Locomotion in bonobos (Pan paniscus): differences and similarities between bipedal and quadrupedal terrestrial walking, and a comparison with other locomotor modes.

One of the great ongoing debates in palaeo-anthropology is when, and how, hominids acquired habitual bipedal locomotion. The newly adopted bipedal gait and the ancestral quadrupedal gait are most often considered as very distinct, with each habitual locomotor mode showing corresponding anatomical adaptations. Bonobos (Pan paniscus), along with common chimpanzees (P. troglodytes), are the closest living relatives to humans and their locomotion is valuable for comparison with other primates, and to gain an insight in the acquisition of human bipedalism. Bonobos are habitual quadrupeds, but they also engage in bipedal locomotion, both on terrestrial and in arboreal substrates. In terms of kinematics and dynamics, the contrast between bipedal and quadrupedal walking seems to be more subtle than one might expect. Apart from the trunk being approximately 37 degrees more erect during bipedal locomotion, the leg movements are rather similar. Apart from the heel, plantar pressure distributions show subtle differences between bipedal and quadrupedal locomotion. Regardless, variability is high, and various intermediate forms of locomotion (e.g. tripedal walking) exist both in captivity and in the wild. Moreover, there is overlap between the characteristics of walking and other locomotor modes, as we show with new data of walking on an inclined pole and of vertical squat jumps. We suggest that there is great overlap between the many locomotor modes in bonobos, and that the required polyvalence is reflected in their anatomy. This may hamper the development of one highly specialized gait (i.e. bipedalism), which would constrain performance of the other types of locomotion.

Multiple breeding females in captive groups of golden-headed lion tamarins (Leontopithecus chrysomelas): causes and consequences.

In Callitrichidae, reproduction in subordinate females is generally inhibited but occurs in rare cases, possibly in association with the presence of an unrelated male, important food resources or low dispersal opportunities. This study investigates the occurrence of groups with multiple breeding females in captive golden-headed lion tamarins (Leontopithecus chrysomelas), the factors leading to their formation and the consequences for the group. Information obtained from studbook data on the world captive population during 1984-1998 revealed that polygynous groups in captivity are very rare: only 7 cases were discovered. Family groups in which daughters started breeding with a related male were larger than average, had a high number of sexually mature sons and eldest offspring that were well past the age of sexual maturity. Following a breeding attempt, severe aggression frequently occurred, especially if the infants were liveborn. Polygynous groups composed of two related females and an unrelated male tended to remain stable for a longer period than families with breeding daughters. Competition for infant care is probably an important factor determining whether the polygynous situation can persist and for how long.

Spatio-temporal gait characteristics of the hind-limb cycles during voluntary bipedal and quadrupedal walking in bonobos (Pan paniscus).

Spatio-temporal gait characteristics (step and stride length, stride frequency, duty factor) were determined for the hind-limb cycles of nine bonobos (Pan paniscus) walking quadrupedally and bipedally at a range of speeds. The data were recalculated to dimensionless quantities according to the principle of dynamic similarity. Lower leg length was used as the reference length. Interindividual variability in speed modulation strategy of bonobos appears to be low. Compared to quadrupedal walking, bipedal bonobos use smaller steps to attain a given speed (differences increase with speed), resulting in shorter strides at a higher frequency. In the context of the ("hybrid") dynamic pattern approach to locomotion (Latach, 1998) we argue that, despite these absolute differences, intended walking speed is the basic control variable which elicits both quadrupedal and bipedal walking kinematics in a similar way. Differences in the initial status of the dynamic system may be responsible for the differences in step length between both gaits. Comparison with data deduced from the literature shows that the effects of walking speed on stride length and frequency are similar in bonobos, common chimpanzees, and humans. This suggests that (at least) within extant homininae, spatio-temporal gait characteristics are highly comparable, and this in spite of obvious differences in mass distribution and bipedal posture.

Application of urinary and fecal steroid measurements for monitoring ovarian function and pregnancy in the bonobo (Pan paniscus) and evaluation of perineal swelling patterns in relation to endocrine events.

Estrone conjugates (E1C), pregnanediol glucuronide (PdG), and estriol (E3) in urine, and immunoreactive E1C, E3, pregnanediol (Pd), and progesterone (P4) in feces were determined along with records of perineal sex skin swelling throughout 7 nonconception cycles and 3 full-term pregnancies of 4 adult female bonobos (Pan paniscus). A typical preovulatory urinary E1C surge and postovulatory increase in urinary PdG were seen during the menstrual cycles. Fecal progestin levels were significantly correlated with those of PdG in urine in all cycles, while E1C measurements in feces were significantly correlated with those in urine in only 3 cycles. On the basis of hormone profiles, a variable follicular phase of 17-40 days and a relatively constant luteal phase of 11-15 days was found, resulting in cycle lengths of 31-51 days. All urinary and fecal hormones were markedly elevated during pregnancy. Measurement of E1C in both urine and feces was most useful for early pregnancy diagnosis, while E3 was of value in confirming pregnancy and assessing fetal viability. The period of perineal swelling during the cycle comprised on average 66.3% of cycle length, half of which was associated with a phase of maximum tumescence. Ovulation usually occurred within the maximum swelling phase, but timing of ovulation within this period was highly variable and was more closely associated with the end rather than the onset of maximum tumescence. The data presented here are of great practical value in the captive breeding management of bonobos and offer new opportunities for investigating basic questions of bonobo reproductive biology both in captivity and in the wild.

Effect of posture on hand preferences during experimental food reaching in bonobos (Pan paniscus).

The effect of posture on hand preferences was examined in an experiment with 5 bonobos (Pan paniscus). To obtain a food reward, the animals had to adopt 1 out of 7 different postures. These postures represented an increasing problem to the maintenance of body equilibrium. It was expected that an increasing demand for equilibrium maintenance would elicit individual preferences and a population-level bias. All animals showed an increasing trend toward left-handedness while shifting to a bipedal posture from a seated posture by way of a quadrupedal posture. The importance of bipedalism in the evolution of left- and right-handedness is discussed briefly.

Maternal differences in infant carriage in golden-headed lion tamarins (Leontopithecus chrysomelas).

Infant-carrying behaviour was observed in two families of captive golden-headed lion tamarins. Although the young were raised in almost identical social situations, we found a reversed involvement of mother-father pairs in the amount of time they carried their offspring. In one case, the parental division of carrying behaviour was consistent with the standard description for callitrichids in that the adult male was the primary carrier. In the other family, the mother carried the infant considerably more than the male. Comparison of transfer initiations and transfer times showed that maternal choice operated. It is suggested that maternal behavior may depend primarily on the female's physical and hormonal condition.