Nest Mounds Research Articles

The impact of termites on soil sheeting properties is better explained by environmental factors than by their feeding and building strategies

Termites are key soil bioturbators in tropical ecosystems. Apart from mound nests constructed by some advanced lineages, most of the species use their faeces, oral secretions, debris, or soil aggregates to protect themselves from predators and desiccation when they go out to forage. Although this soil ‘sheeting’ is considered to play a key role in soil functioning, the properties of this termite-made material has been poorly studied. The few available data showed that sheeting properties are highly variable with positive, neutral or negative impacts on soil C and clay content, and consequently on soil aggregate stability. Therefore, the objective of this study was to determine the factors controlling the physical (particle size fractions and structural stability) and chemical (pH, electrical conductivity and carbon content) properties of soil sheeting produced by termite species encompassing all feeding and building categories using a dataset representative of an important diversity of biotopes coming from 21 countries from all continents colonized by termites. We showed that sheeting properties were explained by the properties of their environment, and especially by those of the bulk soil (linear relationships), followed in a lesser extent by the mean annual precipitation and biotope. Classic hypotheses related to termite feeding and building strategies were not hold by our analysis. However, the distinction of termites into fungus-growing and non-fungus growing species was useful when differentiating the impact of termites on soil electrical conductivity, C content, and structural stability. The large variability observed suggests the need to redefine termite functional groups based on their impacts on soil properties using a trait-based approach from morphological, anatomical and/or physiological traits.

Taxonomic revision of the Palaearctic ant subgenus Coptoformica Müller, 1923 (Hymenoptera, Formicidae)

A taxonomic revision of the Palaearctic ant subgenus Coptoformica Müller, 1923 is presented based on Numeric Morphology-Based Alpha-Taxonomy (NUMOBAT). Indicated by five morphological and one morpho-ethological character, all species of the subgenus Coptoformica form a well-circumscribed group of undoubtedly monophyletic origin. Standardized morphological character systems were described numerically to allow objective hypothesis formation by exploratory data analyses and testing by hypothesis-driven data analyses. NUMOBAT data on 25 characters were recorded in a total of 944 samples (largely nest samples) with 3660 worker individuals and 402 gynes. Further 250 samples were investigated by subjective visual inspection. Comparative tables and keys to workers and gynes are presented. Intraspecific polymorphism is shown to represent a big challenge in Coptoformica taxonomy and is extremely developed in the Palaearctic population of Formica exsecta in which occurrence of distinct, most certainly genetically determined morphs within the same nest mound is no rare phenomenon. With the exception of Formica bruni x pressilabris, no conclusive indications on interspecific hybridization exist in Coptoformica. The complete absence of comparative studies on nuclear DNA and the abundance of cryptic species are probable explanations for this low level of hybrid identification. Considering 32 available names, the survey recognized 14 good species, 15 junior synonyms and 3 names not interpretable to species level (Incertae Sedis). Taxonomic changes relative to the revision of Seifert (2000) were as follows: Elevation to species rank was performed in Formica longiceps Dlussky, 1964 and F. brunneonitida Dlussky, 1964 whereas F. caucasicola spec. nov. was described as new Caucasian endemic species. Formica fossilabris Dlussky, 1965 has been recognized as junior synonym of F. pisarskii Dlussky, 1964. Nomenklatorische Handlungen F. caucasicola spec. nov. – urn:lsid:zoobank.org:act: EFC74CC6-8FDA-4335-B902-E17C87AC8BB3

CO2 biogeochemical investigation and microbial characterization of red wood ant mounds in a Southern Europe montane forest

Red wood ants are ecologically important species in Europe that form large colonies. Their nest mounds are characterized by stable microclimatic conditions, that are favourable to the development of rich invertebrate and microbial communities. Through their respiration processes, all these inhabitants contribute to the total gas emissions of the mounds. Quantifications of red wood ant mounds CO2 production are only available from Northern and Central Europe, and the Alps, where these ants are common. During the second half of the last century some species were transplanted from the Alps to southernmost sites, where they were not present, to be employed as biocontrol agents. No information on the contribution of these low-latitudes populations to the local forest CO2 production is available. The microbial communities living within red wood ant mounds are also poorly known. In this study, we investigated the CO2 gas emissions and the microbiome of the mounds of an introduced population of the red wood ant Formica paralugubris in a Southern Europe montane forest. We found that ant mounds produced more CO2 than the forest soil, and that their CO2 efflux as well as internal concentration were higher during summer than winter, with a lighter CO2 carbon isotopic signature in summer than winter, likely due to an increased ant activity. Moreover, the top part of the mound was characterised by higher CO2 efflux and lower CO2 internal concentration compared to the bottom, probably due to its internal structure and conditions. The isotopic signature of the mound material was similar between summer and winter, suggesting a metabolic similarity of the microbial communities. Also, we estimated the ants’ relative contribution to the total mound CO2 production to be 83%, whereas the microbiota CO2 contribution was estimated at 17%. Finally, the mound microbiome composition varied between summer and winter, though no seasonal difference in the diversity indexes or β-diversity was found. Our results demonstrate the impacts of the introduced red wood ants on the carbon dynamics of the recipient ecosystem.

Leaf-cutting ant (Atta laevigata Smith) in an African mahogany plantation in Minas Gerais state, Brazil

Khaya grandifoliola C. DC. (Meliaceae), known as African mahogany, is used in the establishment of commercial plantations for high-value timber production. This work aims to report the first occurrence of the genus Atta in a commercial plantation of this species. An ant nest mound with 105 m2 of loose soil and five active ant holes were observed. Leaves cut into crescent shaped sections and pieces of young branches were found near these holes, in addition to trees with the apical part of their crown partially defoliated. The collected specimens were identified as Atta laevigata Smith (Hymenoptera: Formicidae: Attini), locally known as the glass-head leaf-cutting ant.

The structure and importance of nest mounds in a tropical ant Diacamma indicum

1. Nest mounds are an integral part of many subterranean insect species, and they aid in thermoregulation, gaseous exchange, and flood prevention. Ants living in subterranean nests are prone to nest flooding particularly during monsoons and this will impact the colonies' fitness.2. Diacamma indicum is a tropical Ponerine ant species that lives in simple, single‐chambered nests with a single entrance. In this study, we characterised the mound architecture and performed field experiments to check functional significance of mounds.3. On examining mound architecture (n = 19 nests), we found that mounds not only elevated the nest entrance by 3.39 cm on average, but they also made the entrance at the top of the mound significantly smaller than the nest entrance at the base of the mound. Both these features are likely to reduce rainwater from falling directly into the nest's entrance tunnel.4. Upon performing partial (n = 18 nests) and complete destruction (n = 20 nests) in two different seasons, colonies were observed to actively rebuilt mounds to pre‐destruction levels within 3 days in all cases.5. Furthermore, examining the amount of water that entered the nest upon flooding in the presence and absence of mounds (n = 18 colonies) revealed that mounds prevented a minimum of 29.2% of water from seeping into the nest from the surrounding area, as mounds could act as a levee. This study highlights the active architectural adaptations to flooding by an organism that dwells in subterranean nests in a tropical habitat.

The bacterial and fungal community composition in time and space in the nest mounds of the ant Formica exsecta (Hymenoptera: Formicidae).

In a subarctic climate, the seasonal shifts in temperature, precipitation, and plant cover drive the temporal changes in the microbial communities in the topsoil, forcing soil microbes to adapt or decline. Many organisms, such as mound‐building ants, survive the cold winter owing to the favorable microclimate in their nest mounds. We have previously shown that the microbial communities in the nest of the ant Formica exsecta are significantly different from those in the surrounding bulk soil. In the current study, we identified taxa, which were consistently present in the nests over a study period of three years. Some taxa were also significantly enriched in the nest samples compared with spatially corresponding reference soils. We show that the bacterial communities in ant nests are temporally stable across years, whereas the fungal communities show greater variation. It seems that the activities of the ants contribute to unique biochemical processes in the secluded nest environment, and create opportunities for symbiotic interactions between the ants and the microbes. Over time, the microbial communities may come to diverge, due to drift and selection, especially given the long lifespan (up to 30 years) of the ant colonies.

Terpenes and fungal biomass in the nest mounds of Formica aquilonia wood ants

Nest mounds of wood ants of the Formica rufa group are built using conifer needles, small branches, other plant materials and soil. Conifer needles contain several mono and sesquiterpenes. Thus, wood ant nests may act as terpene hotspots in conifer forest soils. Some of the terpenes show antifungal activity and may thus cause small-scale heterogeneity in fungal biomass. We compared terpene concentrations and fungal biomass (ergosterol concentration) of nest material of the wood ant Formica aquilonia from the top, core and basement of 14 nest mounds in eastern Finland. Overall, α-pinene, camphene, sabinene, β-pinene, myrcene, limonene, camphor and longifolene were detected the most and were commonly present in all the studied layers. We found that terpene concentrations differed between the sampled nest material layers, being generally highest in the core of the nest and lowest at the basement of the nest. There was no association between the terpene concentration and material moisture. Fungal biomass was highest in the top layer, intermediate in core and lowest in basement; however, it was not negatively associated with terpene concentrations. Fungal biomass in nest mounds was positively associated with moisture and alkalinity. Nest mounds of Formica rufa group wood ants are complex structures with different chemical and microbial properties among its layers.

Fauna associated with the nests of Crocodylus moreletii and Crocodylus moreletii × acutus in Belize

ABSTRACT Morelet’s crocodile (Crocodylus moreletii) and hybrid crocodiles (C. moreletii × acutus) are mound-nesting crocodilians found in the lowlands of northern and southern Belize, respectively. Nests of both crocodilians consist of large mounds of soil, vegetation, leaf litter, and in some cases sand. We here report on the fauna associated with nest mounds of C. moreletii and C. moreletii × acutus, and describe the associations between crocodiles and commensal fauna. Our data were collected during various ecological studies conducted from 1992 through 2000, and we examined 138 active (containing eggs) nests of C. moreletii and 11 active nests of C. moreletii × acutus. We noted the occurrence of at least 14 species of fauna associated with 45 (32.6%) C. moreletii and three (27.2%) C. moreletii × acutus nests. Nest-associated fauna included ants, bees, termites, turtles, squamates, birds, and mammals. Associations included five species dwelling within crocodile nest mounds, four species that deposited eggs in crocodile nest mounds, and five species nesting in close proximity to crocodile nests. Nest-associated fauna presumably benefit from the protection afforded by nest attendance and aggressive defence behaviour of female crocodiles, although these benefits have yet to be empirically established.

Built to last a day: The function and benefits of spider mound nests

AbstractNests are crucial to the survival of offspring and reproductive success of the animals that build them. These benefits are subject to change over time due to fluctuating conditions inside and outside of nests. For many species, nests are assumed to benefit offspring until they disperse and therefore, nest destruction prior to offspring dispersal results in reduced reproductive success for parents. However, the consequences of nest destruction to reproductive success, or lack thereof, remain largely unstudied across diverse taxa. Here, we experimentally investigate the function and benefits of nests of a mound‐building spider. Mason spiders (Castianeira sp.) are wandering spiders that build intricate nests (mounds) on top of their egg sacs. Their offspring inhabit egg sacs at nest sites for up to 7 months, including through winter. We find that despite requiring hundreds of collecting trips and many hours to construct, mason spider nests remain for a small portion of time that offspring occupy nest sites. Our study finds that nest benefits change over time, likely explaining this dynamic. Nests greatly reduce the rate of predation and parasitism of egg sacs by 19.1% and offspring mortality within egg sacs due to abiotic factors by 19.9%. These effects are only present the few days following nest construction. Our study illuminates the idea that nest destruction does not always result in reduced reproductive success for nest builders. We suggest that nest durability, the ability of a nest to withstand environmental conditions, may be subject to natural selection and a critical, yet understudied, aspect of parental care.

P.186 Molecular pathways underlying schizophrenia

Temperature and humidity conditions affect the growth and success of ectotherm insects. Red wood ants of the Formica rufa group are able to regulate the temperature of their nests to be close to the optimum, typically higher than ambient in northern latitudes and higher elevation. The mound-shaped nests are constructed from organic particles (needles, sticks, etc., plant material) and from soil particles. Nest mounds typically have a relatively dry inner structure but moister surface layer which may help the ants to insulate nests against cooling winds. Forest clear felling exposes nest mounds to direct sunlight, drier microclimate and increased wind. We studied whether clear felling affects the nest surface moisture and temperature conditions. We found that i) nest surfaces were significantly drier in clear fells than in forests, ii) a high height/diameter ratio and an increase in the nest volume increases surface dryness in clear fells but not in forests, iii) the nest temperatures relative to ambient temperature was higher in forests than in clear fells, and iv) the relative temperature increased with increasing moisture content of nest surface layer. The drying nest material and more unstable inside temperature may have adverse effects not only on the red wood ants themselves, but also for nest-dwelling soil organisms and myrmecophiles that live in red wood ant nests. In addition, changes in moisture and temperature could have effects on the rate of decomposition and nutrient turnover.

A comparative study of the fauna associated with nest mounds of native and introduced populations of the red wood ant Formica paralugubris

In the second half of the twentieth century, many red wood ant populations were transferred from the Alps to the Apennines as biological control agents. Since the introduction involved the relocation of entire nest mounds, it is presumable that the associated fauna was also relocated. While the introduction of these ants has raised several concerns about their ecological impact, there has been no attempt to investigate the introduction of other nest-associated species. In this study, we collected samples of soil and nest material from three populations of the red wood ant Formica paralugubris, one Alpine native and two imported into the Apennines. We aimed to confirm that nest mounds are hotspots for soil fauna, detect the occurrence of new myrmecophilous species, and compare the nest-associated fauna among sites, to test the hypothesis of mass species relocation. We focused our analyses mainly on two taxa, springtails and oribatid mites, two highly representative groups of the mesofauna inhabiting nest mounds. The results showed higher richness and diversity in nests than soil for oribatids but not for springtails. We found 17 myrmecophilous oribatid species, but only two springtail species. Finally, native and imported sites shared only a few oribatid and springtail species, suggesting that massive relocation did not occur with nest transplants or it was likely limited. Additionally, we found some species never before collected in Italy.

Consequences of Climate Change-Induced Habitat Conversions on Red Wood Ants in a Central European Mountain: A Case Study.

Simple SummaryThe red wood ants are considered to be one of the main ecosystem engineers and keystone species of the habitats in which they exist. Most of the species from this species group inhabit coniferous forests, which, due to the consequences of anthropogenic climate change, are continuously cut down. Therefore, the main habitat of these important species is rapidly disappearing. We investigated the consequences of the absence of conifers (clear-cut area and deciduous forest) on one of the members of this species group, namely Formica polyctena. We have found that compared with the mixed-coniferous forest stand, the absence of coniferous species resulted in significant changes in the colony and nest structure of F. polyctena. In addition, the colony size was also smaller in these sites. These changes suggest that although F. polyctena is able to survive in suboptimal habitats, still their population decline is expected and urges conservation managers to apply necessary action plans for their protection.The consequences of anthropogenic climate change are one of the major concerns of conservation biology. A cascade of negative effects is expected to affect various ecosystems, one of which is Central European coniferous forests and their unique biota. These coniferous forests are the primary habitat of many forest specialist species such as red wood ants. Climate change-induced rising of temperature allows trees to skip winter hibernation, making them more vulnerable to storms that cause wind felling, and in turn, promotes bark beetle infestations that results in unscheduled clear-cuttings. Red wood ants can also be exposed to such habitat changes. We investigated the effects of bark beetle-induced clear-cutting and the absence of coniferous trees on colonies of Formica polyctena, including a mixed-coniferous forest as a reference. Our aim was to investigate how these habitat features affect the nest characteristics and nesting habits of F. polyctena. Our results indicate that, in the absence of conifers, F. polyctena tend to use different alternatives for nest material, colony structure, and food sources. However, the vitality of F. polyctena colonies significantly decreased (smaller nest mound volumes). Our study highlights the ecological flexibility of this forest specialist and its potential to survive under extreme conditions.

Substrates for the Production of Passiflora setácea cv. BRS Pérola do Cerrado Seedlings

ABSTRACT The substrate is essential to ensure suitable conditions for the growth of Passiflora setacea seedlings. Thus, a study was conducted to investigate the effect of alternative substrates formulated with bee nest and termite mound materials on the growth of P. setacea cv. BRS Pérola do Cerrado seedlings. Six substrate combinations formulated from different proportions (v:v) of bee nest material (BNM) and termite mound material (TMM) or commercial substrate were tested considering the randomized block design with four replicates. The following substrates were used: S1 = BNM100%; S2 = BNM75% + TMM25%; S3 = BNM50% + TMM50%; S4 = BNM25% + TMM75%; S5 = TMM100%; and S6 = commercial substrate (Click Mudas®). The plant height, stem diameter, root length, root dry matter (RDM), shoot dry matter (SDM), total dry matter (TDM), and morphological indices were measured. Passiflora setacea seedlings have better development with the use of substrates S1, S2, and S3, with greater emphasis on the substrate S1. The substrate S1 (100% BNM) should be recommended for the production of P. setacea cv. BRS Pérola do Cerrado seedlings, for improving plant development and providing higher quality seedlings.

Bi-layered architecture facilitates high strength and ventilation in nest mounds of fungus-farming termites

Mass–energy transfer across the boundaries of living systems is crucial for the maintenance of homeostasis; however, it is scarcely known how structural strength and integrity is maintained in extended phenotypes while also achieving optimum heat–mass exchange. Here we present data on strength, stability, porosity and permeability of termite mounds of a fungus-farming species, Odontotermes obesus. We demonstrate that the termite mound is a bi-layered structure with a dense, strong core and a porous shell that is constantly remodelled. Its safety factor is extraordinarily high and is orders of magnitude higher than those of human constructions. The porous peripheries are analogous to the mulch layer used in agriculture and help in moisture retention crucial for the survival of fungus gardens, while also allowing adequate wind-induced ventilation of the mounds. We suggest that the architectural solutions offered by these termites have wider implications for natural and industrial building technologies.

Moisture alone is sufficient to impart strength but not weathering resistance to termite mound soil.

Soil is used for the construction of structures by many animals, at times admixed with endogenous secretions. These additives, along with soil components, are suggested to have a role in biocementation. However, the relative contribution of endogenous and exogenous materials to soil strength has not been adequately established. Termite mounds are earthen structures with exceptional strength and durability including weathering resistance to wind and rain. With in situ and laboratory-based experiments, we demonstrate that the fungus-farming termite Odontotermes obesus which builds soil nest mounds, when given a choice, prefers soil close to its liquid limit for construction. At this moisture content, the soil–water mixture alone even in the absence of termite handling undergoes self-weight consolidation and upon drying attains a monolithic, densely packed structure with compressive strength comparable to the in situ strength of the mound soil; however, the soil–water mixture alone has lower resistance to water erosion than the in situ mound samples, suggesting that termite secretions impart weathering resistance and thereby long-term stability to the mound. Therefore, weathering resistance and compressive strength are conferred by different aspects of termite soil manipulation. Our work provides novel insights into termite mound construction and strength correlates for earthen structures built by animals.

Large- and Small-Scale Environmental Factors Drive Distributions of Ant Mound Size Across a Latitudinal Gradient.

Red wood ants are keystone species of forest ecosystems in Europe. Environmental factors and habitat characteristics affect the size of their nest mounds, an important trait being in concordance with a colony’s well-being and impact on its surroundings. In this study, we investigated the effect of large-scale (latitude and altitude) and small-scale environmental factors (e.g., characteristics of the forest) on the size of nest mounds of Formica polyctena in Central Europe. We predicted that the change in nest size is in accordance with Bergmann’s rule that states that the body size of endotherm animals increases with the higher latitude and/or altitude. We found that the size of nests increased along the latitudinal gradient in accordance with Bergmann’s rule. The irradiation was the most important factor responsible for the changes in nest size, but temperature and local factors, like the perimeter of the trees and their distance from the nest, were also involved. Considering our results, we can better understand the long-term effects and consequences of the fast-changing environmental factors on this ecologically important group. This knowledge can contribute to the planning of forest management tactics in concordance with the assurance of the long-term survival of red wood ants.

Nest-site selection and nest size influence the incubation temperature of Morelet's crocodiles.

In oviparous tetrapods, the nesting-site selection by females is related to the habitat characteristics, which influences nest incubation temperature. Females can directly influence the incubation temperature by choosing certain construction materials or by building nests of different sizes. There are few studies focusing on these aspects in crocodilians that build mound nests. The aim of this study was to determine whether the nest size, its exposure to solar radiation, and the environmental temperature influence the incubation temperature of Morelet's crocodile (Crocodylus moreletii) nests. Artificial nests of two sizes (small and large) were constructed with similar characteristics to natural nests and placed in two locations differing in exposure to solar radiation (shaded and sunny). We used temperature and relative humidity data loggers to record the incubation temperature inside each nest every hour during the species' natural nesting period. Likewise, we recorded the ambient temperature every hour where the experiments were set up with temperature data loggers. We found that nest size and its exposure to solar radiation affected the incubation temperature, with smaller nests in shaded locations having lower incubation temperatures than larger nests in sunny locations. We discuss the importance of nest-site selection and maintenance behaviour of the mound nest by female crocodiles on the incubation temperature of the nest.

Stratification effects on flow and scalar transport through a deep cavity: A bioinspired examination

This study investigates the effect of thermal stratification and boundary layer wind on the transport phenomena within a deep cavity. The study is inspired by the ventilation and gas-exchange process within the chimneys of open-vent termite mounds. Large-eddy simulations are conducted over an idealized termite mound subject to different thermal stratifications that are formed based on the observed mean day and night-time air and mound nest temperatures reported in the literature. A thorough analysis of the flow, temperature, and scalar fields indicates that the dynamics of the flow and the ventilation process within the cavity are controlled by the combined effects of the cavity entrance vortex and the stability condition within the lower regions of the cavity. The results show that, despite the small differences in the imposed stratification condition, the ventilation capacity is significantly higher in unstable conditions, owing to the stronger suction at the cavity entrance, together with the positive buoyant forces at the lower sections of the cavity. The results are in agreement with experimental observations of termite mounds in nature.

The negative effect of wood ants (Formica rufa) on microarthropod density and soil biological quality in a semi-arid pine forest

Wood ants (Formica rufa group) are widely distributed in the northern hemisphere and have an important effect on ecosystem processes. The objectives of this study were to evaluate the relationship between F. rufa and the soil biological quality and microarthropod diversity in a semi-arid black pine forest. Microarthropod sampling was conducted for 2 years, from October 2014 to September 2016, at four ant nest mounds of similar size. A total of 288 soil cores were sampled bimonthly, near the nests (designated as the adjacent zone) and at a distance of 10 m away from the nests (designated as the distant zone) during the study period. The results were evaluated by the mean density, QBS-ar index, and Shannon diversity index scores. The mean density of the microarthropods in the adjacent zone (32,797 ind m–2) was lower than the mean density observed in the distant zone (44,462 ind m–2). The Shannon diversity index values were insensitive to differences in microarthropod density, as affected by wood ants, between the adjacent and distant zones, but the QBS-ar values were significantly different between the zones. This suggested that the QBS-ar index may be advantageous in monitoring the impact of wood ants on soil microarthropods in a semi-arid pine forest. Overall, this study reveals that F. rufa may have a significant impact on soil microarthropods in semi-arid forest ecosystems.

Discussion of development processes in insect-fungus association derived from the shaggy parasol fruiting on the nests of hairy wood ants.

Chlorophyllum rhacodes, typically regarded as a rich grassland or open forest “mushroom” species, was found fruiting abundantly on nests of Formica lugubris, occurring in a Pinus silvestris plantation. Fruiting was absent from the rest of the woodland.Research focussed on the activities in the nests that could explain this. Within nests, there was a spatial relationship between C. rhacodes mycelium, insect cadavers, fruitbody initiation, and roots of adjacent trees.In vitro experiments found that C. rhacodes was not mycorrhizal with P. silvestris, but that it had qualities which rendered it suitable for colonization of the rhizosphere in the conditions of the nest mound and for further niche development.Implications of the unusual presence of fruit‐bodies and the distribution of associated hyphae are discussed in relation to the nutritional biology (and recent taxonomical reassignment) of the fungus. This includes reference to the relevant physiology of insects and to the accepted evolution of mutualistic symbioses between fungi and the Attini and Termitidae.An argument is presented that the situation observed in vivo provides evidence of a degree of facultative association and what could be tangible support for the theory for the developmental origin of mutualistic fungus cultivation by insects. It is presented as a context for continued experimental research.