“Magnetic” termite mound surfaces are oriented to suit wind and shade conditions

Summary The termites Amitermes meridionalis and A. laurensis construct remarkable meridional or magnetic mounds in northern Australia. These mounds vary geographically in mean orientation in a manner that suggests such variation is an adaptive response to local environmental conditions. Theoretical modelling of solar irradiance and mound rotation experiments show that maintenance of an eastern face temperature plateau during the dry season is the most likely physical basis for the mound orientation response. Subsequent heat transfer analysis shows that habitat wind speed and shading conditions also affect face temperature gradients such as the rate of eastern face temperature change. It is then demonstrated that the geographic variation in mean mound orientation follows the geographic variation in long-term wind speed and shading conditions across northern Australia such that an eastern face temperature plateau is maintained in all locations.     

Mound-building termites and soil microbial biomass: An interaction influencing termite abundance

Termites are more abundant in the warmer lower latitudinal regions of the earth. Within these broad geographic regions, however, the precise nature of the factors influencing termite abundance is poorly understood. In this paper I have examined the abundance of detritivorous, mound-building termites and certain aspects of the climate, soils and vegetation at 14 sites in tropical northeastern Australia. No relationship between termite mound density and the particle-size characteristics of surface soil horizons, plant available phosphorous or rainfall was found. Microbial biomass carbon level of the surface soil was found to have a strong negative relationship with termite mound numbers. The negative interaction between the soil microbial population and termites may be due to the limiting effect of the organic matter processing capacity of the soil microbial population on the success of termites in occupying the decomposer niche in any particular area. Microbial biomass may therefore be a major factor influencing termite abundance in tropical Australian landscapes and elsewhere.     

Thermoregulatory brood transport in the fire ant, <Emphasis Type="Italic">Solenopsis invicta</Emphasis>

Nest structure in ants is often designed to optimize the colony’s ability to thermoregulate, and this specialization is most highly developed in mound-building ant species. Solenopsis invicta invest a large amount of energy in building mounds and transporting their brood up and down in their nests as a means of thermoregulation. Because few ant species build true mounds, we wanted to determine the effectiveness of these mounds in harvesting solar heat as well as to distinguish what factors (temperature vs. circadian rhythm) govern where fire ants place their brood in the mound and when they place it. We measured temperature patterns in the mound over several days at different depths and under different conditions (under direct sunlight or shade), and then conducted a series of field experiments to manipulate the orientation and time of heating. On cool mornings in spring or fall, surface temperatures of the mound rise at the fastest rate on the side receiving the most direct sunlight (usually the south side). This heating causes a temperature gradient through different depths in the mound, and shows little difference from outside ground temperature at a depth greater than ~40 cm inside the nest. In the morning, fire ants move their brood up into the mound on the side most directly heated, and when temperatures exceed optimal (~32°C) they move their brood down the temperature gradient to lower depths in the nest. In addition to this, mound temperature does not only increase due to direct sunlight, but temperature also increases higher than ground temperatures when the mound is in the shade due to its low specific heat. Experiments in which sunlight was mirrored to the normally shaded side of the mound, or when mounds were heated at night, revealed that S. invicta primarily track temperature patterns and do not rely on behavioral habits or circadian rhythms for the thermoregulatory transport of their brood. When mounds were shaded, S. invicta brood was evenly distributed directly under the surface of the mound rather than aggregating towards a specific side. The fire ant mound is important for thermoregulation because, compared to moundless subterranean nests, it absorbs heat more rapidly both in direct sunlight and shady conditions. Temperature tracking within the nest is key to understanding thermoregulatory placement of fire ant brood, as well as insight into the production of sexual brood and reproduction. Received 9 August 2007; revised 31 January 2008; accepted 7 February 2008.     

Avian navigation: from historical to modern concepts

Studies on avian navigation began at the end of the 19th century with testing various hypotheses, followed by large-scale displacement experiments to assess the capacity of the birds' navigational abilities. In the 1950s, the first theoretical concepts were published. Kramer proposed his ‘Map-and-Compass’ model, assuming that birds establish the direction to a distant goal with the help of an external reference, a compass. The model describes homing as a two-step process, with the first step determining the direction to the goal as a compass course and the second step locating this course with the help of a compass. This model was widely accepted when numerous experiments with clock-shifted pigeons demonstrated the use of the sun compass, and thus a general involvement of compass orientation, in homing. The ‘map’ step is assumed to use local site-specific information, which led to the idea of a ‘grid map’ based on environmental gradients. Kramer's model still forms the basis of our present concept on avian homing, yet route integration with the help of an external reference provides an alternative strategy to determine the home course, and the magnetic compass is a second compass mechanism available to birds. These mechanisms are interrelated by ontogenetic learning processes. A two-step process, with the first step providing the compass course and the second step locating this course with the help of a compass, appears to be a common feature of avian navigation tasks, yet the origin of the compass courses differs between tasks according to their nature, with courses acquired by experience for flights within the home range, courses based on navigational processes for returning home, and courses derived from genetically coded information in first-time migrants. Compass orientation thus forms the backbone of the avian navigational system. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

Trophic interactions among invertebrates in termitaria in the African savanna: a stable isotope approach

Abstract 1. Termites (Isoptera) in tropical savannas are known as ecosystem engineers, affecting the spatial and temporal distribution of water, carbon, cations, and nutrients through their mound structures. Their mounds, however, also offer habitation to diverse taxa and feeding guilds of other invertebrates; a keystone role that has not been properly quantified. 2. The aim of this study was to explore the ecosystem role of termitaria in determining invertebrate diversity and their potential trophic interactions. We used stable isotopes to distinguish termite‐feeding invertebrates from invertebrates merely living in termite mounds under field conditions. 3. The results suggest that inquiline spiders (Arachnida) do not feed on termites directly, but on other invertebrates within the termitaria that are termitophagous, elevating the spiders three trophic levels higher than the termites. 4. This study is the first to demonstrate food web interactions among inquiline invertebrates with a stable isotope approach. It provides evidence that termites play a keystone role in the system by providing habitat for various, trophically interacting invertebrates. These results illustrate a rather unexplored ecosystem property of savanna termites.     

Dynamic environments of fungus‐farming termite mounds exert growth‐modulating effects on fungal crop parasites

This study investigated for the first time the impact of the internal mound environment of fungus‐growing termites on the growth of fungal crop parasites. Mounds of the termite Odontotermes obesus acted as (i) temperature and relative humidity (RH) ‘stabilisers’ showing dampened daily variation and (ii) ‘extreme environments’ exhibiting elevated RH and CO₂ levels, compared to the outside. Yet, internal temperatures exhibited seasonal dynamics as did daily and seasonal CO₂ levels. During in situ experiments under termite‐excluded conditions within the mound, the growth of the crop parasite Pseudoxylaria was greater inside than outside the mound, i.e., Pseudoxylaria is ‘termitariophilic’. Also, ex situ experiments on parasite isolates differing in growth rates and examined under controlled conditions in the absence of termites revealed a variable effect with fungal growth decreasing only under high CO₂ and low temperature conditions, reflecting the in situ parasite growth fluctuations. In essence, the parasite appears to be adapted to survive in the termite mound. Thus the mound microclimate does not inhibit the parasite but the dynamic environmental conditions of the mound affect its growth to varying extents. These results shed light on the impact of animal‐engineered structures on parasite ecology, independent of any direct role of animal engineers.     

Thermoregulation of termite mounds: what role does ambient temperature and metabolism of the colony play?

Summary: Termites are well known for their ability to regulate the environment of their nest such as temperature and humidity. The influence of fluctuating ambient temperature and mound characteristics on mean nest temperature and daily fluctuation of nest temperature was analysed quantitatively in the fungus-cultivating, mound-building termite Macrotermes bellicosus (Macrotermitinae) in the savanna of the Comoé National Park (Côte d'Ivoire). Additionally, the nest temperatures of inhabited and uninhabited mounds were compared to analyse the contribution of ambient temperature to nest temperature in relation to metabolic heat production of the termites and their fungi. Mound structure alone resulted in a relatively constant nest temperature. Abiotic heat production via solar radiation alone yielded nest temperatures that corresponded to mean ambient temperatures. However, only the production of metabolic heat by the termites and the fungi increased these temperatures to the actual nest temperature. Therefore, and due to the high heat capacities of the mounds, large colonies (mound height above 2.0 m) had higher nest temperatures than smaller ones. Only large colonies attain constant nest temperatures of 30 °C that are largely independent from ambient temperatures and optimal for the growth and development of the termites and their fungi.     

The architecture of termite mounds: a result of a trade-off between thermoregulation and gas exchange?

We examined the influence of gas exchange on the architectureof termite mounds. In Comoé National Park (Côted'Ivoire), Macrotermes bellicosus builds, as an adaptation toambient temperature conditions, differently shaped mounds inthe shrub savanna and the gallery forest. Previous studies suggestedthat there might be a constraint that limits the degree of thermalinsulation of the interior (i.e., nest) of the mounds in environmentswith relatively low ambient temperatures. This factor causes,in proximate terms, suboptimal low nest temperatures and ultimatelyleads to reduced reproductive success in the gallery forest.In this study, we examined whether the necessity for gas exchangemight constrain mound architecture. We measured CO₂ concentrationsin the air channels of mounds in different habitats and undermanipulated temperature regimes. During both the dry and therainy season we found higher CO₂ concentrations in mounds ofthe gallery forest than in mounds of the savanna. Additional measurementsin forest mounds, architecturally resembling those of the savanna dueto an experimental increase in ambient temperatures, revealedlower CO₂ concentrations than unmanipulated mounds in this habitat. Generally,concentrations were higher during the rainy season comparedto the dry season and lower during day than during night. Summarizingthese results we present a model that illustrates this trade-offbetween thermoregulation and gas exchange under different temperatureregimes. Both factors together result in different mound architecturesunder different environmental temperatures and may finally limitthe distribution of this species.     

In-situ oxygen profiling and lignin modification in guts of wood-feeding termites

Abstract Reports on the capability of wood-feeding termites (WFTs) in degrading wood particles and on the existence of aerobic environment in the localized guts suggest that their high efficiency of cellulose utilization is not only caused by cellulase, but also by biochemical factors that pretreat lignin. We thus extend the hypothesis that for highly efficient accessibility of cellulose, there should be direct evidence of lignin modification before the hindgut. The lignin degradation/modification is facilitated by the oxygenated environment in intestinal microhabitats. To test our hypothesis, we conducted experiments using a dissolved oxygen microelectrode with a tip diameter < 10 μm to measure oxygen profiles in intestinal microhabitats of both Coptotermes formosanus (Shiraki) and Reticulitermes flavipes (Kollar). Lignin modification during passage through their three gut segments was also analyzed with pyrolysis gas chromatography/mass spectrometry. The data showed relatively high levels of oxygen in the midgut that could have promoted lignin oxidation. Consistent with the oxygen measurements, lignin modifications were also detected. In support of previously proposed hypotheses, these results demonstrate that lignin disruption, which pretreats wood for cellulose utilization, is initiated in the foregut, and continues in the midgut in both termites.     

Orientation to shorelines by the supratidal amphipod Talorchestia longicornis: Wavelength specific behavior during sun compass orientation

If released in water or on sand the supratidal amphipod Talorchestia longicornis Say amphipods moves in the onshore direction. The present study was designed to determine whether this species uses the sun as a cue for orientation and if so, which visual pigment in the compound eyes is involved. When tested in an apparatus with a view of only the sun and sky amphipods were disoriented when the sun was obscured by clouds. However, when the sun was visible, they oriented in the onshore direction of their home beach in both water and air during both the morning and afternoon. Resetting the time of their circadian rhythm in activity with either an altered light:dark or diel temperature cycle also reset the chronometric mechanism associated with sun compass. orientation. T. longicornis has two visual pigments with absorption maxima near 420 nm and 520 nm. Only the 420 nm pigment is used for sun compass orientation, which may be an adaptation for increasing the contrast between the sun and background scattered skylight or for detecting the radiance distribution of skylight. Irradiating the 520 nm absorbing pigment alone induced positive phototaxis to the sun but not onshore orientation. Thus, T. longicornis shows wavelength specific behavior by using only one of its visual pigments for sun compass orientation.     

Mass transfer during lactation of an ice-breeding pinniped, the grey seal (Halichoerus grypus), in Nova Scotia, Canada

The land planarian Microplana termitophaga is one of three invertebrate predators feeding at the open chimneys of the mound of the termite Odontotermes transvaalensis in Harare. This paper records over 4000 field observations of the mound and reports on the planarians over three rainy seasons from 1990 to 1993. Microplana termitophaga is crepuscular with a large early morning and a smaller evening activity peak. Rainfall appears to be of over-riding importance; activity is confined to the rainy season, occurring once the cumulative rainfall reaches 150-250 mm and being suspended during longish dry spells. Activity is also favoured by ambient relative humidity above 70%, light intensity below 50,000 lux (but not total darkness) and ambient temperature between 13 and 23C. Planarians on sun-exposed, but not on shaded, mounds disappeared after a drought. Dispersal occurs during prolonged wet weather.
Microplana termitophaga occurs with two predatory spider species and a commensal phorid fly and they all utilize the same termites. These four species exhibit temporal separation, probably related to their specific micro-climatic needs.     

Wintergoldh?hnchen (Regulus regulus) besitzen einen Inklinationskompa?

During autumn migration, orientation tests were performed with Goldcrests in the morning immediately after the birds had been caught. In the local geomagnetic field (vertical component pointing downward), they showed a significant tendency towards 144° SE; in a magnetic field with the vertical component pointing upward, their mean was at 321° NW. This response to an inversion of the vertical component reveals that the Goldcrests used the magnetic field for orientation and that their magnetic compass is an inclination compass as it has been described for several other species of migrants.     

THE POPULATION OF A LARGE MOUND OF NASUTITERMES EXITIOSUS (HILL) (ISOPTERA: TERMITIDAE)

i
More than 2.5 million termites, weighing 11.05 kg, were obtained from a mound colony of Nasutitermes exitiosus (Hill). Because of the unusually large size of the colony examined, and the favourable conditions that were experienced for extracting the termites, it is thought that this figure is close to the upper limit of nest population attained by this termite.     

The nature of soil pernicious to Coptotermes formosanus

The Formosan subterranean termites, Coptotermes formosanus, were incubated in soils collected from various locations on the island of Hawaii. More than 70% of the termites died within 2 weeks in seven of nine soil samples collected from Kamuela. In control soil termites remained alive after 4 weeks. Entomophthora coronata, Metarrhizium anisopliae, Aspergillus flavus, and an unidentified bacterium were isolated from 60 to 100% of dead termites incubated in the pernicious soils. E. coronata and M. anisopliae were pathogenic to C. formosanus. The innocuous soil from Hilo became pernicious to C. formosanus after it was inoculated with E. coronata or M. anisopliae.     

Resource availability and distribution patterns, indicators of competition between Macrotermes bellicosus and other macro-detritivores in the Comoé National Park, Côte d'Ivoire

Interspecific competition has rarely been demonstrated in field studies. For it to occur a resource must be in limited supply and potential competitors must be concurrently active in time and space. We studied the availability of plant litter during the course of the year and the activity and distribution of macro‐detritivores (termites, diplopods and earthworms) in two habitats in a Guinea savanna (Côte d'Ivoire), to test whether interspecific competition might be important. Plant litter was limited during the rainy season in the savanna, but was never limited in the gallery forest. The termite Macrotermes bellicosus, the dominant macro‐detritivore in this area, and other detritivorous termites (e.g. Microtermes spp., Ancistrotermes spp., Odontotermes spp.) were active all year round with a peak during the rainy season, when diplopods and earthworms were also active. In the savanna at the beginning of the rainy season when food became limiting, other detritivorous termite species were more active in the absence of M. bellicosus than in its presence. This complementary activity pattern of M. bellicosus and other termites indicates that interspecific competition among detritivorous termites may be occurring. However, the spatio‐temporal distribution of diplopods and earthworms suggests that interspecific competition with M. bellicosus is of minor importance.     

The effects of buried magnets on colonies of Amitermes spp. building magnetic mounds in northern Australia1

ABSTRACT Unlike four control colonies of Amitermes which built normal, north-south oriented 'magnetic' mounds in northern Australia, four young colonies failed after exposure to experimental alteration of the earth's magnetic field. In November 1979, bar magnets were buried on either side at the base of each of three new nests of Amitermes laurensis Mjoberg and one new colony of A.vitiosus Hill. As controls, non-magnetized iron bars were disposed similarly in relation to three new nests of the former species and one of the latter. In September 1986, all four control nests had grown normally. However, not one of the treatment colonies survived and from what remained of the former nest in each case it is clear that the demise of the colonies occurred soon after the magnets were placed. We conclude that the failure of these colonies was the result of the changed magnetic environment. Whether 'magnetic' termites use magnetoperception as a cue to achieve their spectacular north-south orientation remains unknown, but the results of this field experiment weigh more for than against this possibility.     

白蚁的生物防治现状与研究进展

白蚁对人类的危害极其严重,被列入世界性的五大害虫之一。用化学药剂防治白蚁仍然是目前最主要、最普遍的手段,虽然这种方法见效快,但其残毒严重,对环境和人类健康已构成极大威胁。生物防治白蚁与其他方法相比具有高效、安全、持久的特性,最重要的是它可以避免化学防治带来的一系列问题,虽然很多白蚁生物防治剂野外测试工作还不太理想,但环保的特点决定了其发展潜力。本文综述了生物防治白蚁的研究现状与进展,并阐述了植物内生菌的代谢产物将是开发新型白蚁防治剂的又一重要来源。     

Fungus culturing, nutrient mining and geophagy: a geochemical investigation of Macrotermes and Trinervitermes mounds in southern Africa

Termite mounds are commonly enriched in clay and nutrients relative to surrounding topsoils. We hypothesized that: (1) nutrient enrichment of mounds differs between fungus-culturing (FC) and non-FC termites; (2) FC termites preferentially acquire materials rich in scarce nutrients which promote growth of their fungus cultures; and (3) micro-nutrient enrichment in mounds of FC termites is beneficial for wildlife. In a preliminary investigation of these hypotheses, we sampled mounds (and adjacent topsoil) of Macrotermes (FC) and Trinervitermes (non-FC) termites in Namibia and South Africa, respectively. Analyses included: 27 elements by ICPMS after a nitric acid–hydrogen peroxide digest, organic carbon, a seven fraction particle size analysis, and pH and EC (1:5 soil:water extracts). Macrotermes mounds showed significant (1.6–3.7-fold) enrichment of 23 of the 27 elements analysed relative to topsoil. By contrast, Trinervitermes mounds showed no enrichment. Clay enrichment of Macrotermes mounds (4.7–6.5-fold) was strongly correlated with element enrichment ( r ² range: 0.76–0.77), suggesting that amendment of soil texture is a main factor in enrichment. Marked enrichment of only certain nutrients in mounds – namely Mn, Co, Cu and Se – was evident at certain nutrient-poor sites, suggesting that specific materials such as Mn oxides (which adsorb Co, Cu and Se) may be gathered by termites in disproportionate amounts relative to their abundance in soils. These nutrients are likely to enhance the productivity of the fungus culture and hence the termite colony. Parts of certain mounds were enriched in Se (1.3–3.6 mg Se kg⁻¹) to a degree likely to attract geophagy. It is suggested that in some landscapes Macrotermes mounds provide a critical supply of micro-nutrients to wildlife.     

Influence of termites on the soil seed bank in an African savannah

In savannah ecosystems, termites drive key ecosystem processes, such as primary production through creation of patchiness in soil nutrients availability around their nests. In this study, we evaluated the role of termites in altering the soil seed bank size, an important ecosystem component that has often been overlooked in previous work. Data on above ground vegetation and soil seed bank samples were collected from four microhabitats, that is, the wooded mound, unwooded mound, tree sub‐canopy and the open grassland matrix in a protected game reserve in south‐central Zimbabwe. The seedling emergence method was then used to identify species present in the soil samples. One‐way analysis of variance followed by Tukey's multiple comparison tests was executed to test for significant differences in plant species richness among the four microhabitats. The results indicate that plant species richness was high on wooded termite mound but did not differ between the unwooded and the sub‐canopy microhabitats. The open grassland microhabitat had the lowest plant species richness. The influence of termites on the soil seed bank composition was also life form specific. The herb and woody life forms had significantly (α = 0.05) higher species richness in the soil seed bank at wooded and unwooded termite mounds when compared to the other two microhabitats. Overall, these results imply that termites alter the soil seed bank and the findings enhance our understanding of the significant role termites play in regulating processes in savannah ecosystem.     

Relation between termite numbers and the size of their mounds

This article provides a meta-analysis of quantitative data available in literature regarding the relation between termite numbers and the volume of their mounds for 24 species belonging to 13 genera. The leading question behind this analysis is: “how do the respiratory gas exchanges regulate the size of termite mounds?” This question is answered through the analysis of the log–log regression between the volume of the mound and the number of inhabitants. The most confident data support the hypothesis of a respiratory regulation that can be achieved through a relation between the termite numbers and (1) the volume of their mounds (slope of the regression near 1, Noditermes), (2) the surface of the outer walls of their mounds (slope of the regression near 0.67, Termitinae and Nasutitermes) or (3) a compromise between the surface of the outer walls of their mounds and some linear structures of their nests (slope of the regression between 0.67 and 0.33, Trinervitermes and Macrotermes). The way this is achieved is linked with the architecture of the mound. A confident relation was found between the number of individuals and the epigeal volume of their mounds for 18 species for which the most reliable data were provided. Three more accurate models are proposed for estimating the termite population based on the nest material and architecture and on the size of the termites.