The organization of work in Polybia occidentalis: costs and benefits of specialization in a social wasp

Summary Nest construction, a complex social activity requiring the coordination of 3 tasks (Fig.2), was compared in large (<350 adults) and small (<50 adults) colonies of Polybia occidentalis. The 3 tasks—water foraging, pulp foraging, and building—are performed by 3 separate groups of workers (Fig.4). Of the 8 acts comprising the 3 tasks, 5 regularly involve the transfer of water or pulp from one worker to another on the nest.Small colonies required nearly twice as long (35.4 worker-min) as large colonies (20.1 workermin) to complete a unit amount of construction work. Behavioral acts involving material transfer among workers were responsible for most of the increase in small colonies. In other words, the waiting times experienced by material donors and recipients were greater in small colonies. In small colonies workers switched among the three tasks more frequently than in large colonies (Fig. 4). This was the result of more frequent switching by generalists (workers that performed 2 or 3 of the tasks), rather than by a decrease in the proportion of specialists (workers performing only 1 task type) (Fig. 3).The series-parallel system by which Polybia occidentalis organizes nest construction has a major advantage over the series operation of solitary wasps. Pulp foragers collect and carry loads that are 6.1 times as large as builders can work with at the nest, and water foragers bring in loads that appear to be limited only by crop capacity and that provide all the moisture necessary for the complete processing of 0.74 of a foraged pulp load. As a result P. occidentalis can collect and process a given amount of nest material using 2.6 times fewer foraging trips than would be required by the series system. This in turn means that P. occidentalis not only achieves an energy saving that probably more than offsets the increased costs of material handling at the nest, but it reduces the exposure of its foragers to predators in the field.     

Parasitism in a social wasp: effect of gregarines on foraging behavior, colony productivity, and adult mortality

Behavior in eusocial insects likely reflects a long history of selection imposed by parasites and pathogens because the conditions of group living often favor the transmission of infection among nestmates. Yet, relatively few studies have quantified the effects of parasites on both the level of individual colony members and of colony success, making it difficult to assess the relative importance of different parasites to the behavioral ecology of their social insect hosts. Colonies of Polybia occidentalis, a Neotropical social wasp, are commonly infected by gregarines (Phylum Apicomplexa; Order Eugregarinida) during the wet season in Guanacaste, Costa Rica. To determine the effect of gregarine infection on individual workers in P. occidentalis, we measured foraging rates of marked wasps from colonies comprising both infected and uninfected individuals. To assess the effect of gregarines on colony success, we measured productivity and adult mortality rates in colonies with different levels of infection prevalence (proportion of adults infected). Foraging rates in marked individuals were negatively correlated with the intensity of gregarine infection. Infected colonies with high gregarine prevalence constructed nests with fewer brood cells per capita, produced less brood biomass per capita, and, surprisingly, experienced lower adult mortality rates than did uninfected or lightly infected colonies. These data strongly suggest that gregarine infection lowers foraging rates, thus reducing risk to foragers and, consequently, reducing adult mortality rates, while at the same time lowering per-capita input of materials and colony productivity. In infected colonies, queen populations were infected with a lower prevalence than were workers. Intra-colony infection prevalence decreased dramatically in the P. occidentalis population during the wet season.An erratum to this article can be found at     

Association of bacteria with bryozoan larvae

Seven species of marine bryozoans were examined for the presence of bacteria associated with the larvae. In three species (Bugula neritina, B. pacifica, and B. simplex), rod-shaped bacteria were consistently observed in the pallial sinus of the larvae, independent of geographic location, year, or season. Larvae of closely related bryozoans (B. stolonifera, B. turrita, Scrupocellaria bertholetti, and Tricellaria occidentalis) occurring sympatrically with those containing bacteria lacked this apparent symbiosis. Those bryozoans examined that possessed the bacteria-larva association are among the most frequently encountered fouling bryozoans.     

Inbreeding in a lek-mating ant species, Pogonomyrmex occidentalis

In this paper we have two goals. First, we examine the effects of sample size on the statistical power to detect a given amount of inbreeding in social insect populations. The statistical power to detect a given level of inbreeding is largely a function of the number of colonies sampled. We explore two sampling schemes, one in which a single individual per colony is sampled for different sample sizes and a second sampling scheme in which constant sampling effort is maintained (the product of the number of colonies and the number of workers per colony is constant). We find that adding additional workers to a sample from a colony makes it easier to detect inbreeding in samples from given number of colonies; however, adding more colonies rather than more workers per colony always gives greater power to detect inbreeding. Because even relatively large amounts of sib-mating generate relatively small inbreeding coefficients, detection of even substantial deviations from random mating will require very large samples. Second, we look at the amount of inbreeding in a large population of the western harvest ant, Pogonomyrmex occidentalis. We find deviations from Hardy-Weinberg equilibrium equivalent to approximately 27% sib-mating in our population ( f = 0.09). Review of past studies on the population structure of other Pogonomyrmex species suggests that inbreeding may be a regular feature of the mating system of these ants. Although P. occidentalisis a swarm-mating species, there are a number of features of its population biology which suggest that the effective population size may be small. These include topographical variation that potentially breaks the population into demes, variation in the reproductive output of colonies, and variation in the size of reproductives produced by colonies. Received: 6 May 1996 / Accepted after revision: 6 October 1996     

Temperature tolerance of the estuarine prawn Upogebia africana (Anomura,Crustacea)

Continuous temperature measurements were made in a typical South East African estuary. Mean summer (November to March) temperatures were in the range 19° to 24°C, and in winter (June to August) from 13° to 16°C. Large daily temperature fluctuations of 6° to 10°C occurred in summer; these appear to result from tidal movement of cool sea water into the estuary. In winter, temperature fluctuations were much smaller (3° to 5°C). The burrowing prawn Upogebia africana (Obtmann) was found to have an upper lethal temperature of 29°C in both winter and summer. The resistance time of prawns to temperatures above 30°C was much greater in summer than in winter. It was possible to acclimate winter prawns and increase their resistance time to a level comparable to that of summer individuals. A latent period of 40 h occurred before acclimation effects were detectable. Long-term exposure of prawns to high temperatures did not increase their resistance above that of summer prawns. Water at a temperature above this upper lethal temperature is not pumped through the burrows. This avoidance behaviour considerably increases the ability of U. africana to withstand short-lived temperature extremes.     

Flexible seed selection by individual harvester ants, Pogonomyrmex occidentalis

Summary Individual seed harvester ants (Pogonomyrmex) have been shown to specialize on specific seed types. We examined possible mechanisms for seed specialization and tested whether fidelity to food type limits the foraging decisions of individual western harvester ants, Pogonomyrmex occidentalis. The seed selection regimes of individually marked ants foraging at piles of two seed types were described and related to differences in seed quality and colonial dietary history. Individual foraging choices were affected by multiple factors, including seed caloric rewards, the previous seed selected, and the dietary history of the colony. Individual seed choices generally converged on the most energetically profitable species, suggesting that foragers exhibit labile preference. However, for a portion of the foragers, seed specialization was also partially due to constancy, defined as a tendency to select seed species that were previously collected. When colonies were presented with one seed type for 1 h and then were offered a mix of that seed and a novel seed type, individuals showed a strong preference for the novel seeds. Such rapid changes in seed preference argue strongly that individual P. occidentalis ants are highly flexible in seed choice and that resource assessment by these ants is more complex than simple maximization of net energetic return.Offprint requests to: J.H. Fewell at the current address     

Forager specialization and the control of nest repair in Polybia occidentalis Olivier (Hymenoptera : Vespidae)

We measured patterns of individual forager specialization and colony-wide rates of material input during periods of response to experimental nest damage and during control periods in three colonies of the tropical social wasp Polybia occidentalis.

Microhabitat and resource utilization in cryptic rocky intertidal echinoderms at Aldabra Atoll,Seychelles

On a sheltered upper eulittoral rocky shore at Aldabra Atoll, 5 cryptic, tropical holothurian species Afrocucumis africana (Semper), Holothuria (Selenkothuria) parva Krauss, Polycheira rufescens (Brandt), H. (Thymiosycia) impatiens (Forskaal) and H. (Mertensiothuria) leucospilota Brandt, in decreasing order of abundance, co-occurred on intact beach-rock, whereas the only ophiuroid Ophiocoma scolopendrina (Lamarck) lived mainly on rubble. The 3 commonest holothurian species (A. africana, H. parva and P. rufescens) utilized significantly different microhabitats. All 5 holothurian species differed appreciably in body size, gut contents and feeding behaviour. The differing holochurian body sized could be related to both particle size classes of the gut contents of these species and microhabitats occupied. The amount of suitable microhabitats is probably more important to the number and abundance of cryptic species than the amount of detrital food resources available. The echinoderm assemblage appeared to be stable over time.     

Studies of marine fouling and boring off Kodiak Island,Alaska

Marine fouling and boring off Kodiak Island, Alaska, was studied at depths of 5, 15, and 30 m by exposing wood/asbestos test panels and retrieving them at monthly and cumulatively longer intervals. Fouling was moderate between June and October and negligible between November and May. The fouling communities at 15 and 30 m were quite dissimilar, probably due to a large surface-to-bottom salinity gradient. The community at the 30 m level was dominated by Balanus crenatus and Pseudochitinopoma occidentalis, that at 15 m by Alcyonidium polyoum and Obelia borealis. At the 5 m deep, pierside site, the most common organisms were B. crenatus, O. borealis and Desmacystis sandalia. Borer attack was a trace at 5 and 15 m and slightly more severe at 30 m.     

Reproductive cycles of tropical sea cucumbers (Echinodermata: Holothuroidea) in southern Taiwan

Reproductive cycles of Afrocucumis africana (Dendrochirotida), Actinopyga echinites, Holothuria leucospilota, H. cinerascens, H. difficilis (Aspidochirotida), Synaptamaculata, Opheodesoma grisea, Patinapta taiwaniensis and Polycheira rufescens (Apodida), representing three orders of intertidal holothurians in southern Taiwan, were determined by gonad index and histological examination from March 1990 through September 1991. All nine species of holothurians have annual spawning periods lasting 2 to 4 mo in spring or summer. The early spawning of H. cinerascens and P. rufescens (suspension feeders) suggests that their feeding mode is related to food resources and may influence the reproductive period. In the direct-developing dendrochirotid (suspension feeder), gonad development occurs in cool months, and gametes are released at the beginning of warm months. In indirect-developing aspidochirotid and apodid (deposit feeder), gamete release occurs in late spring or summer and appears to be correlated with summer phytoplankton growth. The holothurians in the present study display spawning periodicity and duration similar to those of temperate species. Four species of holothurians lengthened spawning season with decreased latitude.     

The social contexts of some very low frequency calls of African elephants

Summary Several types of low frequency calls made by African elephants, Loxodonta africana, and the contexts in which they occurred are described. These calls had fundamental frequencies ranging from 14–35 Hz and sound pressure levels as high as 103±3dB (re 20 Pa) at 5 m from the source. Very low frequency sounds are subject to very little environmental attenuation, suggesting that sounds at the frequencies and sound pressure levels measured from elephants may be audible to conspecifics several km away. Long-term records on the behavior of elephants and on the contexts of specific call types suggest that elephants make use of infrasound in the spatial coordination of groups and as they search for mates.     

Larval depletion by ascidians has little effect on settlement of epifauna

Ascidian densities were manipulated while controlling for negative effects of biodeposition and space preemption to examine the effects of ascidian filter-feeding on larval recruitment in St. Joseph Bay and near Turkey Point, Florida (Northern Gulf of Mexico, Florida, USA). Using three different experimental designs during 1984 and 1985, recruitment near living Styela plicata or Molgula occidentalis was as high as recruitment near ascidian models. Disruption of flow by ascidian bodies had little effect on settlement. Predation rates by ascidians on larvae in six phyla were high in laboratory experiments. The field effects of larval depletion by solitary ascidians are apparently obscured by other factors influencing the abundance of recruiting larvae. Consumption of larvae in the laboratory cannot be used to assume significant inhibitory effects in the field.     

A multispecies assessment of wildlife impacts on local community livelihoods

Conflicts between the interests of agriculture and wildlife conservation are a major threat to biodiversity and human well-being globally. Addressing such conflicts requires a thorough understanding of the impacts associated with living alongside protected wildlife. Despite this, most studies reporting on human–wildlife impacts and the strategies used to mitigate them focus on a single species, thus oversimplifying often complex systems of human–wildlife interactions. We sought to characterize the spatiotemporal patterns of impacts by multiple co-occurring species on agricultural livelihoods in the eastern Okavango Delta Panhandle in northern Botswana through the use of a database of 3264 wildlife-incident reports recorded from 2009 to 2015 by the Department of Wildlife and National Parks. Eight species (African elephants [Loxodonta africana], hippopotamuses [Hippopotamus amphibious], lions [Panthera leo], cheetah [Acinonyx jubatus], African wild dogs [Lycaon pictus], hyenas [Crocuta crocuta], leopards [Panthera pardus], and crocodiles [Crocodylus niloticus]) appeared on incident reports, of which 56.5% were attributed to elephants. Most species were associated with only 1 type of damage (i.e., either crop damage or livestock loss). Carnivores were primarily implicated in incident reports related to livestock loss, particularly toward the end of the dry season (May–October). In contrast, herbivores were associated with crop-loss incidents during the wet season (November–April). Our results illustrate how local communities can face distinct livelihood challenges from different species at different times of the year. Such a multispecies assessment has important implications for the design of conservation interventions aimed at addressing the costs of living with wildlife and thereby mitigation of the underlying conservation conflict. Our spatiotemporal, multispecies approach is widely applicable to other regions where sustainable and long-term solutions to conservation conflicts are needed for local communities and biodiversity.     

Long‐Term Impacts of Poaching on Relatedness,Stress Physiology,and Reproductive Output of Adult Female African Elephants

Abstract: Widespread poaching prior to the 1989 ivory ban greatly altered the demographic structure of matrilineal African elephant (Loxodonta africana) family groups in many populations by decreasing the number of old, adult females. We assessed the long‐term impacts of poaching by investigating genetic, physiological, and reproductive correlates of a disturbed social structure resulting from heavy poaching of an African elephant population in Mikumi National Park, Tanzania, prior to 1989. We examined fecal glucocorticoid levels and reproductive output among 218 adult female elephants from 109 groups differing in size, age structure, and average genetic relatedness over 25 months from 2003 to 2005. The distribution in group size has changed little since 1989, but the number of families with tusked old matriarchs has increased by 14.2%. Females from groups that lacked an old matriarch, first‐order adult relatives, and strong social bonds had significantly higher fecal glucocorticoid values than those from groups with these features (all females R²= 0.31; females in multiadult groups R²= 0.46). Females that frequented isolated areas with historically high poaching risk had higher fecal glucocorticoid values than those in low poaching risk areas. Females with weak bonds and low group relatedness had significantly lower reproductive output (R²[U]=0.21). Females from disrupted groups, defined as having observed average group relatedness 1 SD below the expected mean for a simulated unpoached family, had significantly lower reproductive output than females from intact groups, despite many being in their reproductive prime. These results suggest that long‐term negative impacts from poaching of old, related matriarchs have persisted among adult female elephants 1.5 decades after the 1989 ivory ban was implemented.     

Cover Caption

Cover: African elephants (Loxodonta africana) in Amboseli National Park, Kenya. On pages 1002–1010, Wittemyer examines relations between African elephant mortality and human‐caused wounds and measures of local economic conditions, macroeconomic conditions, and primary productivity. When cattle prices in pastoralist Samburu, Kenya, were low, human‐caused wounds to and adult mortality of elephants increased. Changes in gross domestic product in Kenya and East Asia, the primary markets for ivory, did not explain significant variation in mortality. Results suggest that in some cases, economic metrics are associated with changes in human use of and resulting effects on natural resources. Cover image © 2011 Art Wolfe. Photographer: For the past 30 years, Art Wolfe has worked in hundreds of locations spanning all continents. His photographic style draws on both art and journalism to document his subjects and educate his viewers. His goal is to obtain public support for conservation by focusing on what is beautiful on Earth. Wolfe has published over 60 books for adults and children, including The Living Wild, Vanishing Act, Edge of the Earth–Corner of the Sky, and The Art of Photographing Nature. His book Light on the Land was a gift of state during the Clinton administration, and he has received awards from diverse organizations, including the National Outdoor Book Awards and Graphis. Wolfe is a recipient of the Photographic Society of America's Progress Medal and the first Rachel Carson Award from the National Audubon Society.     

Implications of life history for genetic structure and migration rates of southern African coastal invertebrates: planktonic,abbreviated and direct development

The amount of genetic structure in marine invertebrates is often thought to be negatively correlated with larval duration. However, larval retention may increase genetic structure in species with long-lived planktonic larvae, and rafting provides a means of dispersal for species that lack a larval dispersal phase. We compared genetic structure, demographic histories and levels of gene flow of regional lineages (in most cases defined by biogeographic region) of five southern African coastal invertebrates with three main types of larval development: (1) dispersal by long-lived planktonic larvae (mudprawn Upogebia africana and brown mussel Perna perna), (2) abbreviated larval development (crown crab Hymenosoma orbiculare) and (3) direct development (estuarine isopod Exosphaeroma hylecoetes and estuarine cumacean Iphinoe truncata). We hypothesized that H. orbiculare, having abbreviated larval development, would employ a strategy of larval retention, resulting in genetic structure comparable to that of the direct developers rather than the planktonic dispersers. However, regional population structure was significantly lower in all species with planktonic larvae, including H. orbiculare, than in the direct developers. Moreover, nested clade analysis identified demographic histories resulting from low levels of gene flow (isolation by distance and allopatric fragmentation) in the direct developers only, and migration rates were significantly higher in all three species having planktonic larvae than in the direct developers. We conclude that the amount of genetic structure within marine biogeographic regions strongly depends on the presence or absence of free-swimming larvae. Whether such larvae are primarily exported or retained, whether they have long or short larval duration, and whether or not they are capable of active dispersal seems to have little effect on connectivity among populations.     

Molecular genetic and behavioral analysis of social organization in the Asian elephant (Elephas maximus)

We report on the genetic evaluation and behavioral study of social organization in the Asian elephant (Elephas maximus). Although Asian elephants and African elephants (Loxodonta africana) were previously thought to have similar social organizations, our results demonstrate a substantial difference in the complexity and structure of Asian elephant social groupings from that described for African savanna elephants. Photographic cataloging of individuals, radio telemetry, and behavioral observations in Ruhuna National Park, Sri Lanka, enabled us to assign associated females and young to four groups with overlapping ranges. Genetic sampling of individuals from the four groups in Ruhuna National Park and three other groups in surrounding areas, conducted through PCR amplification and sequencing of mitochondrial DNA from dung, supported the matriarchal nature of female groups and the lack of inter-group transfer of females. Behaviorally and genetically, the identified social groups were best described as ”family groups”. We did not find any evidence for the existence of social groups of higher complexity than family groups. Received: 25 March 2000 / Received in revised form: 28 March 2000 / Accepted: 1 April 2000     

Fuzzy logic-based modeling of the impact of industrial activities on the environmental status of an industrial estate in Nigeria

Industrial growth is being attributed with adverse environmental effects and has necessitated stricter environmental management policies. Formulating such policies is limited by the difficulty in understanding the trends of monitoring data. This study is aimed at the application of fuzzy comprehensive assessment (FCA) to integrate environmental contaminants in Agbara industrial estate, Nigeria, to measure the extent of impact of industrial activities on the host community. Samples of water, plants (Pteridium aquilinum, Sacciolepis africana, and Panicum maximum), soil, and sediments were collected within the estate. Water samples were analyzed for quality parameters using standard methods. Metals (Co, Cr, Cd, Cu, and Mn) were investigated in all the samples using an atomic absorption spectrophotometer. The data were modeled with FCA. The results showed Cr as the major contaminant (34–252?µgL^?1). High phosphate contributed to large plant growth in the area. FCA results showed that water samples were in the pristine classification; sediment samples were extremely impacted. The vegetation growth and the sediment precipitation were responsible for the cleaning-up of the pollutants discharged downstream. The FCA of the plants indicated high metal bioaccumulation and not only showed the plants’ phyto-remediation potential but also that the metals may pose threats to human health through the food web. The activities in the estate are contributing contaminants to the environment with potential negative effects.     

Integrating phenological, chemical and biotic defences in ant-plant protection mutualisms: a case study of two myrmecophyte lineages

Summary. We examined the role of plant phenology in the evolution of anti-herbivore defence in symbiotic ant-plant protection mutualisms. Phenology of the host-plant affects traits of its herbivores, including size, growth rate, development time, and gregariousness. Traits of herbivores in turn determine what traits ants must have to protect their host. Diversity in plant phenological traits could thus help explain the great ecological diversity of coevolved ant-plant mutualisms. We explored the postulated causal chain linking phenology of the plant, herbivore adaptations to phenology, and ant adaptations for protection, by comparing two myrmecophytes presenting strong contrasts in phenology. In Leonardoxa africana, a slow-growing understory tree, growth at each twig terminal is intermittent, the rapid flushing of a single leaf-bearing internode being followed by a pause of several months. In contrast, axes of Barteria nigritana, a tree of open areas, grow continuously. Analysis of the phenology (kinetics of expansion) and chemistry of leaf development (contents of chlorophylls, lignin, and nitrogen during leaf growth) showed that these two species exhibit strongly contrasting strategies. Leonardoxa exhibited a delayed greening strategy, with rapid expansion of leaves during a short period, followed by synthesis of chlorophylls and lignins only after final leaf size has been reached. In contrast, leaves of Barteria expanded more slowly, with chlorophylls and lignin gradually synthesised throughout development. Differences in the phenology of leaf development are reflected in differences in the duration of larval development, and thereby in size, of the principal lepidopteran herbivores observed on these two plants. This difference may in turn have led to different requirements for effective defence by ants. The strategy of phenological defence may thus affect the evolution of biotic defence.     

Chemoautotrophic symbiosis in the tropical clamSolemya occidentalis (Bivalvia: Protobranchia): ultrastructural and phylogenetic analysis

Patterns of algal seasonality, and their effect on the diet and feeding preferences of the herbivorous crab Grapsus albolineatus were investigated over an 18-mo period from March 1993 to August 1994 on an exposed tropical rocky shore (Hok Tsui Peninsula at Cape d' Aguilar, Hong Kong). Algal cover was greatest in the winter months, and lowest in the summer. Foliose algae such as Ulva fasciata, Porphyra suborbiculata, and Dermonema frappieri were dominant in the winter, but died off in the summer. During the hot summer months, perennial encrusting algae e.g., Ralfsia expansa, Hildenbrandia rubra, H. occidentalis, coralline crusts and the encrusting cyanobacteria Kyrtuthrix maculans, were the dominant algal species. Seasonal variation in algal abundance influenced the dietary selectivity of the herbivorous crab G. albolineatus. In the winter, the crab fed selectively on filamentous algae (e.g. Hincksia spp., Cladophora spp., Enteromorpha spp., and the cyanobacteria Lyngbya sp.). Foliose algae (e.g. U. fasciata, P. suborbiculata, Pterocladia tenuis) formed a small part of the diet, despite being the dominant species on the shore. Foliose and filamentous algae were virtually absent from the shore in the summer, and the crabs switched to feeding solely on encrusting algae. Electivity indices revealed preferences for green and brown turf species, and avoidance of foliose algae. Faecal analysis revealed that a greater proportion of the food is digested in the winter, suggesting that G. albolineatus is able to digest filamentous algae more efficiently than encrusting algae. Feeding preferences of G. albolineatus appear to be influenced by a number of factors, including the availability, digestibility and morphology of algae. The foraging behaviour and cheliped morphology of the crab also affect food choice. The monsoonal nature of Hong Kong's climate controls the diversity and abundance of intertidal algae and, therefore, indirectly influences the diet and subsequent growth and reproductive success of the herbivorous crab G. albolineatus.