Fitness consequences of cooperative colony founding in the desert leaf-cutter ant Acromyrmex versicolor

The evolution of cooperative colony foundation (pleometrosis)in ants has been attributed to conversion of extra resourcesinto increased competitive ability. Most cooperative foundingspecies provide these additional resources from internal fatstores; however, in those species that forage for resources, theextent and type of individual investment in multiqueen coloniesis not well understood. We compared singly- and group-foundedlaboratory colonies of the desert leaf-cutter ant Acromyrmexversicolor to investigate how cooperation affects colony survival,foraging success, and worker production. Under laboratory conditions,single foundresses were significantly less likely to initiatea successful symbiotic fungus garden, which inevitably led to colonystarvation and death. If gardens were initiated successfully,however, there was no difference in the growth trajectoriesand foraging patterns between colony types. Cooperation in thisspecies may more likely be maintained by survival benefits thanby growth rate differences, which may be constrained in groupsby individual and colony-level costs.     

Endocrine control of vitellogenesis in the harlequin bug, Dindymus versicolor

An active corpus allatum is essential for the maturation of eggs in the harlequin bug, Dindymus versicolor. The corpus allatum of virgin females remains virtually inactive and the oöcytes are resorbed once they have grown to the stage at which they become competent to incorporate yolk. Mating provides a stimulus which is essential for the initiation and maintenance of corpus allatum activity and, therefore, vitellogenesis. Corpus allatum activity (and vitellogenesis) can be induced in virgin females either by cutting the allatic nerves or by excision of a certain part of the protocerebrum. It is concluded that the corpus allatum of virgin females is inhibited nervously by the brain and that copulation provides a nervous stimulus which lifts this cerebral inhibition thereby permitting allatum activity.The median neurosecretory cells are not essential for vitellogenesis in Dindymus; however, it is suggested that they are necessary for maximum allatum activity. Evidence is provided to show that the growth and maintenance of the previtellogenic oöcytes are also under the control of the corpus allatum. A mechanism is described whereby the number of vitellogenic oöcytes in the ovarioles is maintained constant.     

Genetic determination of female castes in a hybridogenetic desert ant

In most social insects, the brood is totipotent and environmental factors determine whether a female egg will develop into a reproductive queen or a functionally sterile worker. However, genetic factors have been shown to affect the female's caste fate in a few ant species. The desert ant Cataglyphis hispanica reproduces by social hybridogenesis. All populations are characterized by the coexistence of two distinct genetic lineages. Queens are almost always found mated with a male of the alternate lineage than their own. Workers develop from hybrid crosses between the genetic lineages, whereas daughter queens are produced asexually via parthenogenesis. Here, we show that the association between genotype and caste in this species is maintained by a ‘hard‐wired’ genetic caste determination system, whereby nonhybrid genomes have lost the ability to develop as workers. Genetic analyses reveal that, in a rare population with multiple‐queen colonies, a significant proportion of nestmate queens are mated with males of their own lineage. These queens fail to produce worker offspring; they produce only purebred daughter queens by sexual reproduction. We discuss how the production of reproductive queens through sexual, intralineage crosses may favour the stability of social hybridogenesis in this species.     

Isolation and characterization of actinobacteria ectosymbionts from Acromyrmex subterraneus brunneus (Hymenoptera, Formicidae)

The ectosymbiont actinobacterium Pseudonocardia was isolated from the integument of Acromyrmex leaf-cutter ants and seems to play a crucial role in maintaining asepsis of the nest. Currently, there has been an intensive search for Pseudonocardia associated with several attine species, but few studies have indicated that other actinobacteria may be associated with these ants as well. We therefore characterized the culturable actinobacteria community associated with the integument of the fungus-growing ant Acromyrmex subterraneus brunneus Forel, 1893 (Hymenoptera: Formicidae). Ectosymbionts were isolated using four different media and characterized by morphological and molecular (16S rDNA) methods. A total of 20 strains were isolated, of which 17 were characterized as Streptomyces spp., and one isolate each as Pseudonocardia, Kitassatospora and Propionicimonas. Unlike other Acromyrmex species, A. subterraneus brunneus is associated with a diversity of actinobacteria. Even though Pseudonocardia is present on this leaf-cutting ant’s integument, the number and diversity of Streptomyces spp. found differs from those of previous studies with other attine ants and suggest that different culturing approaches are needed to characterize the true diversity of microbes colonizing the integument of attine ants. Moreover, understanding the diversity of the culturable actinobacteria associated with A. subterraneus brunneus should increase our knowledge of the evolutionary relationship of this intricate symbiotic association.     

The role of competition in task switching during colony emigration in the ant Leptothorax albipennis

The decision-making process that determines when an animal should switch between tasks is a fundamental issue in the study of animal behaviour. We investigated, for the first time, such task switching in terms of the dynamics of worker populations in ant colonies. During colony emigration in the ant Leptothorax albipennis, the colony has to carry out the following three tasks: (1) transport of brood and nestmates to the new nest; (2) sorting of the brood into its characteristic pattern; and (3) building the nest wall. At the beginning of the emigration, the stimuli for all three tasks increase simultaneously but the tasks are performed sequentially by populations of workers in the colony. The issue here is how decision making at the colony level is based on the behaviour of individual workers. We used a mathematical model to explore the hypothesis that such colony level task switching is based on tasks competing for workers. The essential feature of this model is that the sequence of tasks performed by an individual worker need not match the sequence of tasks on which the colony concentrates. We base the parameterization of our model on our detailed experimental study of eight emigrations, one for each of eight L. albipennis colonies. We compared our results with earlier work that emphasizes the role of response thresholds in task-related decisions. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Metagenomic and metaproteomic insights into bacterial communities in leaf-cutter ant fungus gardens

Herbivores gain access to nutrients stored in plant biomass largely by harnessing the metabolic activities of microbes. Leaf-cutter ants of the genus Atta are a hallmark example; these dominant neotropical herbivores cultivate symbiotic fungus gardens on large quantities of fresh plant forage. As the external digestive system of the ants, fungus gardens facilitate the production and sustenance of millions of workers. Using metagenomic and metaproteomic techniques, we characterize the bacterial diversity and physiological potential of fungus gardens from two species of Atta. Our analysis of over 1.2 Gbp of community metagenomic sequence and three 16S pyrotag libraries reveals that in addition to harboring the dominant fungal crop, these ecosystems contain abundant populations of Enterobacteriaceae, including the genera Enterobacter, Pantoea, Klebsiella, Citrobacter and Escherichia. We show that these bacterial communities possess genes associated with lignocellulose degradation and diverse biosynthetic pathways, suggesting that they play a role in nutrient cycling by converting the nitrogen-poor forage of the ants into B-vitamins, amino acids and other cellular components. Our metaproteomic analysis confirms that bacterial glycosyl hydrolases and proteins with putative biosynthetic functions are produced in both field-collected and laboratory-reared colonies. These results are consistent with the hypothesis that fungus gardens are specialized fungus–bacteria communities that convert plant material into energy for their ant hosts. Together with recent investigations into the microbial symbionts of vertebrates, our work underscores the importance of microbial communities in the ecology and evolution of herbivorous metazoans.     

Genetic variation in Lumnitzera racemosa, a mangrove species from the Indo-West Pacific

The genetic structure of 18 populations of Lumnitzera racemosa from the Indo-West Pacific, including South China, Malay Peninsula, Sri Lanka, and North Australia, was assessed by inter simple sequence repeat (ISSR) markers. Our results showed a relatively high level of genetic variation at the species level (P = 87.04%, H_e = 0.260). The value of G_st was 0.642, suggesting significant genetic differentiation among populations. At the population level, however, genetic diversity was low (P = 32.17%, H_e = 0.097). When populations were grouped according to geographic regions, i.e., South China Sea, the East Indian Ocean, and North Australia, it was inferred from AMOVA that more than half the total variation (55.37%) was accounted for by differentiation between regions. A UPGMA dendrogram based on genetic distance also revealed a deep split between populations from these regions, indicating that Malay Peninsula and the Indonesia archipelago may play an important part on the genetic differentiation in L. racemosa. The high degree of population differentiation between regions and low genetic variation within populations recorded here highlights the need for appropriate conservation measures for this species, both in terms of incorporating further populations into protected areas, and the restoration strategies for separate regions.     

Spatial effects, sampling errors, and task specialization in the honey bee

Task allocation patterns should depend on the spatial distribution of work within the nest, variation in task demand, and the movement patterns of workers, however, relatively little research has focused on these topics. This study uses a spatially explicit agent based model to determine whether such factors alone can generate biases in task performance at the individual level in the honey bees, Apis mellifera. Specialization (bias in task performance) is shown to result from strong sampling error due to localized task demand, relatively slow moving workers relative to nest size, and strong spatial variation in task demand. To date, specialization has been primarily interpreted with the response threshold concept, which is focused on intrinsic (typically genotypic) differences between workers. Response threshold variation and sampling error due to spatial effects are not mutually exclusive, however, and this study suggests that both contribute to patterns of task bias at the individual level. While spatial effects are strong enough to explain some documented cases of specialization; they are relatively short term and not explanatory for long term cases of specialization. In general, this study suggests that the spatial layout of tasks and fluctuations in their demand must be explicitly controlled for in studies focused on identifying genotypic specialists.     

Resource allocation among worker castes of the leaf-cutting ants Acromyrmex subterraneus subterraneus through trophallaxis

The division of labor between the different worker castes of leaf-cutting ants may reflect in their capacity to exchange liquids by trophallaxis. The crop capacity of and trophallactic exchanges between different size classes of worker leaf-cutting ants of the sub-species Acromyrmex subterraneus subterraneus were investigated. Size classes were defined from head capsule widths and crop capacity of each class was determined following ad libitum feeding on dye solution. Experiments were carried out to investigate trophallactic exchanges between donor ants and recipient ants of each class size combination on a one to one basis. An experiment was also performed to investigate dye distribution within mini-colonies following introduction of three classes of donor ants. Worker ants were categorized into four size classes from their head capsule widths (C1 = 0.8-1.0 mm; C2 = 1.2-1.5 mm; C3 = 1.6-2.0 mm; C4 = 2.1-2.4 mm). C1 ants crop capacity was 0.13 μL; C2: 0.21 μL; C3: 0.52 μL; C4: 1.03 μL. Ants of each class previously fed on the dye solution (donors) were placed individually with an unfed ant of each class (recipients) and the presence of dye solution, passed from the donor to the recipient by oral trophallaxis was observed after 1 h. Results showed that all classes of donor ants performed trophallactic exchanges with all recipient classes. However, statistically fewer exchanges were seen for C2 donor ants when placed with C3 recipient ants. Ten donor ants of each of three classes (C2, C3 and C4) were introduced into mini-colonies without queen ants. It was observed that C1 and C2 ants were poor recipients, whilst C3 and C4 received the highest percentages of dye. Within 10 h of introducing the donor ants, 14 to 20% of their nest-mates had received dye solution, with 58 to 77% of dye passed to recipients. These studies show the altruistic nature of “food-laden” leaf-cutters and indicate that ants involved in garden maintenance activity are less likely to receive liquids from foraging workers.     

Genetic variation and reproduction strategy of Gentiana pannonica in different habitats

Gentiana pannonicascop. (Gentianaceae) is a long-lived perennial mountain species. It is a typical east−Alpine element. The centre of its distribution is situated in the eastern Alps, where the species occurs in alpine and subalpine areas. Besides the Alps, G. pannonica occurs also in the Bohemian Forest, Czech Republic. The reproduction strategy and genetic variation of this species endangered in the Czech Republic were studied. Genetic variation within and among six populations of G. pannonica in the Bohemian Forest and two populations in the Alps was studied using random amplified polymorphic DNAs (RAPD) markers. The variation found between populations from primary habitats and populations situated in the secondary mountain meadows accounted for 5% of the total genetic variation, whereas no significant genetic diversity was found between two different regions (Bohemian Forest, the Alps). Most of the variation is distributed among individuals within populations in the primary habitats, specifically 77% in the Bohemian Forest and 79% in the Alps. The pattern of among-population variation was substantially different between primary and secondary habitats. While among-population variation in primary habitats was low in both of the regions (21–23%), the proportion of RAPD variation among populations in secondary habitats was distinctly higher (65%). Within-population genetic variation was higher in primary habitats than in the secondary ones. This may be a consequence of processes such as genetic drift or bottleneck, and founder effects caused by changes in their distribution during the Holocene period. The differences of vegetation composition, seedlings recruitment and seed set were investigated in the field. Vegetation composition differed between primary and secondary habitats of G. pannonica and seedlings recruitment was recorded only in primary habitats. The reproduction output of the species under study is probably influenced by the availability of pollinators.     

Characterization of two related exoantigens from the biodeteriogenic fungus Aspergillus versicolor

Aspergillus versicolor is one of the most common fungi in damp buildings in U. K., various European and Scandinavian countries as well as the United States and Canada. It is a proxy for species that occur at similar material water activities. Based on studies from Finland, Norway and Germany, it is among the common species resulting in an IgE reaction. Using pre-screened human sera with antibodies to various fungi, two related proteins were discovered with molecular weights 43 and 41 kDa based on SDS electrophoresis. Both proteins were excreted on the surfaces of spores and into culture media. The 41 kDa protein has a pI of 4.5. Based on a partial sequence, it is a serine protease. There are a number of Aspergillus proteases with overlapping sequences but these have different molecular weights and pI values. Polyclonal and monoclonal antibodies were developed that were specific compared to a diverse taxonomic array of related and unrelated fungi that commonly occur in the built environment. Initially this was done to ensure the specificity of the target protein. The measurement of other allergens and antigens associated with the built environment has a number of uses. Most importantly, these can be used to assess reliably biodeterioration and contribute to improved exposure assessments for population health studies.