The burrowing process of Dentalium (Scaphopoda)

Investigations of the burrowing activity of Dentalium , using cine film and electronic recording techniques, have shown it to penetrate the sand in a series of steps, each termed a "digging cycle". Cycles involve first, pedal dilation, second, retraction followed by extension and probing of the foot. The epipodial lobes are elevated during pedal dilation and form a secure pedal anchor so that at retraction the shell is drawn down over the foot.
A comparison of the burrowing process in the Scaphopoda with that of the Bivalvia indicates that essentially the same mechanisms and sequence of activities are involved, for in both digging consists of the integration of pedal protraction and retraction with the application of shell and pedal anchors. The principal differences, such as the absence in Dentalium of water jets to loosen the sand and high pressures in the pedal haemocoele, are related to the form of their shell. The strength of the pedal anchor was determined and, relative to the weight of Dentalium , is comparable to that of bivalves. In contrast the probing force was relatively weak since the shell anchor of Dentalium , which holds the shell still during probing, is largely limited to its own weight, whereas that attained by the Bivalvia is principally due to the valves being pressed against the substrate by the opening moment of the ligament.     

Burrowing criteria and burrowing mode adjustment in bivalves to varying geoenvironmental conditions in intertidal flats and beaches

The response of bivalves to their abiotic environment has been widely studied in relation to hydroenvironmental conditions, sediment types and sediment grain sizes. However, the possible role of varying geoenvironmental conditions in their habitats remains poorly understood. Here, we show that the hardness of the surficial intertidal sediments varies by a factor of 20-50 due to suction development and suction-induced void state changes in the essentially saturated states of intertidal flats and beaches. We investigated the response of two species of bivalves, Ruditapes philippinarum and Donax semigranosus, in the laboratory by simulating such prevailing geoenvironmental conditions in the field. The experimental results demonstrate that the bivalve responses depended strongly on the varying geoenvironmental conditions. Notably, both bivalves consistently shifted their burrowing modes, reducing the burrowing angle and burial depth, in response to increasing hardness, to compensate for the excessive energy required for burrowing, as explained by a proposed conceptual model. This burrowing mode adjustment was accompanied by two burrowing criteria below or above which the bivalves accomplished vertical burrowing or failed to burrow, respectively. The suitable and fatal conditions differed markedly with species and shell lengths. The acute sensitivities of the observed bivalve responses to geoenvironmental changes revealed two distinctive mechanisms accounting for the adult-juvenile spatial distributions of Ruditapes philippinarum and the behavioral adaptation to a rapidly changing geoenvironment of Donax semigranosus. The present results may provide a rational basis by which to understand the ensuing, and to predict future, bivalve responses to geoenvironmental changes in intertidal zones.     

The energy cost and efficiency of burrowing in the sandy-beach whelk Bullia digitalis (Dillwyn) (Nassariidae)

The oxygen consumption of Bullia digitalis (Dillwyn) at 15°C has been measured in the laboratory under conditions which gave rise to repeated digging cycles, and compared with oxygen uptake while the same animals were stationary. The energy cost of burrowing is calculated to be about 5 × 10^?4 Joules (2.1 × 10^?3cal) per digging cycle in a whelk whose dry tissue weight is 750 mg. The overall efficiency of the burrowing process is ≈ 6%, in contrast to the 20% efficiency which has generally been assumed for locomotory activities.     

Evolutionary morphology of oblique ribs of bivalves

Fossil bivalves bearing oblique ribs first appeared in the Mid Ordovician but their diversity remained low during the Palaeozoic. The diversity soon increased after the Early Triassic, peaking in the Early Cretaceous. The Palaeozoic–Mesozoic record is dominated by burrowing bivalves (mainly pholadomyoids and trigonioids), which developed oblique ribs with symmetric profiles, probably adapted for shell reinforcement, although there are indications that the ribs of trigonioids also enhanced burrowing efficiency. After the Paleocene, the main groups of burrowing bivalves were veneroids (primarily tellinoideans and lucinoideans) and nuculoids, which generated oblique ribs of the shingled type, adapted to increase burrowing efficiency. The inferred change in function at the Mesozoic/Cenozoic boundary can be correlated with an increase in mean mobility of the bivalve faunas bearing oblique ribs through time. This implies a major ecological cause for the observed temporal patterns, which forced bivalve faunas to burrow more rapidly and efficiently. In particular, either the Phanerozoic increase in the diversity of durophagous predators or the accelerating rate of sediment reworking (both being a consequence of the Mesozoic Marine Revolution), or both, could have provided the necessary evolutionary force.     

Identification and evaluation of the Atlantic razor clam (Ensis directus) for biologically inspired subsea burrowing systems

In this article, we identify and analyze a subsea organism to serve as a model for biologically inspired burrowing technology to be used in applications such as anchoring, installation of cables, and recovery of oil. After inspecting myriad forms of life that live on or within ocean substrates, the Atlantic razor clam, Ensis directis, stood out as an attractive basis for new burrowing technology because of its low-energy requirements associated with digging (0.21?J/cm), its speed and depth of burrrowing (～1?cm/s and 70?cm, respectively), and its size and simplicity relative to man-made machines. As anchoring is a prime application for the technology resulting from this work, the performance of an Ensis directus-based anchoring system was compared to existing technologies. In anchoring force per embedment energy, the E. directus-based anchor beats existing technology by at least an order of magnitude. In anchoring force per weight of device, the biologically inspired system weighs less than half that of current anchors. The article concludes with a review of E. directus's digging strategy, which involves motions of its valves to locally fluidize the substrate to reduce burrowing drag and energy, and the successful adaptation of E. directus's burrowing mechanisms into an engineering system: the RoboClam burrowing robot, which, like the animal, uses localized fluidization to achieve digging energy that scales linearly with depth, rather than depth squared, for moving through static soil.     

The functional role of burrowing bivalves in freshwater ecosystems

1. Freshwater systems are losing biodiversity at a rapid rate, yet we know little about the functional role of most of this biodiversity. The ecosystem roles of freshwater burrowing bivalves have been particularly understudied. Here we summarize what is known about the functional role of burrowing bivalves in the orders Unionoida and Veneroida in lakes and streams globally. 2. Bivalves filter phytoplankton, bacteria and particulate organic matter from the water column. Corbicula and sphaeriids also remove organic matter from the sediment by deposit feeding, as may some unionids. Filtration rate varies with bivalve species and size, temperature, particle size and concentration, and flow regime. 3. Bivalves affect nutrient dynamics in freshwater systems, through excretion as well as biodeposition of faeces and pseudofaeces. Excretion rates are both size and species dependent, are influenced by reproductive stage, and vary greatly with temperature and food availability. 4. Bioturbation of sediments through bivalve movements increases sediment water and oxygen content and releases nutrients from the sediment to the water column. The physical presence of bivalve shells creates habitat for epiphytic and epizoic organisms, and stabilizes sediment and provides refugia for benthic fauna. Biodeposition of faeces and pseudofaeces can alter the composition of benthic communities. 5. There is conflicting evidence concerning the role of resource limitation in structuring bivalve communities. Control by bivalves of primary production is most likely when their biomass is large relative to the water volume and where hydrologic residence time is long. Future studies should consider exactly what bivalves feed upon, whether feeding varies seasonally and with habitat, and whether significant overlap in diet occurs. In particular, we need a clearer picture of the importance of suspension versus deposit feeding and the potential advantages and tradeoffs between these two feeding modes. 6. In North America, native burrowing bivalves (Unionidae) are declining at a catastrophic rate. This significant loss of benthic biomass, coupled with the invasion of an exotic burrowing bivalve (Corbicula), may result in large alterations of ecosystem processes and functions.     

Climate change, species range limits and body size in marine bivalves

We use data on the Pleistocene and modern range limits of Californian marine bivalves to show that species that shifted their geographical ranges in response to Pleistocene climatic fluctuations were preferentially drawn from the large end of the regional body size–frequency distributions. This difference is not due to phylogenetic effects (i.e. dominance of extralimital species by a few large-bodied clades), differences among major ecological categories (burrowing versus surface-dwelling, or suspension feeding versus non-suspension feeding), or differences in modes of reproduction and larval development. In addition, we show that successful invasive species of bivalves in present-day marine habitats also tend to be large-bodied, despite the difference in mechanisms between present-day and Pleistocene range expansions. These results indicate that range limits of large-bodied bivalve species are more unstable than small-bodied ones, and that body size and its correlates need to be considered when attempting to predict the responses of marine communities to climate change, biotic interchanges and human-mediated invasions.     

Ratchet riposte: more on gastropod burrowing sculpture

Recent warnings concerning paleobiological inferences based upon gastropod shell morphology (Houbrick 1991) merit serious consideration, although the dangers have been overstated. Ratchet sculpture, an asymmetrical sculpture that assists marine invertebrates in burrowing, is not qualitatively different from sculptures that apparently do not aid in burrowing. Therefore, the interpretation of such sculpture might be problematical. Nevertheless, the large body of empirical evidence demonstrating the function of ratchet sculpture in burrowing by bivalves, gastropods, carpoid echinoderms, brachiopods, and arthropods and the lack of evidence supporting alternative functions in the Gastropoda warrant the continued, although cautious, association of ratchet sculpture with burrowing in marine gastropods. □ Functional morphology, Gastropoda, ratchet sculpture, burrowing.     

Movements and burrowing activity in the Antarctic bivalve molluscs<Emphasis Type="Italic"> Laternula elliptica</Emphasis> and<Emphasis Type="Italic"> Yoldia eightsi</Emphasis>

Burrowing was investigated in two Antarctic infaunal bivalve molluscs, Laternula elliptica and Yoldia eightsi, representing amongst the least and most active members of the class Bivalvia in the Southern Ocean. Burrowing rate was expressed via the Burrowing Rate Index (BRI=[³wet weight/time to bury]×10⁴), and produced values of 0.1–10.6 for L. elliptica and 8.8–49.8 for Y. eightsi. These compare with values ranging from 3 to 2,000 for N. American bivalves (mean=222, SE=42.6, n=81), and 200 to 2,200 for Hong Kong bivalves (mean=1,140, SE=346, n=6). Values for the Antarctic species are, therefore, low compared to warmer-water bivalves, and the values below 1 for large L. elliptica are the lowest on record by around ×5. There is no compensation of burrowing activity for low temperature in these species. The relative BRI values for L. elliptica and Y. eightsi reflect the differences in their mode of life, with the former being large, sedentary and suspension-feeding, and the latter being smaller, mobile, ploughing through the sediment and feeding on sediment-surface organic matter. Burrowing in L. elliptica is unexpected, because other members of the Laternulidae do not burrow. This ability is most probably a response to the regular disturbance of sediments in Antarctica by ice, and the strong selective advantage to being able to resume a protected position after disturbance. The burrowing cycle in L. elliptica is composed of three main phases: (1) foot extension and sediment penetration; (2) foot dilation to form an anchor; (3) the drawing down of the shell by contraction of the pedal retractor muscles. Burrowing in Y. eightsi also has three phases: (1) foot extension and penetration of the sediment (digging); (2) rocking movements in the upright position; (3) shell anchorage. In excess of burrowing activity, L. elliptica exhibits a unique suite of movements when exposed at the surface. These comprise levering, where the tips of the siphons are pressed against the sediment to lift the shell from the substratum, looping, where the siphons are extended and rotated and, in the process, translocate the whole animal across the sediment, and jetting, where water is ejected forcibly through the siphons while their tips are directed towards the sediment, lifting part or all of the animal clear of the substratum. In the field, following exhumation by icebergs, these activities serve to place the animal in a favourable position for reburial, which is a clear advantage in disturbed polar environments where predatory nemerteans and asteroids are abundant.     

Behavioral plasticity of the soft-shell clam, Mya arenaria (L.), in the presence of predators increases survival in the field

Soft-shell clams, Mya arenaria, are sessile, suspension-feeding bivalves that are preyed upon by the exotic green crab, Carcinus maenas. Clams evade crab consumers by burrowing deeper into the sediment after perceiving a threat from a nearby predator. The purpose of this study was to determine the types of signals that M. arenaria use to detect predators and the types of behaviors clams use to avoid being eaten. In a field study, clams increased their burial depth in the presence of green crab predators consuming conspecifics that were caged nearby, and also increased burial depth after artificial tactile stimulation in the laboratory assay. These results indicate that clams can use chemical and mechanical cues to detect potential predatory threats. We performed a field study to examine the difference in survivability of clams that had burrowed deeper into the sediment in response to predators vs. control clams that were burrowed less deeply. Significantly higher survival rates were observed in clams that had initially burrowed more deeply, suggesting that increasing burial depth is a valid predator avoidance strategy. Some bivalves also alter their pumping rates in the presence of predators, making them less apparent and providing more structural defense by covering soft tissue, and we measured pumping time of soft-shell clams in the presence and absence of predators, when burrowing was not an option for escape. Soft-shell clams did not alter their pumping time in the presence of green crab predators, possibly because they employ a burrowing method called “hydraulic” or “jet-propelled” burrowing, where it is necessary for the clam to pump in order to burrow. Chemical signals and tactile cues instigated behavioral changes in M. arenaria, and this change in behavior (increasing burial depth) increased clam survival in the field.     

Environmental factors affect swing gates as a barrier to large carnivores entering game farms

Burrowing animals such as warthog (Phacochoerus africanus), Cape porcupine (Hystrix africaeaustralis) and aardvark (Orycteropus afer) are able to compromise the integrity of fenced‐in farmlands by digging holes under game fences. These holes provide access for predators to enter the farm where they can kill livestock or captive game animals. Data collected from the use of swing gates (n = 263) installed along a 23.93 km game fence in the Otjozondjupa region of Namibia was analysed to determine the factors that influenced their efficacy at reducing hole creation along the fence by digging animals. Statistical analyses revealed that soil substrate, grass height, vegetation density, distance to the nearest permanent water source and season influenced digging activity along the fence line. The number of holes created and reopened decreased over time from the start of the study period, probably demonstrating that burrowing animals had learnt to use the swing gates rather than dig holes under the fence. These factors can inform the correct future usage of swing gates as a large predator exclusion method to ensure that they do not enter game farms, which will reduce the need to lethally control carnivores and burrowing animals.     

Chemically induced predator avoidance behaviour in the burrowing bivalve Macoma balthica

The responses of the burrowing bivalves Macoma balthica and Cerastoderma edule to chemical cues emitted by feeding shore crabs Carcinus maenas were investigated. M. balthica held in the laboratory and exposed to chemical signals in effluent water discharging from tanks containing C. maenas fed 20 M. balthica day^− 1 reacted by increasing their burial depths from approximately 30 mm to depths of > 60 mm, over a period of several days. When the signal was removed the bivalves gradually returned to their original depth over 5 days. C. edule similarly exposed to effluent from crabs feeding on conspecifics showed no response. In an attempt to identify the signal inducing this burrowing response, M. balthica were exposed to a variety of chemical signals. Crabs fed M. balthica elicited the strongest response, followed by crabs fed C. edule. There were also small responses to effluent from crabs fed on fish, crabs previously fed on M. balthica and to crab faeces, but no responses to starved crabs, crushed M. balthica, or controls. We conclude that increased burrowing depth of M. balthica is induced by some as yet unidentified chemical cue produced by feeding crabs and is strongest when the crabs were fed on M. balthica. Unexpectedly, neither the presence of crabs themselves, nor of damaged conspecifics, was effective in eliciting a burrowing response. The mortality rates of M. balthica and C. edule selected by crabs when burrowed at normal depths and after exposure to effluent from feeding crabs were different. Crabs selected 1.5 times more C. edule than M. balthica when both species were burrowed at their normal depths, but 15 times more after the tanks had been exposed to effluent from feeding crabs for 5 days. The burrowing response of M. balthica thus appears to reduce mortality significantly by displacing predation pressure on to the more accessible C. edule.     

Seed burial by soil burrowing beetles

Bernhardt, K.-G. 1995. Seed burial by soil burrowing beetles. — Nord J. Bot. 15: 257–260. Copenhagen. ISSN 0107–055X.
This investigation shows the role of soil digging beetles (Carabidae, Heteroceridae) in burial of myxospermous seeds. Field experiments with containers filled with sterilized sand, seeds of different plant species and soil digging beetles, are used. After six months in plots with digging insects seeds were found in deeper soil depths (up to 10 cm soil depth) than seeds in control plots. The study was done with beetles belonging to newly created sandy land. The study shows that beetles can be important for seed dispersal and seed burial and that seeds deep in the soil do not need to be old.     

The evolution of fossoriality and the adaptive role of horns in the Mylagaulidae (Mammalia: Rodentia)

Ceratogaulus, a member of the extinct fossorial rodent clade Mylagaulidae, is the only known rodent with horns and the smallest known horned mammal. The function of the large, dorsally projecting nasal horns on this burrowing animal has been the subject of wide speculation among palaeontologists; suggested uses range from sexual combat to burrowing. Mammals have evolved adaptations for digging repeatedly; horns and other cranial appendages have also evolved numerous times. These two adaptations co-occur in mammals extremely rarely: only two fossil genera (Ceratogaulus and the xenarthran Peltephilus) and no extant mammals are both horned and fossorial. Tracing the evolution of fossoriality in aplodontoid rodents (the larger clade to which Ceratogaulus belongs) reveals that Ceratogaulus descended from ancestors who dug by head-lifting. Whereas this suggests an obvious explanation for the horns of this rodent, evidence from functional morphology, anatomy, phylogeny and geologic context indicates that the horns in Ceratogaulus were used for defence, rather than digging, and evolved to offset increased predation costs associated with spending more time foraging above ground as body size increased.     

Burrowing in frogs

More than 95% of burrowing Anura dig hindfeet first into the soil, a pattern unique to frogs among terrestrial vertebrates. The postero-laterally placed hindlimbs and associated musculature of frogs are preadaptations for hindfeet digging. One fossorial, backwards burrower, Glyphoglossus molossus (Microhylidae), has morphological modifications of the hindlimb for positioning the spade-like metatarsal tubercle and for increasing the force of the lower leg during digging. In contrast, in the headfirst burrower Hemisus marmoratus (Ranidae) there is extensive reorganization of the pectoral-cranial morphology compared to that: of a non-burrowing confamilial species. A model links the shifts in the pectoral morphology in Hemisus marmoratus to specific action patterns of headfirst: burrowing. Finally, data on stomach contents, natural history and energy utilization of frog species are presented to demonstrate the interrelationships of distinct loco. motor patterns with specific feeding strategies.     

Sociality in New World hystricognath rodents is linked to predators and burrow digging

The importance of predation and burrow digging in explainingthe evolution of sociality is generally unclear. We focusedon New World hystricognath rodents to evaluate three key predictionsof the predation hypothesis. First, large-bodied surface-dwellingspecies will be more vulnerable because they are more detectable;thus sociality should be associated with body size. Second,surface-dwelling, diurnal species would be more vulnerable topredators than nocturnal species; thus sociality should be associatedwith the evolution of diurnality. Third, species living in openhabitats will be more vulnerable; thus sociality should evolvein species living in open habitats. Regarding the importanceof burrows, we tested if species that dig burrows can benefitfrom communal labor; thus, sociality should be associated withburrow digging. All traits had significant phylogenetic signal,thus comparative analyses should explicitly address this. Ina comparative analysis on independent contrasts we found thatsociality was correlated with body size (larger species weremore social), diurnality (diurnal species were more social),and burrowing (burrowing species were more social), but we foundno effect of overhead plant cover of habitat on sociality inhystricognath rodents. Somewhat different results were foundwhen we analyzed the raw data. Taken together, our results providesupport for a link between predation risk, burrow digging, andsociality in this group.     

高原鼢鼠挖掘活动的观察

本文通过自制高原鼢鼠挖掘行为观察箱,以直接观察法和摄录像系统观察了在模拟不同土壤坚实度条件下,高原鼢鼠的挖掘行为、掘土速度、掘土持续时间以及在每一掘土回合内的掘土量。结果表明,高原鼢鼠的掘洞活动主要由掘土、扒土、踢土、推土、以及拱土组成;掘土速度和掘土持续时间与土壤坚实度有关;在相同土壤条件下,虽然雄、雌鼢鼠的掘土速度相似,但雄性鼢鼠在每回合内的掘土量明显地高与雌鼠。     

Infaunal hydraulics generate porewater pressure signals

Many activities by infauna, including burrowing and feeding, involve hydraulic mechanisms. We expected these activities to generate low-frequency pressure waves that would propagate through sediments and be detectable at some distance from the source. Pressure sensors in intertidal sediments recorded large-amplitude porewater pressure signals. Laboratory recordings of single individuals allowed us to identify characteristic signals of arenicolid and nereidid polychaetes and tellinid bivalves. In the bivalve Macoma nasuta, these high-amplitude signals were associated with burrowing, expulsion of pseudofeces, and siphon relocation. In the polychaetes Neanthes brandti and Abarenicola pacifica, the high-amplitude pressure signals were associated with burrowing, burrow construction, burrow ventilation, and defecation. These signals were detectable in the field at distances of at least 20 cm. Since the waveforms are species-specific as well as activity-specific, they may provide a mechanism for prey detection, for predator avoidance, for competitor detection, and perhaps even for mate detection.     

Transport of juvenile clams: effects of species and sediment grain size

Erosion and transport of juvenile benthic invertebrates, including bivalves, have the potential to alter patterns of distribution and abundance during the early post-settlement period. However, the factors influencing rates of postlarval dispersal are not well understood. Both hydrodynamics and behaviour (e.g. burrowing) are likely to play a role in determining patterns of transport of juvenile bivalves. To determine the relationship between sediment transport and bivalve dispersal, experiments were conducted in a racetrack flume to examine the effect of grain size, flow, and clam size on rates of erosion of two species of juvenile clams (Mya arenaria and Mercenaria mercenaria). Results of the experiments were compared to predictions of erosion thresholds based on the physical characteristics of the sediment and clams. Erosion of Mercenaria was greater than Mya, the opposite of predictions based on Mercenaria's greater density, indicating the importance of burrowing behaviour. In most cases, erosion also was greater in the finer sand, in contrast to the predicted similarity of erosion thresholds of the two sediments. However, clam erosion did increase with increasing shear velocity and decrease with clam size, as expected. The results of this study indicate that both hydrodynamics and behaviour play roles in the transport of these two species of juvenile bivalves and that their vulnerability to passive erosion cannot be predicted solely from knowledge of sediment transport.     

Locomotory adaptations in entoptychine gophers (Rodentia: Geomyidae) and the mosaic evolution of fossoriality

Pocket gophers (family Geomyidae) are the dominant burrowing rodents in North America today. Their fossil record is also incredibly rich; in particular, entoptychine gophers, a diverse extinct subfamily of the Geomyidae, are known from countless teeth and jaws from Oligocene and Miocene-aged deposits of the western United States and Mexico. Their postcranial remains, however, are much rarer and little studied. Yet, they offer the opportunity to investigate the locomotion of fossil gophers, shed light on the evolution of fossoriality, and enable ecomorphological comparisons with contemporaneous rodents. We present herein a quantitative study of the cranial and postcranial remains of eight different species of entoptychine gophers as well as many contemporary rodent species. We find a range of burrowing capabilities within Entoptychinae, including semifossorial scratch-digging animals and fossorial taxa with cranial adaptations to burrowing. Our results suggest the repeated evolution of chisel-tooth digging across genera. Comparisons between entoptychine gophers and contemporaneous rodent taxa show little ecomorphological overlap and suggest that the succession of burrowing rodent taxa on the landscape may have had more to do with habitat partitioning than competition.