Shell Temperature, Activity and Resistance to Desiccation in the Polymorphic Land Snail Cepaea Vindobonensis

Shell temperature during the morning hours, and the 24-houractivity pattern have beenstudied in the two distinct morphsof the polymorphic land snail Cepaea vindobonensis. Shelltemperaturesbetween the two morphs differed significantly when snails wereplaced in the sunand the temperature difference was about 1°C. Activity observations in the field and in the laboratory revealedthat adult dark-banded snailswere in general less active thanboth morphs of juveniles and adult faint-banded snails duringsunnymornings or under severe heat load. In the field and duringcloudy mornings nostatistically significant differences betweenmorphs were seen. Resistance to desiccation was studied among the two morphs ofthe same population inwhich activity was observed and anotherpopulation coming from a more northern and morehumid habitat.A clear intraspecific difference was found in resistance todesiccation. Snails fromthe southern population living in amore arid habitat were more resistant than snails from thenorthernpopulation. Within the same population percentage water lossdid not differsignificantly between the two morphs but thefaint-banded snails seemed better adapted to ariditysince onlyin these snails was no difference detected in relative bodywater afterdesiccation. (Received 28 July 1997; accepted 20 June 1998)     

Laterality Influences Schooling Position in Rainbowfish,Melanotaenia spp

Cerebral lateralization is a widespread trait among animals, is often manifested as side biases in behaviour (laterality) and has been suggested to provide fitness benefits. Here we examined the influence of laterality on the organisation of fish schools using rainbowfish (Melanotaenia spp) as model species. The pattern and strength of laterality for each individual was determined by examining eye preferences whilst examining their reflection in a mirror. Schools of four fish of known laterality were then created and the preferred position for each fish within the school was repeatedly observed in a flume. Fish which showed right eye preferences in the mirror test preferentially adopted a position on the left side of the school. Conversely, fish that showed left eye preferences in the mirror test or where non-lateralised preferentially adopted a position slightly to the right side of the school. However, this general pattern varied depending on the species and sex of the school. Our results strongly implicate individual laterality in the geometry of school formation.     

Three Mechanisms for the Calcium Alleviation of Mineral Toxicities

Ca²⁺ in rooting medium is essential for root elongation, even in the absence of added toxicants. In the presence of rhizotoxic levels of Al³⁺, H⁺, or Na⁺ (or other cationic toxicants), supplementation of the medium with higher levels of Ca²⁺ alleviates growth inhibition. Experiments to determine the mechanisms of alleviation entailed measurements of root elongation in wheat (Triticum aestivum L. cv Scout 66) seedlings in controlled medium. A Gouy-Chapman-Stern model was used to compute the electrical potentials and the activities of ions at the root-cell plasma membrane surfaces. Analysis of root elongation relative to the computed surface activities of ions revealed three separate mechanisms of Ca²⁺ alleviation. Mechanism I is the displacement of cell-surface toxicant by the Ca²⁺-induced reduction in cell-surface negativity. Mechanism II is the restoration of Ca²⁺ at the cell surface if the surface Ca²⁺ has been reduced by the toxicant to growth-limiting levels. Mechanism III is the collective ameliorative effect of Ca²⁺ beyond mechanisms I and II, and may involve Ca²⁺-toxicant interactions at the cell surface other than the displacement interactions of mechanisms I and II. Mechanism I operated in the alleviation of all of the tested toxicities; mechanism II was generally a minor component of alleviation; and mechanism III was toxicant specific and operated strongly in the alleviation of Na⁺ toxicity, moderately in the alleviation of H⁺ toxicity, and not at all in the alleviation of Al³⁺ toxicity.     

Subconductance States of a Mutant NMDA Receptor Channel Kinetics,Calcium, and Voltage Dependence

The kinetic properties of main and subconductance states of a mutant mouse N-methyl-d-aspartate (NMDA) receptor channel were examined. Recombinant receptors made of ζ-ε₂ (NR1-NR2B) subunits having asparagine-to-glutamine mutations in the M2 segment (ζN598Q /ε₂N589Q) were expressed in Xenopus oocytes. Single channel currents recorded from outside-out patches were analyzed using hidden Markov model techniques. In Ca²⁺-free solutions, an open receptor channel occupies a main conductance (93 pS) and a subconductance (62 pS) with about equal probability. There are both brief and long-lived subconductance states, but only a single main level state. At −80 mV, the lifetime of the main and the longer-lived sub level are both ∼3.3 ms. The gating of the pore and the transition between conductance levels are essentially independent processes. Surprisingly, hyperpolarization speeds both the sub-to-main and main-to-sub transition rate constants (∼120 mV/e-fold change), but does not alter the equilibrium occupancies. Extracellular Ca²⁺ does not influence the transition rate constants. We conclude that the subconductance levels arise from fluctuations in the energetics of ion permeation through a single pore, and that the voltage dependence of these fluctuations reflects the modulation by the membrane potential of the barrier between the main and subconductance conformations of the pore.     

Environmental versus Anthropogenic Effects on Population Adaptive Divergence in the Freshwater Snail Lymnaea stagnalis

Repeated pesticide contaminations of lentic freshwater systems located within agricultural landscapes may affect population evolution in non-target organisms, especially in species with a fully aquatic life cycle and low dispersal ability. The issue of evolutionary impact of pollutants is therefore conceptually important for ecotoxicologists. The impact of historical exposure to pesticides on genetic divergence was investigated in the freshwater gastropod Lymnaea stagnalis, using a set of 14 populations from contrasted environments in terms of pesticide and other anthropogenic pressures. The hypothesis of population adaptive divergence was tested on 11 life-history traits, using Q_ST -F_ST comparisons. Despite strong neutral differentiation (mean F_ST = 0.291), five adult traits or parameters were found to be under divergent selection. Conversely, two early expressed traits showed a pattern consistent with uniform selection or trait canalization, and four adult traits appeared to evolve neutrally. Divergent selection patterns were mostly consistent with a habitat effect, opposing pond to ditch and channel populations. Comparatively, pesticide and other human pressures had little correspondence with evolutionary patterns, despite hatching rate impairment associated with global anthropogenic pressure. Globally, analyses revealed high genetic variation both at neutral markers and fitness-related traits in a species used as model in ecotoxicology, providing empirical support for the need to account for genetic and evolutionary components of population response in ecological risk assessment.     

Current Status of the Availability,Development, and Use of Host Plant Resistance to Nematodes

Host plant resistance (HPR) to nematodes has been identified in many major crops and related wild germplasm. Most HPR is to the more specialized, sedentary endoparasitic genera and species, e.g., Globodera, Heterodera, Meloidogyne, Nacobbus, Rotylenchulus, and Tylenchulus. Some HPR has been developed or identified also to certain migratory endoparasites (Aphelenchoides, Ditylenchus, Pratylenchus, Radopholus) in a few hosts. Commercial use of HPR remains limited, despite its benefits to crop production when deployed appropriately. Restricted use and availability of HPR result from problems associated with transfer of resistance into acceptable cultivars. Difficulties occur in gene transfer to acceptable cultivars because of incompatibility barriers to hybridization or linkage to undesirable traits, for example in cucurbitaceous and solanaceous crops and sugarbeet. Specificity of HPR to only one species, or one or few pathotypes, as it relates to resistance durability and nematode virulence, and HPR response to abiotic factors such as high soil temperature, also limit availability and utility. A scheme for HPR development is presented to emphasize nematology research and information requirements for expanding HPR use in nematode control programs, for example in common bean, sugarbeet, and tomato. Nonbiological factors that influence HPR usage are discussed, including heavy reliance on nematicide programs, low priority of nematode HPR in many breeding programs, and insufficient breeder-nematologist collaboration.     

Variation in Aboveground Cover Influences Soil Nitrogen Availability at Fine Spatial Scales Following Severe Fire in Subalpine Conifer Forests

Following fire, fine-scale variation in early successional vegetation and soil nutrients may influence development of ecosystem structure and function. We studied conifer forests burned by stand-replacing wildfire in Greater Yellowstone (Wyoming, USA) to address two questions: (1) How do the variability and spatial structure of aboveground cover and soil nitrogen availability change during the first 4 years following stand-replacing fire? (2) At fine scales (2–20 m), are postfire soil inorganic N pools and fluxes related to aboveground cover? Aboveground cover, soil N pools, and annual net N transformations were measured from 2001 to 2004 using a spatially explicit sampling design in four 0.25-ha plots that burned during summer 2000. Within-stand variability (coefficient of variation) in postfire live vegetative cover declined with time since fire, whereas variability in bare mineral soil, charred litter and fresh litter was greatest 2-3 years postfire. The soil nitrate pool was more variable than the soil ammonium pool, but annual net nitrification was less variable than annual net N mineralization. Spatial structure (quantified by semivariograms) was observed in some aboveground cover variables (for example, graminoids and fresh litter), but there was little spatial structure in soil N variables and no obvious congruence in spatial scales of autocorrelation for soil N and aboveground cover. Significant Spearman correlations (at the sample point) indicated that aboveground cover and soil N were coupled following severe fire, and the dominant influence was from aboveground cover to soil N, rather than from soil N to vegetation. Initial patterns of fire severity and re-vegetation contributed to fine-scale heterogeneity in soil N availability for at least 4 years after severe fire.     

The Heritability of Shell Morphometrics in the Freshwater Pulmonate Gastropod Physa

The cosmopolitan freshwater pulmonate snail Physa acuta hybridizes readily with Physa carolinae in the laboratory, although their F1 progeny are sterile. The two species differ qualitatively in shell shape, the former bearing a more globose shell and the latter more fusiform. We performed a hybridization experiment, measuring a set of 14 traditional (linear) and landmark-based shell morphological variables on even-aged parents and their offspring from both hybrids and purebred control lines. Parent-offspring regression yielded a strikingly high heritability estimate for score on the first relative warp axis, h² = 0.819 ± 0.073, a result that would seem to confirm the value of geometric morphometrics as a tool for retrieving evolutionary relationships from gastropod shell form. Score on the second relative warp axis was also significantly heritable (h² = 0.312 ± 0.123), although more moderate, as were scores on second principal components extracted from traditional measurements (correlation h² = 0.308 ± 0.069, covariance h² = 0.314 ± 0.050). Although score on the first relative warp axis was significantly correlated with centroid size (p < 0.001), scores on none of the three second axes were so correlated. This result suggests that second axis score might prove especially useful for estimating genetic divergence among mixed-age populations of gastropods sampled from the field.     

Iceberg Scour and Shell Damage in the Antarctic Bivalve Laternula elliptica

We document differences in shell damage and shell thickness in a bivalve mollusc (Laternula elliptica) from seven sites around Antarctica with differing exposures to ice movement. These range from 60% of the sea bed impacted by ice per year (Hangar Cove, Antarctic Peninsula) to those protected by virtually permanent sea ice cover (McMurdo Sound). Patterns of shell damage consistent with blunt force trauma were observed in populations where ice scour frequently occurs; damage repair frequencies and the thickness of shells correlated positively with the frequency of iceberg scour at the different sites with the highest repair rates and thicker shells at Hangar Cove (74.2% of animals damaged) compared to the other less impacted sites (less than 10% at McMurdo Sound). Genetic analysis of population structure using Amplified Fragment Length Polymorphisms (AFLPs) revealed no genetic differences between the two sites showing the greatest difference in shell morphology and repair rates. Taken together, our results suggest that L. elliptica exhibits considerable phenotypic plasticity in response to geographic variation in physical disturbance.     

A Neurosecretory Phenomenon in Some Cerebral Nervous Cells of the Land Snail

Some cerebral neurosecretory cells of the land snail Helix aspersa maxima have been studied using light microscopy combined with image analysis. The amount of neurosecretion varies during the course of the day, displaying a peak at 22:00 GMT. This peak is in phasis with the maxima of the locomotor and food-intake activities recorded by means of a video apparatus.     

Direct Interaction of Otoferlin with Syntaxin 1A, SNAP-25, and the L-type Voltage-gated Calcium Channel CaV1.3

The molecular mechanisms underlying synaptic exocytosis in the hair cell, the auditory and vestibular receptor cell, are not well understood. Otoferlin, a C2 domain-containing Ca²⁺-binding protein, has been implicated as having a role in vesicular release. Mutations in the OTOF gene cause nonsyndromic deafness in humans, and OTOF knock-out mice are deaf. In the present study, we generated otoferlin fusion proteins containing two of the same amino acid substitutions detected in DFNB9 patients (P1825A in C2F and L1011P in C2D). The native otoferlin C2F domain bound syntaxin 1A and SNAP-25 in a Ca²⁺-dependent manner (with optimal 61 μm free Ca²⁺ required for binding). These interactions were greatly diminished for C2F with the P1825A mutation, possibly because of a reduction in tertiary structural change, induced by Ca²⁺, for the mutated C2F compared with the native C2F. The otoferlin C2D domain also bound syntaxin 1A, but with weaker affinity (K_d = 1.7 × 10^–5 m) than for the C2F interaction (K_d = 2.6 × 10^–9 m). In contrast, it was the otoferlin C2D domain that bound the Ca_v1.3 II-III loop, in a Ca²⁺-dependent manner. The L1011P mutation in C2D rendered this binding insensitive to Ca²⁺ and considerably diminished. Overall, we demonstrated that otoferlin interacts with two main target-SNARE proteins of the hair-cell synaptic complex, syntaxin 1A and SNAP-25, as well as the calcium channel, with the otoferlin C2F and C2D domains of central importance for binding. Because mutations in the otoferlin C2 domains that cause deafness in humans impair the ability of otoferlin to bind syntaxin, SNAP-25, and the Ca_v1.3 calcium channel, it is these interactions that may mediate regulation by otoferlin of hair cell synaptic exocytosis critical to inner ear hair cell function.Calcium is a key regulator of synaptic vesicle fusion (reviewed in Ref. 1). In mechanosensory hair cells, calcium microdomains (2) and possibly nanodomains (3) are formed when voltage-gated calcium channels open upon depolarization. Calcium at these sites is thought to activate protein interactions, leading to vesicle fusion. Some of the key players in this process are the target-SNARE² proteins, syntaxin 1A and SNAP-25, and the vesicle-SNARE, synaptobrevin (4). Vesicle-SNARE synaptotagmin 1 plays a crucial role as a calcium sensor at the neuronal synapse, modulating calcium channels and vesicle release by a Ca²⁺-dependent interaction with other SNARE proteins in the presence of lipid molecules (4–6). However, in vertebrate mechanosensory hair cells, synaptotagmin 1 is not detected (7). Instead, fast neurotransmitter release in auditory and vestibular hair cells, facilitated largely by an L-type voltagegated calcium channel, Ca_v1.3 (8, 9), is thought to be modulated by a newly discovered protein, otoferlin, acting as the Ca²⁺ sensor and vesicle-binding protein. When mutated, otoferlin causes DFNB9 nonsyndromic deafness (10). Gene sequences of different deaf families show that the OTOF gene can undergo mutation at multiple locations (11–13). Recently, it has been demonstrated that otoferlin is necessary for synaptic exocytosis from hair cells (14). Further, an engineered mutation in the C2B domain of otoferlin has been shown to cause deafness in mice (15). However, the precise function of otoferlin as a synaptic protein is not well understood.Specific mutations in the otoferlin C2F (P1825A) or C2D (L1011P) domains in humans have been documented to cause DFNB9 deafness (11, 12). Previous studies suggested that a region of otoferlin containing all three C2 domains, D, E, and F, binds directly to the t-SNARE molecules syntaxin 1A and SNAP-25 in response to an increase in Ca²⁺ concentration (14). However, it is not understood how a single amino acid substitution in one domain of otoferlin, such as C2F (11) or C2D (12), might independently lead to deafness. Here, we examine the role of otoferlin as a Ca²⁺ sensor as well as a facilitator of vesicle fusion, as indicated by protein-protein interactions and their [Ca²⁺] dependence.     

Optimization of Mitochondrial DNA-based Hybridization Assays to Diagnostics in Soil

Nucleic acid hybridization among root-knot nematode mitochondrial DNAs can be used to identify several Meloidogyne species. Research was initiated to optimize mitochondrial DNA-based molecular diagnostics for the demanding environments likely to be encountered in field isolates. DNA hybridization using reconstituted DNA-soil mixtures revealed a loss of assay sensitivity ranging from 34% to 92% with four agronomic soils tested. This problem was alleviated by the addition of exogenously added DNA. Variation in nematode egg lysis procedures also affected hybridization efficiency, with NaOC1 treatment most effective at disrupting Meloidogyne eggs. These optimized conditions permit detection of mtDNA released from one to five Meloidogyne eggs using standard nucleic acid hybridization procedures.     

Streptococcus pyogenes c-di-AMP Phosphodiesterase,GdpP, Influences SpeB Processing and Virulence

Small cyclic nucleotide derivatives are employed as second messengers by both prokaryotes and eukaryotes to regulate diverse cellular processes responding to various signals. In bacteria, c-di-AMP has been discovered most recently, and some Gram-positive pathogens including S. pyogenes use this cyclic nucleotide derivative as a second messenger instead of c-di-GMP, a well-studied important bacterial second messenger. GdpP, c-di-AMP phosphodiesterase, is responsible for degrading c-di-AMP inside cells, and the cellular role of GdpP in S. pyogenes has not been examined yet. To test the cellular role of GdpP, we created a strain with a nonpolar inframe deletion of the gdpP gene, and examined the properties of the strain including virulence. From this study, we demonstrated that GdpP influences the biogenesis of SpeB, the major secreted cysteine protease, at a post-translational level, susceptibility to the beta lactam antibiotic ampicillin, and is necessary for full virulence in a murine subcutaneous infection model.     

Conservation Status of a Recently Described Endemic Land Snail,Candidula coudensis,from the Iberian Peninsula

We assessed the distribution, population size and conservation status of Candidula coudensis, a recently described endemic land snail from Portugal. From March 2013 to April 2014, surveys were carried out in the region where the species was described. We found an extent of occurrence larger than originally described, but still quite small (13.5 km²). The species was found mainly in olive groves, although it occurred in a variety of other habitats with limestone soils, including grasslands, scrublands and stone walls. Minimum population estimate ranged from 110,000–311,000 individuals. The main identified potential threats to the species include wildfires, pesticides and quarrying. Following the application of IUCN criteria, we advise a conservation status of either “Least Concern” or “Near-threatened” under criterion D (restricted population).     

Oviposition Behavior and Offspring Emergence Patterns in Succinea thaanumi, an Endemic Hawaiian Land Snail

In this field study, newly laid egg clutches of Succinea thaanumi, an endemic Hawaiian land snail, were labeled and observed weekly over a 12‐mo period. Snails usually laid their clutches under leaf tips and, moreover, this placement affected snail emergence by mitigating the effects of dehydration through the leaf‐drip phenomenon. During droughts, the gel surrounding egg clutches dehydrated, pasting the embryos to the backs of leaves. The hygroscopic gel rehydrated once rains resumed. The majority of newly laid clutches contained shell‐less embryos which required more time for emergence than embryos laid with visible shells. More shelled embryos were laid subsequent to a 3‐wk drought, indicating that snails retained their eggs during adverse environmental conditions and laid them when conditions improved. The snails’ abilities to retain eggs in adverse conditions, but to lay more unshelled embryos over their lifetimes, contributed to their overall reproductive success.     

Response to Phosphorus Limitation Varies among Lake Populations of the Freshwater Snail Potamopyrgus antipodarum

Local adaptation – typically recognized as higher values of fitness-related traits for native vs. non-native individuals when measured in the native environment - is common in natural populations because of pervasive spatial variation in the intensity and type of natural selection. Although local adaptation has been primarily studied in the context of biotic interactions, widespread variation in abiotic characteristics of environments suggests that local adaptation in response to abiotic factors should also be common. Potamopyrgus antipodarum, a freshwater New Zealand snail that is an important model system for invasion biology and the maintenance of sexual reproduction, exhibits local adaptation to parasites and rate of water flow. As an initial step to determining whether P. antipodarum are also locally adapted to phosphorus availability, we examined whether populations differ in their responses to phosphorus limitation. We found that field-collected juvenile P. antipodarum grew at a lower rate and reached an important size threshold more slowly when fed a relatively low vs. a relatively high- phosphorus diet. We also detected significant across-population variation in individual growth rate. A marginally significant population-by-dietary phosphorus interaction along with a two-fold difference across populations in the extent of suppression of growth by low phosphorus suggests that populations of P. antipodarum may differ in their response to phosphorus limitation. Local adaptation may explain this variation, with the implication that snails from lakes with relatively low phosphorus availability should be less severely affected by phosphorus limitation than snails from lakes with higher phosphorus availability.     

Influence of Soil Temperature on Meloidogyne incognita Resistant and Susceptible Cotton,Gossypium hirsutum

The degree of resistance by a cotton plant to Meloidogyne incognita is affected by soil temperature, particularly in moderately resistant cultivars, The total number of nematodes in the resistant and moderately resistant rools at 35 C was equal to, or greater than, the number in susceptible roots at 20, 25, or 30 C. A shift in numbers to developing and egg-bearing forms of nematodes in the susceptible cultivar as tentperature increased indicates development was affected by temperature rather than by genetic resistance mechanisms. However, the nematode resistant cultivar did not support maturation of nematodes until a soil tempurature of 35 C was attained. This indicated that resistance mechanisms are partially repressed at 35 C and differences in nematode development cannot be explained in terms of accumulated heat units. The moderately resistant cultivar was significantly more sensitive to the effects of high temperature than was the resistant cultivar.