The shape of compass termite mounds and its biological significance

Summary In northern Australia, compass termites build tall wedge-shaped mounds with an elongated axis that has a striking north-south orientation. Various hypotheses have been advanced to account for this remarkable mound architecture. However, behavioural aspects of mound orientation have rarely been investigated. The currently accepted hypothesis considers mound orientation as an adaptation to local long-term environmental conditions to maintain a temperature plateau at the eastern face of the mound. According to this hypothesis termites should concentrate at the eastern face when ambient temperature conditions are not ideal. This was tested in the current study by applying a new, non-destructive technique that allows monitoring of termites through solid material. Termatrac®, a tool developed for termite pest detection, uses microwaves to detect the movement of termites. As predicted by the eastern- face-plateau hypothesis, termites concentrated in the morning at the eastern face of the mound. However, this pattern was not found at sunrise or noon despite a similar temperature gradient between eastern and western face. This might indicate that only the morning heating of the eastern face is important for the termites, while it plays no prominent role during the rest of the day. The eastern-face-plateau hypothesis is then compared with other hypotheses to develop a general framework that addresses the different characteristics of compass mound architecture: shape, orientation and geographic variation in orientation.Received 1 November 2002; revised 28 January 2003; accepted 12 February 2003.     

Indigenous utilization of termite mounds and their sustainability in a rice growing village of the central plain of Laos

Background

This study was conducted to identify medicinal plants and spices used for medicine by the community of Beni-Sueif, Upper Egypt.

Methods

Ethnobotanical data from local people was collected using direct interviews and a semi-structured questionnaire.

Results

Forty-eight plant species belonging to twenty-seven families and forty-seven genera were encountered during the study. Their botanical and vernacular names, plant parts used and medicinal uses are given. Results of the study were analyzed using two quantitative tools. The factor informant consensus indicated the agreement in the use of plants and the fidelity level indicated the ratio between the number of informants who independently suggested the use of a species for the same major purpose and the total number of informants who mentioned the plant for any use. The results of the factor informant consensus showed that the cardiovascular category has the greatest agreement, followed by the immunological, gastrointestinal and respiratory categories. The most important species according to their fidelity are: Hibiscus sabdariffa L. for the cardiovascular category; Trigonella foenum-graecum L. for the immunological category; Mentha piperita L. for the gastrointestinal category and Pimpinella anisum L. for the respiratory category.

Conclusions

Medicinal plants are still used for treatment in Beni-Sueif community despite the availability of prescribed medications. Documentation of this ethnomedicinal knowledge is important. Evaluation of pharmacological activity for the promising medicinal plants is suggested.     

Differences between bacterial communities in the gut of a soil-feeding termite (Cubitermes niokoloensis) and its mounds

In tropical ecosystems, termite mound soils constitute an important soil compartment covering around 10% of African soils. Previous studies have shown (S. Fall, S. Nazaret, J. L. Chotte, and A. Brauman, Microb. Ecol. 28:191-199, 2004) that the bacterial genetic structure of the mounds of soil-feeding termites (Cubitermes niokoloensis) is different from that of their surrounding soil. The aim of this study was to characterize the specificity of bacterial communities within mounds with respect to the digestive and soil origins of the mound. We have compared the bacterial community structures of a termite mound, termite gut sections, and surrounding soil using PCR-denaturing gradient gel electrophoresis (DGGE) analysis and cloning and sequencing of PCR-amplified 16S rRNA gene fragments. DGGE analysis revealed a drastic difference between the genetic structures of the bacterial communities of the termite gut and the mound. Analysis of 266 clones, including 54 from excised bands, revealed a high level of diversity in each biota investigated. The soil-feeding termite mound was dominated by the Actinobacteria phylum, whereas the Firmicutes and Proteobacteria phyla dominate the gut sections of termites and the surrounding soil, respectively. Phylogenetic analyses revealed a distinct clustering of Actinobacteria phylotypes between the mound and the surrounding soil. The Actinobacteria clones of the termite mound were diverse, distributed among 10 distinct families, and like those in the termite gut environment lightly dominated by the Nocardioidaceae family. Our findings confirmed that the soil-feeding termite mound (C. niokoloensis) represents a specific bacterial habitat in the tropics.     

Studies on a population of large termite mounds in Uganda

• 1 Two study-sites near Kampala were mapped and all of the termite mounds within them were measured. Changes were recorded in the three succeeding years. A method was developed for estimating mound volumes from height and diameter.
• 2 Macrotermes bellicosus mounds reached a volume of about 2.4 m³ in 3 years after which they grew more slowly to a maximum from 4 to 6 m³. Growth in volume during the first 3 years was approximately linear and its rate did not vary seasonally, probably because growth is related to temperature which was nearly constant throughout the year.
• 3 M.bellicosus mounds had an average length of life of about 10 years, although colonies survived on average only 4 years. The corresponding figures for Pseudacanthotermes spp. were 5 and 2 1/2 years. Some mounds were recolonized after the death of the original colony.
• 5 Fresh earth was brought up at a minimum rate of about 10 m³ ha^-1 yr^-1 but more was lost by erosion and destruction and the populations of mounds were decreasing.
• 4 The number of ventilation shafts in M.bellicosus mounds increased with the volume of the mound. Many mounds, both dead and alive, supported vegetation.
• 6 Local opinion is that Pseudacanthotermes are harmless but M.bellicosus is regarded as a pest and attempts are made to destroy its mounds.

     

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.     

Spatial variability and abiotic determinants of termite mounds throughout a savanna catchment

Termite mounds contribute to the spatial heterogeneity of ecological processes in many savannas, but the underlying patterns and determinants of mound distributions remain poorly understood. Using the Carnegie Airborne Observatory (CAO), we mapped the distribution of termite mounds across a rainfall gradient within a river catchment (～ 27 000 ha) of the Kruger National Park, South Africa. We assessed how different factors were associated with the distribution and height of termite mounds at three spatial scales: the entire catchment, among three broad vegetation types, and on individual hillslope crests. Abiotic factors such as the underlying geology and mean annual precipitation shaped mound densities at broad scales, while local hillslope morphology strongly influenced mound distribution at finer scales, emphasising the importance of spatial scale when assessing mound densities. Fire return period had no apparent association with mound densities or height. Mound density averaged 0.46 mounds ha^?1, and exhibited a clustered pattern throughout the landscape, occurring at relatively high densities (up to 2 mounds ha^?1) on crests, which are nutrient‐poor elements of the landscape. Mounds exhibited significant over‐dispersion (even spacing) at scales below 60 m so that evenly spaced aggregations of termite mounds are embedded within a landscape of varying mound densities. The tallest mounds were found in dry savanna (500 mm yr^?1) and were positively correlated with mound density, suggesting that dry granitic savannas are ideal habitat for mound‐building termites. Mound activity status also varied significantly across the rainfall gradient, with a higher proportion of active (live) mounds in the drier sites. The differential spacing of mounds across landscapes provides essential nutrient hotspots in crest locations, potentially sustaining species that would otherwise not persist. The contribution to biodiversity and ecosystem functioning that mounds provide is not uniform throughout landscapes, but varies considerably with spatial scale and context.     

Ventilation of termite mounds: new results require a new model

In 1955, Lüscher proposed a ventilation mechanism forcathedral-shaped termite mounds to exchange respiratory gases. This mechanism was generally accepted, although it had neverbeen tested critically. We tested this mechanism by investigatingtemperatures, CO₂ concentrations, and air currents in and aroundtwo types of Macrotermes bellicosus mounds: cathedral-shapedmounds with many ridges and thin walls located in the savannaand dome-shaped mounds without ridges and with thick wallsin the forest. These two mound shapes have two different mechanismsof ventilation, depending on the environmental temperature.In the savanna during the day, sun heats the air in the peripheralair channels inside the ridges of the mound above the centralnest temperatures and produces a temperature gradient in theperipheral air channels with decreased temperatures at thetop of the mound. This temperature gradient leads to convectioncurrents with air rising inside the air channels of the ridgesto the top of the mound, meanwhile exchanging CO₂. In contrast,in the savanna during the night and generally in the forest,the temperatures inside the air channels are lower than thoseof the central nest, and no air currents rising upward insidethe air channels were detected. The CO₂ concentrations in theair channels of savanna mounds at night and forest mounds ingeneral were higher than during the day in the savanna. Therefore,our data do not support Lüscher's proposed mechanism.     

Relation between extinction angle and molecular size

The relation between the observed extinction angle of flow birefringence measurements and the dimensions of the dissolved macromolecules is presented in graphical form for rapid computation. The calculations are based on a rigid ellipsoidal model for the solute particles.     

‘Magnetic’ termite mounds: is their unique shape an adaptation to facilitate gas exchange and improve food storage?

Social insects can build impressive nest mounds but the functional significance of their architecture is rarely studied in experiments. The ‘magnetic’ termite mounds of monsoonal northern Australia built by Amitermes meridionalis are notable for their elongated wedge shape and north–south axial orientation. We tested whether the shape is an adaptation to facilitate gas exchange and the preservation of food stores by two experimental manipulations of mounds in situ covering all seasons. First, mounds were shaded to limit drying after rain and second, mound shape was amended from wedge to (approximate) sphere. Food storage, fungal contamination, and internal CO₂ concentration were unaffected by manipulation, but showed a distinct seasonal dynamic, with storage peaking towards the onset of rains and fungal load towards the end of the rainy season. Internal CO₂ concentrations were subject to a diurnal cycle, but also showed elevation during rains. We propose that one advantage of the wedge shape is the efficient use of building effort to achieve good passive ventilation for the food storage areas.     

Litter-forager termite mounds enhance the ectomycorrhizal symbiosis between Acacia holosericea A. Cunn. Ex G. Don and Scleroderma dictyosporum isolates

The hypothesis of the present study was that the termite mounds of Macrotermes subhyalinus (MS) (a litter-forager termite) were inhabited by a specific microflora that could enhance with the ectomycorrhizal fungal development. We tested the effect of this feeding group mound material on (i) the ectomycorrhization symbiosis between Acacia holosericea (an Australian Acacia introduced in the sahelian areas) and two ectomycorrhizal fungal isolates of Scleroderma dictyosporum (IR408 and IR412) in greenhouse conditions, (ii) the functional diversity of soil microflora and (iii) the diversity of fluorescent pseudomonads. The results showed that the termite mound amendment significantly increased the ectomycorrhizal expansion. MS mound amendment and ectomycorrhizal inoculation induced strong modifications of the soil functional microbial diversity by promoting the multiplication of carboxylic acid catabolizing microorganisms. The phylogenetic analysis showed that fluorescent pseudomonads mostly belong to the Pseudomonads monteillii species. One of these, P. monteillii isolate KR9, increased the ectomycorrhizal development between S. dictyosporum IR412 and A. holosericea. The occurrence of MS termite mounds could be involved in the expansion of ectomycorrhizal symbiosis and could be implicated in nutrient flow and local diversity.     

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.     

Multi-scale relationships between numbers and size in the evolution of arthropod body features

Size-related changes of form in animals with periodically patterned body axes and post-embryonic growth discontinuously obtained throughout a series of moulting episodes cannot be accounted for by allometry alone. We address here the relationships between body size and number and size of appropriately selected structural units (e.g., segments), which may more or less closely approximate independent developmental units, or unitary targets of selection, or both. Distinguishing between units fundamentally involving one cell only or a small and fixed number of cells (e.g., the ommatidia in a compound eye), and units made of an indeterminate number of cells (e.g., trunk segments), we analyze and discuss a selection of body features of either kind, both in ontogeny and in phylogeny, through a review of current literature and meta-analyses of published and unpublished data. While size/number relationships are too diverse to allow easy generalizations, they provide conspicuous examples of the complex interplay of selective forces and developmental constraints that characterizes the evolution of arthropod body patterning.     

谈谈白蚁与人类的密切关系

白蚁对人类的危害众所周知 ,白蚁对人类的有益方面 ,人们知之甚少。该文重点论述白蚁对人类有益的方面。白蚁在自然界中 ,是一个名符其实的“清道夫” ,它将林地中的枯枝、落叶等转化为有益的肥料 ,回归自然 ,再被植物吸收 ;白蚁本身可加工成营养丰富的美味佳肴食品 ,也可精制成防病治病的良药和效果明显的保健补品 ;白蚁的附生物 ,如鸡菌更是美味佳肴 ,菌圃和炭棒菌也能精制成治疗多种疾病的良药。     

Geophagic termite mounds as one of the resources for African elephants in Ugalla Game Reserve,Western Tanzania

Knowledge of the distribution and nutrient values of key resources supporting the survival of wildlife species is integral for an effective conservation planning and management of the species. In the Miombo ecosystem of the Ugalla Game Reserve, African elephants (Loxodonta africana Blumenbach 1797), eat soil, that is geophagy, from certain termite mounds. We mapped that all the geophagic termite mounds are exclusively situated in the flood plain. To understand why soils from some termite mounds are eaten, we collected and analysed soil samples from 10 geophagic termite mounds, seven nongeophagic termite mounds and 13 samples from the surrounding flood plain. Percentage of clay content did not differ significantly among the soil samples. Soils from geophagic termite mounds were richer in mineral elements compared with other soil samples. The results demonstrate that the driver for geophagic behaviour is related to rich mineral element contents found in geophagic termite mounds made of the mineral‐enriching termites (Macrotermes). Thus, geophagic termite mounds play a role in elephant's dietary needs and possibly influence their movement patterns in Ugalla, as the elephants cannot obtain enough minerals from their feeds. Geophagic termite mounds should be protected from potential destructive land uses, such as airstrip construction.