Зоология / Реферат: Mammals

Реферат: Mammals

The macaques, a genus of some 13 to 20 species (there is disagreement among taxonomists on the actual number), are found in North Africa and throughout southern Asia from Afghanistan to Japan. The most familiar form is the rhesus monkey, which is often seen by tourists in the towns and cities of India. Fossils dating to six million years indicate that the macaques originated in northern Africa and once roamed over Europe as far north as London. These earlier macaques were not very different in appearance from the Barbary monkeys that survive today in Morocco, Algeria, and on Gibraltar. However, once the Macaques reached Asia, at least by three million years ago, they diversified into a variety of forms. Few are as distinctly different as the lion-tails, with their black coats, silver facial ruffs, and strongly arboreal habitats. Lion-tails are one of the two macaque species that are listed as in danger of extinction, but we may realistically expect the Tibetan, Formosan, and Sulawesian species to fall into that category before the year 2000.

Their geographical range snakes along the slope's and highest crests of the Western Ghat Mountains where, today, the forest is reduced to about one percent of the total land cover. Like its captive counterpart, the wild living lion-tail was ignored by primatologists until well into the 1970s. Although opinions vary, most would agree that the wild population today numbers between 2,000 and 5,000 individuals. Initial field reports indicate that wild lion-tails prefer to spend about 99 percent of their time in the trees. Like other macaques, their diet is dominated by wild fruits, but includes a variety of flowers, leaves, buds, grasses, insects, and even a few nestlings of birds and mammals. One of the more interesting forms of feeding reported by Dr. Steven Green of Miami University involves a simple form of tool use. In order to protect their hands while feeding on stinging caterpillars, lion-tails have been seen to pluck large tree leaves and lay them over the caterpillars before pouncing on them.

In the wild state, lion-tail groups average about 20 individuals, usually with more than a single adult male present. Males are larger than females by about a third and are typically ranked relative to one another in a social hierarchy. Males usually emigrate from their natal group to join another during the early stages of adulthood. Being macaques, lion-tails are intensely social and are highly aggressive toward unfamiliar individuals. Preliminary work on our captive population indicates that much of the behavior between group members is dependent upon one's relationship to a small number of female-headed lineages. It is possible to have up to four living generations within each matriline and four or five matrilines within a group. Dominance relationships among and within matrilines play a crucial role in the everyday life of females and their offspring, as they do for adult males. One's social position determines access to essential resources such as food, perches, and social partners.

LION-TAILED MACAQUES: FUTURE PLANS

This highly endangered primate has been exhibited at the San Diego Zoo since 1923. In 1979, the existing population of three males and three females was relocated to the Primate Research Pad for concentrated study of their reproductive biology. Within the next decade their reproductive cycles were characterized, as were their sexual and social behavior, parturition and infant rearing, and various other aspects of the captive experience. Nearly a dozen scientific papers from these studies have been published in peer-reviewed journals or as book chapters.

BY 1989 the Zoo's captive population had grown to 38 individuals. This same year the program undertook a significant change in direction. Seven individuals, including five born at the Primate Research Pad, were released into a state-of-the-art exhibit in Sun Bear Forest. Although these individuals are no longer under study, it was knowledge gained over the previous decade that contributed to the design of an exhibit facility which, by anyone's criteria, is an outstanding success.

A second troop of 11 individuals was simultaneously relocated to the newly constructed 3/4-acre breeding kraal at the Wild Animal Park. It is this population which will be a major research focus during the next five years. This troop has been exempted from Species Survival Plan management, a program of the American Association of Zoological Parks and Aquariums, providing freedom to pursue several interesting lines of inquiry. One of these has to do with the impact of traditional management regimes on certain life history parameters. The second investigation will pursue experiments designed to prepare the troop for reintroduction to suitable habitat in India in five to seven years.

The lion-tailed macaque is by nature a highly social mammal. Group members are organized in a social hierarchy that appears to remain stable over many years. Individual troops are highly xenophobic. This trait, combined with natural aggressiveness, results in potentially fatal conflict when new individuals are introduced. In the wild state, males will leave their natal troop at sexual maturity and join a new one. Females remain in their natal troops throughout their lives.

Transfer by males is accompanied by a substantial amount of aggression, but is presumably a necessary event to preclude inbreeding. These natural attributes of wild troops would seemingly have profound implications for the transfer of individuals, especially of females, between zoological institutions to satisfy genetic and reproductive objectives.

It is relevant to ask if the ongoing disturbance of the social order through frequent inter-institutional transfers might negatively impact on such parameters as infant mortality, female fecundity, and perhaps even the neonatal sex ratio. Our kraal group has been together for the past 24 years, the only social disturbances having been the replacement of breeding males. We have learned how to integrate new males into groups with a minimum of social upheaval. We therefore have a unique opportunity to compare findings from our relatively undisturbed population with those from more traditionally managed populations in other zoos over the next several years.

Preparation of this same troop for reintroduction to the wild has two components. The first entails a number of experimental procedures designed to "teach" natural foraging, avoidance of predators (including humans), and appropriate social cohesiveness. In addition, the troop must be routinely evaluated for any pathogens that would pose a hazard to the existing wild population.

The second component is evaluation of potential release sites in the wild. The area selected for a test-case reintroduction must not only be protected from human activity, but must contain adequate food and shelter to insure the long-term survival of the troop. CRES anticipates working closely with Indian colleagues on this aspect.

NIGHTTIME IS THE NORM: LABOR AND BIRTH IN THE LION-TAILED MACAQUE

Lion-tailed macaque neonates (newborns) are born with black fur, and their faces, hands, and feet are pink and hairless. Their characteristic silver manes do not begin to grow in until the babies are several weeks old, and their faces gradually acquire the black pigmentation of adults.

When the lion-tailed macaque breeding and management program began at the CRES primate facility more than ten years ago, little was known about the gestation, labor, and delivery of infants in this species. There was extensive documentation of parturition in some other macaques, but no comparable data were available on the much rarer lion-tailed macaque. How long is the normal gestation length? At what time are births most likely to occur? How long does labor last? What factors indicate that there may be a delivery problem requiring veterinary intervention? Answers to these and other important questions were needed in order to ensure the best captive management procedures and to maximize the breeding success for this species.

The primary reason these data had not been collected previously is that most new infants were usually discovered in the morning, after the keepers arrived at work. We began collecting data on each lion-tailed macaque birth by setting up 24-hour "birth watches" that began several days before the dam was due to deliver. Conception dates were determined partially through hormone data from daily urine samples, and also by keeping careful track of menstruation, sex-skin swellings, and mating episodes. Parturition-date predictions were based on the 168-day gestation length documented for the rhesus macaque. However, because this is an average length, we began our observations about ten days before the due date in order not to miss the early deliveries.

The birth watch involved round-the-clock observations at 15-minute intervals during successive, 4-hour shifts. Observations were recorded by keepers, technicians, and trained volunteers. As soon as any signs of straining or birth fluids were noted, continuous notes were kept and each subsequent contraction or birth-related event was timed and recorded. Behavioral indications of impending labor included restlessness and manual exploration of the vaginal area. Although these signs eventually proved reliable, we used the first, clear contraction as the starting point for measuring the duration of labor. (In human terms, this is equivalent to second-stage labor. The usual criterion of first-stage labor, cervical dilatation, cannot be observed in the wild primate unless restraint is used.) During actual labor, several straining postures were noted; most common were variations of squatting postures and arched-back stretches.

The first birth was to an experienced mother (this was her third delivery) and was documented on videotape. After nearly 8 full hours of labor and 188 contractions, the dam gave birth to a healthy, female infant. These initial observations led us to believe that a labor of this duration was not a basis for concern; however, we soon learned that this was far beyond the average labor length and number of contractions common for this species.

Over an 8-year period, we were able to collect data on 18 births from 8 different mothers in our colony. Our program has provided some valuable information about species-typical birth patterns that we can now use to direct management decisions. We found that the average length of labor to expulsion of the fetus was about 2 hours and 15 minutes, and the shortest labor was only 50 minutes total. The female that required eight hours to deliver in the first case observed then delivered her subsequent infant in only a little over an hour! Although our sample is still small, it would appear that, on the average, first-time mothers have longer and more difficult labors.

Our study determined that the average number of contractions to delivery for lion-tails was 54. The female with the longest labor also had the largest number of contractions (454). In her next delivery, the infant arrived after only 14 contractions, the lowest number recorded during the entire birth study. Based on the average number of contractions seen in 17 successful deliveries, and one ending in stillbirth, contraction frequencies approaching 75 to 100 in number may serve as a warning that intervention will be necessary.

The average length of gestation for 14 pregnancies in our colony was 169.5 days, with a range of 163 to 176 days. This is very similar to what has been reported for other macaques. Our observers quickly discovered that those who watched during the 7 to 11 P.M. shifts were the most successful at being present when births occurred: labor began between the hours of 7:15 P.M. and 3:15 A.M. in every case but one. The exception was one first-time mother that began straining in the early afternoon. This female had a difficult labor, and a dead fetus was later removed by cesarean section after 8 hours of straining and 193 contractions. All the other births resulted in live offspring and occurred between the hours of 8:05 P.M. and 6:28 A.M. Based on previous primate birth records, daytime births are not the norm and may indicate an increased risk to both fetus and dam.

Expulsion of the placenta always took place within about 20 minutes after parturition, and usually it was immediately consumed by the mother. In a few cases, first-time mothers carried the placenta around for several hours, along with the infant, until it could be removed by keepers. Whenever possible, a sample of the placenta is saved for analysis by Zoo pathologists, who check it for abnormalities. After delivery, the mothers carefully lick the birth fluids off their infants, and the neonates begin nursing within a few hours. Each and every female in the study provided excellent maternal care immediately following parturition.

The lion-tailed macaque breeding colonies are now located in the Sun Bear Forest exhibit at the Zoo (one adult male and six females) and in a large, off-exhibit kraal at the Wild Animal Park (one adult male, two juvenile males, one infant male, and ten females). Together these represent the largest captive group of lion-tailed macaques in the world -- about 20 percent of the total captive population. Eight years of patient monitoring, birth watches, record keeping, and evaluation have brought us a long way in the breeding and captive management of this macaque species.

ZOONOOZ, May, 1990 "Nighttime Is the Norm: Labor and Birth in the Lion-tailed Macaque," by Helena Fitch-Snyder, Animal Behavior Specialist/CRES and Donald Lindburg, Ph.D. Behaviorist/CRES.