Hua Mei tends to one of her oneday-old twins. Cubs cry to get mom's attention. For more on pandas and to watch a real-time video of the San Diego Zoo's bears, visit: www.sandiego2oo.org/ pandas/pandacam/index.html
With scientists pandas a^ raising heaithy cu captivity. These ba hears cnuid l(eep the species fror disappearing] BY BRITT N D R L A N D I R Last year, a California celebrity left her sunny home for a new address. The star a popular panda named Hua Mei (WAH MAY). The bear first grabbed headlines when she was bom at the San Diego Zoo in 1999. She was the first Giant Panda, Ailumpoda meumoleiica (AL-yer-uh-POH-dah mel- AN-uh-LOO-kah), in the United States to survive after being bom in captivity. Hua Mei stayed at the zoo until she was old enough to have cubs. Then, last February, she moved to China's Wolong (WOO-long) Giant Panda Breeding and Research Center. There, as part of an intemational project to breed pandas, scientists introduced Hua Mei to potential mates. And last September, she made headlines again this time after delivering two cubs. "We still tliitik of her as our baby; now she has Lwins of her own," says Barbara Durrant, the head reproductive physiologist (scientist who One of Hua Mei's m twins about w one month old tries to lift itself up.,^ SCIENCE WORLD B
studies reproduction) at the San Diego Zoo's Department of Conservation and Research for Endangered Species. Hoping to save pandas from extinction (no organisms of the species remain), biologists around the world are working together to try to breed the bears in captivity. As part of the project, China panda's native land lends pandas (like Hua Mei's parents) to foreign zoos with the hope that the bears will have cubs. Then, the offspring leave mom and dad behind and move to Chinese breeding centers to start a new family. "BEARLY" HANGING ON With fewer than 1,600 wild pandas remaining, scientists think captive-bom bears may help rescue wild pandas one day. The bears once roamed over most of China and into other countries to the south. But humans have taken over most of their forest home (see map, right). "Pandas have been pushed to the edges of China that humans do not want to live in," says Colby Loucks, a conservation scientist at the Worid Wildhfe Fund. Squeezed into small, isolated patches of steep forest, the bears' lives are at risk. For instance, bamboo makes up about 99 percent of a panda bear's diet. In the 1980s, large patches of China's bamboo died off Surrounded by humans, over 200 wild pandas were tanable to move to areas where bamboo still grew and the bears starved to death. To prevent another disaster, scientists are working to protect panda habitat (region where an animal lives). Then, they nxay be able to boost the panda poptilation one day by releasing captive-bom bears into the wild. PERFECT TIMING For now, scientists are trying to learn how to breed pandas in captivity. Their first step with Hua Mei: setting her up on several blind dates. Captive male pandas are very picky about their female partners. The scientists needed to fmd Hua Mei's perfect match. The next, step choosing the moment to introduce the bears to eacb otber was even trickier. That's because a female panda's estrus, the time during which she can become pregnant, occurs only once a year for one to foiu* days. Ditrijig this time, the female produces an egg (female sex ceil). The egg then needs to he fertilized, or joined, with a spenn (male sex cell). Unfertilized eggs don't survive long, so fertilization needs to happen quickly. "[There is] a very, very small window about 24 hours [in which fertilization can occur]," says Durrant. In the wild, solitary female pandas call out to alert nearby males that the time is right. In captivity, scientists need to introduce pandas normally kept separated to each other during this period. If fertilization occurs, a single cell called a zygote forms from the joined egg and sperm. Then, a cycle of cell divisions begins to form a panda fetits (imbom yoting) and eventually a cub (see Nuts & Bolts, p. 11). CARE BEARS It turned out that everything was timed right for Hua Mei, and she gave birth to twins each only about the size of a stick of butter. "The size ratio of a panda mother to her cub is the largest of any bear and one of the largest of any animal," says Durrant. Their extra-small size means the cubs need a lot of care. like many new moms, Hua Mei initially seemed unsure of her motherly role. Soon, however, she settled into motherhood. Since au panda cubs are bom blind and hairless, moms gently pick them up in their mouths. They keep the tiny cubs cozy against their fur. A panda mother usually won't leave her baby even to eat or drink imtil the cub is about 10 days old. She stays with her cub, teaching it how to survive, until it is about 18 months old. Then the cub leaves to hve a mostly solitary life. In captivity, panda cubs are slowly weaned, or removed fi-om tbeir motber's care, after roughly one and a half yeara. DOUBLE TROUBLE It's tough to care for even one growing bear, but like Hua Mei pandas give birth to twins about 50 percent of the time. Because the cubs need so I D JANUARY 24. 2DQ5
much attention, a mother in the wild usually neglects one of her twins. "The cubs are so small and require so much care, she just can't hold [or feed] two of them all the time," says Durrant. Unfed, the neglected cub dies. Even captive pandas follow these instincts. So in the past, when twins were bom in captivity, veterinarians would remove one of the cubs and hand-raise it: They fed it from a bottle and cared for it without any help from mom. But until recently, scientists had never successfully handraised a cub to adulthood. CUBS WIN Luckily, scientists have now developed liquid formulas that are better matched to natural panda milk. Also, tbey have designed special "cub holders" tbat exactly copy the position in which mother pandas hold their babies when they nurse. Scientists use fake fur that feels and smells just like mom to help a cub feel right at home. Hua Mei's twins also benefit from another new technique: Instead of completely hand-raising one cub, veterinarians periodically swap twins. They remove the cubsfi"om the mother's care one at a time feeding each for a few hours before returning it. Each cub gainsfi"om spending time with mom: "Since twin swapping and improved formulas have been used at Wolong, they went from losing one of the twins 100 percent of the time to saving both twins 100 percent of the time," says Durrant. This success is spreading: In 2003, 16 healthy pandas were bom in captivity around the world. This baby boom along with expanded protection of wild habitat may help keep the black-andwhite bears from disappearing. ^ Nuts & Bolts Like I. CELLS UNITE A male sperm joins with a female egg. Result: a zygote, or fertilized egg. The nucleus (area containing D/V/A-chemical that carries genetic information) has 42 chromosomes (structures that contain DNA), half from each parent. Four chromosomes are shown. NUCLEUS FERTILIZED EGG SPINDLE FIBER FROM FEMALE all animals, pandas start out as a single cell. Through a process called mitosis, this cell divides over and over again. These divisions form millions of cells that eventually develop into a panda cub. DUPLICATED FROM FEMAiE DUPLICATED FROM MALE 2. DUPLICATION The nucleus breaks down and each of the cell's chromosomes is copied. The chromosome pairs line up, moving along spindle fibers. Each pair splits and one complete set of chromosomes moves to each end of the cell. MALE 7. CUB DEVELOPS For between 30 to 50 days, the fetus grows inside the uterus. Then, Ihe female delivers a baby panda. At birth, the tiny cubs are blind and hairless. FROM MALE 3. CELL DIVIDES Two new nuclei form at opposite ends of the cell. Each nucleus contains a set of 42 chromosomes. Then, the cell divides into two identical cells. CELL CELL LINING OF UTERUS B. ATTACHMENT Eventually, the blastocyst attaches to the lining of the female panda's uterus, the hollow organ in which a baby develops. The cells in the inner cell mass grow to become a panda fetus. INNER CELL MASS 5. REDRBANIZATION 4. CELLS MULTIPLY The new cells continue to divide: After one more cycle of cell divisions, four identical cells have formed. Another cycle yields eight cells. This continues doubling the number of cells each time. After about five days, a blastocyst forms: Cells move to form a thin layer around the edge and a group of small cells, called the inner cell mass, assembles along one side. SCIENCE WORLD