Burrow Systems Research Articles

Decreased burrowing activity of endogeic earthworms and effects on water infiltration in response to an increase in soil bulk density

Endogeic earthworms live and burrow in the soil to find their food. They burrow by pushing the soil aside or ingesting it and are thus sensitive to soil compaction. However there is a scarcity of data regarding the effects of soil bulk density on the burrowing behavior and activity of endogeic earthworms. We carried out laboratory experiments using repacked soil cores with various levels of bulk density (from 1.18 to 1.38 g cm−3) in which individuals of Aporrectodea caliginosa or Allolobophora chlorotica were incubated for six weeks. The burrow systems inside the soil cores and the compaction around the burrows were then analyzed using X-ray tomography. Soil water infiltration measurements were also carried out. The increase in bulk density had a negative impact on all burrow system characteristics (length, volume, diameter, continuity, number of burrows). When bulk density increased from 1.18 to 1.38 g cm−3, volume, diameter, continuity and the number of burrows decreased on average by 77 %, 21 %, 81 % and 58 %, respectively. The increase in density due to compaction around the burrows was similar whatever the species and the bulk density. Increasing soil bulk density from 1.18 to 1.38 g cm-3 also greatly decreased water infiltration (−89 % for both species) and increased breakthrough time (10 and 25-fold for A. chlorotica and A. caliginosa respectively). However, compared to a control without earthworms, water infiltration in cores incubated with endogeic species was only increased significantly at 1.18 and 1.23 g cm−3. This illustrates that burrows made by endogeic earthworms moderately increase water infiltration and only when the soil bulk density is low. Data provided in this study could be used to refine simulation models of earthworm burrowing behavior where burrowing is assumed to be mainly governed by soil water content, temperature and soil bulk density.

Burrow emergence rhythms of Nephrops norvegicus by UWTV and surveying biases

Underwater Television (UWTV) surveys provide fishery-independent stock size estimations of the Norway lobster (Nephrops norvegicus), based directly on burrow counting using the survey assumption of “one animal = one burrow”. However, stock size may be uncertain depending on true rates of burrow occupation. For the first time, 3055 video transects carried out in several Functional Units (FUs) around Ireland were used to investigate this uncertainty. This paper deals with the discrimination of burrow emergence and door-keeping diel behaviour in Nephrops norvegicus, which is one of the most commercially important fisheries in Europe. Comparisons of burrow densities with densities of visible animals engaged in door-keeping (i.e. animals waiting at the tunnel entrance) behaviour and animals in full emergence, were analysed at time windows of expected maximum population emergence. Timing of maximum emergence was determined using wave-form analysis and GAM modelling. The results showed an average level of 1 visible Nephrops individual per 10 burrow systems, depending on sampling time and depth. This calls into question the current burrow occupancy assumption which may not hold true in all FUs. This is discussed in relation to limitations of sampling methodologies and new autonomous robotic technological solutions for monitoring.

Regulation of HIF-1α and p53 in stress responses in the subterranean rodents Lasiopodomys mandarinus and Lasiopodomys brandtii (Rodentia: Cricetidae)

The response mechanism and interaction patterns of HIF-1α and p53 in animals in an hypoxic environment are crucial for their hypoxic tolerance and adaptation. Many studies have shown that underground rodents have better hypoxic adaptation characteristics. However, the mechanism by which HIF-1α and p53 in underground rodents respond to hypoxic environments compared with in ground rodents remains unclear. Further, whether a synergy between HIF-1α and p53 enables animals tolerate extremely hypoxic environments is unclear. We studied HIF-1α and p53 expression in the brain tissue and cell apoptosis in the hippocampal CA1 region during 6 hours of acute hypoxia (5% oxygen) in Lasiopodomys mandarinus (Milne-Edwards, 1871) and Lasiopodomys brandtii (Radde, 1861), two closely related small rodents with different life characteristics (underground and aboveground, respectively), using a comparative biology method to determine the mechanisms underlying their adaptation to this environment. Our results indicate that HIF-1α and p53 expression is more rapid in L. mandarinus than in L. brandtii under acute hypoxic environments, resulting in a significant synergistic effect in L. mandarinus. Correlation analysis revealed that HIF-1α expression and the apoptotic index of the hippocampal CA1 regions of the brain tissues of L. mandarinus and L. brandtii, both under hypoxia, were significantly negatively and positively correlated, respectively. Long-term existence in underground burrow systems could enable better adaptation to hypoxia in L. mandarinus than in L. brandtii. We speculate that L. mandarinus can quickly eliminate resulting damage via the synergistic effect of p53 and HIF-1α in response to acute hypoxic environments, helping the organism quickly return to a normal state after the stress.

Why does the plateau zokor (Myospalax fontanieri: Rodentia: Spalacidae) move on the ground in summer in the eastern Qilian Mountains?

AbstractSubterranean rodents spend most of their lives in underground burrow systems, and most studies to date on their morphological, behavioral, and physiological, adaptations have been based on their whole-life existence in subterranean ecotopes. However, a few studies have reported that some subterranean rodents exhibit aboveground activity under particular circumstances, and the results of these studies help zoologists to better understand the adaptations of subterranean rodents coping both with belowground and aboveground environments. These studies, however, do not include direct observations of the aboveground activity of these rodents. Moreover, studies into the factors that influence the movement of these subterranean rodents outside of their burrow systems are relatively scarce. Here, we report the aboveground activity pattern of plateau zokor (Myospalax fontanieri) based on videos and photographs captured by infrared cameras combined with radiotracking technology in the eastern Qilian Mountains, northwest China. In addition, the potential factors that influence the aboveground activity of plateau zokor, including temperature, humidity, food, dispersal, and mating, were studied in 2015 and 2016. We found that, of the 16 zokors with radiocollars, five females moved aboveground during the day and night in June and July 2015, with the frequency of their aboveground activity being higher during the day than that at night. Temperature, humidity, mating, and dispersal, had no effects on aboveground plateau zokor movement. However, results of a binary logistic regression indicated that the crude fat contents of aboveground and belowground plants were positively and negatively correlated with the aboveground activity of these zokors, respectively. We infer that plateau zokor move on the ground to forage for plants with higher fat content and that changes in available nutrients might serve as potential cues that affect the surface activity of plateau zokor.

Depth distribution of soil organic matter and burrowing activity of earthworms—mesocosm study using X-ray tomography and luminophores

Earthworms feed on organic matter present at the soil surface or within the soil. Thus, its distribution in the soil profile is likely to greatly influence earthworm behavior and, in turn, their burrow system. To test this idea, two anecic and two endogeic earthworm species were introduced into repacked soil cores (depth = 30 cm) upper half filled with a top soil containing 4% organic matter (0–15 cm) and lower half filled with a deep soil at 2% organic matter (15–30 cm). Earthworm behavior was studied using X-ray tomography combined with luminophores (colored particulate tracers of 63–125 μm size) placed at 0, 3, and 12 cm depth, a method widely used in sediment ecology. We observed that anecic and endogeic earthworms had contrasting reactions to the conditions with only endogeic species burrowing more intensively in the upper part. From a quantitative point of view, only a few percent of luminophores were displaced. However, luminophore displacements also provided qualitative information to complement the tomography: (i) endogeic species and especially Aporrectodea caliginosa bioturbated the most soil close to the surface (3 cm depth) and (ii) the two anecic species influenced the luminophore distribution differentially with Lumbricus terrestris displacing significantly more luminophores, whatever their initial depth, than Aporrectodea nocturna due to intense surface cast activity. Beyond methodological developments, our study found that endogeic earthworms burrow more in zones with higher organic matter contents and this explains why they are mainly found close to the soil surface in non-tilled soils.

Ecosystem Engineering Effects of Mongolian Marmots (Marmota sibirica) on Terrestrial Arthropod Communities

The Mongolian marmot (Marmota sibirica) is a large, endangered rodent species that ranges across the steppe regions of Mongolia, and parts of China and Russia. Marmot lives colonially and creates extensive burrow systems that change the soil nutrient profiles and influence plant and animal community composition and productivity. We examined the role of marmots on the diversity and abundance of ground-dwelling and flying insects. We hypothesize that the arthropod communities differ between marmot colonies and surrounding grasslands in diversity and abundance. We trapped 4765 individuals of arthropods representing 178 species of insects and 12 families of spiders. Marmot colony sites differed significantly from off colony sites by communities of ground-dwelling and flying insects. Our findings indicate that abundance and species richness of arthropods are largely associated with marmot burrows, which might be a reason for increased habitat heterogeneity, such as bare ground, specific vegetation structure, and thermoregulatory site by ecosystem engineering. Our results demonstrate that the marmots are keystone species in arid ecosystems, and have complementary, additive effects on steppe arthropod communities.

A Sweet Story of Metabolic Innovation in the Naked Mole-Rat.

The naked mole-rat's (Heterocephalus glaber) social and subterranean lifestyle imposes several evolutionary pressures which have shaped its physiology. One example is low oxygen availability in a crowded burrowsystem which the naked mole-rat has adapted to via several mechanisms. Here we describe a metabolic rewiring which enables the naked mole-rat to switch substrates in glycolysis from glucose to fructose thereby circumventing feedback inhibition at phosphofructokinase (PFK1) to allow unrestrained glycolytic flux and ATP supply under hypoxia. Preferential shift to fructose metabolism occurs in other species and biological systems as a means to provide fuel, water or like in the naked mole-rat, protection in a low oxygen environment. We review fructose metabolism through an ecological lens and suggest that the metabolic adaptation to utilize fructose in the naked mole-rat may have evolved to simultaneously combat multiple challenges posed by its hostile environment.

Behavioural imprint of the Ordovician Radiation: Evidence from Middle–Upper Ordovician deep-sea trace fossils in western Inner Mongolia, North China

Trace fossils are unique evidence of the body plan and behavioural complexity of animals. Major radiation periods in the Phanerozoic were associated with not only changes in biodiversity, biomass, and ecosystems but also transformations in the relatively implicit, behavioural world. Here we report on a diverse ichnoassemblage from the Middle–Upper Ordovician deep-marine deposits of Inner Mongolia, North China, totalling 24 ichnogenera (including two undetermined forms). They include Alcyonidiopsis, Bifasciculus, Bifungites, Chondrites, Circulichnis, ?Cochlichnus, Dendrorhaphe, Diplocraterion, Halopoa, Gyrophyllites, Monofungites, Multina, Nereites, Paleodictyon, Phymatoderma, Ptychoplasma, Rhizocorallium, Sinusichnus, Taenidium, Thalassinoides, Trichichnus, Zoophycos, bag-like trace, and closed ring trace. Highly regular and complex burrow systems have been discovered, i.e., the branched circular pattern of Circulichnis sinensis, elaborate radial graphoglyptid tunnel system Dendrorhaphe racemosa ichnosp. nov., sinusoid mazework Sinusichnus sinuosus, and the boxwork bag-like trace consisting of highly symmetric horizontal galleries and numerous semi-equidistant vertical shafts. The occurrence of these complex trace fossils suggests distinct behavioural complication and novelty in deep-sea communities during the Middle–Late Ordovician. We speculate that along with the onshore–offshore displacement of ichnofauna and significant expansion of deposit-feeding structures possibly driven by accelerated competition in the shallow-marine niches and aided by ameliorated deep-sea benthic food level, there was underlying behavioural evolution towards more delicate, geometric, and efficient feeding patterns. The Late Ordovician may represent the early peak not only in ichnodiversity but also in ichnodisparity and behavioural complexity of deep-sea ichnofauna, which probably reflect the complex interplay of biodiversity, biomass, and ecological changes during the Ordovician Radiation.

Long bone histomorphogenesis of the naked mole-rat: Histodiversity and intraspecific variation.

Lacking fur, living in eusocial colonies and having the longest lifespan of any rodent, makes naked mole-rats (NMRs) rather peculiar mammals. Although they exhibit a high degree of polymorphism, skeletal plasticity and are considered a novel model to assess the effects of delayed puberty on the skeletal system, scarce information on their morphogenesis exists. Here, we examined a large ontogenetic sample (n=76) of subordinate individuals to assess the pattern of bone growth and bone microstructure of fore- and hindlimb bones by using histomorphological techniques. Over 290 undecalcified thin cross-sections from the midshaft of the humerus, ulna, femur, and tibia from pups, juveniles and adults were analyzed with polarized light microscopy. Similar to other fossorial mammals, NMRs exhibited a systematic cortical thickening of their long bones, which clearly indicates a conserved functional adaptation to withstand the mechanical strains imposed during digging, regardless of their chisel-tooth predominance. We describe a high histodiversity of bone matrices and the formation of secondary osteons in NMRs. The bones of pups are extremely thin-walled and grow by periosteal bone formation coupled with considerable expansion of the medullary cavity, a process probably tightly regulated and adapted to optimize the amount of minerals destined for skeletal development, to thus allow the female breeder to produce a higher number of pups, as well as several litters. Subsequent cortical thickening in juveniles involves high amounts of endosteal bone apposition, which contrasts with the bone modeling of other mammals where a periosteal predominance exists. Adults have bone matrices predominantly consisting of parallel-fibered bone and lamellar bone, which indicate intermediate to slow rates of osteogenesis, as well as the development of poorly vascularized lamellar-zonal tissues separated by lines of arrested growth (LAGs) and annuli. These features reflect the low metabolism, low body temperature and slow growth rates reported for this species, as well as indicate a cyclical pattern of osteogenesis. The presence of LAGs in captive individuals was striking and indicates that postnatal osteogenesis and its consequent cortical stratification most likely represents a plesiomorphic thermometabolic strategy among endotherms which has been suggested to be regulated by endogenous rhythms. However, the generalized presence of LAGs in this and other subterranean taxa in the wild, as well as recent investigations on variability of environmental conditions in burrow systems, supports the hypothesis that underground environments experience seasonal fluctuations that may influence the postnatal osteogenesis of animals by limiting the extension of burrow systems during the unfavorable dry seasons and therefore the finding of food resources. Additionally, the intraspecific variation found in the formation of bone tissue matrices and vascularization suggested a high degree of developmental plasticity in NMRs, which may help explaining the polymorphism reported for this species. The results obtained here represent a valuable contribution to understanding the relationship of several aspects involved in the morphogenesis of the skeletal system of a mammal with extraordinary adaptations.

Using the ecosystem engineer concept to test the functional effects of a decrease in earthworm abundance due to an historic metal pollution gradient

In a companion study, carried out in a fallow meadow close to a lead recycling factory, we showed that earthworms were absent in the first 20 m and then gradually increased in abundance from 30 to 110 m from the factory. Here we assessed in the same meadow whether these differences in earthworm abundance were associated with the loss of physical soil properties. Soil cores were sampled and infiltration measured in situ at five distances from the factory (10, 30, 50, 80 and 110 m). X-ray tomography was used to characterize the earthworm burrow systems within cores. The burrow systems were minimal at the first two distances, with the only macropores observed probably produced by insects such as ants. Typical earthworm burrows were seen at 50 m but most of their characteristics (volume, diameter, continuity) were similar to those observed at 10 or 30 m. Dense and well-developed burrow systems were observed at 80 and 110 m from the factory with significantly larger volume and continuity. Burrow diameter at 80 m was significantly higher than at closer distances but it significantly decreased at 110 m associated with the higher abundance of endogeics earthworm species. Water infiltration followed the same trend with significantly lower rates at the first two distances compared to those further from the factory, where rates increased from 70 to 250%. This study emphasizes the need to develop a more functional approach to study the spatial effects of contamination on soil ecological processes and fertility, beyond modifications in earthworm communities.

CrowdedTrichophycusichnofabrics in the early Ordovician successions of central Iran: insight into the Ordovician radiation

The Tremadocian-to-Floian siliciclastic deposits of the Shirgesht Formation in the Kalmard Block of central Iran show abundant occurrences of the mid-tier Trichophycus venosus, a common ichnotaxon in the archetypical Cruziana ichnofacies. This trace fossil records a considerable increase in exploitation of offshore infaunal ecospace in comparison with older formations. Here, Trichophycus is relatively long and wide, with numerous and deep successively stacked causative burrows, which form dense burrow systems building the Crowded Trichophycus ichnofabric (CTI). Such development of CTI and the increase in depth of bioturbation had a negative effect on preservation of shallow-tier traces, for example arthropod burrows and trackways. This resulted in decreasing abundance of trilobite-produced trace fossils towards the top of the succession. The palaeobiological and palaeoecological interpretation of CTI points to stable habitats in muddy substrates above the storm wave base with high content of food and oxygen in pore waters, low-energy hydrodynamic regimes and a long colonization window. Moreover, the architecture and the morphological features of Trichophycus suggest a combined dwelling-feeding activity of the resident fair-weather producer showing the K-selected/climax strategy. The ethology of the producer, palaeoecological interpretations and taphonomic signatures revealed that it preferred dewatered, compacted muddy substrates (firmgrounds) in offshore settings, which might be related to minor hiatuses or short-lived discontinuities. Although the appearance of Trichophycus is concomitant to the earliest Cambrian agronomic revolution, it was uncommon until the early Ordovician, when locally it records infaunalization related to the Great Ordovician Biodiversification Event.

Earthworm ecological categories are not functional groups

Seven earthworm ecological categories, including anecics, endogeics and epigeics, were defined by Marcel Bouche in 1972 based only on morpho-anatomical characteristics measured on European lumbricids. These categories had an outstanding success, and their use was generalized even outside of Europe. However, most of the time, only the three main categories are used, and over two decades, these categories have been considered functional groups, i.e. to presume how earthworms influence the soil functioning. Moreover, this relationship between ecological categories and functional groups is seldom tested and often uncritically accepted by soil biology researchers. It is then not surprising to observe unexpected trends when earthworm species are gathered in ecological categories to, for instance, analyze burrow systems or cast properties. We believe it is time to acknowledge that ecological categories are not functional, because they were not made for this purpose. We also propose three future directions in order to either improve our knowledge on the functional effects of earthworms or to build new authentically functional groups: (i) going back to the seven initial ecological categories to provide greater accuracy than the usage of the simplified three-level classification; (ii) testing, for a set of selected species, the functionality of the groups, being ecological categories or new tailored ones; and (iii) using trait-based approach in order to study the correlation between some earthworm traits and main soil functions.

Does wild boar rooting affect spatial distribution of active burrows of meadow-dwelling voles?

Soil overturn by wild boar Sus scrofa is known to affect biodiversity, from plant communities to invertebrates, reptiles and small mammals. Rooting activity has been shown to be particularly intensive in open areas and particularly on fallows and meadows located on hill or mountain tops. In these habitat types, the impact of wild boar on small mammal assemblies has never been assessed. In this work, we evaluated whether rooting activity affected the spatial distribution of the Savi’s pine vole Microtus savii in a hilly area of Central Italy, throughout four seasons. The spatial distribution of this vole has been determined through the open-hole index, i.e. by assessing the vole propensity to reopen tunnel entrances which we previously closed with soil. Rooting intensity was the highest in cold months, i.e. when drive hunting may increase wild boar occurrence within protected areas and outside wooded areas. According to our GLMM, reopening of vole burrow entrances increased with increasing distances from rooted areas and with increasing geophytic diversity. Meadow-dwelling voles living on shallow underground burrow systems seem to avoid soil overturn by wild boar and that they prefer creating their tunnels where plant diversity building up the staple of their diet is the highest. Our results furtherly emphasized the importance of wild boar monitoring also in open areas and hill grasslands, particularly when rooting intensity is the highest, i.e. in cold months.

Fossoriality in a risky landscape: badger sett use varies with perceived wolf risk

AbstractMany medium‐sized carnivores are fossorial and use burrow systems to reduce predation risk or avoid predators. But fossorial species cannot stay safely underground forever, and they must also risk emerging overground, to forage and find mates. To make this trade‐off effectively and maximize their own fitness, it is imperative they assess how predation risk varies in space and time, and adapt their denning behaviour accordingly. We used European badger (Meles meles) burrows (setts) in Białowieża Forest, Poland as a model for investigating how the denning behaviour of a fossorial mesocarnivore varies across gradients of landscape scale perceived risk imposed by wolves (Canis lupus) and humans, defined as wolf space use and distance to settlements, respectively. We monitored seventeen setts with varying levels of perceived human and wolf risk with camera traps for two months to study three denning behaviours: frequency of badger sett use, frequency of badger sett sharing with other mesocarnivore species and badger emergence time. Frequency of sett use varied relative to perceived wolf but not human risk. Setts in the highest risk areas were used ca. 60% less often than those in the lowest perceived risk areas, and setts with juveniles were only present in areas of lower perceived risk. Food availability, quantified as earthworm abundance in an area of 2.1 km2 around setts, did not affect the frequency setts were used. Emergence time and frequency of sett sharing with other mesocarnivores, which have been proposed to be anti‐predator strategies, did not vary with either perceived risk factor. These results show fossorial species can adapt their use of burrows to the prevailing risk landscape and suggest burrows deserve more attention in studies on the ecological impacts of apex predators.

Using X-ray microtomography to characterize the burrowing behaviour of earthworms in heterogeneously polluted soils

Large amounts of chemicals are released into soil environments due to human activities, thereby harming organisms and their habitats. Earthworms are important bioindicators for chemical risk assessments of soil ecosystems, but the question remains of how they respond to different patterns of pollution. Laboratory experiments in soil mesocosms were carried out to observe changes in the burrowing behaviour of two earthworm species (Aporrectodea caliginosa and Lumbricus terrestris) with regard to different spatial distributions of benzo(a)pyrene, cadmium and copper, using X-ray computed microtomography (μCT). This is, to our knowledge, the first contribution of μCT to study earthworm behaviour in heterogeneously multi-polluted soils. Columns (14 × 30 cm) were filled with a silt loam soil and packed to represent two scenarios of heterogeneous pollution: a) ‘binary’, containing polluted soil in the low half part and unpolluted soil on top; and b) ‘patches’, containing small portions of polluted soil randomly placed into an unpolluted matrix. Earthworms were introduced individually in the columns and left in climatic chambers for 7 weeks. μCT images revealed that earthworms avoided the polluted zones differently (e.g. A. caliginosa>L. terrestris, ‘binary’ configuration). Individuals of L. terrestris that entered polluted areas showed a lower burrowing activity (volume and length of the burrow system) than those that did not enter. The presence of ‘patches’ of polluted soil did not cause a reduction of the burrowing activity such as that found in the ‘binary’ columns, although earthworms showed avoidance. Our results indicate that pollutants had a greater effect on earthworms’ burrowing behaviour in the presence of larger portions of contaminated soil compared with small random ones. The more evident avoidance behaviour of A. caliginosa pinpoints its usefulness in toxicity bioassays based on avoidance patterns, but questions its use in assays based on bioaccumulation of pollutants in tissues, for which L. terrestris may perform better.

Compound biogenic structures resulting from ontogenetic variation: An example from a modern dipteran

Several families of Diptera are known to be active burrowers. Fly larvae of the genus Symplecta (family Limoniidae) were observed in a sandy substrate of an orange grove in Lepe, SW Spain. Traces produced by Symplecta display: (1), a proximal segment characterized by a winding furrow trail; (2), an intermediate part consisting of burrow segments arranged in zigzag; and (3), a distal part formed by a complex U-shaped burrow. The most complex morphology is present in the intermediate zigzag burrow system, which varies from irregularly sinuous and curved in its most proximal part to spiraled. In the fossil record, the trace would be ascribed to different ichnotaxa depending on the part preserved. In fact, this is a compound trace recording multiple behavioural patterns. The winding furrow shows affinities with Helminthopsis, the zigzag burrows with Treptichnus, and the U-shaped burrow with Arenicolites. Furthermore, the spiral portion shows some similarities with Spirophycus and Spirodesmos. Interestingly, formation of these compound traces is connected with different ontogenetic stages of the producer. The winding and zigzag segments are produced, respectively, by Symplecta larvae and pupae for feeding purposes, whereas the U-shaped burrow is excavated during the end of pupal stage for protection until adulthood. In the fossil record, this incipient compound trace potentially may occur in lake-margin, fluvio-estuarine and overbank deposits, including levee, crevasse splay and pond deposits, forming part of the Scoyenia or the Mermia ichnofacies. Structures similar to those produced by modern diptera are known from freshwater ichnofaunas since the Devonian

Gas composition and its daily changes within burrows and nests of an Afroalpine fossorial rodent, the giant root-rat Tachyoryctes macrocephalus

Fossorial mammals are supposed to face hypoxic and hypercapnic conditions, but such conditions have been rarely encountered in their natural burrow systems. Gas composition in burrows after heavy rains, deeper burrows and especially nest chambers, where animals usually spend most of the day, could be even more challenging than in shallow burrows. Such situations, however, have been rarely surveyed in the wild. In our study, we determined concentrations of O2, CO2 and CH4 in active burrows and nests of the giant root-rat Tachyoryctes macrocephalus, a large fossorial rodent endemic to the Afroalpine zone of the Bale Mountains in Ethiopia. We were able to determine the precise location of nests by tracking individuals equipped with radio-collars. To the best of our knowledge, this is the first study that analyses air samples taken directly from the nests of actually occupied burrow systems in any free-living fossorial mammal. We found no evidence for environmental hypoxia in the examined burrows and nests (range 19.7–21.6% O2). Concentrations of CO2 in the burrows increased after the burrows were plugged in the evening, but did not reach physiologically problematic levels. The highest CO2 concentrations in burrows were detected in the evening during a wet period (up to 0.44%). In root-rat nest chambers, the highest (but still harmless) CO2 concentrations (up to 1.31%) were detected in the morning (measured in the late dry season only) together with an elevated concentration (up to 13.5ppm) of CH4. Regular surface activity of giant root-rats, combined with the relatively large dimensions of their nest chambers and tunnels, and the absence of heavy soils, may contribute to harmless atmospheres within their burrow systems.

RECOGNITION OF FOSSIL NEBKHA DEPOSITS: CLUES FROM NEOICHNOLOGY AND SEDIMENTOLOGY

ABSTRACTThis study includes the first neoichnologic characterization of the burrow systems of Tympanoctomys barrerae (Rodentia: Octodontidae) and also considers sedimentologic features of the modern nebkhas where they occur. Tympanoctomys is a South American solitary and fossorial rodent that has ecomorphofunctional adaptations for living in saline environments and constructs its burrow in nebkhas with halophyte shrubs. The purpose of this work is to identify the ichnologic signatures of T. barrerae burrow systems and to provide combined ichnologic-sedimentologic criteria for identification of Cenozoic nebkha deposits. Tympanoctomys barrerae burrow systems are subhorizontal, typically with ten or more entrances, two or three levels, closed circuits, average complexity of 48, average tortuosity of 3.25, and an average ratio of total chamber volume to total tunnel volume of 0.04. The size of the tunnels averages 85 mm in horizontal diameter and 64 mm in vertical diameter, and cross-section shape ranges from elliptical flattened to plano-convex with incipient bilobed floor. Surface ornamentation is typified by a coexistence of primary (sets of four claw traces forming an arcuate pattern produced during digging) and secondary (numerous arthropod burrows excavated from the burrow lumen) surface ornamentation. Nebkha deposits in upper Cenozoic sequences can be recognized by the combination of ichnologic and sedimentologic features: fossil burrows having the ichnologic features characteristic of T. barrerae burrow systems and presence of rhizoliths of shrubby plants occurring in well-sorted sandy deposits with low-angle crossbedding. These criteria can be potentially applied to fossil sequences dating back to the early Oligocene.

The naked mole-rat has a functional purinergic pain pathway despite having a non-functional peptidergic pain pathway

Naked mole-rats (Heterocephalus glaber) have adaptations within their pain pathway that are beneficial to survival in large colonies within poorly ventilated burrow systems, with lower O2 and higher CO2 ambient levels than ground-level environments. These adaptations ultimately lead to a partial disruption of the C-fiber pain pathway, which enables naked mole-rats to not feel pain from the acidosis associated with CO2 accumulation. One hallmark of this disruption is that naked mole-rats do not express neuropeptides, such as Substance P and calcitonin gene-related peptide in their cutaneous C-fibers, effectively making the peptidergic pain pathway hypofunctional. One C-fiber pathway that remains unstudied in the naked mole-rat is the non-peptidergic, purinergic pathway, despite this being a key pathway for inflammatory pain. The current study aimed to establish the functionality of the purinergic pathway in naked mole-rats and the effectiveness of cannabinoids in attenuating pain through this pathway. Cannabinoids can manage chronic inflammatory pain in both humans and mouse models, and studies suggest a major downstream role for the purinergic receptor, P2X3, in this treatment. Here we used Ca2+-imaging of cultured dorsal root ganglion neurons and in vivo behavioral testing to demonstrate that the P2X3 pathway is functional in naked mole-rats. Additionally, formalin-induced inflammatory pain was reduced by the cannabinoid receptor agonist, WIN55 (inflammatory, but not acute phase) and the P2X3 receptor antagonist A-317491 (acute and inflammatory phases). This study establishes that the purinergic C-fiber pathway is present and functional in naked mole-rats and that cannabinoid-mediated analgesia occurs in this species.

The earliest known Spongeliomorpha from the Lower Devonian of the northwestern Yangtze Platform, South China

Crustacean trace fossils provide invaluable information to paleobilogical, environmental and ecological interpretations in the Earth history. Here we report an unusually large (segments up to 58 mm across), three-dimensional burrow system from the Lower Devonian Pingyipu Formation, which was deposited in a nearshore setting on the northwestern Yangtze Platform, South China. The burrow system is dominated by horizontally-developed networks probably with vertical shafts connecting to the sediment-water interface. The burrow surfaces show no signs of lining but are characterized by scratches including ridges and bundles of ear-shaped striae, implying an assignation to Spongeliomorpha aff. S. chevronensis (Muñiz and Mayoral 2001). The overall morphological and taphonomic features suggest permanent, open burrows, produced in a substrate with considerable firmness. Further investigation indicates that the burrow system may have been constructed by a colony of large, unknown crustacean with thoracic appendages decorated with acute seta or denticulations. They generally served a combined purpose of dwelling and perhaps feeding on microbial growth accumulating on the tunnel margins. These burrows represent the earliest known three-dimensional burrow systems constructed by a crustacean that may be comparable to their modern analogues in both morphological and functional aspects. The unusually large size of the burrows may have been favored by a higher atmospheric oxygen level during the Early Devonian.