Antennation of nectar-receivers encodes colony needs and food-source profitability in the ant Camponotus mus

In social insects, interactions among individuals are important in colony organisation because they can be used in decision making. During trophallaxis in ants, antennal and foreleg contacts between both partners are established. It has been suggested that a modulatory communication channel could be involved in such contacts, but it remains undemonstrated. The aim of this work was to find variables plausible to be encoded in such contacts and quantify the consequent changes in the tactile stimulation the food-donor ant receives. We recorded nectar transference between pairs of workers in experimental arenas once one of them had returned from collecting sucrose solution (15 or 40%w/w), with different situations of colony’s sugar deprivation. The frequency of antennal strokes that the food-donor ant received on her head depended on both the colony’s sugar-deprivation and the concentration, the latter showed differences within 3–5 deprivation days. Antennal and foreleg movements of the food-receiver increase with increasing level of colony’s carbohydrate deprivation, as well as with increasing concentration of the transferred food. Not only does this study reopen an interesting question, but it gives evidence that variables related to the appetitive context are indeed encoded in the tactile stimulation during the trophallaxis as well. Consequently, they have the effective potentiality to play a communicational role in the organization of colony activities. Received 22 December 2005; revised 5 April 2006; accepted 12 April 2006.     

Flood control by ants: a Southeast Asian bamboo-dwellingTetraponera (Formicidae,Pseudomyrmecinae) bails water from its internode nests

Summary The Southeast Asian antTetraponera sp. nearattenuata F. Smith inhabits internodes of large bamboo species that it shares with symbiotic pseudococcids. It finds access to this nesting habitat via small holes made by wood-boring insects. During heavy rain, runoff water collects in these punctured internodes. TheTetraponera workers remove the water by ingesting it, walking to the entrance hole, and regurgitating it to the outside. In this way, they 1) reduce the danger of colony members drowing, 2) enable their symbionts to feed also on the internode floor, and 3) prevent excessive growth of microbes in the nest.     

Cold hardiness of the overwintering black carpenter ant

Abstract Cold hardiness was investigated in overwintering field nests of the black carpenter ant Camponotus pennsylvanicus (De Geer) in the Commonwealth of Virginia. No active nest thermoregulation was observed: temperatures of galleries, worker bodies, worker clusters, and larval clusters were within 3°C of ambient temperature. Nest temperatures generally fluctuated less rapidly and severely than did ambient temperature; thus, the nest afforded protection from potentially fatal sudden temperature drops. Glycerol, the only polyol cryoprotectant detected, was found in all castes and larvae. Supercooling points were low and ranged from ? 17°C in major workers to ?22°C in larvae. A second heat release peak, occurring around ? 8°C, was seen in all adults, but it was not observed in larvae. This higher temperature peak in adults probably represents the freezing of the gut contents, as adults were found to overwinter with the crop full or partially full. Larvae did not overwinter with liquid food in the gut.     

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.     

Population structure and the co-evolution between social parasites and their hosts

Co-evolutionary trajectories of host-parasite interactions are strongly affected by the antagonists' evolutionary potential, which in turn depends on population sizes as well as levels of recombination, mutation, and gene flow. Under similar selection pressures, the opponent with the higher evolutionary rate is expected to lead the co-evolutionary arms race and to develop local adaptations. Here, we use mitochondrial DNA sequence data and microsatellite markers to assess the amount of genetic variability and levels of gene flow in two host-parasite systems, each consisting of an ant social parasite--the European slavemaker Harpagoxenus sublaevis and the North American slavemaker Protomognathus americanus--and its two main host species. Our population genetic analyses revealed limited gene flow between individual populations of both host and parasite species, allowing for a geographic mosaic of co-evolution. In a between-system comparison, we found less genetic variability and more pronounced structure in Europe, where previous behavioural studies demonstrated strong local adaptation. Within the European host-parasite system, the larger host species Leptothorax acervorum exhibited higher levels of both genetic variability and gene flow, and previous field data showed that it is less affected by the social parasite H. sublaevis than the smaller host Leptothorax muscorum, which has genetically depleted and isolated populations. In North America, the parasite P. americanus showed higher levels of gene flow between sites, but overall less genetic diversity than its hyper-variable main host species, Temnothorax longispinosus. Interestingly, recent ecological and chemical studies demonstrated adaptation of P. americanus to local host populations, indicating the importance of migration in co-evolutionary interactions.     

Respiratory physiology and water relations of three species of Pogonomyrmex harvester ants (Hymenoptera: Formicidae)

The respiratory physiology and water relations of three harvester ant species (Pogonomyrmex rugosus Emery, P. occidentalis[Cresson] and P. californicus[Buckley]) were examined at three temperatures (15, 25 and 35°C) using a flow-through respirometry system. As intact ants tended to be active during testing, we performed a parallel set of experiments on individuals rendered motionless by decapitation. Both intact and decapitated ants exhibited discontinuous ventilation. Decapitation caused metabolic rate (V˙CO₂) and burst frequency to decrease in all three species. Burst volume either remained constant or increased after removal of the head, though mass-specific V˙CO₂ was unaffected except in P. rugosus. Mass-specific V˙CO₂s of headless harvesters were comparable with published values derived from motionless specimens of other ant species. The mean Q₁₀ for intact ants of all three species was 2.37; for decapitated insects the mean was 2.32. Respiratory water constituted a small (< 5%) fraction of total loss, and we believe that discontinuous ventilation does not act to conserve water in these organisms, although it may serve other functions.     

Parasitic and Infectious Disease Responses to Changing Global Nutrient Cycles

Parasitic and infectious diseases (PIDs) are a significant threat to human, livestock, and wildlife health and are changing dramatically in the face of human-induced environmental changes such as those in climate and land use. In this article we explore the little-studied but potentially important response of PIDs to another major environmental change, that in the global nutrient cycles. Humans have now altered the nitrogen (N) cycle to an astonishing degree, and those changes are causing a remarkable diversity of environmental and ecological responses. Since most PIDs are strongly regulated by ecological interactions, changes in nutrients are likely to affect their dynamics in a diversity of environments. We show that while direct tests of the links between nutrients and disease are rare, there is mounting evidence that higher nutrient levels frequently lead to an increased risk of disease. This trend occurs across multiple pathogen types, including helminths, insect-vectored diseases, myxozoa, and bacterial and fungal diseases. The mechanistic responses to increased nutrients are often complex and frequently involve indirect responses that are regulated by intermediate or vector hosts involved in disease transmission. We also show that rapid changes in the N cycle of tropical regions combined with the high diversity of human PIDs in these regions will markedly increase the potential for N to alter the dynamics of disease. Finally, we stress that progress on understanding the effects of nutrients on disease ecology requires a sustained effort to conduct manipulative experiments that can reveal underlying mechanisms on a species-specific basis.     

Are ontogenetic shifts in foliar structure and resource acquisition spatially conditioned in tank‐bromeliads?

The phenotypic plasticity of plants has been explored as a function of either ontogeny (apparent plasticity) or environment (adaptive plasticity), although few studies have analyzed these factors together. In the present study, we take advantage of the dispersal of Aechmea mertensii bromeliads by Camponotus femoratus or Pachycondyla goeldii ants in shaded and sunny environments, respectively, to quantify ontogenetic changes in morphological, foliar, and functional traits, and to analyze ontogenetic and ant species effects on 14 traits. Most of the morphological (plant height, number of leaves), foliar (leaf thickness, leaf mass area, total water content, trichome density), and functional (leaf δ¹³C) traits differed as a function of ontogeny. Conversely, only leaf δ¹⁵N showed an adaptive phenotypic plasticity. On the other hand, plant width, tank width, longest leaf length, stomatal density, and leaf C concentration showed an adaptation to local environment with ontogeny. The exception was leaf N concentration, which showed no trend at all. Aechmea mertensii did not show an abrupt morphological modification such as in heteroblastic bromeliads, although it was characterized by strong, size‐related functional modifications for CO₂ acquisition. The adaptive phenotypic variation found between the two ant species indicates the spatially conditioned plasticity of A. mertensii in the context of insect‐assisted dispersal. However, ant‐mediated effects on phenotypic plasticity in A. mertensii are not obvious because ant species and light environment are confounding variables. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175 , 299–312.