Uptake of bacterial extracellular polymer by a deposit-feeding holothurian (Isostichopus badionotus)

A laboratory experiment shows that exopolymer (=mucopolysaccharide) produced by the estuarine marine bacterium Pseudomonas atlantica can be a source of nutrition for the deposit-feeding holothurian Isostichopus badionotus (Selenka). Holothurians fed sediment prepared with ¹⁴C-labeled exopolymer incorporated radioactive carbon into their rete mirabile.     

Feeding selectivity and coexistence in two deposit-feeding gastropods

The diets of 2 ecologically similar deposit-feeding gastropods (Batillaria attramentaria and Cerithidea california) are described from 3 salt marsh localities in central California, USA. Gut contents revealed high similarity in dietary composition and a predominance of benthic diatoms. Sympatric and allopatric populations of the gastropods did not differ in diet. In both species, diatom food size increased with snail length with large B. attramentaria selecting longer diatom sizes than large C. californica. Size distributions of B. attramentaria differed in sympatric and allopatric populations. In sympatric populations, snail size classes which exhibited the greatest amounts of overlap in diatom size did not occur together. Effects of size-specific behavioral interactions in the gastropods may explain these differences.     

Effects of organic additions to sediment,and maternal age and size,on patterns of offspring investment and performance in two opportunistic deposit-feeding polychaetes

The investment made by a reproducing organism in its offspring can be affected by both extrinsic (environmental) and intrinsic (female condition) factors. The purpose of this study, conducted between December 1990 and June 1992, was to examine the influence of organic additions to sediment, and female age and size, on patterns of offspring investment and performance in the opportunistic polychaete Capitella sp. I (cf. Capitella capitata Farbricius). Sediment treatments were composed of marsh mud enriched with sewage or algae, or spiked with #2 fuel oil. All three of these additions are associated with opportunistic responses in Capitella sp. I populations in the laboratory and field. As a means of comparison,effects of sewage additions were also examined on the spionid Streblospio benedicti Webster. Organic additions to mud had no detectable effect on the C or N content of embryos in either species. However, sewage had a positive effect on juvenile performance in Capitella sp. I. Juveniles produced by adult Capitella sp. I in the sewage treatment grew 2 times larger (in 2 wk) than juveniles produced by adults in the mud treatment when these juveniles were raised in the same sediment type (mud). Such effects may facilitate opportunistic responses in Capitella sp. I offspring by reducing time to first reproduction. In addition to treatment sediment effects, maternal age and size had a strong influence on patterns of offspring investment in Capitella sp. I. The material investiment measured in collected embryos declined with maternal age in the oil and sewage treatments. The C:N ratio of embryos increased with maternal age for Capitella sp. I except in the algae treatment, which showed no effect of maternal age. Juvenile growth decreased with maternal age in the sewage treatment for Capitella sp. I. Maternal size appeared to have a positive effect on embryo investment in the mud and oil treatments, where reproducing worms were smallest. Previous studies of Capitella sp. I have documented a broad range of environmentally induced responses in growth and fecundity.The results of this study emphasize the importance of maternal environment, age, and size effects on the relationship between offspring investment and performance.Such effects may have profound consequences for the dynamics of populations and the fitness of individuals. Present address: WES-ES-F, USAE Waterways Experiment Station, 3909 Halls Ferry Rd., Vicksburg, Mississippi 39180-6199, USA     

Reproduction and genetic variation in the deposit-feeding sea star Ctenodiscus crispatus

The gonad index in the deposit-feeding asteroid Ctenodiscus crispatus (Retzius) in the Gulf of Maine (USA) is seasonally less variable than in any other sea star, ranging from 2.99 to 4.98% of dry body weight in females and from 2.28 to 3.42% in males, and varies in concert with, rather than reciprocal to, the pyloric caecum index. Biochemical composition and, hence, caloric content, of the gonads also show little seasonal change, suggesting that reproduction is aseasonal and continuous in this population. Oocyte development is asynchronous, all females having a full size range of oocytes (from less than 30 m to greater than 400 m diameter) throughout the year. Seasonally determined size-frequency distributions of juveniles, oocyte cytology and size-frequency distributions, responsiveness of adult females to 1-methyladenine, and oxygen uptake rates indicate that variations in reproductive intensity are superimposed on continuous reproduction, and seem related to changes in phytoplankton production rather than to temperature. The rich neutral lipid content (ca. 50% of total lipid) and large egg size (>400 m) in the ovaries suggest that development is direct. The population is extremely variable genetically, polymorphism among 13 enzyme-coding genes being 77% and average heterozygosity being 0.174. The reproductive pattern and genetic variation in the eurybathic C. crispatus are similar to those in deep-sea echinoderms. This may be related to the constancy of the population's detrital food source, to small-scale heterogeneity of its physical environment, and to low individual vagility.     

Studies on the functional role of tintinnids in the Southern California Bight. I. Grazing and growth rates in laboratory cultures

Five species of tintinnids, Amphorella quadrilineata (Claparède and Lachmann, 1858), Tintinnopsis cf. beroidea Stein (1867), T. cf. acuminata Daday (1887), Eutintinnus pectinis (Kofoid and Campbell, 1929), and Helicostomella subulata (Ehrenberg, 1833), were isolated from Southern California coastal waters and maintained in laboratory cultures which were used to investigate, several aspects of the feeding dynamics and population growth rates of this group of planktonic ciliates. Data are most complete for the latter three species. Both E. pectinis and H. subulata displayed ingestion and growth rates which increased with increasing food concentration until a maximum rate was obtained which then remained essentially constant as food levels increased further. Maximum hourly ingestion was equivalent to approximately 10 to 20% of the body weight of the tintinnids. T. cf. acuminata showed no such maximum ingestion rate, as ingestion rates increased throughout the entire range of food concentrations used. The dependence of growth rate of T. cf. acuminata on food concentration also differed from the other species, being characterized by a broad region of maximum growth at intermediate food levels with reduced growth at both lower and higher food concentrations. Maximum observed growth rates represented doubling times of approximately 12 h for both E. pectinis and T. cf. acuminata and 24 h for H. subulata. The data suggested gross growth efficiencies exceeding 50% over much of the range of food concentrations used. No strong evidence supporting the existence of feeding thresholds or switching behavior was collected during these experiments, although apparently selective feeding was observed in one experiment with E. pectinis.     

Reproductive biology of a deposit-feeding amphipod, Casco bigelowi, with extended parental care

The reproductive traits of a deposit-feeding amphipod that engages in extended parental care were examined. At the study site in Lowes Cove, Maine, USA, Casco bigelowi (Blake, 1929) occurred in highest densities in soft sediments just below mean low water (MLW). During most months, the sex ratio was ≃1. Many females hosted males in their burrows throughout the summer, but after fertilization of females in September, all adult males disappeared from the study area. In October almost 80% of the females were ovigerous, and in November about the same percentage was parental, i.e. caring for juveniles in their burrows. The females produced only one brood each in late fall which they accommodated in their burrows for 2 mo or longer. The average number of juveniles per female was ∼20 in November, and continuously decreased until January. Juveniles reached sizes >10 mm length in the maternal burrows. In early December the first juveniles were found in their own burrows, but major recruitment took place in late December and January. It is concluded that for C. bigelowi, the delay of recruitment into the winter months with low predation pressure and the large offspring size at this time are major advantages gained by extended parental care. C. bigelowi is host to the peritrich ciliate Cothurnia sp. on its gills, and during the summer months >70% of all amphipods had ciliates on their gills. Juveniles still living in their mother's burrows showed infestation rates similar to that of the parent; those of highly infested mothers were more heavily infested than those of “clean” mothers. Facilitated epibiont transmission during intimate and long-lasting (2␣mo) parent–offspring associations may be a consequence of extended parental care. Received: 25 November 1997 / Accepted: 14 April 1998     

Uptake of arsenate, trimethylarsine oxide, and arsenobetaine by the shrimp Crangon crangon

Common shrimp, Crangon crangon (L.), were exposed to inorganic arsenic (arsenate), trimethylarsine oxide, or arsenobetaine in sea water (100 μg As l⁻¹) or in food (1 mg As g⁻¹ wet wt) for up to 24 d, followed by 16 d depuration in clean sea water with undosed food, in order to determine the efficiency of uptake and retention of the compounds. Accumulation of arsenic in the tail muscle, gills, midgut gland, exoskeleton, and remaining tissues was found to depend on the chemical form of the arsenic and the route of exposure. No arsenic was accumulated by C. crangon exposed to arsenate or trimethylarsine oxide in sea water. Shrimps exposed to waterborne arsenobetaine initially accumulated a small amount of arsenic in their tail muscle and gills. After 16 d, C. crangon fed arsenate, trimethylarsine oxide, or arsenobetaine had accumulated arsenic in their tail muscle to levels ∼2-, 2-, or 40-times, respectively, that of the control group. A roughly linear rate of accumulation was shown by shrimps fed trimethylarsine oxide or arsenobetaine, but C. crangon fed arsenate accumulated arsenic for 16 d, then lost arsenic such that their concentration on Day 24 was not significantly different from that of the control group. Patterns of arsenic accumulation in the gills of shrimps fed the compounds were similar to those seen in the tail muscle. On a whole animal basis, C. crangon retained ∼1.2% of the arsenate, 1.6% of the trimethylarsine oxide, and 42% of the arsenobetaine consumed over the first 16 d of exposure, with roughly half present in the tail muscle in each case. Data obtained support the view that the direct uptake of arsenobetaine from sea water does not make a significant contribution to the relatively high concentrations of this compound in marine crustaceans, and that food is the primary source. Naturally occurring arsenic compounds in C. crangon and possible transformations of the administered arsenic compounds were examined by high performance liquid chromatography using an inductively coupled plasma mass spectrometer as the arsenic-specific detector. Control C. crangon contained arsenobetaine as the major arsenic compound (>95% of total arsenic); tetramethylarsonium ion (0.7%) and an unknown arsenic compound (1.7%) were also present as minor constituents. Shrimp ingesting arsenobetaine accumulated it unchanged. Shrimp ingesting arsenate did not form methylated arsenic compounds; they appeared to contain their accumulated arsenic as unchanged arsenate only, although the possibility that some of the arsenic was reduced to arsenite could not be excluded. C. crangon ingesting trimethylarsine oxide biotransformed the compound predominantly to dimethylarsinate. Received: 9 October 1997 / Accepted: 11 February 1998     

Hydrocarbon bioaccumulation from contaminated sediment by the deposit-feeding polychaeteAbarenicola pacifica

This study examines the role of the organic carbon content of sediment in aromatic hydrocarbon bioaccumulation and assesses the importance of two routes of hydrocarbon uptake: (1) the uptake of the particulate contaminant fraction from ingested sediment; (2) the uptake of the dissolved contaminant fraction from interstitial or overlying water. The lugwormAbarenicola pacifica was collected from San Juan Island, Washington, USA, in January 1989, and exposed to three sediments contaminated with [³H]benzo (a) pyrene (BaP). By manipulating the organic content of these sediments, it was possible to establish three treatments with similar BaP concentrations in the interstitial water, but differing in the amount of BaP in the bulk sediment. BaP bioaccumulation over the first few days of exposure was correlated with feeding rate, suggesting that ingested sediments were a source of BaP. The greatest body burden, however, was attained in those individuals held in sediments with the lowest organic carbon content and the lowest BaP concentration. Body burden at steady state was not correlated with either BaP concentrations in bulk sediment (dry weight or organic carbon-normalized bases) or the interstitial water. Increased organic matter decreased BaP bioavailability in a non-linear fashion. Bioaccumulation factors relative to water and organic content were relatively constant between 1 and 2% organic carbon in the sediment, but these same accumulation factors substantially underestimated body burden if applied to sandy sediments with little (0.3%) organic carbon.     

Egg production and feeding by copepods prior to the spring bloom of phytoplankton in Fram Strait,Greenland Sea

Reproductively activeCalanus hyperboreus (Krøyer) andC. glacialis Jaschnov were captured in the upper 100 m of Fram Strait (77° to 79°N) in late winter 1987. There was no evidence of a phytoplankton bloom; chlorophylla concentrations were uniformly low (<0.1 mg m^–3), and nitrate concentrations were uniformly high (>11.3 mg-at m^–3). Gut-fullness measurements indicated that females were ingesting very little. The maturation state of gonads of bothC. hyperboreus andC. glacialis indicated that 75% of females were in a ripe condition consistent with observed egg laying. The lipid content of females laying eggs was reduced in both species compared to that of females not laying eggs. InC. hyperboreus the reduction was 39% and inC. glacialis it was 44%. All the evidence suggests that bothC. hyperboreus andC. glacialis were laying eggs in late winter by using lipids stored previously; they were not relying on ambient concentrations of phytoplankton. The daily rate of egg laying byC. glacialis using lipids in late winter exceeded the rate reported for summer when ambient food supplies have been shown to be necessary. It is suggested that individuals, spawned well in advance of the spring bloom of phytoplankton, may comprise a major portion of the annual recruitment to the entire population ofC. glacialis in this area, and that their life cycle can be completed within 1 yr. NeitherMetridia longa (Lubbock) norC. finmarchicus (Gunnerus) laid eggs during this study.     

Host range and resistance to aspergillosis in three sea fan species from the Yucatan

Knowledge of host range and mechanisms of disease resistance is fundamental to predicting impacts and spread of marine diseases. Prevalence of signs of aspergillosis, caused by the terrestrial fungus Aspergillus sydowii, was assessed in the Yucatan among three species of sea fan: Gorgonia ventalina, G. cf. mariae, and G. flabellum. The Yucatan is unusual in that ranges of all three sea fan species overlap at many sites along a cline of increasing depth, allowing us to evaluate potential causes of differing prevalence among species. Signs of aspergillosis were observed in all the three species. However, the prevalence of infection in G. cf. mariae, a deep-water species, was consistently low even at sites where G. ventalina was common and had moderate levels of infection. Because G. cf. mariae is a relatively small-stature sea fan, we compared the prevalence of signs in G. cf. mariae to a subset of comparatively sized G. ventalina. G. ventalina had a significantly higher prevalence of aspergillosis, indicating that size does not explain the lower prevalence in G. cf. mariae. Prevalence of disease signs on the shallow-water G. flabellum was also significantly higher than G. cf. mariae, but did not differ from G. ventalina. To test the hypothesis that higher chemical resistance accounts for the low prevalence of disease in G. cf. mariae, we measured the response of A. sydowii in culture to antifungal extracts from each sea fan species. Significantly lower fungal growth rates on extracts of G. cf. mariae than G. ventalina support the hypothesis that G. cf. mariae is more chemically resistant to aspergillosis. When comparing sea fan disease across different regions of the Yucatan, we detected significantly higher prevalence in G. ventalina near Akumal than further north near Cozumel and Puerto Morelos. In Akumal, there was a strong positive correlation between sea fan size and disease, with the largest fans showing the highest prevalence and severity in all three species. In addition, prevalence of aspergillosis in G. ventalina was density-dependent in Ak.     

<Emphasis Type="Italic">Cytherella</Emphasis> as a tool to reconstruct deep-sea paleo-oxygen levels: the respiratory physiology of the platycopid ostracod <Emphasis Type="Italic">Cytherella</Emphasis> cf. <Emphasis Type="Italic">abyssorum</Emphasis>

The reconstruction of past climates is a major challenge. One approach is the use of paleoceanography, which looks for clues to the past activity of deep-sea currents by associating them with the melting of the poles. In different sampling zones, fossil biomarkers are used to reconstruct the oxygenation levels of the sea bottom. Among the ostracods (crustaceans), the family Cytherellidae is considered to be resistant to significant decreases in oxygen and their fossil valves are used as biomarkers for oxygenation levels in the past. We studied the basic principles behind Cytherella cf. abyssorum’s ability to adapt to variations in water oxygenation levels in an attempt to determine what could differentiate it from other ostracods. Cytherella cf. abyssorum Sars 1866 has an activity level and ventilatory frequency only half that of ostracods studied previously. When subjected to a decrease in oxygenation, it demonstrates the beginnings of ventilatory adaptation which is unknown in the other studied ostracods. Some morpho-functional aspects are also remarkable, such as the presence of thick valves, which can close hermetically by means of powerful adductor muscles. Compared with already studied ostracods, Cytherella cf. abyssorum has, therefore, characteristics which suggest an ability to present increased resistance in hypoxia. We discuss these results in the paleoceanographical context by describing a scenario suggesting why an increased proportion of the ostracod population could indicate the existence of ocean bottoms with low oxygenation.     

Selectivity in feeding by the deposit-feeding bivalve Macoma nasuta

Macoma nasuta Conrad is primarily a deposit-feeding bivalve sucking the top millimeter of the sediment surface. Growth experiments show that surface sediment supports growth better than detritus falling from the water column. Gut clearance time is between 1 and 9 h (12°C). Fecal pellets are ejected in a regular rhythm. However, the total amount of feces per unit time shows considerable individual variation. Due to sorting in the mantle cavity, about 97% (dry weight) of the surface material is ejected again as pseudofeces. Selectivity by the bivalve is estimated by comparison of particle size and organic composition of sandy and muddy sediments and compared with feces produced by clams fed these sediments. Fecal pellets are in all cases richer in organic components than the sediment, indicating a high degree of selectivity. Ingestion and digestion of small animals (meiofauna) occur, but many of the ingested specimens survive. It is not possible to estimate the assimilation of organic matter by simple difference between the ingested sediment and the ejected feces. The difficulties in calculating energy budgets which arise from selective feeding and associated bacteria are discussed.     

Role of the nutritive value of sediment in regulating population dynamics of the deposit-feeding polychaete Streblospio shrubsolii

The importance of changes in nutritive value of the sediment in regulating the dynamics of the small deposit-feeding polychaete Streblospio shrubsolii (Buchanam, 1890) was examined. First, fluctuations in the population dynamics of S. shrubsolii and in the nutritive content of the sediment were studied on a seasonal scale. Subsequently, a manipulative field experiment was used to test the hypothesis that, in summer, availability of food regulates aspects of the population dynamics of S. shrubsolii. In summer 1997, sharp increases in protein concentrations and in the number of individuals of S. shrubsolii were found compared to all the other seasons. Densities of S. shrubsolii also showed an increase in the subsequent season. Newly recruited juveniles (19-31 setigers) were abundant in summer and autumn 1997, whereas the number of juveniles (32-42 setigers) increased in autumn 1997. Large numbers of adults were found in summer 1997. Significant negative correlations occurred in summer 1997 between the concentrations of proteins and the total number of individuals, the number of newly recruited juveniles and the density of adults. No differences in densities of juveniles, adults or total number of individuals were found among plots before starting the experiment. After 20 days of experimental enrichment, proteins showed a tendency to increase. After 40 days of enrichment, the total number of individuals was significantly greater in the enriched plots. Large numbers of newly recruited larvae and postlarval adults were found in the enriched plots. The experiment corroborated the model that the growth of population was limited by the availability of food in summer. Thus, in this season, patches of food could have a fundamental role in determining the population dynamics of small deposit-feeders under natural conditions and over short time scales.     

Sequestration of cucurbitacin analogs by New and Old World chrysomelid leaf beetles in the tribe Luperini

Summary Two South American polyphagous leaf beetles,Diabrotica speciosa andCerotoma arcuata, selectively accumulated the bitter tasting compound 23,24-dihydrocucurbitacin D in their body after ingesting root tissues of cucurbit plants. Similarly, three Asian Cucurbitaceae-feeding specialists in the genusAulacophora were found to sequester the same compound. Cucurbitacin analogs were shown to deter feeding by a bird predator, indicating an allomonal role for these compounds in cucurbitacin-associated chrysomelid leaf beetles both of New and Old Worlds. The strong affinity to cucurbitacins, selective sequestration of the analogs and consequent protection from predators suggested an ecological adaptation mechanism developed in common among these two geographically isolated subtribes in the Luperini.     

Growth and reproduction in the Antarctic brooding bivalve Adacnarca nitens (Philobryidae) from the Ross Sea

We present information on the reproductive biology, population structure, and growth of the brooding Antarctic bivalve Adacnarca nitens Pelseneer 1903, from the Ross Sea, Antarctica. Individuals ranging from 0.85 to 6.00 mm were found attached to a hydrozoan colony. This species shows low fecundity and large egg size, common to other brooding species. The minimum size at which oogenesis was detected was 2.3 mm and the minimum size at which brooding was evident was 3.9 mm. Embryos of a full range of developmental stages were brooded simultaneously in females. The population showed a log–normal distribution and results suggest non-periodic reproduction with continuous embryonic development. The reproductive traits of A. nitens are discussed in the context of circum-Antarctic species distribution and limitations to dispersal in brooding benthic invertebrates.     

Defensive and chemical characterization of the froth produced by the cercopid Aphrophora cribrata

Nymphs of the cercopid Aphrophora cribrata cover themselves with a frothy exudate while ingesting sap from their preferred host plant, the eastern white pine, Pinus strobus. Chemical analyses of froth collected from A. cribrata nymphs revealed an array of metabolites belonging to five chemical classes, including fatty acid-derived alcohols, γ-lactones and a single 1-monoacylglycerol, as well as the polyol pinitol and the polyhydroxyalkanoate, poly-3-hydroxybutyrate. Bioassays showed the natural A. cribata froth, as well as a synthetic mixture comprised of representative compound classes identified therein, to be repellent to ants but largely devoid of topical irritancy in tests with cockroaches.     

Phenotypic assortative mating and genetic population structure in the crab Trapezia digitalis

Colonies of Pocillopora spp. containing the crab Trapezia digitalis were collected from Hawaii in summer of 1979 and of 1980. Individuals of T. digitalis in Hawaii vary extensively in coloration of the carapace: crabs were separated into phenotypic classes by their degree of carapace reticulation. When presented with two females of different phenotype, males preferentially paired with the female which was similar to them in reticulation. The genetic population structure of T. digitalis was unusual by comparison with other species of Trapezia. Previously reported homozygote excesses at esterase-4, hexokinase-1, phosphoglucoseisomerase, and general protein-2 cannot be explained by the single-locus Wahlund effect, since there was not significant genetic differentiation among phenotypic classes, as measured by Wright's F _ST statistic. There was significant variation among classes in allele frequencies at a fifth locus, hexokinase-2. Two pairs of loci were in significant gametic disequilibrium. Gametic disequilibrium was not detected in seven other species of Trapezia. It is suggested that multi-locus genetic analysis and an increased geographic sampling range are needed to determine the genetic population structure of T. digitalis in relation to observed variation in coloration.     

Co-operative breeding by the Australian Bell Miner Manorina melanophrys Latham: A test of kin selection theory

Summary A population of Bell Miners Manorina melanophrys cosisted of two social units (clans), each consisting of one or more monogamous paris and numerous helpers. Individuals of a breeding pair occupied one home range, while non-breeding individuals occupied partially overlapping home ranges. Attendants (i.e. parents and helpers) showed clear preferences as to whom they aided (fed) and how much aid they provided. A significant correlation was found between the amount of aid given by an attendant and the genetic relationship between the attendant and the recipient. This provides strong quantitative evidence for the theory of kin selection. Only 14% of eggs laid produced juveniles which lived longer than 3 months. It is suggested that the extremely high juvenile mortality favours individuals which help relatives, even while such individuals have dependent offspring of their own.     

Factors influencing the gas composition in the vesicles of Sargassum

The composition of gas in the vesicles of Sargassum cf. leptopodum Sonder has been investigated. The oxygen content depends upon the oxygen partial pressure of the surrounding medium. It does not depend upon the photosynthetic activity of the vesicle. Evidence is provided that the lower limit of the vertical distribution zone of Sargassum cf. leptopodum Sonder is not controlled by the vesicles' capability of resisting hydrostatic pressure.     

Social and ecological influences on activity budgets of vervet monkeys,and their implications for group living

Summary Activity patterns were documented over a 20-month period in six groups of vervet monkeys (Cercopithecus aethiops) in Amboseli National Park, Kenya. Group size varied both among groups and within groups through time. The home ranges of two groups were located in Acacia xanthophloea habitat whereas those of four adjacent groups were located in A. tortilis habitat. Repeated measures analysis of variance, three-way analysis of variance, and meta-analysis of group size effects were carried out on feeding, moving, resting, scanning, allo-grooming, and other behavior. Time spent feeding varied seasonally, peaking during periods when A. tortilis seeds were eaten. However, time spent feeding did not vary within or among groups, or between habitats, males and females, or dominants and subordinates. Males spend more time scanning and less time allo-grooming than females, and high-ranking individuals of both sexes spent more time scanning than low-ranking individuals. Among females, subordinates spent more time moving, whereas among males, dominants spent more time moving. Groups living in A. xanthophloea habitat spent more time moving and allo-grooming than groups in A. tortilis habitat but this may have been confounded by the fact that these two groups were on average larger than the others. Significant differences in activity budgets among groups demonstrate that activity patterns observed in one group are not always readily generalized to other groups even when they come from the same population. Group size analyses examined potential costs and benefits of group living. Increased intragroup competition, measured by time spent moving and feeding, was only weakly evident in larger groups. Individuals in larger groups allo-groomed more than individuals in smaller groups. Self-grooming also increased in larger groups. Individuals in larger groups spent less time scanning than individuals in smaller groups, but there was more scanning per group in larger groups than in smaller groups. Correspondence to: L.A. Isbell