High-density Colonies Research Articles

Foraging habitats and floral resource use by colonies of long- and short-tongued bumble bee species in an agricultural landscape with kabocha squash fields

Bumble bees pollinate and forage on flowers of crop and wild plants in agricultural landscapes. These interactions may depend on landscape patterns and bumble bee traits. We studied the abundance, colony density, and foraging range in long-tongued Bombus diversus Smith and short-tongued B. hypocrita Perez, and evaluated their visits to flowers of wild plants and cultivated kabocha squash (Cucurbita maxima Duchesne). In forests in a farmland, B. hypocrita workers were trapped more frequently in the canopy. Full-sibs determined by nuclear microsatellite genotypes among workers collected in the farmland showed higher colony density and a larger foraging radius in B. hypocrita (30.8 km−2 and 848 m) than in B. diversus (8.3 km−2 and 723 m), respectively. Regarding wild plants, workers more frequently visited shallow flowers in B. hypocrita and deep flowers in B. diversus. These results suggest that bumble bees with different traits forage on different wild flowers in different habitats. Squash flowers were visited by both bumble bee species at similar frequency in the latter period of colony growth when males and new queens appeared. Composition of full-sib workers visiting squash and wild flowers did not depend on the number of collected workers of individual colonies, indicating that foraging on squash flowers was not associated with colony growth. Thus, growth and reproduction of bumble bee colonies may be supported by various wild plants and cultivated squash, respectively.

Sick ants become unsociable

Parasites represent a severe threat to social insects, which form high-density colonies of related individuals, and selection should favour host traits that reduce infection risk. Here, using a carpenter ant (Camponotus aethiops) and a generalist insect pathogenic fungus (Metarhizium brunneum), we show that infected ants radically change their behaviour over time to reduce the risk of colony infection. Infected individuals (i) performed less social interactions than their uninfected counterparts, (ii) did not interact with brood anymore and (iii) spent most of their time outside the nest from day 3 post-infection until death. Furthermore, infected ants displayed an increased aggressiveness towards non-nestmates. Finally, infected ants did not alter their cuticular chemical profile, suggesting that infected individuals do not signal their physiological status to nestmates. Our results provide evidence for the evolution of unsociability following pathogen infection in a social animal and suggest an important role of inclusive fitness in driving such evolution.

The influence of intraspecific competition on resource allocation during dependent colony foundation in a social insect

Organisms face a trade-off between investment in fewer, larger offspring, or more, smaller offspring. Most organisms can adjust investment through variation in the size and number of offspring in response to factors such as resource availability and competition. In some social animals, established colonies divide into groups of individuals that become autonomous, a process known as colony fission (also dependent colony foundation in social insects). Resource allocation under fission can be fine-tuned by adjusting the number of new groups (offspring number) and the number of individuals in each new group (offspring size). We assessed the influence of competition on resource allocation during fission in the ant Cataglyphis cursor, by allowing colonies to fission in experimental enclosures of high or low conspecific colony density. The pattern of colony fission was similar to that observed in the field: each fissioning colony produced a few new nests comprising a highly variable number of workers and a single queen, the old queen was often replaced, and new queens were produced in excess. The number of new nests produced depended on the available workforce in the parent colony but was not affected by differences in colony density. Comparison with data from fission under natural field conditions, however, indicates that colonies in enclosures produced fewer, larger new nests, suggesting that resource investment patterns during fission are indeed subject to extrinsic factors. The density of conspecific colonies in the immediate surroundings may be an unreliable estimate of competition intensity and other factors should be considered.

Spatial and temporal aspects of the relationships between Latibulus argiolus (Rossi) (Hymenoptera: Ichneumonidae) parasitoid and the resocial host wasp Polistes nimpha (Christ) (Hymenoptera: Vespidae)

The observations have shown that under the conditions of the Proval‘skaya steppe of the Lugansk nature reserve females of the first generation of parasitoid Latibulus argiolus display a behavioral response to the distribution of the host, the resocial wasp Polistes nimpha. L. argiolus females concentrate their searching activity on the sites with a high host colony density, and their distribution depends on the nest size. When the parasitoid number increases, they start parasitizing the host earlier, sometimes even before worker emergence. The density-dependent behavioral response observed in the nature is conditioned in the first place by the influence of the numerical response component since when the parasitoid number increases, they start parasitizing the host earlier, sometimes even before worker emergence.

The depletion of skeletal muscle satellite cells with age is concomitant with reduced capacity of single progenitors to produce reserve progeny

Satellite cells are myogenic progenitors that reside on the myofiber surface and support skeletal muscle repair. We used mice in which satellite cells were detected by GFP expression driven by nestin gene regulatory elements to define age-related changes in both numbers of satellite cells that occupy hindlimb myofibers and their individual performance. We demonstrate a reduction in satellite cells per myofiber with age that is more prominent in females compared to males. Satellite cell loss also persists with age in myostatin-null mice regardless of increased muscle mass. Immunofluorescent analysis of isolated myofibers from nestin–GFP/Myf5nLacZ/+ mice reveals a decline with age in the number of satellite cells that express detectable levels of βgal. Nestin–GFP expression typically diminishes in primary cultures of satellite cells as myogenic progeny proliferate and differentiate, but GFP subsequently reappears in the Pax7+ reserve population. Clonal analysis of sorted GFP+ satellite cells from hindlimb muscles shows heterogeneity in the extent of cell density and myotube formation among colonies. Reserve cells emerge primarily within high-density colonies, and the number of clones that produce reserve cells is reduced with age. Thus, satellite cell depletion with age could be attributed to a reduced capacity to generate a reserve population.

Diet of two sympatric Pheidole spp. ants in the central Monte desert: implications for seed–granivore interactions

Ants of the genus Pheidole are important seed consumers in several desert ecosystems. In South American deserts, although several Pheidole spp. have been characterized as seed harvesters, studies on their diet and ecological role are still missing. Pheidole spininodis (Mayr) and Pheidole bergi (Mayr) are capable of removing seeds in the central Monte desert. The aim of this study was to quantify and compare the diet of these species and to interpret the results in the context of seed–granivore interactions. Diet was estimated during mid-summer by collecting items brought back to the nest by foragers in ten colonies per species. While P. spininodis was mainly granivorous, P. bergi was mainly insectivorous. However, they both collected ~40% of other types of items. Among seeds, the diet of P. spininodis included mostly grass seeds, whereas the diet of P. bergi was mainly made up of shrub and tree seeds, usually retrieved cooperatively. This behavior allowed P. bergi to carry larger seeds, resulting in diet partitioning in terms of seed size. However, diet of P. spininodis is very similar to that of three sympatric Pogonomyrmex species. Thus, specialized harvester ants remove large quantities of grass seeds in the central Monte desert during the summer, potentially affecting their abundance in the soil seed bank. P. bergi directs its feeding pressure to shrub and tree seeds, and although seeds constitute ~10% of its diet, its high colony density and high activity levels, added to the lower proportion of large seeds in the soil seed bank, indicate that their importance as seed consumers cannot be ruled out.

Alloparental feeding in Adélie penguins: why is it uncommon?

We investigated alloparental interactions and conditions which could facilitate or prevent the expression of alloparental behaviours in Adelie penguins (Pygoscelis adeliae), a long-lived seabird which nests in high-density colonies around Antarctica. Observation sessions were carried out during the creche stage on 48 identified pairs and 50 identified chicks in a 217-nest subcolony. As the season progressed, young were fed less often by their own parents because these were increasingly absent from the breeding site and less responsive to their offspring’s solicitations. As a consequence, young and particularly those with a low body mass, coming from a two-chick brood, opted for gradually soliciting more from other adults to obtain food, preferentially those nesting in their direct vicinity. Unsuccessful breeders represented a low and constant part of the adult population and were not specifically solicited by unrelated young. Despite the increasing chick demand, only 4.1% (3 out of 73) of alloparental solicitations resulted in feeding, which is negligible compared to parental feeding. To investigate factors that could trigger the appearance of alloparental care, we carried out comparisons with king (Aptenodytes patagonicus) and emperor penguins (Aptenodytes forsteri) which represent the closest species for which data on alloparental behaviour were available. Our results show different trends to those observed in these species and three factors may explain the low occurrence of alloparental behaviour in Adelie penguins: (1) the low and constant proportion of unsuccessful breeders, (2) the absence of chick selectivity towards unsuccessful breeders, and (3) the late period of chick accessibility for potential alloparents.

Long-Distance Dispersal of the Gypsy Moth (Lepidoptera: Lymantriidae) Facilitated Its Initial Invasion of Wisconsin

Gypsy moth (Lymantria dispar L.) spread is dominated by stratified dispersal, and, although spread rates are variable in space and time, the gypsy moth has invaded Wisconsin at a consistently higher rate than in other regions. Allee effects, which act on low-density populations ahead of the moving population that contribute to gypsy moth spread, have also been observed to be consistently weaker in Wisconsin. Because a major cause of an Allee effect in the gypsy moth is mate-finding failure at low densities, supplementing low-density populations with immigrants that arrive through dispersal may facilitate establishment and consequent spread. We used local indicator of spatial autocorrelation methods to examine space-time gypsy moth monitoring data from 1996 to 2006 and identify isolated, low-density colonies that arrived through dispersal. We measured the distance of these colonies from the moving population front to show that long-distance dispersal was markedly present in earlier years when Wisconsin was still mainly uninfested. Recently, however, immigrants arriving through long-distance dispersal may no longer be detected because instead of invading uninfested areas, they are now supplementing high-density colonies. In contrast, we observed no temporal pattern in the distance between low-density colonies and the population front in West Virginia and Virginia. We submit that long-distance dispersal, perhaps facilitated through meteorological mechanisms, played an important role in the spread dynamics of the initial Wisconsin gypsy moth invasion, but it currently plays a lesser role because the portion of Wisconsin most susceptible to long-distance immigrants from alternate sources is now heavily infested.

Determinants of agonistic interactions in California sea lions

Summary California sea lions aggregate in high density colonies during the breeding season. Competition for space and mates results in agonistic interactions that may have long-term population consequences. We explored how demographic, behavioral, and environmental variables influence the rate of agonistic interactions in male and female California sea lions at three breeding colonies with varying population trends and distributed across a wide latitudinal gradient within the Gulf of California, Mexico. Our results indicate that male agonistic interactions are related to environmental and spatial parameters, whereas female interactions are related to male interactions, operational sex ratio (OSR) and environmental parameters. Most demographic and environmental parameters were inversely related to rates of agonistic interactions, with the exception of positive relationships between agonistic interactions and territory size for males and OSR for females. In addition, the highest overall rates of aggression were associated with a declining population. Our findings suggest agonistic interactions may be useful in assessing population dynamics, but additional research is needed to identify mechanistic relationships.

Szilard's dream

With the advent of microfluidics technology and the development of a user-friendly device, studying high-density colonies of microorganisms in controlled chemostatic conditions now becomes a reality.

Improved vectors for transcriptional/translational signal screening in corynebacteria using the melC operon from Streptomyces glaucescens as reporter.

The tyrosinase operon ( melC) from Streptomyces glaucescens was cloned and functionally expressed in Brevibacterium lactofermentum and Corynebacterium glutamicum under the control of the promoter of the kan gene from Tn 5. Recombinant corynebacterial cells containing the tyrosinase operon produced melanin on agar plates and in liquid culture when supplemented with copper and tyrosine. A conjugative bifunctional replacement vector for transcriptional/translational signal screening (pEMel-1) was constructed using expression of the melC operon from S. glaucescens, which can be used for cloning promoter sequences as EcoRI- NdeI fragments. When the DNA fragments with promoter activity such as cspBp or trpp were inserted into pEMel-1, B. lactofermentum harboring the chimeric plasmids produced melanin at different stages of growth, allowing temporal detection of promoter activity. The vector was also used to detect the activity of a Streptomyces promoter ( xysAp), which was inactive in B. lactofermentum, after PCR mutagenesis. The melC operon can be used for the visual, inexpensive (compared to the high price of starch azure for amylase detection), and non-selective (in contrast to the kan or cat genes) screening of several thousand clones at high colony density without killing of the transformants due to the presence of iodine (as in the case of amylase assay).

Recruitment density can determine adult morphology and fecundity in the barnacle, Semibalanus balanoides

Although consequences of the settlement preference of larvae have been well documented, the consequence of these settlement choices on subsequent mortality, morphology and fecundity has been little studied. The aim of this study was to determine the relationship between recruit and adult density and to determine the effect of recruitment on adult morphology and egg tissue mass. This study follows 48 718 barnacles (Semibalanus balanoides) from recruitment at the end of the settling season to reproductively mature adults at a field site in the Clyde Sea (UK). Overall survivorship of the recruits to adulthood was 8.5%, although survivorship was up to 42% on low density settlement panels. In low density colonies (<10 recruits cm‐2), recruitment density was related to adult density (P<0.001), whereas no relationship was found for higher density colonies. A shell morphology index measured at adulthood was related to recruitment density for low density recruited colonies (P<0.001) but not high density colonies. Using ANCOVA, variations between the colonies in shell and egg tissue mass were not explained by mass of somatic tissue. However, egg mass was explained by recruitment density (P<0.01). These results show that adult density is not a reliable indicator of the previous population density of the colony. Moreover, there are marked differences in population development between colonies with high and low recruit densities in terms of impact upon shell morphology and egg production. The dynamics that operate between recruits at the end of the settlement season and sexually mature adults to create the patterns elucidated in this paper, and other literature, remain unclear.

Identification of scFv antibody fragments that specifically recognise the heroin metabolite 6-monoacetylmorphine but not morphine

Use of phage display of recombinant antibodies and large repertoire naı̈ve antibody libraries for identifying antibodies of high specificity has been extensively reported. Nevertheless, there have been few reported antibodies to haptens that have originated from naı̈ve antibody libraries with potential use in diagnostics. We have used chain shuffling of lead single-chain fragment variable (scFv) antibodies, isolated from a naı̈ve antibody library, to screen for antibodies that specifically recognise the major metabolite of heroin, 6-monoacetylmorphine (6MAM). The antibodies were identified by screening high-density colonies of Escherichia coli expressing soluble scFv antibody fragments without prior expression on bacteriophage (phage display). The antibodies recognise 6MAM with affinities of 1–3×10 −7 M with no crossreactivity to morphine. These antibodies can potentially be used for developing a rapid immunoassay in drug-testing programs. To our knowledge, this is the first report of an antibody that distinguishes 6MAM from its de-acetylated form, morphine.

Recruitment Density can Determine Adult ⊥Morphology and Fecundity in the Barnacle, Semibalanus balanoides

Although consequences of the settlement preference of larvae have been well documented, the consequence of these settlement choices on subsequent mortality, morphology and fecundity has been little studied. The aim of this study was to determine the relationship between recruit and adult density and to determine the effect of recruitment on adult morphology and egg tissue mass. This study follows 48,718 barnacles (Semibalanus balanoides) from recruitment at the end of the settling season to reproductively mature adults at a field site in the Clyde Sea (UK). Overall survivorship of the recruits to adulthood was 8.5%, although survivorship was up to 42% on low density settlement panels. In low density colonies (< 10 recruits cm-2), recruitment density was related to adult density (P < 0.001), whereas no relationship was found for higher density colonies. A shell morphology index measured at adulthood was related to recruitment density for low density recruited colonies (P < 0.001) but not high density colonies. Using ANCOVA, variations between the colonies in shell and egg tissue mass were not explained by mass of somatic tissue. However, egg mass was explained by recruitment density (P < 0.01). These results show that adult density is not a reliable indicator of the previous population density of the colony. Moreover, there are marked differences in population development between colonies with high and low recruit densities in terms of impact upon shell morphology and egg production. The dynamics that operate between recruits at the end of the settlement season and sexually mature adults to create the patterns elucidated in this paper, and other literature, remain unclear.

Colony Density and Wing Development inToxoptera citricida(Homoptera: Aphididae)

Factors influencing the development of the alatoid form of the brown citrus aphid, Toxoptera citricida (Kirkaldy), were investigated in the laboratory using Carrizo citrange as a host plant. No evidence of maternal influences on wing development was observed and nymphs were not irreversibly committed to wing development until the late second or early third instar. Both alatae and apterae were significantly larger when they developed on young, flushing terminals citrus than on older, hardening terminals. Similar numbers of late second/early third instars from high-density colonies developed wings when transferred to young and old citrus terminals, but mortality was significantly higher among aphids on the older shoots. When all adults were harvested daily from high-density colonies the percentage of aphids maturing into alatae reached a peak after about 4 d and then declined with aphid density, despite the advancing age of the plant tissues. The density of aphids in a colony was positively correlated with the proportion maturing into alatae.

Intraspecific variation in size and density of Avocet colonies: effects of nest‐distances on hatching and breeding success

In many colonial bird species there is considerable intraspecific variation in colony size and inter‐nest distance (colony density). Possible causes of this variation and its effects on hatching success (survival of eggs) and breeding success (probability of a pair raising chicks) were studied in 48 Avocet Recurvirostra avosetta colonies in Schleswig‐Holstein (Germany) between 1991 and 1996. Colony density was influenced by time of year and habitat (categories: island or mainland, close to or far from feeding grounds). Colonies on islands had the highest densities. When all available space at a colony site was used, colonies became very dense (mean nearest‐neighbour nest distance less than 1 m). Colony size (number of clutches) was influenced by time of year, but not by habitat. Hatching success was low in high density colonies and in very low density ‘colonies’ (single nests) and high over a broad range of intermediate nest densities. The low success rate of single nests was caused by a very high predation rate, whereas the low success rate in very dense colonies was caused by a high rate of nest abandonment. Nest abandonment in very dense colonies was associated with a high level of aggressiveness among Avocets during the egg‐laying period. Due to territorial behaviour, Avocets seemed to be expelled from the densest breeding sites. In very dense colonies, high frequencies of clutches of unusual size occurred due to conspecific nest parasitism. The number of Avocets taking part in attacks on potential egg predators was small and (in colonies of more than one clutch) depended neither on colony size nor on colony density. Despite a low hatching success in very dense colonies, individuals breeding in the densest colonies had significantly better chances of raising chicks than Avocets breeding in less dense colonies. Coloniality seemed to be obligatory for Avocets in order to ensure hatching success. The size and density of colonies seemed to be associated with the availability of suitable nesting habitats (islands).

Cysteamine pretreatment of the astroglial substratum (mitochondrial iron sequestration) enhances PC12 cell vulnerability to oxidative injury.

Much of the excess iron reported in the substantia nigra of subjects with Parkinson's disease (PD) implicates nonneuronal (glial) cellular compartments. Yet, the significance of these glial iron deposits vis-a-vis toxicity to indigent nigrostriatal dopaminergic neurons remains unclear. Cysteamine (CSH) induces the appearance of iron-rich (peroxidase-positive) cytoplasmic inclusions in cultured rat astroglia, which are identical to glial inclusions that progressively accumulate in substantia nigra and other subcortical brain regions with advancing age. We previously demonstrated that the iron-mediated peroxidase activity in these cells oxidizes dopamine and other catechols to potentially neurotoxic semiquinone radicals. In the present study, we cocultured catecholamine-secreting PC12 cells (as low-density dispersed cells or high-density colonies) atop monolayers of either CSH-pretreated (iron-enriched) or control rat astroglial substrata. In some experiments, the PC12 cells were differentiated with nerve growth factor (NGF). The nature of the glial substratum did not appreciably affect the growth characteristics of the PC12 cells. However, undifferentiated PC12 cells grown atop CSH-pretreated astrocytes (a senescent glial phenotype) were far more susceptible to dopamine(1 microM)-H2O2(1 microM)-related killing than PC12 cells cultured on control astroglia. Differentiated PC12 cells behaved similarly although the fraction killed was about half that seen with the undifferentiated PC12 cells. In the latter experiments, PC12 cell death was abrogated by coadministration of the antioxidants, ascorbate (200 microM), melatonin (100 microM), or resveratrol (50 microM) or the iron chelator, deferoxamine (400 microM), attesting to the role of oxidative stress and catalytic iron in the mechanism of PC12 cell death in this system. The aging-associated accumulation of redox-active iron in subcortical astrocytes may facilitate the bioactivation of dopamine to neuronotoxic free radical intermediates and thereby predispose the senescent nervous system to PD and other neurodegenerative disorders.

Pup density related to terrestrial habitat use by New Zealand fur seals

Features of the terrain are important in the selection of terrestrial habitat by otariid seals. Fur seals use rocky shorelines where terrain features such as crevices and ledges may provide shelter for pups. New Zealand fur seals (Arctocephalus forsteri) are increasing in number and expanding their range, requiring them to select new habitat for breeding. Predicting population expansion is important for assessing potential conflicts with commercial fisheries. We quantified terrain features at 25 breeding colonies and 8 nonbreeding colonies around South Island. Univariate tests demonstrated some differences in terrain between breeding and nonbreeding colonies, although principal components analysis (PCA) did not reveal any obvious differences. We suggest that the power to detect differences is reduced by the tendency for nonbreeding colonies to become breeding colonies over time as the population increases. We found a significant relationship between pup density and terrain (i.e., PCA variables) within breeding colonies. The terrain occupied by high-density colonies contained more and smaller rocks, more crevices and ledges, less-pronounced slopes, higher cliffs, and a more westerly exposure than that occupied by low-density colonies. Smaller rocks may provide more spaces in which pups can find shelter; less-pronounced slopes may facilitate pup mobility and higher cliffs may increase shading. We suggest that in addition to terrain features, other phenomena are also involved in breeding-site selection.

Density-Dependent Competition in Fire Ants: Effects on Colony Survivorship and Size Variation

1. Competition among ants can drive changes in both the density and the sizes of colonies. Models of competitive interactions produce conflicting predictions concerning size variation; these predictions have not previously been tested in social insect populations. 2. To measure the effects of early competition on population dynamics of the fire ant Solenopsis invicta, 2284 incipient colonies, each grown from a single queen, were planted in replicate arrays in an irrigated field. In a series of three experiments, colonies were planted in square grids with either 13-5, 15, 40, 60 or 120 cm between nearest neighbours. 3. Soon after planting, active colonies organized brood raids, which ended when victorious colonies acquired the brood and workers of one or more neighbours. 4. Initial colony density had strong effects upon the percentage of colonies engaged in raids, which ranged from 0% at the lowest density to 68-5% at the highest density. High colony density markedly increased raid complexity, colony mortality and queen migration. 5. The complex brood raids seen at high colony density rapidly reorganized clusters of incipient colonies. Excavation of surviving colonies showed that the number of workers per colony was more variable on plots with numerous raids; thus, competition by brood raiding tended to increase the degree of size inequality among colonies. This result is consistent with models and observations of «asymmetric competition» among sessile organisms. 6. During raids, queens sometimes moved to nearby nests where they joined or usurped the original queen. Queen usurpation was especially likely on high-density plots. 7. Brood raids were restricted to the first few weeks following worker emergence and were reduced by low surface moisture, apparently because worker activity declines in dry conditions. By 10 weeks following emergence, the ants developed intolerance of workers from neighbouring colonies, and the mechanism of competition changed from brood raids to group fighting at food resources or foraging trails

Construction and application of streptomycete promoter probe vectors which employ the Streptomyces glaucescens tyrosinase-encoding gene as reporter

We have constructed multicopy and integrative streptomycete promoter probe vectors that employ the promoterless tyrosinase ( melC) operon of Streptomyces glaucescens as the chromogenic transcriptional reporter. Each vector contains the reporter cassette, RC3, which comprises part of the melC operon flanked by transcription terminators; RC3 may be easily inserted into any vector. We demonstrate the use of the pIJ101-based mel vector, pMT3010, for the isolation of mutations which alter expression of the S. coelicolor glycerol operon. The S. glaucescens mel reporter system is well-suited for the visual, non-selective identification of regulatory mutants and can be used efficiently for screening several thousand clones at high colony density.