Community‐wide changes in intertaxonomic temporal co‐occurrence resulting from phenological shifts

Global climate change is known to affect the assembly of ecological communities by altering species' spatial distribution patterns, but little is known about how climate change may affect community assembly by changing species' temporal co‐occurrence patterns, which is highly likely given the widely observed phenological shifts associated with climate change. Here, we analyzed a 29‐year phenological data set comprising community‐level information on the timing and span of temporal occurrence in 11 seasonally occurring animal taxon groups from 329 local meteorological observatories across China. We show that widespread shifts in phenology have resulted in community‐wide changes in the temporal overlap between taxa that are dominated by extensions, and that these changes are largely due to taxa's altered span of temporal occurrence rather than the degree of synchrony in phenological shifts. Importantly, our findings also suggest that climate change may have led to less phenological mismatch than generally presumed, and that the context under which to discuss the ecological consequences of phenological shifts should be expanded beyond asynchronous shifts.     

Gating current harmonics. I. Sodium channel activation gating in dynamic steady states.

Internally perfused and pronase-treated giant axons were prepared for gating current measurements. Gating current records were obtained under large-amplitude sinusoidal voltage clamp after allowing for settling times into dynamic steady states. The current records were analyzed as functions of the mean membrane potential of the test sinusoid for which the amplitude and frequency were held constant. The nonlinear analysis consisted of determining the harmonic content (amplitudes and phases) of the distorted periodic current records. The most pronounced feature found in the analysis is a dominant second harmonic centered at Emean = +10 mV. A number of other characteristic harmonic behaviors were also observed. The harmonics tend to die away for very small (less than -60 mV) and very large (greater than +72 mV) values of Emean. The harmonic behavior seen in the axonal data is basically different from that seen in gating current simulations generated by the sodium-activation kinetics of standard models, including the Hodgkin-Huxley model. Some of the differences can be reconciled without requiring fundamental changes in the model kinetic schemes. However, the dominant harmonic feature seen in the axonal data cannot be reconciled with the model kinetics without a fundamental change in the models. The axonal data suggest two moving molecular components with independent degrees of freedom whose properties are outlined on the basis of the data presented herein.     

Sodium ionic and gating currents in mammalian cells

Ionic and gating currents from voltage-gated sodium channels were recorded in mouse neuroblastoma cells using the path-clamp technique. Displacement currents were measured from whole-cell recordings. The gating charge displaced during step depolarizations increased with the applied membrane potential and reached saturating levels above 20 mV Prolonged large depolarizations produced partial immobilization of the gating charge, and only about one third of the displaced charge was quickly reversed upon return to negative holding potentials. The activation and inactivation properties of macroscopic sodium currents were characterized by voltage-clamp analysis of large outside-out patches and the single-channel conductance was estimated from nonstationary noise analysis. The general properties of the sodium channels in mouse neuroblastoma cells are very similar to those previously reported for various preparations of invertebrate and vertebrate nerve cells. Offprint requests to: O. Moran     

Responses of insects to the current climate changes: from physiology and behavior to range shifts

Climate change (first of all the rise in temperature) is currently considered one of the most serious global challenges facing mankind. Here we review the diversity of insect responses to the current climate warming, with particular focus on true bugs (Heteroptera). Insects as ectotherms are bound to respond to the temperature change, and different species respond differently depending on their specific physiological and ecological traits, seasonal cycle, trophic relations, etc. Insect responses to climate warming can be divided into six categories: changes in (1) ranges, (2) abundance, (3) phenology, (4) voltinism, (5) morphology, physiology, and behavior, and (6) relationships with other species and in the structure of communities. Changes in ranges and phenology are easier to notice and record than other responses. Range shifts have been reported more often in Lepidoptera and Odonata than in other insect orders. We briefly outline the history and eco-physiological background of the recent range limit changes in the Southern green stink bug Nezara viridula (Heteroptera, Pentatomidae) in central Japan. Range expansion in individual species can lead to enrichment of local faunas, especially at high latitudes. Phenological changes include not only advances in development in spring but also shifts in phenology later in the season. The phenophases related to the end of activity usually shift to later dates, thus prolonging the period of active development. This may have both positive and negative consequences for the species and populations. As with any other response, the tendencies in phenological changes may vary among species and climatic zones. The proven cases of change in voltinism are rare, but such examples do exist. Application of models based on thermal parameters of development suggests that a rise in temperature by 2°C will result in an increased number of annual generations in many species from different arthropod taxa (up to three or four additional generations in Thysanoptera, Aphidoidea, and Acarina). The warming-mediated changes in physiology, morphology, or behavior are difficult to detect and prove, first of all because of the absence of reliable comparative data. Nevertheless, there are examples of changes in photoperiodic responses of diapause induction and behavioral responses related to search of shelters for summer diapause (aestivation). Since (1) individual species do not exist in isolation and (2) the direction and magnitude of responses even to the same environmental changes vary between species, it may be expected that in many cases the current stable relationships between species will be affected. Thus, unequal range shifts in insects and their host plants may disrupt their trophic interactions near the species?? range boundaries. Studies of responses to climate warming in more than one interrelated species or in entire communities are extremely rare. The loss of synchronism in seasonal development of community members may indicate inability of the higher trophic levels to adapt fully to climate warming or an attempt of the lower trophic level to escape from the pressure of the higher trophic levels. It is generally supposed that many insect species in the Temperate Climate Zone will benefit in some way from the current climate warming. However, there is some experimental evidence of an opposite or at least much more complex response; the influence of warming might be deleterious for some species or populations. It is suggested that species or populations from the cold or temperate climate have sufficient phenotypic plasticity to survive under the conditions of climate warming, whereas species and populations which already suffer from stress under extreme seasonal temperatures in warmer regions may have a limited ??maneuver space?? since the current temperatures are close to their upper thermal limits. Without genetic changes, even moderate warming will put these species or populations under serious physiological stress. The accumulated data suggest that responses of insects and the entire biota to climate warming will be complex and will vary depending on the rate of warming and ecological peculiarities of species and regions. Physiological responses will vary in their nature, direction, and magnitude even within one species or population, and especially between seasons. The responses will also differ in different seasons. For example, warming may negatively affect nymphal development during the hot season but at the same time accelerate growth and development during the cold season and/or ensure milder and more favorable overwintering conditions for adults. All these factors will affect population dynamics of particular species and relationships among the members of ecosystems. We should keep in mind that (1) not only selected insect species but almost all the species will be affected, (2) temperature is not the only component of the climatic system that is changing, and (3) responses will be different in different seasons. Host plants, phytophagous insects, their competitors, symbionts, predators, parasites, and pathogens will not only respond separately to climate changes; individual responses will further affect the responses of other species, thus making reliable prediction extremely complicated. Responses are expected to (1) be species- or population-specific, (2) concern basically all the aspects of organism/ species biology and ecology (individual physiology, population structure, abundance, local adaptations, phenology, voltinism, and distribution), and (3) occur at scales ranging from an undetectable cellular level to major distribution range shifts or regional extinctions. The scale of insect responses will depend on the extent and rate of climate warming. Slight to moderate warming may cause responses only in a limited number of species with more flexible life cycles, whereas a substantial increase in temperature may affect a greater number of different species and ecological groups.     

Sodium channel gating currents in frog skeletal muscle

Charge movements similar to those attributed to the sodium channel gating mechanism in nerve have been measured in frog skeletal muscle using the vaseline-gap voltage-clamp technique. The time course of gating currents elicited by moderate to strong depolarizations could be well fitted by the sum of two exponentials. The gating charge exhibits immobilization: at a holding potential of -90 mV the proportion of charge that returns after a depolarizing prepulse (OFF charge) decreases with the duration of the prepulse with a time course similar to inactivation of sodium currents measured in the same fiber at the same potential. OFF charge movements elicited by a return to more negative holding potentials of -120 or -150 mV show distinct fast and slow phases. At these holding potentials the total charge moved during both phases of the gating current is equal to the ON charge moved during the preceding prepulse. It is suggested that the slow component of OFF charge movement represents the slower return of charge "immobilized" during the prepulse. A slow mechanism of charge immobilization is also evident: the maximum charge moved for a strong depolarization is approximately doubled by changing the holding potential from -90 to -150 mV. Although they are larger in magnitude for a -150-mV holding potential, the gating currents elicited by steps to a given potential have similar kinetics whether the holding potential is -90 or -150 mV.     

Neuromediator shifts in the peripheral blood of dogs resulting from negative emotiogenic exposure

The analysis of negative emotiogenic influence in dogs carried out according to dynamics of levels of acetylcholine and catecholamine content in peripheral blood and concomitant changes of the higher nervous activity, allows to conclude about the participation of both cholinergic and catecholaminergic neurotransmitter systems in reactions to this influence with a relative predominance of the first one. In animals with decreased reactivity and with compensatory abilities of the cholinergic system, the same influence leads to enhancement of the specific significance of the reaction of the catecholaminergic system, and especially of its transmitter, noradrenergic component.     

A plant Shaker-like K+ channel switches between two distinct gating modes resulting in either inward-rectifying or "leak" current

Among the Shaker-like plant potassium channels, AKT2 is remarkable because it mediates both instantaneous "leak-like" and time-dependent hyperpolarisation-activated currents. This unique gating behaviour has been analysed in Xenopus oocytes and in COS and Chinese hamster ovary cells. Whole-cell and single-channel data show that (i) AKT2 channels display two distinct gating modes, (ii) the gating of a given AKT2 channel can change from one mode to the other and (iii) this conversion is under the control of post-translational factor(s). This behaviour is strongly reminiscent of that of the KCNK2 channel, recently reported to be controlled by its phosphorylation state.     

Missed medical appointments during shifts to and from daylight saving time

Transitions into and out of Daylight Saving Time (DST) can provide insights into how a minor change to a regular sleep–wake cycle can inadvertently affect health. We examined the relationship between DST and missed medical appointments. Using a large dataset, the proportion of missed appointments were examined prior and post spring and autumn clock changes. As predicted, the number of missed medical appointments significantly increased following the spring (forward) clock change and the week of the clock change. This trend was reversed following the transition out of DST. The implications of scheduling appointments around DST to increase attendance are discussed.     

Patterns of accumulation resulting from Taxes and changes in motility of micro-organisms

Summary An analysis is made of the development of patterns of accumulation of micro-organisms, as governed by tactic responses, changes in motility, and the effects of diffusion.When a soluble crystal is placed in a suspension of micro-organisms, the first manifestation is the development of a clear zone surrounding the crystal. This effect is a physical one, produced by a transfer of momentum from the solute molecules to the organisms.As the solute spreads and its boundary moves more slowly, the organisms are distributed in patterns which depend upon the occurrence of tactic responses and the influence of the solute upon motility. A congregation in the zone occupied by the solute can correspond either to a positive chemotaxis or to an inhibition of motility by the solute. Conversely, a withdrawal from the solute can signal either a negative chemotaxis or an enhancement of motility by the solute.The proper interpretation of the patterns described in Figs. 10 and 11 requires a microscopic study of individual organisms, in which the effect of the reagent upon motility is noted.     

Regime shifts and heterogeneous trends in malaria time series from Western Kenya Highlands

Large malaria epidemics in the East African highlands during the mid and late 1990s kindled a stream of research on the role that global warming might have on malaria transmission. Most of the inferences using temporal information have been derived from a malaria incidence time series from Kericho. Here, we report a detailed analysis of 5 monthly time series, between 15 and 41 years long, from West Kenya encompassing an altitudinal gradient along Lake Victoria basin. We found decreasing, but heterogeneous, malaria trends since the late 1980s at low altitudes (<1600 m), and the early 2000s at high altitudes (>1600 m). Regime shifts were present in 3 of the series and were synchronous in the 2 time series from high altitudes. At low altitude, regime shifts were associated with a shift from increasing to decreasing malaria transmission, as well as a decrease in variability. At higher altitudes, regime shifts reflected an increase in malaria transmission variability. The heterogeneity in malaria trends probably reflects the multitude of factors that can drive malaria transmission and highlights the need for both spatially and temporally fine-grained data to make sound inferences about the impacts of climate change and control/elimination interventions on malaria transmission.     

When similar ecological patterns in time emerge from different initial conditions: equifinality in the breeding performance of animal populations

In many behavioural, ecological and evolutionary trade-offs, patterns and trends, the same/similar outcomes are often expected from the different initial conditions. One of the most frequently encountered problems in ecology is how to disentangle two or more different hypotheses possibly explaining the emergence of an ecological pattern based on limited data that would fit both. Using previously published interaction patterns between floaters and breeders of an eagle population (Penteriani et al., 2006), it was possible to detect and to find an explanation to the singular case of the emergence of a similar ecological pattern under two very different scenarios, that is when different factors are affecting the intrinsic dynamic of a population.     

Possible origin of gating current in nerve membrane.

The present information about gating current observed in squid giant axons points towards the distinct possibility of the current arising from the Debye relaxation of the carboxyl groups in the side chains of the globular proteins enclosing the ionic channels. These carboxyl groups form dipole chains stretching across the membrane. A dipole model is constructed to study the relaxation process under the assumption that the relaxation time tau of the dipoles is modified by dipole-dipole interaction. This model explains qualitatively some of the features of the asymmetric gating current, but is not indicative of any specific mechanism leading to the opening of the gates in the ionic channels. We speculate that the conformational change in the protein globules as a result of dipole reorientation would be the key to the mystery.     

Computation of axon gating currents from dipole moment changes in channel subunits.

The gating polarizational currents were computed on the basis of the dipole moment changes occurring in nerve membrane ionic channel subunits. Membrane thickness and surface density of channels were the only parameters used in addition to the Hodgkin-Huxley model. The gating currents computed for membrane potentials where the Hodgkin-Huxley empirical formulae are reliable were found to be in good agreement with the available experimental data. It is demonstrated that the gating currents of the n and h subunits are responsible for the late slowly decaying gating currents.