Consistent Spatial Relationship Research Articles

CytoSpatio: Learning cell type spatial relationships using multirange, multitype point process models.

Recent advances in multiplexed fluorescence imaging have provided new opportunities for deciphering the complex spatial relationships among various cell types across diverse tissues. We introduce CytoSpatio, open-source software that constructs generative, multirange, and multitype point process models that capture interactions among multiple cell types at various distances simultaneously. On analyzing five cell types across five tissues, our software showed consistent spatial relationships within the same tissue type, with certain cell types like proliferating T cells consistently clustering across tissue types. It also revealed that the attraction-repulsion relationships between cell types like B cells and CD4-positive T cells vary with tissue type. CytoSpatio can also generate synthetic tissue structures that preserve the spatial relationships seen in training images, a capability not provided by previous descriptive, motif-based approaches. This potentially allows spatially realistic simulations of how cell relationships affect tissue biochemistry.

A surrogate modeling method for distributed land surface hydrological models based on deep learning

Surrogate modelling methods have been used to estimate spatially distributed parameters of land surface hydrological models due to their computational efficiency. However, traditional surrogate techniques have trouble in modelling high-dimensional input–output maps. In addition, their applications to a distributed model over large spatial and temporal domains are very unlikely to produce consistent spatial pattern and dynamic relationship of model input and output, leading to unbalanced model performance across different spatiotemporal domains. To address these issues, we employ a deep autoregressive neural network to construct an accurate and reliable surrogate system of distributed dynamic model outputs. The network uses a deep convolutional encoder-decoder architecture to take full advantage of the deep convolutional layers in high-dimensional image processing and spatial feature extraction. Moreover, the autoregressive strategy makes the network good at handling dynamic relationship between the time-varying model input and output. We apply this deep learning (DL) network to building a surrogate model of the Variable Infiltration Capacity (VIC) model simulated soil moisture over the Huaihe river basin of China. The results show that the adopted deep autoregressive neural network can provide an accurate surrogate model of the high-dimensional dynamic relationship between 15 input fields and 1 output field, each covering 408 grids, over multiple years. This surrogate model significantly outperforms the popular long short-term memory (LSTM) model, achieving an average mean squared error (MSE) of 0.26 and an average R2 of 0.76 using the test datasets. The surrogate's MSE and R2 performance represents an average improvement of 43% and 33%, respectively, compared to the LSTM model. In addition, it shows better spatial performance than the LSTM model, demonstrating its superior performance in approximating spatial patterns of VIC simulated soil moisture. The accuracy of this surrogate method and its ability to handle high-dimensional data is promising for advancing parameter uncertainty quantification of distributed land surface hydrological models, which usually have high dimensionality due to the large number of variables involved, including distributed parameters, input forcing variables, and output variables.

Automatically detecting human-object interaction by an instance part-level attention deep framework

Automatically detecting human-object interactions (HOIs) from an image is a very important but challenging task in computer vision. One of the significant problems in HOI detection is that similar human-object interactions are difficult to distinguish. Recently, many instance-centric HOI detection schemes, based on appearance features and coarse spatial information, have been proposed. These methods, however, lack the capacity of capturing and analyzing the fine-grained context between human poses and object parts, which plays a crucial role in HOI detection. To address these problems, we propose a novel instance part-level attention deep framework for HOI detection. Specifically, our approach consists of a human/object-part detection phase and an HOI detection phase. In the former phase, a part-level visual pattern estimation model is designed for capturing the fine-grained human body parts and object parts. In the latter phase, a self-attention-based deep network is proposed to learn the visual composite around the human-object pair that implicitly expresses the consistent spatial, scale, co-occurrence, and viewpoint relationships among human body parts and object parts across images, which are effective for predicting HOI. To the best of our knowledge, we are the first to propose a framework where the fine-grained part-level mutual context of a human-object pair is extracted to improve HOI detection. By comparing our approach with state-of-the-art HOI detection methods on benchmark datasets, we demonstrated that our proposed framework outperformed the existing HOI detection methods, such as significantly improving the performance of part-level visual pattern estimation, HOI detection, and the quality of the self-attention-based deep network structure.

Genetic and phenotypic variation exhibit both predictable and stochastic patterns across an intertidal fish metapopulation.

Interactions among selection, gene flow, and drift affect the trajectory of adaptive evolution. In natural populations, the direction and magnitude of these processes can be variable across different spatial, temporal, or ontogenetic scales. Consequently, variability in evolutionary processes affects the predictability or stochasticity of microevolutionary outcomes. We studied an intertidal fish, Bathygobius cocosensis (Bleeker, 1854), to understand how space, time, and life stage structure genetic and phenotypic variation in a species with potentially extensive dispersal and a complex life cycle (larval dispersal preceding benthic recruitment). We sampled juvenile and adult life stages, at three sites, over three years. Genome-wide SNPs uncovered a pattern of chaotic genetic patchiness, that is, weak-but-significant patchy spatial genetic structure that was variable through time and between life stages. Outlier locus analyses suggested that targets of spatially divergent selection were mostly temporally variable, though a significant number of spatial outlier loci were shared between life stages. Head shape, a putatively ecologically responsive (adaptive) phenotype in B.cocosensis also exhibited high temporal variability within sites. However, consistent spatial relationships between sites indicated that environmental similarities among sites may generate predictable phenotype distributions across space. Our study highlights the complex microevolutionary dynamics of marine systems, where consideration of multiple ecological dimensions can reveal both predictable and stochastic patterns in the distributions of genetic and phenotypic variation. Such considerations probably apply to species that possess short, complex life cycles, have large dispersal potential and fecundities, and that inhabit heterogeneous environments.

White matter fascicles and cortical microstructure predict reading-related responses in human ventral temporal cortex

Reading-related responses in the lateral ventral temporal cortex (VTC) show a consistent spatial layout across individuals, which is puzzling, since reading skills are acquired during childhood. Here, we tested the hypothesis that white matter fascicles and gray matter microstructure predict the location of reading-related responses in lateral VTC. We obtained functional (fMRI), diffusion (dMRI), and quantitative (qMRI) magnetic resonance imaging data in 30 adults. fMRI was used to map reading-related responses by contrasting responses in a reading task with those in adding and color tasks; dMRI was used to identify the brain's fascicles and to map their endpoint densities in lateral VTC; qMRI was used to measure proton relaxation time (T1), which depends on cortical tissue microstructure. We fit linear models that predict reading-related responses in lateral VTC from endpoint density and T1 and used leave-one-subject-out cross-validation to assess prediction accuracy. Using a subset of our participants (N=10, feature selection set), we find that i) endpoint densities of the arcuate fasciculus (AF), inferior longitudinal fasciculus (ILF), and vertical occipital fasciculus (VOF) are significant predictors of reading-related responses, and ii) cortical T1 of lateral VTC further improves the predictions of the fascicle model. In the remaining participants (N=20, validation set), we show that a linear model that includes T1, AF, ILF and VOF significantly predicts i) the map of reading-related responses across lateral VTC and ii) the location of the visual word form area, a region critical for reading. Overall, our data-driven approach reveals that the AF, ILF, VOF and cortical microstructure have a consistent spatial relationship with an individual's reading-related responses in lateral VTC.

Climate and plant community diversity in space and time

Climate strongly shapes plant diversity over large spatial scales, with relatively warm and wet (benign, productive) regions supporting greater numbers of species. Unresolved aspects of this relationship include what causes it, whether it permeates to community diversity at smaller spatial scales, whether it is accompanied by patterns in functional and phylogenetic diversity as some hypotheses predict, and whether it is paralleled by climate-driven changes in diversity over time. Here, studies of Californian plants are reviewed and new analyses are conducted to synthesize climate-diversity relationships in space and time. Across spatial scales and organizational levels, plant diversity is maximized in more productive (wetter) climates, and these consistent spatial relationships are mirrored in losses of taxonomic, functional, and phylogenetic diversity over time during a recent climatic drying trend. These results support the tolerance and climatic niche conservatism hypotheses for climate-diversity relationships, and suggest there is some predictability to future changes in diversity in water-limited climates.

Ultrasensitive Electrochemical DNA Biosensor Based on a Label-Free Assembling Strategy Using a Triblock polyA DNA Probe.

Multiblock DNA probe attracted a large amount of scientific attention, for the development of multitarget biosensor and improved specificity/sensitivity. However, the development of multiblock DNA probes highly relied on the chemical synthesis of organic linkers or nanomaterials, which limited their practicability and biological compatibility. In this work, we developed a label-free assembling strategy using a triblock DNA capture probe, which connects two DNA probes with its intrinsic polyA fragment (probe-PolyA-probe, PAP). The middle polyA segment has a high affinity to the gold electrode surface, leading to excellent reproducibility, stability, and regeneration of our biosensor. Two flanking capture probes were tandemly co-assembled on the electrode surface with consistent spatial relationship and exactly the same amount. When combined with the target DNA, the hybridization stability was improved, because of the strong base stacking effect of two capture probes. The sensitivity of our biosensor was proved to be 10 fM, with a wide analysis range between 10 fM to 1 nM. Our PAP-based biosensor showed excellent specificity when facing mismatched DNA sequences. Even single nucleotide polymorphisms can be distinguished by each probe. The excellent practicability of our biosensor was demonstrated by analyzing genomic DNA both with and without PCR amplification.

Distribution of the Specialist Aphid Uroleucon nigrotuberculatum (Homoptera: Aphididae) in Response to Host Plant Semiochemical Induction by the Gall Fly Eurosta solidaginis (Diptera: Tephritidae).

Many plants use terpenoids and other volatile compounds as semiochemicals. Reception of plant volatiles by conspecifics may trigger a defensive phytochemical response. These same compounds can also function as host recognition signals for phytophagous insects. In this experiment, we find that when the specialist gall-forming fly Eurosta solidaginis (Fitch; Diptera: Tephritidae) attacks its tall goldenrod (Solidago altissima (L.; Asterales: Asteraceae)) host plant, the fly indirectly induces a phytochemical response in nearby tall goldenrod plants. This phytochemical response may, in turn, act as a positive signal attracting the goldenrod specialist aphid Uroleucon nigrotuberculatum (Olive; Hemiptera: Aphididae). Laboratory-based experiments exposing ungalled tall goldenrod plants to the volatiles released by E. solidaginis galls demonstrated a consistent increase in foliar terpenoid concentrations in ungalled plants. Analysis of tall goldenrod stem and gall tissue chemistry revealed induction of terpenoids in gall tissue, with a simultaneous decrease in green leaf volatile concentrations. Field experiments demonstrated a consistent spatial relationship in tall goldenrod foliar terpenoid concentrations with distance from an E. solidaginis gall. Both laboratory and field experiments establish consistent induction of the terpene β-farnesene, and that this compound is a strong positive predictor of U. nigrotuberculatum aphid presence on goldenrod plants along with plant biomass and several other foliar terpenoids. These findings suggest E. solidaginis induced phytochemistry, especially β-farnesene, may be acting as a kairomone, driving aphid distribution in the field.

Size Distributions of Arctic Waterbodies Reveal Consistent Relations in Their Statistical Moments in Space and Time

Arctic lowlands are characterized by large numbers of small waterbodies, which are known to affect surface energy budgets and the global carbon cycle. Statistical analysis of their size distributions has been hindered by the shortage of observations at sufficiently high spatial resolutions. This situation has now changed with the high-resolution (<5 m) circum-Arctic Permafrost Region Pond and Lake (PeRL) database recently becoming available. We have used this database to make the first consistent, high-resolution estimation of Arctic waterbody size distributions, with surface areas ranging from 0.0001 km2 (100 m2) to 1 km2. We found that the size distributions varied greatly across the thirty study regions investigated and that there was no single universal size distribution function (including power-law distribution functions) appropriate across all of the study regions. We did, however, find close relationships between the statistical moments (mean, variance, and skewness) of the waterbody size distributions from different study regions. Specifically, we found that the spatial variance increased linearly with mean waterbody size (R2 = 0.97, p < 2.2e-16) and that the skewness decreased approximately hyperbolically. We have demonstrated that these relationships (1) hold across the 30 Arctic study regions covering a variety of (bio)climatic and permafrost zones, (2) hold over time in two of these study regions for which multi-decadal satellite imagery is available, and (3) can be reproduced by simulating rising water levels in a high-resolution digital elevation model. The consistent spatial and temporal relationships between the statistical moments of the waterbody size distributions underscore the dominance of topographic controls in lowland permafrost areas. These results provide motivation for further analyses of the factors involved in waterbody development and spatial distribution and for investigations into the possibility of using statistical moments to predict future hydrologic dynamics in the Arctic.

Responses of competitive understorey species to spatial environmental gradients inaccurately explain temporal changes

Understorey plant communities play a key role in the functioning of forest ecosystems. Under favourable environmental conditions, competitive understorey species may develop high abundances and influence important ecosystem processes such as tree regeneration. Thus, understanding and predicting the response of competitive understorey species as a function of changing environmental conditions is important for forest managers. In the absence of sufficient temporal data to quantify actual vegetation changes, space-for-time (SFT) substitution is often used, i.e. studies that use environmental gradients across space to infer vegetation responses to environmental change over time. Here we assess the validity of such SFT approaches and analysed 36 resurvey studies from ancient forests with low levels of recent disturbances across temperate Europe to assess how six competitive understorey plant species respond to gradients of overstorey cover, soil conditions, atmospheric N deposition and climatic conditions over space and time. The combination of historical and contemporary surveys allows (i) to test if observed contemporary patterns across space are consistent at the time of the historical survey, and, crucially, (ii) to assess whether changes in abundance over time given recorded environmental change match expectations from patterns recorded along environmental gradients in space. We found consistent spatial relationships at the two periods: local variation in soil variables and overstorey cover were the best predictors of individual species’ cover while interregional variation in coarse-scale variables, i.e. N deposition and climate, was less important. However, we found that our SFT approach could not accurately explain the large variation in abundance changes over time. We thus recommend to be cautious when using SFT substitution to infer species responses to temporal changes.

Novel approaches in Extended Principal Component Analysis to compare spatio-temporal patterns among multiple image time series

Extended Principal Component Analysis (EPCA) aims to examine the patterns of variability shared among multiple datasets. In image time series analysis, this is conventionally done by virtually extending the spatial dimension of the time series by spatially concatenating the different time series and then performing S-mode PCA. In S-mode analysis, samples in space are the statistical variables and samples in time are the statistical observations. This paper introduces the concept of temporal concatenation of multiple image time series to perform EPCA. EPCA can also be done with a T-mode orientation in which samples in time are the statistical variables and samples in space are the statistical observations. This leads to a total of four orientations in which EPCA can be carried out. This research explores these four orientations and their implications in investigating spatio-temporal relationships among multiple time series. This research demonstrates that EPCA carried out with temporal concatenation of the multiple time series with T-mode (tT) is able to identify similar spatial patterns among multiple time series. The conventional S-mode EPCA with spatial concatenation (sS) identifies similar temporal patterns among multiple time series. The other two modes, namely T-mode with spatial concatenation (sT) and S-mode with temporal concatenation (tS), are able to identify patterns which share consistent temporal phase relationships and consistent spatial phase relationships with each other, respectively. In a case study using three sets of precipitation time series data from GPCP, CMAP and NCEP-DOE, the results show that examination of all four modes provides an effective basis for comparison of the series.

Ex situ reproduction of Portuguese endangered cyprinids in the context of their conservation

The captive breeding of highly endangered species is considered to be an indispensable instrument when the natural habitats of those species are extremely degraded and/or when the effective population sizes are so reduced that there is an eminent risk of extinction (Bentsen and Olesen 2002; Maitland and Morgan 2002; Faria et al. 2010). Several authors agree that captive breeding programs do not completely solve conservation problems and should only be adopted as a safeguard against species extinction until the natural habitats are restored and the animals can be reintroduced into their original habitats under appropriate conditions (Johnson and Jensen 1991; Philippart 1992; Caughley and Gunn 1996; Naslund 1998; Snyder et al. 1999; Berejikian 2000; Bobori et al 2001; Maitland and Morgan 2002; Schonhuth et al. 2003), a strategy known as supportive breeding (Wang and Ryman 2001). This strategy has been applied in several countries when it is urgent to preserve fish populations in considerable risk of extinction (Cambray 1997; Arkush and Siri 2001; Schonhuth et al. 2003; CIP El Palmar 2006; Cardoso and Carrapato 2008; Kitanishi et al. 2013). Indeed, a vast array of factors is threatening freshwater fishes at a global scale (Duncan and Lockwood 2001). The Mediterranean populations are among the most threatened (Hermoso and Clavero 2011) due to the introduction of alien species, impoundment of rivers, habitat degradation and fragmentation, summer droughts and water quality deterioration (Collares-Pereira and Cowx 2004). In the Iberian Peninsula there is a consistent spatial relationship between the incidence of threats and the level of imperilment of species, whereby the presence of invasive species and the water extraction are the main drivers of native fish declines (Clavero et al. 2010). With the tendency for global warming, the typical summer droughts in Iberia are expected to become more intense and extended in time. This could pose an additional extinction risk factor for the Portuguese native cyprinid fish species, around 67 % of which are already considered to be ‘‘Threatened’’, ‘‘Vulnerable’’ or ‘‘Critically endangered’’ according to the Portuguese Red Book [Cabral et al. 2005; Electronic Supplementary Material (ESM) Table S1]. These species are small cyprinids with no economical value, which show restricted geographic ranges and low levels of genetic diversity (Sousa-Santos et al. 2013). A pioneer project of supportive breeding of critically endangered endemic fish species started in 2007 with nine populations belonging to six endangered and critically endangered cyprinid species endemic to the Iberian Peninsula: Achondrostoma occidentale, Iberochondrostoma almacai, Iberochondrostoma lusitanicum, Squalius pyrenaicus, Squalius aradensis and Squalius torgalensis (Fig. 1; Table 1). In this paper we describe the implementation and major results of this project and discuss the advantages of the adopted breeding scheme. Also, potential disadvantages of supportive breeding programs targeting endangered fish species are discussed. Ex situ conditions and the adoption of a ‘‘naturalistic approach’’ of reproduction. Following the research Electronic supplementary material The online version of this article (doi:10.1007/s10228-013-0383-6) contains supplementary material, which is available to authorized users.

Neogene rejuvenation of central Appalachian topography: Evidence for differential rock uplift from stream profiles and erosion rates

The persistence of topography within ancient orogens remains one of the outstanding questions in landscape evolution. In the eastern North American Appalachians, this question is manifest in the outstanding problem of whether topographic relief is in a quasi-equilibrium state, decaying slowly over many millennia, or whether relief has increased during the late Cenozoic. Here we present quantitative geomorphic data from the nonglaciated portion of the Susquehanna River drainage basin that provide insight into these end-member models. Analysis of channel profiles draining upland catchments in the northern Valley and Ridge, Appalachian Plateau, Blue Ridge, and Piedmont provinces reveals that a large number of streams have well defined knickpoints clustered at 300–600m elevation but not systematically associated with transitions from weak to resistant substrate. Cosmogenic 10Be inventories of modern stream sediment indicate that erosion rates are spatially variable, ranging from ~5–30m/Myr above knickpoints to ~50–100m/Myr below knickpoints. Overall, channel gradients, normalized for drainage area, scale linearly with catchment-averaged erosion rates. Collectively, regionally consistent spatial relationships among erosion rate, channel steepness, and knickpoints reveal an ongoing wave of transient channel adjustment to a change in relative base level. Reconstructions of relict channel profiles above knickpoints suggest that higher rates of incision are associated with ~100–150m of relative base level fall that accompanied epierogenic rock uplift rather than a change to a more erosive climate or drainage reorganization. Channel response timescales imply that the onset of relative base level change predates ~3.5Ma and may have begun as early as ~15Ma. We suggest that adjustment of the channel network was likely driven by changes in mantle dynamics along the eastern seaboard of North America during the Neogene.

Factors that influence negative summation in a spatial-search task with pigeons

A variant of the standard conditioned inhibition procedure was used to evaluate landmark-based spatial search in a touchscreen preparation. Pigeons were given compound trials with one landmark (A) positioned in a consistent spatial relationship to a hidden goal and another landmark (B) positioned randomly with respect to A and the hidden goal (AB+). On half of the non-reinforced inhibitory trials, A was paired with landmark X (AX-) and on the remaining trials B was paired with Y (BY-). All subjects were also given reinforced trials with a transfer excitor (T+). During conditioned inhibition training, subjects showed no change in overall responding during AX- trials but did show a decrease in the number of pecks to the goal location signaled by A. During non-reinforced summation tests with landmark T, X had a greater suppressive effect than did Y on overall responding but the percentage of pecks at the goal did not differ unless X was positioned near the expected goal signaled by T. These data demonstrate that the effectiveness of a stimulus trained as an inhibitor is dependent on the strength of the association between its training excitor (A) and the US, as well as, the spatial arrangement of stimuli during testing.

Foraging distribution of Pacific harbor seals (Phoca vitulina richardii) in a highly impacted estuary

Assessing the relative importance of environmental and anthropogenic influences on the distribution of wild populations is an important step in designing spatially explicit plans for their management and protection. We examined environmental variables correlated with the spatial distribution of eastern Pacific harbor seals (Phoca vitulina richardii), a marine mammal common to coastal waters, in a large, highly urbanized estuary. We assessed the relationship between prey abundance, depth, bottom relief, proximity to terrestrial haul-out sites and 3 potential sources of anthropogenic influence, and the in-water spatial distribution of seals. We identified locations of seals using satellite-linked telemetry, and used partial Mantel tests to assess which environmental variables were most strongly linked to seal foraging distribution, given spatial autocorrelation within variables. Mann-Whitney tests were used to compare environmental characteristics of locations of seals with a random distribution of locations. Because harbor seals are central-place foragers, we incorporated spatial distribution of seals relative to the central place into our analyses. High prey abundance and proximity to the haul-out site were strongly associated with the spatial distribution of seals. Harbor seals also tended to use deeper waters and areas of high bottom relief within the estuary. There was no consistent spatial relationship between the 3 anthropogenic factors and the distribution of seals, although seals tended to be found closer than expected to sites of high human activity. In highly impacted coastal areas where limited alternate suitable habitat exists, foraging seals may need to rely on disturbed (suboptimal) areas, and as a result may habituate to human presence in areas rich in food resources.

Facilitation of learning spatial relations among locations by visual cues: generality across spatial configurations

Spatial pattern learning permits the learning of the location of objects in space relative to each other without reference to discrete visual landmarks or environmental geometry. In the present experiment, we investigated conditions that facilitate spatial pattern learning. Specifically, human participants searched in a real environment or interactive 3-D computer-generated virtual environment open-field search task for four hidden goal locations arranged in a diamond configuration located in a 5 x 5 matrix of raised bins. Participants were randomly assigned to one of three groups: Pattern Only, Landmark + Pattern, or Cues + Pattern. All participants experienced a Training phase followed by a Testing phase. Visual cues were coincident with the goal locations during Training only in the Cues + Pattern group whereas a single visual cue at a non-goal location maintained a consistent spatial relationship with the goal locations during Training only in the Landmark + Pattern group. All groups were then tested in the absence of visual cues. Results in both environments indicated that participants in all three groups learned the spatial configuration of goal locations. The presence of the visual cues during Training facilitated acquisition of the task for the Landmark + Pattern and Cues + Pattern groups compared to the Pattern Only group. During Testing the Landmark + Pattern and Cues + Pattern groups did not differ when their respective visual cues were removed. Furthermore, during Testing the performance of these two groups was superior to the Pattern Only group. Results generalize prior research to a different configuration of spatial locations, isolate spatial pattern learning as the process facilitated by visual cues, and indicate that the facilitation of learning spatial relations among locations by visual cues does not require coincident visual cues.

Histological analysis of spermatogenesis and the germ cell development strategy within the testis of the male Western Cottonmouth Snake, Agkistrodon piscivorus leucostoma

Cottonmouth (Agkistrodon piscivorus leucostoma) testes were examined histologically to determine the germ cell development strategy employed during spermatogenesis. Testicular tissues from Cottonmouths were collected monthly from swamps around Hammond, Louisiana. Pieces of testis were fixed in Trump's fixative, dehydrated in ethanol, embedded in Spurr's plastic, sectioned with an ultramicrotome, and stained with toluidine blue and basic fuchsin. Spermatogenesis within Cottonmouths occurs in two independent events within a single calendar year. The testes are active during the months of March-June and August-October with spermiation most heavily observed during April-May and October. To our knowledge, this is the first study that describes bimodal spermatogenesis occurring in the same year within the subfamily Crotalinae. During spermatogenesis, no consistent spatial relationships are observed between germ cell generations. Typically, either certain cell types were missing (spermatocytes) or the layering of 3-5 spermatids and/or spermatocytes within the same cross-section of seminiferous tubule prevented consistent spatial stages from occurring. This temporal pattern of sperm development is different from the spatial development found within birds and mammals, being more reminiscent of that seen in amphibians, and has now been documented within every major clade of reptile (Chelonia, Serpentes, Sauria, Crocodylia). This primitive-like sperm development, within a testis structurally similar to mammals and birds, may represent an intermediate testicular model within the basally positioned (phylogenetically) reptiles that may be evolutionarily significant.

Electric Tomography — A Real-Time Technique for Measuring Cardiac Performance

Introduction: Electric Tomography (ET) shows great promise as a tool for reproducibly measuring cardiac performance in an operator-independent manner. ET tracks the motion of electrodes on cardiac leads by detecting changes in voltage as they move through 3D electric fields. Since the electrodes maintain a consistent spatial relationship with underlying myocardium, cardiac displacement, velocity, and acceleration can be determined. A prior clinical study (n=35) demonstrated that ET tracks cardiac motion in a physiologically meaningful manner.

A stereotactic device for rabbits based on mandibular and cranial landmarks

The authors have developed a stereotactic device for use in rabbits that uses the plane at the base of the mandible combined with cranial sutures as an anatomical reference. The device was developed for a study designed to evaluate catheters for infection prophylaxis, and this required the implantation of silicone catheters along a reproducible trajectory through the lateral ventricle. Cadaver and atlas studies demonstrated consistent spatial relationships between intracranial structures and the surface plane on which the animals were resting during the surgery. This plane is formed by the 2 mandibular angles and the mandibular tip. The authors developed a stainless steel stereotactic device that uses this mandibular plane as well as the coronal and sagittal sutures as spatial references. Operations were performed in 60 animals using the stereotactic device, and postmortem dissections of the animals' brains demonstrated 78.6% accuracy of the trajectory within a tolerance of deviation of 5 degrees , and 94.6% accuracy within a tolerance of 10 degrees . The accuracy of the trajectory of the last 18 consecutively operated animals was constantly within a tolerance of 5 degrees . The device can be autoclaved and, since it is relatively simple and inexpensive to build, the authors manufactured 3 identical frames and used them alternately to operate under sterile conditions. The fast and pain-free head fixation minimized anesthesia-related risks. The authors' experiences suggest that the device is suitable for ventricular punctures and, dependant on the individual requirements of accuracy, other procedures that require "approximate" stereotactic guidance especially when a series of animals need to undergo operations quickly.

Cytological evaluation of the germ cell development strategy within the testis of the American alligator, Alligator mississippiensis

AbstractThe cytological changes to germ cells were investigated within the seminiferous epithelium of the American alligator (Alligator mississippiensis). Testicular tissues were collected, embedded in plastic, sectioned on an ultramicrotome, and stained with the periodic acid–Schiff+ procedure followed by a haematoxylin counterstain. Alligators have a prenuptial pattern of germ cell development, where spermatogenesis begins in early spring and sperm is mature by the time mating begins in May. Consistent spatial relationships between germ cells are absent within the seminiferous epithelium of the alligator. Their germ cells progress through the phases of spermatogenesis as a single cohort, leading to one continuous spermiation event that occurs during their mating season (May–June). This temporal germ cell development is different from the consistent spatial development seen within seasonally breeding birds and mammals but is similar to the recently described germ cell development strategies of two other temperate breeding reptiles, the slider turtle and the European wall lizard. The germ cell development strategy shared by these three temperate reptiles representing three different taxa within the class Reptilia is reminiscent of the temporal strategy seen within the anamniotic testis. Thus, alligators and at least two other temperate reptiles exhibit primitive spermatogenic cycles within derived amniotic testes and may be consider intermediates in terms of testicular organization, which may have significance phylogenetically.