Juvenile Gorilla Research Articles

Functional morphology in the pages of the AJPA

Functional morphology in the pages of the <i>AJPA</i>

Juvenile gorilla smile, framed by vegetation

Juvenile Gorilla Smile, Framed by Vegetation. Taken August 2015 at the Bwindi Impenetrable Forest, Uganda. Photograph by Cindy Bitter, MD, MA.

Ontogenetic changes in limb bone structural proportions in mountain gorillas (Gorilla beringei beringei)

Behavioral studies indicate that adult mountain gorillas (Gorilla beringei) are the most terrestrial of all nonhuman hominoids, but that infant mountain gorillas are much more arboreal. Here we examine ontogenetic changes in diaphyseal strength and length of the femur, tibia, humerus, radius, and ulna in 30 Virunga mountain gorillas, including 18 immature specimens and 12 adults. Comparisons are also made with 14 adult western lowland gorillas (Gorilla gorilla gorilla), which are known to be more arboreal than adult mountain gorillas. Infant mountain gorillas have significantly stronger forelimbs relative to hind limbs than older juveniles and adults, but are nonsignificantly different from western lowland gorilla adults. The change in inter-limb strength proportions is abrupt at about two years of age, corresponding to the documented transition to committed terrestrial quadrupedalism in mountain gorillas. The one exception is the ulna, which shows a gradual increase in strength relative to the radius and other long bones during development, possibly corresponding to the gradual adoption of stereotypical fully pronated knuckle-walking in older juvenile gorillas. Inter-limb bone length proportions show a contrasting developmental pattern, with hind limb/forelimb length declining rapidly from birth to five months of age, and then showing no consistent change through adulthood. The very early change in length proportions, prior to significant independent locomotion, may be related to the need for relatively long forelimbs for climbing in a large-bodied hominoid. Virunga mountain gorilla older juveniles and adults have equal or longer forelimb relative to hind limb bones than western lowland adults. These findings indicate that both ontogenetically and among closely related species of Gorilla, long bone strength proportions better reflect actual locomotor behavior than bone length proportions.

Dental wear, wear rate, and dental disease in the African apes

The African apes possess thinner enamel than do other hominoids, and a certain amount of dentin exposure may be advantageous in the processing of tough diets eaten by Gorilla. Dental wear (attrition plus abrasion) that erodes the enamel exposes the underlying dentin and creates additional cutting edges at the dentin-enamel junction. Hypothetically, efficiency of food processing increases with junction formation until an optimal amount is reached, but excessive wear hinders efficient food processing and may lead to sickness, reduced fecundity, and death. Occlusal surfaces of molars and incisors in three populations each of Gorilla and Pan were videotaped and digitized. The quantity of incisal and molar occlusal dental wear and the lengths of dentin-enamel junctions were measured in 220 adult and 31 juvenile gorilla and chimpanzee skulls. Rates of dental wear were calculated in juveniles by scoring the degree of wear between adjacent molars M1 and M2. Differences were compared by principal (major) axis analysis. ANOVAs compared means of wear amounts. Pearson correlation coefficients were calculated to compare the relationship between molar wear and incidence of dental disease. Results indicate that quantities of wear are significantly greater in permanent incisors and molars and juvenile molars of gorillas compared to chimpanzees. The lengths of dentin-enamel junctions were predominantly suboptimal. Western lowland gorillas have the highest quantities of wear and the most molars with suboptimal wear. The highest rates of wear are seen in Pan paniscus and Pan t. troglodytes, and the lowest rates are found in P.t. schweinfurthii and G. g. graueri. Among gorillas, G. b. beringei have the highest rates but low amounts of wear. Coefficients between wear and dental disease were low, but significant when all teeth were combined. Gorilla teeth are durable, and wear does not lead to mechanical senescence in this sample.

Fine‐tuning of social play in juvenile lowland gorillas (gorilla gorilla gorilla)

Social play, which involves cooperation, communication, and learning, may represent a suitable field for the investigation of cognitive ability in a given species. We collected data on a captive group of gorillas in order to evaluate the potential cognitive skill of juveniles in fine-tuning play behavior. This study revealed that juvenile gorillas are able to "place" the play session in a proper spatial/temporal context, thus evaluating a complex net of factors (e.g., play partner, play roughness, group activity, space availability). When animals play fight, they use patterns of agonistic functional contexts. Since these actions are not intrinsically different from their "serious" context, it may be hard to distinguish them. One of the most important function of play in the ontogeny of primate social cognition may be to recognize stimuli, which may indicate the intentions of conspecifics. Accordingly, we found that juvenile gorillas are able to use play signals appropriately when a clear statement of purpose is necessary (i.e., during male-male competitive play sessions and when the escape opportunities are limited). The ability to interpret such ambiguous features of social signaling could represent a central issue in the evolution of behavioral flexibility and intelligence in primates.

A Faithful Record of Stressful Life Events Preserved in the Dental Developmental Record of a Juvenile Gorilla

A Faithful Record of Stressful Life Events Preserved in the Dental Developmental Record of a Juvenile Gorilla

A Faithful Record of Stressful Life Events Recorded in the Dental Developmental Record of a Juvenile Gorilla

The pattern and rate of dental development are critical components of the life history of primates. Much recent research has focused on dental development in chimpanzees and other hominoids, but comparatively little is known about dental development in Gorilla. To date, dental chronologies for Gorilla are based on a sample of 1 and information about variations in the time and timing of crown initiation and completion is lacking. We provide data on dental development in 1 captive, juvenile, female, western lowland Gorilla gorilla gorilla of known age, sex, life events, and date of death (carefully documented as part of zoo records) that experienced various physical insults during her first year of life. The perfect natural experiment allowed us to test the association of the timing of accentuated stress lines in teeth with significant physiological and psychological events during ontogeny of this juvenile gorilla. We analyzed histological sections from 14 permanent teeth (maxillary and mandibular I1-M2) and assessed crown initiation (CI) and crown formation times (CFT) using short- and long-period incremental lines in both enamel and dentine; they are advanced for all teeth compared to previously published chronology. The data suggest a relatively accelerated pace of dental development in gorillas compared to chimpanzees and fit an emerging pattern of an accelerated life history schedule in gorillas. Data on the timing of major accentuated lines in the developing dentition are tightly associated with exact dates of surgical procedures and follow-up hospital visits as recorded on zoo medical records. Our data highlight the importance of captive individuals with well-documented medical records for studying life history.

Hyperkeratotic mange caused by Sarcoptes scabiei (Acariformes: Sarcoptidae) in juvenile human-habituated mountain gorillas (Gorilla gorilla beringei).

To facilitate ecotourism and behavioral research, free-ranging mountain gorillas (Gorilla gorilla beringei) have been habituated to humans. During routine health monitoring, five juvenile gorillas were observed with active crusted dermatitis and alopecia. Papular and vesicular lesions and crusts with papular eruption and oozing were numerous and disseminated over the body of one gorilla with a confirmed infestation of scabies. In this gorilla, the hyperkeratotic crusts were loose and thick with a flaky and scaly appearance. Histologically, the epidermis was thickened, displayed hyperkeratosis and was infiltrated with lymphocytes and neutrophils. Examination of skin scraping yielded a positive identification of adults and eggs of Sarcoptes scabiei mites. The gorillas were treated with ivermectin, 200 mg kg(-1). As S. scabiei mites can cross-infect various mammalian species causing self-limiting dermatitis, these ectoparasites can be propagated in the habitats shared by gorillas, people, and livestock, and therefore they represent an anthropozoonotic threat.

Capillaria hepatica (Nematoda) Infections in Human-Habituated Mountain Gorillas (Gorilla gorilla beringei) of the Parc National de Volcans, Rwanda

Habituation to humans of free-ranging populations of endangered mountain gorillas (Gorilla gorilla beringei) raised concern of anthropozoonotic transmission of parasitic helminths and protozoans. Examinations of liver tissue of 19 gorillas found dead in the Parc National de Volcans, Rwanda, revealed 10 cases of hepatic nematodiasis due to Capillaria hepatica. Identifiable C. hepatica eggs were present in the liver of 4 gorillas (3 juveniles, 1 adult), and nematode cross-sections were found in 1 juvenile gorilla. Six other adult gorillas had areas of periportal and subcapsular fibrosis with calcified eggs. Histologically, the lesions surrounded by the areas of mild inflammatory reaction were characterized by subcapsular, periportal foci of fibrosis in which were embedded numerous C. hepatica eggs. Control of hepatic capillariasis in the remaining populations of mountain gorillas should be focused on eradication or control of populations of rodent pests (i.e., mice and rats) that sustain the reservoir of C. hepatica in habitats shared by gorillas and humans.

Gorillas' (Gorilla gorilla gorilla) spatial memory in a foraging task.

The spatial memory of 2 gorillas (Gorilla gorilla gorilla) was explored in a simulated foraging task. Trials consisted of 2 parts separated by a delay. In the 1st part, half of the total number of food sites were baited with a highly preferred food, and the subject was allowed to search, find, and consume these items (search phase). During the delay the same locations were again baited. After the delay the animal was reintroduced to the test enclosure and allowed to search through the sites again (re-search phase). In Experiment 1, an adult gorilla was very accurate in remembering locations that had previously contained food at delay intervals of 24 hr or more. In Experiment 2, a juvenile gorilla was also accurate in remembering locations that had previously contained food at delays up to 10 min. The adult gorilla appeared to use a counting strategy during the search phase to minimize the number of sites visited.

Possible osteomyelitis of skull causes death of a wild lowland gorilla in the Lopé Reserve, Gabon

The remains of a juvenile gorilla, apparently dead for 3-4 days, were found in the Lopé Reserve, Gabon. The skull was recovered and showed a chronic lesion involving the insertion of the masseter muscle, consistent with chronic osteomyelitis.

Effects of hand-rearing on the behavioral development of infant and juvenile gorillas (Gorilla g. gorilla).

Nineteen hand-reared and seven mother-reared infant and juvenile gorillas were observed for a period of 3 years. Almost all hand-reared individuals developed stereotyped behaviors during the first months. In most cases these behaviors disappeared in the first or second year. Social behaviors, solitary play, nest building and grooming developed at about the same age in hand-reared and mother-reared infants. Hand-reared immatures showed significantly more solitary play, more aggression and less social play than mother-reared ones, especially when raised in pairs. When young gorillas were kept in groups, the frequencies of these behaviors came nearer to those of mother-reared immatures. No significant differences were noted in social play. When introduced to conspecifics, hand-reared infants sometimes reacted with indiscriminant aggression. Gorillas should thus preferably be reared in peer groups and be introduced to adults not later than one year of age.

Play behaviour in lowland gorillas: Age differences, sex differences, and possible functions

A study on lowland gorilla (Gorilla gorilla gorilla) play behaviour was conducted on four exhibits at three different zoological parks so that 19 gorillas were observed. Juvenile gorillas played the most, but play continued at fairly high frequencies through adolescence. Most social play occurred between dyads. Triadic groups usually chased each other. No sex differences in type of play were observed, but gender differences in partner preferences were observed. Males played with both other males and females, while females seldom played together. These data support the social skills hypothesis (Baldwin & Baldwin, 1974) of play.

Behavioral changes of a juvenile gorilla after a transfer to a more naturalistic environment

AbstractPlay behavior and stress‐associated behavior of a captive juvenile gorilla were observed before and after his transfer to a larger and more natural environment. The gorilla was observed for 4 months after the transfer and at 1 and 4 years after the transfer. Throughout his first month in the new environment play decreased dramatically. Although play subsequently increased again 2 months and 1 year after the transfer, it never reached the levels of play in the old environment. Four years after the move his play had decreased again to the low level of his first month in the new environment. Two of his stress‐associated behaviors, coprophagy and regurgitation/reingestion, decreased after the transfer. Self‐clasping behavior increased initially in the new environment and remained at high levels 1 year after the move. Four years after the move his self‐clasping behavior was significantly less than at 1 year after the move; however, it continued to be significantly greater than in the old environment. These findings suggest that larger and more natural environments do not necessarily result in more play activity or a reduction in all stress‐associated behavior.

Premaxillary-maxillary suture asymmetry in a juvenile Gorilla. Implications for understanding dentofacial growth and development.

A specimen of juvenile gorilla was found that had the premaxillary-maxillary suture coursing between the lateral deciduous incisor and deciduous canine on one side of the jaw, but between the central and lateral deciduous incisors on the other; in the latter, the suture also separates the alveolus of the lateral deciduous incisor from the crypt of the growing successional lateral incisor. Rather than dismiss this exception to the traditional dictum of tooth identification--which is based on the position to teeth relative to this suture--as some inconsequential anomaly, an attempt is made to understand how this can occur within the confines of present understanding of dentofacial growth and development and developmental theory. An hypothesis relating tooth and tooth class identification is presented in the context of ectomesenchymally predifferentiated stem progenitors and subsequent tooth class proliferation.

Discrimination reversal skills of the lowland gorilla (Gorilla g. gorilla).

The acquisition and reversal performances of 5 juvenile gorillas in a discrimination-reversal task were found to correlate highly and positively. Number of acquisition trials (7 and 13) influenced the frequency with which the various pre-reversal mastery levels were achieved, but did not otherwise influence reversal performance.

Fossil Hand Bones from Olduvai Gorge

IN Nature of December 17, 1960, Dr. L. S. B. Leakey reported on the discovery of a number of fossil bones of the hand and the foot on a living floor some 20 ft. below the uppermost limit of Bed I, Olduvai. Later (Nature of February 25, 1961), Dr. Leakey reported the discovery of a mandible and two parietal fragments of a juvenile from the same site and associated with a well-defined living floor of an Oldowan culture. Fifteen of the hand bones pertaining to at least two individuals, an adult and a juvenile, have been identified and examined, and are described here. Their allocation is given in Table 1. The middle phalanges (Fig. 1, second row) from the juvenile hand, lacking only their epiphyses, constitute a series II-V from the right hand. They are robust bones, rather more so than phalanges of comparable length of juvenile Gorilla and adult Homo sapiens. They are strongly curved and, palmad, bear well-defined grooves which are situated in the distal half of the bone for the insertion of flexor digitorum superficialis. The adult proximal phalanges (Fig. 1, third row) are also more robust than bones of comparable length in modern man; they are strongly curved both longitudinally and transversely, fusiform in shape and deeply hollowed out on the palmar aspect; sharply defined fibrous flexor sheath ridges extend from the base of the bones to their necks. The terminal phalanges (Fig. 1, top row) which are juvenile, having incompletely fused epiphyses, are characteristically sapiens in form. The terminal phalanx of the thumb is of particular interest; it is stout and broad and bears a deep impression for the insertion of flexor pollicis longus. The carpal bones (Fig. 1, 4th row) are all damaged, but sufficient of their original form remains to determine their structural and functional affinities. The lunate surface of the scaphoid has a rectangular outline; and the tubercle, which is broken off at its root, was probably somewhat elongated, though not as long as in the anthropoid apes. The trapezium has a well-defined saddlesurface but the evidence provided by the other articular surfaces indicates that its 'set' in the carpus was unlike that found in modern man and similar to the condition in Gorilla. The capitate, though badly eroded, is generally more sapiens than apelike. Morphologically, the Olduvai hand bones cannot be closely matched with any known hominoid species living to-day. They bear, however, a greater similarity to juvenile Gorilla and adult H.s. sapiens than to adult Gorilla, Pan or Pongo. This is due largely to the absence in the fossil bones of any features peculiarly characteristic of brachiators. The adult gorilla hand has a number of specializations that are presumably related to its secondarily terrestrial mode of life and its great body-weight; these features, again, are absent from the fossil bone. The juvenile gorilla hand lacks the secondary specializations of the adult, and it is possibly for this reason alone that its bones have affinities with those of the fossil. The fossil bones differ from those of modern man in a number of features: (1) robustness; (2) dorsal curvature of the shafts of the phalanges; (3) distal insertion of the flexor digitorum superficialis; (4) strength of fibrotendinous markings; (5) 'set' of trapezium in the carpus; (6) the form of the scaphoid; (7) the depth of the carpal tunnel. The fossil bones resemble modern man in the following features: (1) presence of broad, stout terminal phalanges on fingers and thumb; (2) form of the distal articular surface of the capitate; (3) ellipsoidal form of metacarpo-phalangeal joint surfaces. TABLE 1