Shell Acquisition Research Articles

A framework for optimizing the acquisition protocol multishell diffusion-weighted imaging for multimodel assessment.

Complementary aspects of tissue microstructure can be studied with diffusion-weighted imaging (DWI). However, there is no consensus on how to design a diffusion acquisition protocol for multiple models within a clinically feasible time. The purpose of this study is to provide a flexible framework that is able to optimize the shell acquisition protocol given a set of DWI models. Eleven healthy subjects underwent an extensive DWI acquisition protocol, including 15 candidate shells, ranging from 10 to 3500 s/mm2. The proposed framework aims to determine the optimized acquisition scheme (OAS) with a data-driven procedure minimizing the squared error of model-estimated parameters. We tested the proposed method over five heterogeneous DWI models exploiting both low and high b-values (i.e., diffusion tensor imaging [DTI], free water, intra-voxel incoherent motion [IVIM], diffusion kurtosis imaging [DKI], and neurite orientation dispersion and density imaging [NODDI]). A voxel-level and region of interest (ROI)-level analysis was conducted over the white matter and in 48 fiber bundles, respectively. Results showed that acquiring data for the five abovementioned models via OAS requires 14 min, compared with 35 min for the joint recommended acquisition protocol. The parameters derived from the reference acquisition scheme and the OAS are comparable in terms of estimated values, noise, and tissue contrast. Furthermore, the power analysis showed that the OAS retains the potential sensitivity to group-level differences in the parameters of interest, with the exception of the free water model. Overall, there is a linear correspondence (R2= 0.91) between OAS and reference-derived parameters. In conclusion, the proposed framework optimizes the shell acquisition scheme for a given set of DWI models (i.e., DTI, free water, IVIM, DKI, and NODDI), combining low and high b-values while saving acquisition time.

The shell-acquisition behaviour of the bivalve-using hermit crab Porcellanopagurus nihonkaiensis Takeda, 1985 (Decapoda, Anomura, Paguroidea)

Almost all species of hermit crabs inhabit dead gastropod shells; however, species of some genera have evolved to inhabit bivalve or patelliform shells. It has been assumed that these species carry their shells using uropodal rasps and the hooked dactyls of their fourth pereopods, although no detailed description of the shell acquisition behaviour of those species has previously been documented. We have therefore observed the shell acquisition behaviour of Porcellanopagurus nihonkaiensis Takeda, 1985, which was collected by dredge at Shimoda, Shizuoka Prefecture, Japan. Our observation suggests that the shell is fixed in place by only the uropodal rasps in combination with hydrostatic pressure in the telson.

Poster #M49 FUNCTIONAL AND GRAY MATTER ASYMMETRIES IN PATIENTS WITH SCHIZOPHRENIA AND BIPOLAR DISORDERS

Many recent high angular resolution diffusion imaging (HARDI) reconstruction techniques have been introduced to infer an orientation distribution function (ODF) of the underlying tissue structure. These methods are more often based on a single-shell (one b-value) acquisition and can only recover angular structure information contained in the ensemble average propagator (EAP) describing the three-dimensional (3D) average diffusion process of water molecules. The EAP can thus provide richer information about complex tissue microstructure properties than the ODF by also considering the radial part of the diffusion signal. In this paper, we present a novel technique for analytical EAP reconstruction from multiple q-shell acquisitions. The solution is based on a Laplace equation by part estimation between the diffusion signal for each shell acquisition. This simplifies greatly the Fourier integral relating diffusion signal and EAP, which leads to an analytical, linear and compact EAP reconstruction. An important part of the paper is dedicated to validate the diffusion signal estimation and EAP reconstruction on real datasets from ex vivo phantoms. We also illustrate multiple q-shell diffusion propagator imaging (mq-DPI) on a real in vivo human brain and perform a qualitative comparison against state-of-the-art diffusion spectrum imaging (DSI) on the same subject. mq-DPI is shown to reconstruct robust EAP from only several different b-value shells and less diffusion measurements than DSI. This opens interesting perspectives for new q-space sampling schemes and tissue microstructure investigation.

The Role of Red Algae in Abrupt Appearance of Animals in the Early Cambrian on Siberian Platform

Calcified rock-forming marine filamented benthic micro- and macrophytes of Dzhelindia Kolosov, 1970 (Figure 1(а)) and Chaptchaica Kolosov, 1975 (Figure 1(b)) genera, thrived in Neoproterozoic (1000-541 million years ago) Siberia together with cyanobacteria. Their belonging to Rhodophyta is well-grounded. These and other Neoproterozoic rodofits, as well as Epiphyton Bornemann 1886 (Figure 1(c)) and other Early Cambrian (541-513 million years ago) benthic algae, oxygenating floor of epicontinental sea basin, formed conditions, favorable for the animals. In combination with other biotic, and such abiotic factors as: equatorial position and tectonic feature of Siberian platform; volcanism; transgression of the sea; diversity of ecologic niches, these conditions were prerequisites of skeleton and shell acquisition by Early Cambrian animals, and as a consequence, accelerated morphologic evolution, increased diversity of taxons of different groups of animals.

Bessel Fourier Orientation Reconstruction (BFOR): An analytical diffusion propagator reconstruction for hybrid diffusion imaging and computation of q-space indices

The ensemble average propagator (EAP) describes the 3D average diffusion process of water molecules, capturing both its radial and angular contents. The EAP can thus provide richer information about complex tissue microstructure properties than the orientation distribution function (ODF), an angular feature of the EAP. Recently, several analytical EAP reconstruction schemes for multiple q-shell acquisitions have been proposed, such as diffusion propagator imaging (DPI) and spherical polar Fourier imaging (SPFI). In this study, a new analytical EAP reconstruction method is proposed, called Bessel Fourier Orientation Reconstruction (BFOR), whose solution is based on heat equation estimation of the diffusion signal for each shell acquisition, and is validated on both synthetic and real datasets. A significant portion of the paper is dedicated to comparing BFOR, SPFI, and DPI using hybrid, non-Cartesian sampling for multiple b-value acquisitions. Ways to mitigate the effects of Gibbs ringing on EAP reconstruction are also explored. In addition to analytical EAP reconstruction, the aforementioned modeling bases can be used to obtain rotationally invariant q-space indices of potential clinical value, an avenue which has not yet been thoroughly explored. Three such measures are computed: zero-displacement probability (Po), mean squared displacement (MSD), and generalized fractional anisotropy (GFA).

Shell and food acquisition behaviors: Evidence for Contextual Decision Hierarchies in hermit crabs

Shell and food acquisition behaviors of the hermit crab, Pagurus samuelis, were examined in response to cues of shell and food availability. Tactile, visual, and chemical cues were presented in a factorial manner, and time was measured between initial contact and either inhabitation of a shell or initiation of feeding. We considered the time difference between initial contact and subsequent behavior to be a measure of hermit crab ‘decision time’. For shell acquisition experiments, treatments that included tactile cues elicited significantly shorter decision times (8.5–117.1s), than treatments without tactile cues (294.5–765.2s). In contrast to the shell acquisition experiment, we found that in food acquisition experiments, treatments that included chemical cues elicited significantly shorter decision times (78.4–450.5s), than those without chemical cues (570.0–778.1s). Although primary cues elicited the shortest decision times during foraging and shell-seeking, in the absence of the primary cue, secondary cues could still be used to make appropriate decisions, albeit with significantly longer decision times. Therefore we propose that hermit crabs sort environmental information in ‘Contextual Decision Hierarchies’ in order to make accurate and efficient behavioral choices.

Multiple q-shell diffusion propagator imaging

Many recent high angular resolution diffusion imaging (HARDI) reconstruction techniques have been introduced to infer an orientation distribution function (ODF) of the underlying tissue structure. These methods are more often based on a single-shell (one b-value) acquisition and can only recover angular structure information contained in the ensemble average propagator (EAP) describing the three-dimensional (3D) average diffusion process of water molecules. The EAP can thus provide richer information about complex tissue microstructure properties than the ODF by also considering the radial part of the diffusion signal. In this paper, we present a novel technique for analytical EAP reconstruction from multiple q-shell acquisitions. The solution is based on a Laplace equation by part estimation between the diffusion signal for each shell acquisition. This simplifies greatly the Fourier integral relating diffusion signal and EAP, which leads to an analytical, linear and compact EAP reconstruction. An important part of the paper is dedicated to validate the diffusion signal estimation and EAP reconstruction on real datasets from ex vivo phantoms. We also illustrate multiple q-shell diffusion propagator imaging (mq-DPI) on a real in vivo human brain and perform a qualitative comparison against state-of-the-art diffusion spectrum imaging (DSI) on the same subject. mq-DPI is shown to reconstruct robust EAP from only several different b-value shells and less diffusion measurements than DSI. This opens interesting perspectives for new q-space sampling schemes and tissue microstructure investigation.

Social context of shell acquisition in Coenobita clypeatus hermit crabs

Vacancy chains involve unique patterns of resource acquisition behaviors that determine how reusable resources are distributed through animal populations. Shell vacancy chains have been described for several hermit crab species, both terrestrial and marine, but little is known about the ecological and behavioral dynamics of shell choice in social versus solitary contexts. Here, we present a novel conceptual framework that differentiates 2 types of shell vacancy chain in hermit crabs and discuss fundamentally distinct predictions concerning the behavioral and ecological costs and benefits associated with synchronous versus asynchronous vacancy chains. In laboratory studies of the terrestrial hermit crab Coenobita clypeatus, we found support for the prediction that social context alters shell acquisition behaviors. Field observations demonstrated that both synchronous and asynchronous vacancy chains are common and revealed previously undescribed waiting and piggybacking behaviors that appear to facilitate synchronous vacancy chains. Additionally, simulation results from an agent-based model showed that population density and waiting behaviors can both influence the likelihood of synchronous vacancy chains. Together, these results indicate that better understanding of hermit crab resource acquisition requires studying social behaviors, including vacancy chain formation.

Shell acquisition by hermit crabs: which tactic is more efficient?

Gastropod shells are limited resources for most hermit crab species, acting as primary factors in various aspects of their biology. To investigate the efficacy of different behavioral tactics adopted for their acquisition (locomotion, attendance at shell-supplying sites, interactions with conspecifics in aggregation) we conducted observations and experiments at a salt marsh in New England (USA). Locomotion, fast and meandering, significantly increased the chances of encountering empty shells and conspecifics. However, shell exchanges were rare. Simulated gastropod predation sites quickly attracted a larger number of hermit crabs than the other shell-supplying sites tested (live and dead conspecifics, live snails) and induced the rapid occupancy of all the empty shells offered, usually by the first crabs arriving at the site. Aggregations seemed not to function as shell exchange markets, as previously suggested for several other species. In the short run, exploitation seems to be more efficient for the acquisition of new shells by Pagurus longicarpus. In the long run, it is the density of nondestructive gastropod predators that regulates the availability of new shells of good quality in the pool available to this hermit crab species.

De la Pena Lubricants and the Shell acquisition

De la Pena Lubricants and the Shell acquisition

Shell acquisition

Shell acquisition

Chemical mediation of behavior in hermit crabs: Alarm and aggregation cues

Field studies with three common local species of hermit crabs,Clibanarius vittatus, Pagurus longicarpus, andPagurus pollicaris, showed that these crabs responded behaviorally to chemicals originating from crushed conspecifics. Hermit crabs are attracted specifically and in a manner similar to previously reported crab responses to odors from dead gastropods. Responses byC. vittatus to both kinds of odor are of three types: (1) aggregation/shell investigation responses (previously reported for odors from dead gastropods), characterized by increased locomotor activity, investigation of shells in the vicinity, and switching into empty shells; (2) alarm responses, in which crabs flee the area; and (3) withdrawal responses, in which crabs pull into their shells and do not come out. Studies withC. vittatus showed that the stimulatory chemicals originate from hemolymph, are less than 500 D, adsorb to octadecyl silica, and are recovered by elution with 20% methanol. Responses ofC. vittatus are dependent upon crab size, type of shell occupied, and shell fit. Chemicals originating from dead conspecifics provide a forum for shell acquisition by crabs in relatively small shells and alarm by crabs in relatively large shells.

Chains of opportunity: A Markov model for acquisition of reusable resources

A vacancy chain is a unique type of resource acquisition process composed of an interconnected series of events in which the gaining of a particular resource unit by one individual depends directly on prior acquisition events by other individuals. Taken from the sociological literature, vacancy chains may also describe the distribution of many types of animal resources such as burrows, dwellings and shelters. Using data on hermit crabs, we present a Markov model simulating a vacancy chain process, and test the model against field data. Our results show that a simple Markov model adequately describes shell acquisition in hermit crabs, and that models combining shell size and crude estimates of quality fit the data extremely well. We illustrate in detail how to generate vacancy chain models from ecological data, how to determine the number and size of organisms gaining new resource units from resource introductions of specific sizes, and how to statistically evaluate the accuracy of Markov models. Not recognizing the presence of a vacancy chain system may lead to serious errors in estimating resource dynamics and therefore in demographic and competition models based on these dynamics. Finally, we suggest some ways in which vacancy chain models can aid studies of competition, population dynamics, life histories, and conservation in species using this type of resource acquisition process.

Memory of information gained during shell investigation by the hermit crab, Pagurus bernhardus

Hermit crabs have the opportunity to assess shells by sight, initial contact and active investigation with their appendages, and it might be expected that information thus gained would be remembered. This possibility was tested by offering crabs shells with partially blocked apertures so that the subsequent rejection could be timed. Crabs appeared unable to distinguish between a previously rejected shell and a novel shell by sight or contact alone but they actively investigated a previously rejected shell for less time than they did a novel shell. The data indicate that it is the shell itself that is recognized, not the location of the shell. The longer the interval between two investigations of the same shell the less was the reduction in the duration of active investigation. These data are discussed with reference to optimal mechanisms for shell acquisition.

Field studies on chemically mediated behavior in land hermit crabs: Volatile and nonvolatile odors

Land hermit crabs,Coenobita rugosis, were tested in the field in Costa Rica for behavioral responses to odors. Volatile odors associated with horse feces, fruit, and honey attracted crabs within minutes. Odors from dead gastropod flesh were not immediately attractive, but after aging, odors from a variety of flesh sources attracted crabs. Crabs fed actively upon the materials that attracted them. Feeding behavior was stimulated by components of fruit juice and fresh gastropod flesh juices of less than 10,000 daltons, honey, a 0.5 M sucrose solution, and a saturated solution of tyrosine. Twenty additional amino acid solutions tested at 0.1 M concentration were weak feeding stimulants at best. Chemical cues controlled feeding behavior, but not shell acquisition;C. rugosis were not differentially attracted to flesh odors or to living gastropods whose shells they occupied.

Resource partitioning and competition for shells in a subtidal hermit crab species assemblage.

Shell and habitat utilization are quantified for 12 hermit crab species occurring subtidally in the San Juan Archipelago, Washington. The mechanism of competition for shells between these species is investigated using laboratory experiments to determine shell preferences, shell acquisition rates, and rates of exchange of shells via shell fighting. This information is used to estimate relative intensities of inter- and intra-specific competition for shells between the species in this assemblage. In contrast to earlier findings on intertidal hermit crab assemblages, a significant number (5) of the species in this assemblage appear to experience a greater reduction in their shell supply due to members of other species than due to other members of their own species. The relative amounts of inter- and intra-specific competition differ greatly for different species in the community. The high average figures for interspecific/intraspecific competition are largely a result of the presence of three abundant and very generalized species. In spite of the large number of species and relatively high ratios of interspecific to intraspecific competition, the species in this group are not close to a limiting similarity in resource use. There is suggestive evidence that greater selection pressures for divergence in habitat use may have resulted in the lower amounts of overlap observed in intertidal hermit crab assemblages in previous studies.

Predaceous gastropods regulate new-shell supply to salt marsh hermit crabs

Marsh hermit crabsPagurus longicarpus Say directly acquire new shells as the predatory gastropodMelongena corona Gmelin consumes marsh periwinkles,Littorina irrorata Say. The influx rate of new shells into a salt marsh hermit crab population was measured by marking live periwinkles and daily recovering the shells from hermit crabs over periods of 3 to 6 d. Average rates of new shell acquisition ranged from 4.0 to 23.3 new shells per day from salt marsh areas of 4×10 m. Such consistently high rates contrast with the negligible rates generally assumed for new shell entry into hermit crab populations. The number of new shells acquired each day varied directly with the number of the predatory gastropod,M. corona, present in each study area at both natural and manipulated predator densities. Empty shells on the substrate are usually considered as the primary source of new shells to hermit crabs. However, over 500 empty shells had to be placed on the substrate in a 4×10 m area to provide a daily rate of 20 new shells to the hermit crab population.

New shell acquisition in the hermit crab,Pagurus geminus

The process of how the hermit crab,Pagurus geminus, acquires a new shell was investigated in the natural habitat at Ezura in Shirahama, Wakayama Prefecture, during the non-breeding season, and the following results were obtained. Hermit crabs acquired new shells most frequently by shell exchange between 2 individuals and occasionally by attacking snails. Acquisition through location of empty shells was not found. At the snail attacking site or the site of shell exchange attempts, sometimes many other individuals appeared and, frequently, confusing or complex shell changes were observed. The importance of introduction of fresh shells to a hermit crab population and the possibility for a certain individual to acquire a shell introduced by others through shell exchange attempts are discussed.

Rate of New Shell Acquisition by Hermit Crabs in a Salt Marsh Habitat

ABSTRACT We predicted that measurable numbers of new snail shells are transferred daily to hermit crabs in habitats where gastropods frequently prey upon other gastropods. The rate of new shell acquisition by hermit crabs, Pagurus longicarpus, was monitored daily in northeastern Gulf of Mexico salt marshes where crown conchs, Melongena corona, prey heavily upon marsh periwinkles, Littorina irrorata. Periwinkle shells, marked while housing live snails, appeared on P. longicarpus at daily rates ranging from 1 to >20 for selected areas of approximately 60 m2 in three marshes. The maximum number (22.8) of new periwinkle shells appearing among P. longicarpus in the immediate area (300 m2) represented 16.5% of crabs present there each day.

Direct shell acquisition by hermit crabs from gastropods

Freilandbeobachtung des Erwerbs von Schalen einer durch Raubschnecken frisch getöteten Schnecke durch Einsiedlerkrebse.