appearance alone. These two dog look quite different from one another, but they are considered the same Scientists often define a species as a group of species—Canis lupus familiaris. Two fruit may look like twins individuals with two important characteristics . but actually be different species.

1 . They have the potential to interbreed in . Under this definition, most hybrids don’t 2 . They can produce viable offspring if they do qualify as separate species because they cannot interbreed—that is, their offspring are healthy reproduce . Some are unable to reproduce because enough to produce offspring of their own . they’re sterile, like mules, but even hybrids that can make reproductive cells may not be able to have offspring .

Hybrid Animals • Level Z2 11 12 Can a - Hybrid Find a Mate? Take the narwhal- hybrid spotted It depends; which narwhal off the coast of Greenland in 2009 . Scientists mate is male and which is female? don’t know whether it is biologically capable of narwhal- beluga producing reproductive cells, but even if it can, beluga Maybe? it needs a mate to produce offspring . Narwhal- hybrid beluga whale hybrids (narlugas? barwhals?) are narwhal- Probably not; beluga narwhal-beluga hybrids rare, so it is unlikely to come across another of hybrid are extremely rare. its kind . Also, a male hybrid may not have much success with a female narwhal because In other cases, the line between hybrids and it lacks the male narwhal’s characteristic spiral distinct species is trickier to determine . tusk—which turns out to be an important factor provide a great example of this situation . when a female narwhal chooses a mate . To understand ring species, imagine a group of preschoolers sitting in a circle . Each preschooler represents a separate species sitting within arm’s reach of two others . Now imagine them playing a game of telephone . The first child whispers something to the second, who whispers to the next, and so on until the last child gets the message, which is usually something completely beluga different from the starting words .

The changes in the whispered message are similar to the changes you see around a circle of ring species: each species is similar to those on either side, until you reach the point where the circle’s ends overlap . Any two adjacent species in a ring species group are similar enough that they narwhal can—and do—interbreed, until the overlap point .

Hybrid Animals • Level Z2 13 14 When Species Overlap Evidence suggests that ring species members picta have changed slowly as they have adapted to (PIK-tuh) specific environmental conditions . Their ranges overlap in some regions; where they do, hybrids oregonensis arise . With far more of each parent species than (or-e-guh-NEN-sis) the hybrids, though, these hybrids do not greatly San Joaquin Valley platensis (plah-TEN-sis) influence the parent .

Sometimes, though, two species that were isolated from one another are brought together abruptly . In this situation, hybrids can cause xanthoptica croceater (zan-THOP-ti-kuh) (KROH-see-ay-tur) problems for their parent species . They may compete for food, , or other resources . They may compete for mates . They may even change the genetic makeup of one or both of the original species . eschscholtzii klauberi (es-SHOHLT-zee-y) (KLOU-bur-y) Over the past decades, changing environmental conditions have brought together numerous species that were previously separated . Climate change has had its greatest effects in the Arctic, which is warming two to four times faster than the rest of the world . Animal species native to the Arctic region are changing their natural ranges in response to rising temperatures and melting sea ice . Animals from farther south that might have previously found northern regions too cold are extending their ranges northward .

Hybrid Animals • Level Z2 15 16 As a result, species that used to be What’s the Big Deal? geographically separate—such as grizzly and So grizzlies and polar might have some polar bears—are now interbreeding . One of the little brown-and-white grolar bear cubs . Is that first grizzly-polar bear hybrids, called a grolar bear, really a big deal? was spotted in 2006 . The bear had thick white fur, brown legs and paws, and a wide grizzly-like head . If there were plenty of polar bears and grizzly Other grolar bears have been identified since, bears roaming the world, the answer might be no, a few hybrids wouldn’t be a big deal—especially with increasing frequency, which suggests that if hybrids only occurred in a few areas where grizzlies and polar bears are interbreeding fairly the bears’ ranges overlapped . The problem is that frequently in the wild . At least one was a second- polar bears are at risk of going extinct . When generation hybrid, which indicates that the there aren’t that many of a species to start with, hybrids are able to reproduce . every birth makes a difference . Every polar bear that breeds with a grizzly is a polar bear that isn’t bringing more polar bears into the world .

It becomes a numbers game . The more polar bears that interbreed with grizzly bears, the more their —specialized for surviving in the harsh Arctic environment—get diluted by grizzly bear genes . Eventually, polar bears might simply disappear .

On top of that, grolar bears may not be very well adapted to either of their parents’ environments . Grolar bears in a German seem to have a polar bear’s instinct for seal hunting but not its strong swimming ability . Do these hybrids While not a confirmed grolar bear, this bear’s body shape, short neck, survive as well as non-hybrids in the wild? At this and odd face (when compared to other polar bears) suggest that it is a grizzly-polar hybrid. point, no one knows .

Hybrid Animals • Level Z2 17 18 The Problem with Hybrids and Threatened Species

If one species greatly × outnumbers another, Polar Bear Grizzly Bear hybridization can overwhelm the one with × fewer numbers. Every time a polar bear or polar southern flying ½ Polar Bear Grizzly Bear bear hybrid breeds with ½ Grizzly Bear a grizzly, the polar bear Invasion! genes become further The Arctic isn’t the only region where animal species are × diluted. Unless polar bears beginning to bump into one another. In Ontario, Canada, southern breed with other polar flying seem to be taking advantage of the warmer climate ¼ Polar Bear Grizzly Bear ¾ Grizzly Bear bears as much as—or to expand their range northward—into the of their cousins, more than—they breed the northern flying squirrels. with grizzlies, they could 1 / 8 Polar Bear The southern flying squirrels are smaller, with white belly fur; 7 / 8 Grizzly Bear simply disappear. the northerners have gray-and-white belly fur; and the hybrids, as you might expect, have a mash-up of the parents’ traits. Scientists studying one band of northern squirrels say that 4 percent of the Although hybrids are often sterile, scientists animals in the group are now hybrids of the two species. Obviously, expect that many arctic —grizzly and these squirrels are similar enough genetically that the hybrids are polar bears, seals, sea lions, and walruses, to name able to reproduce! a few—will be able to interbreed successfully with their southern cousins . In fact, scientists recently Creatures by Design published a list of thirty-four hybrids of arctic What if you want a hybrid animal that mammals that are likely to occur as climate combines traits from species so different that change brings formerly isolated species into even mating in a test tube won’t work? How about contact . Because northern animal species these traits: the ability to produce silk diverged from their southern relatives fairly (an ability unique to ) and the ability to recently in evolutionary terms, it is likely that produce large quantities of milk (an ability limited many of the hybrids will be fertile . to mammals)?

Hybrid Animals • Level Z2 19 20 Spider silk is one of the strongest fibers Since spider genes were artificially in the world—stronger and more flexible than introduced—inserted into embryos in steel or Kevlar . It’s also hypoallergenic and has the laboratory—“spider ” are considered antimicrobial properties, making it ideal for use in transgenic rather than hybrid animals . medicine . The fine, nearly invisible thread could Animal Hybrids: Problem or Solution? be used during eye surgery, for example, or even to create artificial ligaments . Unfortunately, In the past, scientists thought that animal a single ounce of spider silk requires fourteen hybrids represented an evolutionary dead end . thousand spiders—and since spiders tend to eat Most hybrid offspring were sterile, and while their neighbors, large-scale “spider farms” are out the parents were probably well adapted to their of the question . specific environments, by combining their characteristics, the hybrid would end up adapted Since standard animal hybridization to neither . In most cases, this is exactly what we techniques won’t work for species that are too see in nature: hybrid species tend to be poorly different from one another, scientists used genetic adapted to their environments and often fail to engineering techniques to insert silk proteins survive and reproduce . from the golden orb weaver spider into goat DNA . Goats then produce the spider silk proteins in However, when animals face drastic their milk, and scientists environmental changes, the process of extract those proteins in may occur too slowly for species to adapt to the lab . The process and changing conditions . Hybrids provide a way for results are still imperfect, two species to exchange genetic information, but researchers hope to potentially combining it in new and useful ways . engineer goats that can Are hybrid animals a threat to biodiversity produce useful amounts in the world today? Or are they nature’s way of of spider silk someday . expediting the process of in the face of rapidly changing environmental conditions? They These “spider kids” are twins: Armstrong (left) and may be a of both—only time will tell! (right).

Hybrid Animals • Level Z2 21 22 Glossary meiosis (n.) the process of cellular division biodiversity (n.) the of forms on that reduces the number of or in a specific or chromosomes to half, producing (p . 22) reproductive cells that contain one of each pair of homologous chromosomes (n.) rod-shaped structures inside cells chromosomes (p . 6) that carry genes (p . 5) offspring (n.) a person’s child or another diverged (v.) moved apart from the same point; animal’s young; descendants (p . 4) became different (p . 19) reproduce (v.) to make offspring that are similar DNA (n.) a code that carries genetic to the original living thing (p . 8) information about a living thing; abbreviation of deoxyribonucleic species (n.) a group of living things that acid (p . 21) are physically similar and can reproduce (p . 4) embryos (n.) unborn offspring in the early stages of growth (p . 22) sterile (adj.) not able to produce offspring (p . 5) expediting (v.) speeding up something, especially susceptible (adj.) easily affected or influenced; a process (p . 22) vulnerable (p . 7) fertilize (v.) to combine male and female test tube (n.) a narrow glass tube that is closed reproductive cells to create a new at one end and open at the other animal or (p . 11) end, commonly used in scientific laboratories (p . 11) genetic (adj.) having to do with and variation in living things (p . 5) transgenic (adj.) of or relating to an whose DNA has been altered by hybrids (n.) offspring produced from two the transfer of genes from another different parent types, breeds, species or breed (p . 22) or species (p . 4) interbreeding (v.) mating two different species of animals to form offspring with a combination of traits from each parent; crossbreeding (p . 9)

Hybrid Animals • Level Z2 23 24

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