Party composition and dynamics inPan paniscus

The pygmy chimpanzee, or bonobo, Pan paniscus,diplays a fission-fusion social organization in which individuals associate in parties that vary in size and composition. Data from a 2-year field study of nonprovisioned P. paniscusshow that party composition varies with party size. Although females, on average, outnumber males, the proportion of males in the party increases in larger parties. This effect was not due to the greater number of known females. Both females and males will join and leave a party in the company of others, but only males appear frequently to join or leave as lone individuals. All-male parties were not observed, but all-female (nonnursery) parties were relatively common. These trends reflect greater cohesion among females than observed in P. troglodytes schweinfurthii.Cohesion between males and female P. paniscusmay increase with party size.     

Factors Affecting Party Size in Chimpanzees of the Mahale Mountains

We studied factors affecting party size and composition of wild chimpanzees at Mahale (M group) over an 11-month period. Parties with 1–5 individuals were most frequent (37.8%; 153/405 parties); they included 94.7% of all male parties (n = 76) and 81.3% of all female parties (n = 75). The median of monthly values was the standard for analysis. We divided the year into four periods based on the median size of monthly bisexual parties (30.9 individuals; includes both males and females): monthly bisexual party sizes were larger in May–June (period II) and October–January (period IV) and smaller in February–April (period I) and July–September (period III). Only bisexual parties changed in size with period. The number of fruit items (=species) eaten was fewer in periods II and IV when abundance per item appeared to be great. The sizes of bisexual parties, which included cycling females with maximal anogenital swelling, were larger, and their representation (%) in all bisexual parties was greater in periods III and IV. The numbers of both cycling females and cycling females with maximal anogenital swelling were also larger in periods III and IV. The percentage of cycling females with maximal anogenital swelling was greater in periods II and III. The results of this study and those of Nishida (1979) suggest that seasonal variation in party size of Mahale chimpanzees maintains a relatively consistent annual cycle. The factors assumed to affect party sizes are fruit availability and the presence of cycling females with maximal anogenital swelling.     

What Factors Affect the Size of Chimpanzee Parties in the Kalinzu Forest,Uganda? Examination of Fruit Abundance and Number of Estrous Females

We examined factors affecting the size of chimpanzee parties in the Kalinzu Forest, Uganda. We found that the number of individuals in a party increased with observation time. Therefore, we employed two methods to reduce this bias: (1) we evaluated party size via the mean number of individuals observed in each 1-h period during the observation of a party (1-h party size), and (2) we used the number of all individuals observed in a party (1-day party size) and performed an analysis of covariance, with observation time of the party as the covariant. We examined factors that might affect party size: fruit abundance, fruit distribution, and number of estrous females. There was no relationship between party size and fruit abundance or distribution. Conversely, the number of males has a significant positive correlation with the number of estrous females, though there is no correlation with the number of anestrous females. These results suggest that males tended to join parties with more females in estrous, irrespective of differences in fruit availability.     

Agonistic Interactions and Matrifocal Dominance Rank of Wild Bonobos (Pan paniscus) at Wamba

I studied dominance relations in a wild group of bonobos at Wamba, Democratic Republic of Congo. Although agonistic interactions between males occurred frequently, most of them consisted only of display, and physical attacks were infrequent. Dominance rank order seemed to exist among males, but its linearity is unclear. Dominant males rarely disturbed copulatory behavior by subordinate males. However, high-ranking males usually stayed in the central position of the mixed party and, so, would have more chance of access to estrous females. Among females, older individuals tended to be dominant over younger individuals. However, agonistic interactions between females occurred rather infrequently, and most consisted of displacement without any overt aggressive behavior. Dominance between males and females is unclear, but females tended to have priority of access to food. The close social status between males and females may be related to the prolonged estrus of females and their close aggregation during ranging. Existence of a male's mother in the group and her dominance status among females seemed to influence his dominance rank among males. Young adult males whose mothers were alive in the group tended to have high status. In some cases, change in dominance between high-ranking males was preceded by a corresponding change in dominance between their mothers. As the dominance status of females is similar to that of males, mothers may be able to support their sons to achieve high status, stay in the center of the mixed party, and so have greater access to females, which may maximize the number of descendants of the mothers.     

Seasonal variation in association patterns of wild spider monkeys (<Emphasis Type="Italic">Ateles belzebuth belzebuth</Emphasis>) at La Macarena,Colombia

Spider monkeys exhibit a fission–fusion type of social organization. I studied party size and party composition in wild long-haired spider monkeys (Ateles belzebuth belzebuth) in three study periods at La Macarena, Colombia and found that overall party size was larger in the fruit-abundant season. Mean party size in which males were observed was relatively stable across seasons. In contrast, the mean party size of females varied. Females were observed in larger parties in the fruit-abundant season than in the fruit-scarce season. Moreover, whereas males associated with each other at an almost equal frequency across seasons, females associated with each other more frequently in the fruit-abundant season. Females with infants or small juveniles were more often in association with other individuals than were cycling females. The intensity of individual relationships varied according to season, such that even mothers and sons were not always strongly associated. In a large party, females with infants may gain from predation avoidance but they are at a disadvantage in terms of scramble competition. The balance between these factors may change with fruit availability and may influence party size in different periods. For males, party formation may facilitate the defense of resources from neighboring groups more than provide predation avoidance. Electronic Publication     

Grouping Patterns and Competition Among Female <Emphasis Type="Italic">Pan troglodytes schweinfurthii</Emphasis> at Ngogo,Kibale National Park,Uganda

In mammals, access to mates is probably the most important influence on male reproductive success, whereas foraging efficiency is probably the most important influence on female reproductive success Emlen and Oring (Science 197:215–223, 1977). Male chimpanzees (Pan troglodytes) are highly gregarious and form cooperative relationships with other males. In contrast, female social relationships vary within and between populations. Females in most East African populations, e.g., Gombe, Mahale, Kibale-Kanyawara, are less gregarious than males and spend most of their time alone or with only their dependent offspring. Researchers have attributed low female gregariousness to the high potential for feeding competition. I provide the first data on association patterns and agonistic interactions of female chimpanzees (Pan troglodytes schweinfurthii) from the unusually large Ngogo community, Kibale National Park, Uganda. Ngogo females were less gregarious than males, but spent a mean of 64% of their time in association with ≥1 other females and as much time in all-female parties as they did alone. Further, female dyads associated nonrandomly and they formed associative cliques. Association levels within cliques were similar to those among the relatively gregarious West African chimpanzee females at Taï (Pan troglodytes verus) and among bonobo (P. paniscus) females. Agonistic interfemale interactions were extremely rare, and monthly mean party size and the numbers of anestrous females per party do not correlate significantly with fruit availability. Thus, Ngogo females maintained relatively high levels of gregariousness, but avoided detrimental feeding competition by preferentially associating with a small subset of other community females.     

Grouping patterns of wild pygmy chimpanzees (Pan paniscus) observed at a marsh grassland amidst the tropical rain forest of Yalosidi,Republic of Zaïre

Fixed point observation to ascertain the grouping patterns of wild pygmy chimpanzees was carried out at a marsh grassland known locally as Iyoko amidst the tropical rain forest of Yalosidi, Republic of Zaïre. The chimpanzees were seen alone or in parties consisting of up to 32 individuals. The mean size of parties which arrived at Iyoko was 7.9 (N=67), although the modal party size was 2–5. The majority (76%) of all observed parties including those that reformed after joining/parting while staying at Iyoko (N=96) was of the mixed type, i.e., consisting of adult male(s), adult female(s), and dependent individual(s). There was a tendency for parties to be composed of approximately equal numbers of adult males and females. All “social” activities such as sexual behavior and branch-dragging displays were recorded only in mixed parties consisting of more than ten individuals. The joining of parties of pygmy chimpanzees after arriving separately at Iyoko was seen 13 times and the parting of those before departing from Iyoko occurred seven times in total. In contrast, antagonistic encounters between two parties were recorded twice. These observations suggest that the joining/parting between parties is an intra-unit-group phenomenon while antagonistic encounters between parties are inter-unit-group interactions. It was assumed that at least two such unit-groups of pygmy chimpanzees consisting of 80–90 individuals in total utilized Iyoko without intermingling with each other. A comparison on grouping patterns among three pygmy chimpanzee populations (Yalosidi, Wamba, and Lomako) indicates that in terms of basic social organization they show many similarities except for the mean unit-group size, the mean party size, and the modal party size. Perhaps differences in the unit-group size were simply reflected as a whole in the differences of the mean party size as well as the modal party size observed across the three populations.     

Pubic symphyseal synostosis and sexual dimorphism of the pelvis inPresbytis cristata andPresbytis rubicunda

This study examines the relationship between public symphyseal synostosis and sexual dimorphism of the pelvis in two sympatric species ofPresbytis—P. cristata andP. rubicunda. Whereas no specimen ofP. cristata shows fusion of the interpubic joint, a high percentage of female (43.8%) and male (83.3%)P. rubicunda have a fused public symphysis. As females of both species are similar in body size, they are predicted to give birth to similarly sized newborns. Based on comparison with other anthropoids, the percentage dimorphism in the ischiopubic index inP. cristata andP. rubicuda suggests selection on pelvic capacity in relation to obstetrics. In species characterized by cephalopelvic constriction (i.e., the size of the fetal cranium closely approximates the capacity of the maternal birth canal), successful birth seems possible only by a hormonally induced increase in pelvic joint mobility during delivery. However, fusion of the interpubic joint obviates pelvic joint mobility. Consequently, this study tests the hypothesis thatP. rubicunda shows obstetric adaptations of the pelvis that are not found inP. cristata. The results show that pelvic capacity is larger in females than males in bothP. cristata andP. rubicunda; the sexual difference is most pronounced at the inlet. Moreover, the pattern of pelvic dimorphism is nearly identical between the species. When females of the two species are compared,P. rubicunda evidences a shorter distance between the sacroiliac and hip joints and a wider bituberous diameter. The former is related to interspecific differences in locomotion, and the latter is associated with obstetrics.     

General Gregariousness and Specific Social Preferences among Wild Chimpanzees

Wild chimpanzees form temporary parties that vary in size and composition. Previous studies have revealed considerable intraspecific variation in party compositions. We examined patterns of association among age, sex, and reproductive classes of chimpanzees at Ngogo in the Kibale National Park, Uganda. We employed a class-based association index and a randomization procedure to control for confounding factors and to test for differences between classes. Results indicate that males associated with other males significantly more than expected if all classes behaved equivalently, while females generally associated with individuals of the same sex less than expected. To interpret these patterns we used two additional indices that separate associations into two components: general gregariousness and preference for particular classes of associates. Males and estrous females were more gregarious than other classes, while anestrous females were less so. After controlling for general gregariousness, adult males as a class showed no specific preference for associating with each other. Anestrous females preferred each other as party members, and estrous females avoided each other. These results are consistent with previous findings that adult males are more gregarious than females. They diverge from the standard picture of chimpanzee society, however, by suggesting a mutual affinity among anestrous females, but not among adult males as a class.     

Population Variation in Patch and Party Size in Muriquis (Brachyteles arachnoides)

We examined the relationship between food patch size and feeding party size with comparative data from two populations of muriquis (Brachyteles arachnoides) in the 37,797-ha forest at the Parque Estadual de Carlos Botelho (PECB), São Paulo, and the 800-ha forest at the Estação Biológica de Caratinga (EBC), Minas Gerais. Precipitation was more abundant and less seasonal at PECB than EBC, and the density of large trees (>25.0 cm) was higher at PECB (206 ha ^–1 ) than at EBC (132 ha ^–1 ). At both sites, the size of feeding parties is positively related to the size of food patches. As predicted, food patches at PECB are significantly larger than those at EBC for both fruit and leaf sources. Contrary to expectations, feeding parties were larger at EBC than PECB. The higher population density of muriquis and sympatric primates at EBC may make large associations more advantageous to these muriquis than to muriquis living at lower population densities in PECB.     

The behavior of postreproductive females in a wild population of toque macaques (Macaca sinica) in Sri Lanka

I compared the behavior of three old postreproductive females in a wild population of toque macaques (Macaca sinica)in Polonnaruwa with those of reproductive females via focal-animal sampling techniques. Postreproductives foraged less, slept more, and were less active overall than reproductive females were. They also had significantly lower rates of agonistic behavior, were more peripheral, and had lower frequencies of overall affiliative contact. Although postreproductives initiated contact with others as frequently as reproductives did, group members initiated contact with them significantly less than they did with reproductive females. Postreproductives associated more with adult females than reproductives did and less with adult and subadult males than high-ranking reproductives did. Juvenile and infant females associated more frequently with reproductive females of high or low rank than with postreproductives. Postreproductives resembled low-ranking reproductive females in giving less grooming to others than they received. This contrasts with high-ranking females, which gave more grooming to others than they received. The results suggest that old age and cessation of reproduction are evident through the manifestation of distinct behavioral characteristics in toque macaque females.     

Grouping behavior of Sumatran orangutans (Pongo abelii) and Tapanuli orangutans (Pongo tapanuliensis) living in forest with low fruit abundance

In contrast to the African great apes, orangutans (Pongo spp.) are semisolitary: Individuals are often on their own, but form aggregations more often than expected by chance. These temporary aggregations provide social benefits such as mating opportunities. When fruit availability is high, costs of aggregating should be lower, because competition is less pronounced. Therefore, average party size is expected to be higher when fruit availability is high. This hypothesis would also explain why orangutans in highly fruit-productive habitats on Sumatra are more gregarious than in the usually less productive habitats of Borneo. Here, we describe the aggregation behavior of orangutans in less productive Sumatran habitats (Sikundur and Batang Toru), and compare results with those of previously surveyed field sites. Orangutans in Sikundur were more likely to form parties when fruit availability was higher, but the size of daily parties was not significantly affected by fruit availability. With regard to between-site comparisons, average party sizes of females and alone time of parous females in Sikundur and Batang Toru were substantially lower than those for two previously surveyed Sumatran sites, and both fall in the range of values for Bornean sites. Our results indicate that the assessment of orangutans on Sumatra as being more social than those on Borneo needs revision. Instead, between-site differences in sociality seem to reflect differences in average fruit availability.     

Sexual swelling,receptivity, and grouping of wild pygmy chimpanzee females at Wamba,Zaïre

The sexual swelling and copulatory behavior of ten pygmy chimpanzee (Pan paniscus) females in a wild group were studied at Wamba, Republic of Zaïre. Since the maximum size of the sexual skin revealed great individual variations depending on age and adolescent females showed little cyclic fluctuation in size, the sexual swelling was measured according to its firmness which periodically fluctuated in all age classes. The duration of maximum swelling and the cycle length were longer inP. paniscus than inP. troglodytes. Although pregnant females and those with newborn infants were sexually inactive, females with infants older than 3 years copulated as frequently as those without dependent infants. Contrary to previous reports on the sexuality ofP. paniscus, copulation was mostly restricted to the maximum swelling phase. All females were usually found in a large mixed party containing both sexes and offspring, regardless of their sexual receptivity.     

Sexual Differences in Ranging of <Emphasis Type="Italic">Ateles belzebuth belzebuth</Emphasis> at La Macarena,Colombia

I examined sex differences in the ranging patterns of 3 female and 3 male wild spider monkeys. Each of the focal males used the home range widely, whereas each of the focal females used a distinct, restricted area of the home range. The males traveled longer distances than the females did. Although males were consistently in larger parties than females were, travel speed was affected by party composition rather than party size. All-male parties traveled faster than other party types did. Foraging manner also differed between sexes. Males spent more time feeding on fruits and less time on flowers and traveled longer distances between feeding trees. Both males and females used salados, where they ate soil and drank water. Salado location is likely to have affected the ranging pattern. Males used boundary areas more frequently than females did, often traveling along the boundary area in alliance with other males. Males also used areas that had been part of neighboring groups home ranges and were not used at all by females of the group. Greater travel distance of males is likely to be facilitated by consumption of a higher caloric diet. I compare the social structure of spider monkeys with that of chimpanzees, whose society is characterized by male-philopatry and female dispersion.     

Assortative pairing in the amphipod <Emphasis Type="Italic">Paracalliope fluviatilis</Emphasis>: a role for parasites?

The potential impact of parasitism on pairing patterns of the amphipod Paracalliope fluviatilis was investigated with regard to the infection status of both males and females. Two helminth parasites commonly use this crustacean species as second intermediate host. One of them, Coitocaecum parvum, is a progenetic trematode with an egg-producing metacercaria occasionally reaching 2.0 mm in length, i.e. more than 50% the typical length of its amphipod host. The amphipod was shown to exhibit the common reproductive features of most precopula pair-forming crustaceans, i.e. larger males and females among pairs than among singles, more fecund females in pairs, and a trend for size-assortative pairing. Although effects of parasitism were expected a priori, no major influence of the two trematodes was shown on the host reproductive patterns herein investigated. In particular, the occurrence of pairs of infected individuals conformed exactly to what can be expected under the null hypothesis of completely random pair formation. The absence of parasite effect was also illustrated by a similar fecundity of infected and uninfected females. This study thus tends to moderate the widespread view of a strong influence of parasitism on host mating patterns, as suggested by the recent literature on this specific subject.     

Genetic variability in two hydrophilous species ofPotamogeton,P. pectinatus andP. filiformis (Potamogetonaceae)

Genetic variability inPotamogeton pectinatus andP. filiformis was studied by means of isozymes. The overall levels of variability were similar to some other well studied hydrophilous species, and were shown to be distributed more between than within populations. This partitioning of variability was attributed to three main factors. (1) Clonal growth (as measured by the frequency of multi-enzyme phenotypes) was shown to be a major factor in both species, although more important inP. pectinatus. (2) Low levels of sexual reproduction were shown to be a likely contributor to the partitioning of variability inP. pectinatus; such reproduction is probably limited by seedling recruitment rather than by infrequent flowering. (3) Geographical isolation was indicated as a factor regulating gene flow at distances of more than about 1000 km in both species, with the data suggesting that dispersal between populations is mainly by seed rather than by vegetative means.     

Decomposition ofCarex andNuphar plants in a subalpine marsh

To assess the effect of water depth on the decomposition process, I measured the losses in dry mass of the above- and belowground materials ofCarex utriculata andNuphar luteum ssp.potysepalum as well as cellulose (Whatman filter paper) in the top 10 cm of sediment/soil in a subalpine marsh. Samples were examined by the litter bag technique at three flooding levels (0 to 5, 60, and 100 cm water depth). Over a 374-d period, the % mass losses of cellulose,Carex leaves and roots, andNuphar leaves and rhizomes ranged from 98.5 to 99.0, 74.8 to 81.8, 36.3 to 44.9, 95.8 to 97.7, and 78.4 to 91.5%, respectively. Rates for cellulose decay in this study were much higher than for samples from other wetlands; this difference resulted from the location of the litter bag (in the top 10 cm of soilvs in the water column). Water depth significantly affected the decomposition ofCarex roots andNuphar rhizomes. The rate of loss for K was highest in all tissues ofCarex andNuphar, followed by Na inCarex and P inNuphar. N and Ca loss rates generally were low. The C/N ratio tended to converge to a common value over the long term. This convergence has an important implication in the paleoecological interpretation of the C/N ratio change in sediment; i.e., this ratio shift in the sediment core results from a change in the environment, rather than the source material.     

Post‐conflict third‐party affiliation in chimpanzees: what's in it for the third party?

Affiliative behavior after conflicts between conflict participants and other group members is common in many primate species. The proposed functions for such triadic interactions are numerous, mostly concerning the benefit for the former conflict opponents. We investigated post‐conflict third‐party affiliation (TPA) in captive chimpanzees (Pan troglodytes) with the aim of assessing what the affiliating third parties may gain from affiliation. Specifically, we tested whether third‐party‐initiated affiliation protects the third parties from further aggression by conflict opponents. We found support for this “self‐protection hypothesis,” in that third parties selectively directed affiliation to those opponents who more often gave further aggression to them, and affiliation effectively decreased their chance of receiving aggression from these opponents. However, a subset of affiliation, provided to conflict victims by their own kin, appeared to not be self‐protective and the function of it remained open. We conclude that chimpanzee third‐party‐initiated affiliation is a more heterogeneous behavior than thus far assumed. Am. J. Primatol. 71:409–418, 2009. © 2009 Wiley‐Liss, Inc.     

Characterization of type II protein secretion (xcp) genes in the plant growth-stimulatingPseudomonas putida, strain WCS358

InPseudomonas aeruginosa, the products of thexcp genes are required for the secretion of exoproteins across the outer membrane. Despite structural conservation of the Xcp components, secretion of exoproteins via the Xcp pathway is generally not found in heterologous organisms. To study the specificity of this protein secretion pathway, thexcp genes of another fluorescent pseudomonad, the plant growth-promotingPseudomonas putida strain WCS358, were cloned and characterized. Nucleotide sequence analysis revealed the presence of at least five genes, i.e.,xcpP, Q, R, S, andT, with homology toxcp genes ofP. aeruginosa. Unlike the genetic organization inP. aeruginosa, where thexcp cluster consists of two divergently transcribed operons, thexcp genes inP. putida are all oriented in the same direction, and probably comprise a single operon. Upstream ofxcpP inP. putida, an additional open reading frame, with no homolog inP. aeruginosa, was identified, which possibly encodes a lipoprotein. Mutational inactivation ofxcp genes inP. putida did not affect secretion, indicating that no proteins are secreted via the Xcp system under the growth conditions tested, and that an alternative secretion system is operative. To obtain some insight into the secretory pathway involved, the amino acid sequence of the N-terminus of the major extracellular protein was determined. The protein could be identified as flagellin. Mutations in thexcpQ andR genes ofP. aeruginosa could not be complemented by introduction of the correspondingxcp genes ofP. putida. However, expression of a hybrid XcpR protein, composed of the N-terminal one-third ofP. aeruginosa XcpR and the C-terminal two-thirds ofP. putida XcpR, did restore protein secretion in aP. aeruginosa xcpR mutant.