Subterranean Nests Research Articles

Cryptic combat against competing microbes is a costly component of parental care in a digger wasp

Microorganisms are ubiquitous and key selective agents in parental care behaviour. Various animal species have thus evolved diverse means to prevent and combat detrimental effects of microbial competitors and pathogens on their offspring. The European beewolf, Philanthus triangulum , is a solitary crabronid wasp that stores paralysed honeybees as larval provisions in subterranean nests. In the soil the highly nutritious provisions can be attacked by a large number of microorganisms. We investigated the effect of fungal infestations of larval provisions on the reproductive success of beewolves. Although fungal infestations reduced larval survival, female beewolves largely eliminated this effect by embalming larval provisions with ample amounts of hydrocarbons. However, this came at the cost of a reduced ability to apply hydrocarbons to the provisions of future offspring. This reduced investment in embalming resulted in a higher risk of mould infestations. Embalming of the prey in P. triangulum thus meets the criterion of parental investment and females have to balance this investment of hydrocarbons in current and future offspring to maximize their lifetime reproductive success.

Formyltetrahydrofolate synthetase gene diversity in the guts of higher termites with different diets and lifestyles.

In this study, we examine gene diversity for formyl-tetrahydrofolate synthetase (FTHFS), a key enzyme in homoacetogenesis, recovered from the gut microbiota of six species of higher termites. The "higher" termites (family Termitidae), which represent the majority of extant termite species and genera, engage in a broader diversity of feeding and nesting styles than the "lower" termites. Previous studies of termite gut homoacetogenesis have focused on wood-feeding lower termites, from which the preponderance of FTHFS sequences recovered were related to those from acetogenic treponemes. While sequences belonging to this group were present in the guts of all six higher termites examined, treponeme-like FTHFS sequences represented the majority of recovered sequences in only two species (a wood-feeding Nasutitermes sp. and a palm-feeding Microcerotermes sp.). The remaining four termite species analyzed (a Gnathamitermes sp. and two Amitermes spp. that were recovered from subterranean nests with indeterminate feeding strategies and a litter-feeding Rhynchotermes sp.) yielded novel FTHFS clades not observed in lower termites. These termites yielded two distinct clusters of probable purinolytic Firmicutes and a large group of potential homoacetogens related to sequences previously recovered from the guts of omnivorous cockroaches. These findings suggest that the gut environments of different higher termite species may select for different groups of homoacetogens, with some species hosting treponeme-dominated homoacetogen populations similar to those of wood-feeding, lower termites while others host Firmicutes-dominated communities more similar to those of omnivorous cockroaches.

Nest architecture and traffic flow: large potential effects from small structural features

1. Research on human pedestrian dynamics predicts that seemingly small architectural features of the surroundings can have large effects on the behaviour of crowds and the flow of pedestrian traffic, particularly when a crowd is panicked. This theoretical framework might usefully be applied to the study of collective movement within subterranean nests of social insects.2. We examined the rate of egress from artificial nests by alarmed Linepithema humile ants. In accord with model predictions, but counter to intuition, we found that a partially obstructed exit enhanced the average rate of escape from the nest.3. The study of traffic flows in subterranean nests is almost non‐existent, but it would be worth studying the effect of nest design elements on collective movements, given the great variety of nest forms among ants and termites.

Methods for Casting Subterranean Ant Nests

The study of subterranean ant nests has been impeded by the difficulty of rendering their structures in visible form. Here, several different casting materials are shown to make perfect casts of the underground nests of ants. Each material (dental plaster, paraffin wax, aluminum, zinc) has advantages and limitations, which are discussed. Some of the materials allow the recovery of the ants entombed in the casts, allowing a census of the ants to be connected with features of their nest architecture. The necessary equipment and procedures are described in the hope that more researchers will study this very important aspect of ant natural history.

The Nest Architecture of the AntOdontomachus brunneus

The architecture of the subterranean nests of the ant Odontomachus brunneus (Patton) (Hymenoptera: Formicidae) was studied by means of casts with dental plaster or molten metal. The entombed ants were later recovered by dissolution of plaster casts in hot running water. O. brunneus excavates simple nests, each consisting of a single, vertical shaft connecting more or less horizontal, simple chambers. Nests contained between 11 and 177 workers, from 2 to 17 chambers, and 28 to 340 cm2 of chamber floor space and reached a maximum depth of 18 to 184 cm. All components of nest size increased simultaneously during nest enlargement, number of chambers, mean chamber size, and nest depth, making the nest shape (proportions) relatively size-independent. Regardless of nest size, all nests had approximately 2 cm2 of chamber floor space per worker. Chambers were closer together near the top and the bottom of the nest than in the middle, and total chamber area was greater near the bottom. Colonies occasionally incorporated cavities made by other animals into their nests.

Polistes dominulus(Christ, 1791) (Hymenoptera: Polistinae: Vespidae) Newly Recorded from South Africa

South Africa has three indigenous genera of paper wasp, Polistes, Rhopalidia and Belonogaster (family Vespidae). These wasps are mostly brown in colour, usually with pale maculation, and construct nests that are exposed. Thirty four years ago Whitehead & Prins (1975) recorded the European wasp, Vespula germanica (Fabricius, 1793), from Cape Town. This paper wasp builds subterranean nests. Occasionally V. germanica makes nests in closed cavities, such as cavities within the walls of houses, and may also have nests that project outside such cavities. This species has slowly expanded its range to include a substantial area around Cape Town, including the Cape Peninsula, Stellenbosch and the Hottentots-Holland Mountains (Tribe & Richardson 1994, G. Tribe, pers. comm.), and further spread is expected.

Effects of Urban Development on Ant Communities: Implications for Ecosystem Services and Management

Research that connects the effects of urbanization on biodiversity and ecosystem services is lacking. Ants perform multifarious ecological functions that stabilize ecosystems and contribute to a number of ecosystem services. We studied responses of ant communities to urbanization in the Lake Tahoe basin by sampling sites along a gradient of urban land development. We sampled ant communities, measured vegetation characteristics, quantified human activities, and evaluated ant-community responses by grouping ants into service-providing units (SPUs), defined as a group of organisms and their populations that perform specific ecosystem services, to provide an understanding of urbanization impacts on biodiversity and their delivery of ecosystem services. Species richness and abundance peaked at intermediate levels of urban development, as did the richness of 3 types of ant SPUs (aerators, decomposers, and compilers). With increasing land development aerator and decomposer ants significantly declined in abundance, whereas compiler ants significantly increased in abundance. Competing models demonstrated that precipitation was frequently among the strongest influences on ant community structure; however, urban development and human activities also had a strong, negative influence on ants, appearing in most models with DeltaAIC(c) < 2 for species richness and abundance patterns of SPUs and generalists. Response diversity was observed within SPUs, which suggests that the corresponding ecosystem services were maintained until development reached 30-40%. Our data provide evidence that ecosystem functions, such as water infiltration and soil productivity, may be diminished at sites subject to greater levels of urbanization and that conserving ant communities and the ecosystem services they provide could be an important target in land-use planning and conservation efforts.

Abundance and diversity of termites in a savanna woodland reserve in tropical Australia

AbstractThis study contributes to the paucity of knowledge on the structure of Australian tropical savanna termite assemblages, compared with that available for tropical savannas elsewhere in the world. Termite species diversity, frequency of occurrence and functional diversity in Charles Darwin National Park, a savanna woodland reserve in tropical northern Australia, were assessed. In four 50 × 50 m sites, a direct search and bait sampling protocol was used to sample mounds, standing and lying dead wood, litter, soil and arboreal nest microhabitats for termites between April and June 2003. Results were compared with a priori predictions of termite community structure based on the work by Braithwaite et al. (1988). Sixteen species from nine genera and three families (Mastotermitidae, Rhinotermitidae and Termitidae) were recorded, including the first record of Ephelotermes taylori (Hill) from open savanna woodland habitat and the first official record of Macrognathotermes errator Miller from north Australian savanna. The family Termitidae represented 69% of termite occurrences. From this family, the wood/soil interface feeder Nasutitermes eucalypti (Mjöberg) represented 30% of encounters. High levels of termite activity were recorded at baits within 6 weeks. Four nesting habits were represented: epigeal (mounds above ground), hypogeal (subterranean nests), nests within wood and arboreal nests. Termites were most frequently encountered in epigeal mounds and lying dead wood. Wood and wood/soil interface feeders were the most common. The findings partially supported the a priori predictions proposed. The termite assemblage structure was represented by species commonly found in other Northern Territory savanna woodland habitats. However, species diversity was lower; soil feeders and live wood feeders were less common and grass‐harvesting species were absent. Soil nitrogen and phosphorus and species richness and patchiness of ground vegetation may contribute to these differences. The lower species diversity recorded contrasts with the richer termite faunas of tropical savannas recorded elsewhere.

Soil temperature, digging behaviour, and the adaptive value of nest depth in South American species of Acromyrmex leaf-cutting ants

In leaf-cutting ants, workers are expected to excavate the nest at a soil depth that provides suitable temperatures, since the symbiotic fungus cultivated inside nest chambers is highly dependent on temperature for proper growth. We hypothesize that the different nesting habits observed in Acromyrmex leaf-cutting ants in the South American continent, i.e. superficial and subterranean nests, depend on the occurrence, across the soil profile, of the temperature range preferred by workers for digging. To test this hypothesis, we first explored whether the nesting habits in the genus Acromyrmex are correlated with the prevailing soil temperature regimes at the reported nest locations. Second, we experimentally investigated whether Acromyrmex workers engaged in digging use soil temperature as a cue to decide where to excavate the nest. A bibliographic survey of nesting habits of 21 South American Acromyrmex species indicated that nesting habits are correlated with the soil temperature regimes: the warmer the soil at the nesting site, the higher the number of species inhabiting subterranean nests, as compared to superficial nests. For those species showing nesting plasticity, subterranean nests occurred in hot soils, and superficial nests in cold ones. Experimental results indicated that Acromyrmex lundi workers use soil temperature as an orientation cue to decide where to start digging, and respond to rising and falling soil temperatures by moving to alternative digging places, or by stopping digging, respectively. The soil temperature range preferred for digging, between 20 degrees C and maximally 30.6 degrees C, matched the range at which colony growth would be maximized. It is suggested that temperature-sensitive digging guides digging workers towards their preferred range of soil temperature. Workers' thermopreferences lead to a concentration of digging activity at the soil layers where the preferred range occurs, and therefore, to the construction of superficial nests in cold soils, and subterranean ones in hot soils. The adaptive value of the temperature-related nesting habits, and the temperature-sensitive digging, is further discussed.

Causes and predictors of nest mortality in a European rabbit population

We conducted a study on nest mortality of an individually marked population of European rabbits ( Oryctolagus cuniculus L., 1758) living in a field enclosure. Over 4 years, we determined maternities and quantified pup mortality during the nest period of 703 pups born in subterranean breeding burrows. Overall, pup mortality occurred in 42.7% of the litters, whereas 32.4% of all born pups were affected. Mortality was highest during the first few postnatal days. In about 50% of the cases, we managed to quantify different causes of mortality such as malnutrition, flooding, cooling of the pups, infanticide, or predation. The pups’ body mass on postnatal day 1, the thermal environment and the number of litter mates were the most important predictors of nest mortality. Litter mortality risk decreased with increasing soil temperature around the subterranean nests. A comparatively higher average pup body mass lowered the nest mortality risk of a litter, whereas this effect was more pronounced when soil temperatures were low. Furthermore, mortality was lowest in medium-sized litters, most probably due to the balance between the thermal benefits of huddling with litter siblings and the costs of having them due to the lower share of milk obtained by the individual pups in larger litters. In addition, nest mortality depended on characteristics of the mother; mortality was increased in litters of low-ranking females and of mothers with lower body mass. In conclusion, our study highlights multiple causes and the effects of different environmental and social factors on nest mortality of this small mammal.

Thermoregulatory brood transport in the fire ant, Solenopsis invicta

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.

Optimal litter size for individual growth of European rabbit pups depends on their thermal environment

In altricial mammals and birds, the presence of a large number of litter or brood mates often affects the development of individual offspring by reducing the share of resources provided by the parents. However, sibling presence can also be favourable, conferring thermoregulatory benefits when ambient temperatures are low. Consequently, shifts in the relation between costs and benefits of sibling presence can be expected as a function of the thermal environment. In a study of a European rabbit population (Oryctolagus cuniculus) living in a field enclosure, we investigated the effects of litter size and soil temperature on pup growth over 7 years. Temperatures inside the subterranean nests were positively correlated with soil temperature and with litter size. Soil temperature varied strongly across the breeding season, ranging from 3 to 21 degrees C. Under warmer soil temperature conditions (10-15 degrees C and >15 degrees C), pup growth decreased with increasing litter size, where litters of two pups (smallest litter size considered) showed the highest growth rates. In contrast, under colder soil temperature conditions (<10 degrees C), the highest growth rates were found in litters of three pups. We also asked if such temperature-dependent differences in the optimal pup growth rates might be explained by differences in maternal characteristics, which might affect lactational performance. We assessed maternal performance using females' postpartum body mass and social rank. However, we did not find consistent differences in maternal characteristics between females giving birth to different-sized litters during different soil temperature conditions, which would have provided an alternative explanation for the observed differences in litter size-dependent pup growth. We conclude that under colder soil temperature conditions, the thermal benefits of a greater number of littermates outweigh the negative consequences of competition for milk, leading to an environment-dependent shift in the optimal litter size for individual growth in this species.

The nest architecture of the ant, Pheidole oxyops Forel, 1908 (Hymenoptera: Formicidae)

Abstract Pheidole oxyops builds subterranean nests, with an external architecture that is distinctive and easily recognizable by its wide and specific entrance hole, measuring up to 12.2 cm in diameter, denoting a pitfall‐trap. In order to study the nests’internal architecture, seven nests were excavated; four were identified with neutral talc, while the others were cast in cement and then excavated. Measurements were made in order to gain a better understanding of their structures, and a photographic documentation was obtained as well. The excavations revealed that the nests are perpendicular relative to the ground, beginning with a cylindrical channel with a mean length of 13.5 cm, containing irregular formations, and whose diameter becomes progressively narrower until the first chamber is formed. As the channel continues, dish‐like chambers appear, interconnected by channels that become progressively narrower and longer, while the chambers are arranged at greater distances from each other as nest depth increases. Both channels and chambers are located on the vertical projection of the entrance hole. Nests may reach a depth of up to 5.09 m, with a number of chambers ranging between 4 and 14.

Substrates and Materials Used for Nesting by North American &lt;I&gt;Osmia&lt;/I&gt; Bees (Hymenoptera: Apiformes: Megachilidae)

Abstract Nesting substrates and construction materials are compared for 65 of North America’s 139 described native species of Osmia bees. Most accounts report Osmia bees nesting in preexisting cavities in dead wood or pithy stems such as elderberry (Sambucus spp.), with cell partitions and plugs made from a pulp of finely masticated leaf tissue. Mud is widely used by species constructing free-form clumps of nest cells against stone surfaces. Some Osmia bees adopt abandoned nests of other Hymenoptera, particularly those of mud dauber wasps (Sceliphron spp.) and larger ground-nesting bees (e.g., Anthophora spp.). Reports of subterranean nesting by Osmia species are uncommon but possibly under-represent the habit, because subterranean nests are obscure and likely to be scattered. Ground- or surface-nesting habits are suspected for species that are absent from intensive trap-nesting programs in their native ranges but that otherwise have been commonly taken at flowers. The range of nesting habits and material...

Food Wrapping with the Postpharyngeal Gland Secretion by Females of the European beewolf Philanthus triangulum

Ground-nesting animals share their habitat with countless microorganisms that can play important roles as pathogens or competitors for food resources. Thus, species that store food in the soil, either for themselves or for their progeny, must protect these resources against microbial degradation. Females of the European beewolf, Philanthus triangulum, hunt honeybees as provisions for their brood and store the paralyzed prey in their subterranean nests. A previous study had shown that females lick the surface of prey before oviposition and that this licking treatment delays mold growth. Here, we showed that females apply large amounts of a secretion from their postpharyngeal glands onto the surface of their prey during the licking behavior. Inhibition-zone assays showed that comparatively large amounts of the gland secretion had no direct antimycotic effect. We discuss our findings with regard to other possible mechanisms of the postpharyngeal gland secretion against fungal growth.

Termite Resource Partitioning Related to Log Diameter

The termites Reticulitermes virginicus and R. flavipes are sympatric in forests along the eastern United States from Florida to Maryland. These congeners construct subterranean nests, forage on surface and buried wood, and appear to have very similar ecological requirements. In the present study, I examined host-wood selection by these species in a coastal forest over two years. Logs inhabited by R. virginicus had significantly greater diameters than those used by R. flavipes. It is not known whether this pattern resulted from species-specific differences in preference for host size or competition for preferred logs. Host-wood temperature did not differ for R. virginicus and R. flavipes.

Opportunistic predation and offspring sex ratios of cicada‐killer wasps (Sphecius speciosus Drury)

Abstract 1. The way in which hunting of prey affects the sex ratio of the predator’s offspring is not well understood. Female cicada‐killer wasps are convenient for study because they specialise in capturing cicadas to provision their offspring. Cicada prey are nearly twice as heavy as the wasps that carry them, hence some degree of prey selectivity by the wasps is to be expected. It has been suggested that wasps bias their offspring towards females by foraging selectively for female prey, whereas there is some evidence that sex ratios are actually male‐biased. This study was designed to establish the connection between foraging and offspring sex ratio.2. Three, non‐exclusive, hypotheses of selective predation were tested. The frequency of predation on different classes of prey in conjunction with their availability was estimated by intercepting the wasps on their way to their nests and by sampling cicadas in the environment. The hypothesis of selective predation was not supported; predation appears to be opportunistic and non‐selective. Cicada prey weight was not a simple linear function of wasp weight, although the smallest wasps were constrained to carry small prey.3. Wasp offspring (larvae) were excavated from subterranean nests and found to be male‐biased (3 : 1 or 4 : 1) in 2 years. The observed ratios are close to expectation from Fisher’s equal‐investment model, taking account of sexual size dimorphism, and are evidently unrelated to the sex of the prey. A simple binomial probability rule of sex allocation provides a behavioural mechanism for producing the observed sex ratio of offspring.

Defensiveness of the fire ant, Solenopsis invicta, is increased during colony rafting

Colonies of the fire ant, Solenopsis invicta, can survive flood conditions by forming a raft of ants that floats on the water’s surface until the flood recedes or higher ground is found. Having been forced from the protection of their subterranean nests, rafting colonies are totally exposed and are without retreat. I tested the hypothesis that rafting S. invicta colonies would compensate for their elevated vulnerability by increasing their defensiveness. I measured defensiveness using the amount of venom workers delivered per sting (venom dose), since the repellent effects (i.e., pain and tissue damage) of fire-ant venom are dose-dependent. In the laboratory I assayed colony defensiveness before and after flooding colonies from their nests with water. Colonies were consistently and significantly more defensive while rafting (i.e., each colony’s workers delivered higher venom doses when their colony was rafting than they did when it was assayed pre-flood). The larger venom doses of rafting colonies may reduce their chances of being damaged by encounters with other animals by reducing the duration of such encounters through increased repellency. Encounters with S. invicta during flood conditions have the potential to be unusually dangerous; large concentrations of workers are exposed and available for defense, and they deliver significantly larger venom doses when they sting.

Spatial Navigation: Spatial Learning in Real and Virtual Environments

Humans and many non-human animals need to accurately and efficiently navigate from one place to the next in their environment. Over 3,000 years ago the volcanic islands of the Pacific were settled by the people of Polynesia (Gibbons, 2001). These navigators sailed in craft from Samoa to Hawaii covering an area extending some 4,500 km without the benefits of modern navigational equipment. Errors in the es timation of direction or position during trips to and from the islands in this region could have dire consequences. Some 2,400 years later, European sailors had started mastering oceanic navigation and were probably surprised to discover that people had already traveled to, and were living on, these remote Pacific islands. Today, few humans make such long trips without the benefits of modern navigational tools. Traditionally investigations of human and nonhuman place learning have used very different approaches to understand the underlying mechanisms involved in spatial learning. Although these approaches and associated techniques have provided each respective research area with valuable information about spatial processing, one important problem has been the minimal communication between the two disciplines which share such a common interest. Our review examines the two main theories of place learning—the associative approach and the cognitive mapping theory—through the examination of current research using three main behavioral techniques that were developed for the study of spatial navigation in animals but modified for the study of human spatial navigation. Although the focus of our review is at a behavioral level, we consider how these approaches have strengthened our understanding of the neurological mechanisms of place learning in animals and discuss how future research, comparative in nature, will allow for an excellent opportunity for future comparative studies of spatial place learning. Many non-human animals were engaging in impressive feats of navigation long before people were navigating across oceans. Desert ants (Cataglyphis fortis) live in subterranean nests that insulate them from arid conditions above ground. During the course of the day foraging ants depart their nest in search of food, in this case other insects that have succumbed to the desert heat. The foraging desert ant may be required to take a rather long (several hundred meters) and circuitous route before it finds a food item, since the loca tion of food items vary dramatically from day to day. Once the foraging ant has found food, it takes a direct route back to the entrance of the subterranean nest (Wehner, 2003). Errors in the estimation of the nest location could easily prove fatal. Notably, like an early human navigator on the ocean, the ant’s impressive feat of navigation is accomplished in a relatively homogeneous environment lacking surfaces that could be used as landmarks to help indicate the position of the nest.

Effect of different termite feeding groups on P sorption and P availability in African and South American savannas

Nest structures of six termite species, four with epigeous (above-ground) and two with subterranean nests were analysed to find out how their building and feeding habits could be related to their nests phosphorus status compared with control soils. Termite nest structure was found to affect significantly the P status in savanna soils: mounds of the African Trinervitermes geminatus and the South American Nasutitermes ephratae (both grass-feeders) displayed a greater amount of available P, especially in the inner part of the nest, than the surrounding soil. The abundant quantities of dead grass material stored in the mound can explain the available soil P increase. A similar increase in P availability was also found for the soil-feeder Cubitermes severus. In mounds of Macrotermes bellicosus, on the other hand, there was a drastic increase in P sorption (and a corresponding decrease in available P) compared to adjacent soils, which was attributed to the building strategy of this species. M. bellicosus selected clay from subsoil to build its nest structure. The data obtained for the subterranean species Ancistrotermes cavithorax and Microtermes toumodiensis indicated also that there is an increase in P sorption in mounds when compared with associated topsoils. Consequently, the nest structures of only certain termite species should be considered, and utilised, as a soil amendment in place of fertilisers. This impact on the P cycle in savannas seems to be related to the termite feeding status and to the type of material utilised in nest building. This should be taken into account before using termite nest material in soil fertility status improvement.