Effect of selected marine and freshwater microalgae on development and survival of the mosquito <Emphasis Type="Italic">Aedes aegypti</Emphasis>

We isolated and identified strains of marine and freshwater planktonic and benthic microalgae from the vicinity of Indian River County, Florida (≈27.5°N, 80.34°W), cultivated them in batch culture, and examined their allelopathic activity against mosquito larvae. Additional algal material was obtained from Syracuse University and the University of Texas—Austin Algal Culture Collection. Mosquito larvae (Aedes aegypti (L.)) from colonies maintained at the Florida Medical Entomology Laboratory were challenged with the microalgae using log-growth phase and senescent-phase cultures. Appropriate controls (no algae) were used for each treatment. There were no significant differences in development time between treatments across all trials and a few significant treatment effects on development times, mortality, or mosquito size in the individual trials; however, there was a tendency for treatments with senescent microalgae to develop faster than controls with no algae. Effects consistent with algal toxicity included the two trials with Microcystis aeruginosa, where the larvae exposed to the strain-producing microcystin had significantly longer development times than the controls or those grown with the non-microcystin-producing strain, and the trial with the dinoflagellate Akashiwo sanguinea, where larvae exposed to this species had significantly higher mortality than the controls. No consistent patterns or differences between experimental and control treatments in the value of λ′, an estimate of the population finite rate of increase, were discernible from the data.     

Persistence of Toxic Activity and Recycling of Bacillus thuringiensis var. israelensis in Cold Water: Field Experiments Using Diffusion Chambers in a Pond

The persistence of the larvicidal activity of Bacillus thuringiensis var. israelensis (Bti) was tested over a five-month period in a low-temperature aquatic environment. Diffusion chambers filled with a suspension of Bti (100 mg l - 1) and different experimental substrates (pond water, periphyton, sediments and vegetation), but without mosquito larvae, were placed near the bottom of a large pond and removed at various intervals to measure residual toxic activity to mosquito larvae, spore concentration and proteolytic activity. Within the pond water substrate, 50% of the initial toxicity was still present after one month in cold water, while with the periphyton substrate, 30% remained in the liquid fraction after the same period of exposure. Within the vegetation substrate (blue-joint grass, Calamagrostis canadensis), an average of 30% of the initial toxicity was still present in the liquid fraction between day 84 to day 154. Solid fractions of vegetation became toxic very early and remained toxic for five months. At the end (day 154), there was still 54% of the original toxic activity put in the chambers associated with the vegetation samples. In the absence of mosquito larvae, spore recycling was observed in the chambers especially with sediments and vegetation. But spore recycling did not appear to play a major role in the observed persistence, but rather rapid absorption onto vegetation substrates was responsible for the persistence of Bti in a cold climate.     

Elemental and biochemical composition of<Emphasis Type="Italic"> Nephrops norvegicus</Emphasis> (Linnaeus 1758) larvae from the Mediterranean and Irish Seas

The Norway lobster, Nephrops norvegicus, is a commercially exploited decapod which is widely distributed throughout the north-eastern Atlantic and the Mediterranean Sea. Ovigerous females originating from the Mediterranean and the Irish Seas were held in the laboratory until larvae hatched. Biomass and biochemical composition, as well as digestive gland structure, were examined in newly hatched larvae from these two regions. In addition, previously published data from a North Sea population were included in our comparison. Elemental analyses showed that the absolute quantities of dry mass (DM), carbon (C), nitrogen (N) and hydrogen (H) (collectively referred to as CHN) per individual, and the C:N mass ratios, were significantly lower, while the relative CHN, protein and lipid values (in % of DM) were higher in samples from the Irish Sea compared to larvae originating from either the Mediterranean or the North Sea. As in CHN, the absolute level of protein per individual was higher in larvae from the Mediterranean, while no significant differences were observed in the individual lipid contents. Likewise, the digestive gland structure at hatching did not show any differences between study areas. Intraspecific variability in biomass and chemical composition of newly hatched larvae from different regions may be related to differential patterns of reproduction in regions with different climatic conditions. Lobster larvae hatch in the Mediterranean Sea predominantly in winter when both water temperature and planktonic food availability are at a minimum, while hatching in the Irish Sea occurs under more favourable conditions in spring. Hence, significantly higher wet mass, dry mass and protein values in Mediterranean larvae may represent adaptive traits allowing for early posthatching survival and development under food-limited conditions in an oligotrophic environment.Communicated by H.-D. Franke     

The circadian locomotor rhythm of Hemideina thoracica (Orthoptera; Stenopelmatidae): the circadian clock as a population of interacting oscillators

ABSTRACT. The behaviour of the circadian locomotor rhythm of the New Zealand weta, Hemideina thoracica (White), supports the model that the underlying pacemaker consists of a population of weakly coupled oscillators. Certain patterns of locomotor activity, previously demonstrated almost exclusively in vertebrates, are presented here as evidence for the above hypothesis. They include after-effects of various pre-treatments, rhythm-splitting and spontaneous changes in the rhythm. After-effects, which describe the unstable behaviour of free-running circadian rhythms following particular experimental perturbations, have been observed in Hemideina following single light pulses, constant dim light, and laboratory and natural entrainment. Period changes occurred in the activity rhythm after single light pulses of 8-h and 12-h duration (25 lx). Constant dim light (0.1 lx) increased the free-running period (τ) of the activity rhythm, but the after-effect of constant dim light was either an increase or a decrease in τ. After-effects upon both τ and the active phase length of the activity rhythm were found following non-24-h light entrainment cycles with 8-h and 12-h light phases of 25 lx. Qualitative measurements of these after-effects upon τ are presented which reveal a relationship between both the direction and amount of change in τ, and the difference between entrainment cycle length (T) and pre-entrainment free-running period. The after-effect of natural entrainment was an initial short-period free-run (τ < 24h) lasting 5–10 days, generally followed by a rapid period lengthening to τ= 25–26 h. Support for the population model was provided by spontaneous dampening, recovery, and period changes of the rhythm, together with the disruption of the active phase following critical light perturbations, and rhythm-splitting. These Hemideina results are compared with the simulations of the Coupled Stochastic System of Enright (1980).     

Synchronous spawning in a recently established population of the zebra mussel,Dreissena polymorpha,in western Lake Erie,USA

Seasonal patterns of reproduction in a newly established population of Dreissena polymorpha are described for a site in the western basin of Lake Erie. Reproduction was monitored by histological examination of gonads, analysis of shell length-dry weight relationships, and following abundance of planktonic and settling larvae. Patterns of planktonic larval abundance and settling showed a distinct bimodal pattern in July and August, but conflicted with histological and length-dry weight data that showed spawning was a brief, highly synchronous event occurring in late August. Differences between histological data and abundance of larvae in the plankton can be explained as resulting from drift of larvae from disjunct populations of D. polymorpha which spawned earlier, into the study area. Veliger larvae were present in the plankton at low densities throughout the warm months before and after periods of peak abundances. The presence of these larvae can be explained by a combination of asynchronous spawning among local populations and postponed settlement by planktonic larvae.     

Polymorphism in developmental mode and its effect on population genetic structure of a spionid polychaete, Pygospio elegans

Population genetic structure of sedentary marine species is expected to be shaped mainly by the dispersal ability of their larvae. Long-lived planktonic larvae can connect populations through migration and gene flow, whereas species with nondispersive benthic or direct-developing larvae are expected to have genetically differentiated populations. Poecilogonous species producing different larval types are ideal when studying the effect of developmental mode on population genetic structure and connectivity. In the spionid polychaete Pygospio elegans, different larval types have been observed between, and sometimes also within, populations. We used microsatellite markers to study population structure of European P. elegans from the Baltic Sea (BS) and North Sea (NS). We found that populations with planktonic larvae had higher genetic diversity than did populations with benthic larvae. However, this pattern may not be related to developmental mode, since in P. elegans, developmental mode may be associated with geography. Benthic larvae were more commonly seen in the brackish BS and planktonic larvae were predominant in the NS, although both larval types also are found from both areas. Significant isolation-by-distance (IBD) was found overall and within regions. Most of the pair-wise F(ST) comparisons among populations were significant, although some geographically close populations with planktonic larvae were found to be genetically similar. However, these results, together with the pattern of IBD, autocorrelation within populations, as well as high estimated local recruitment, suggest that dispersal is limited in populations with planktonic larvae as well as in those with benthic larvae. The decrease in salinity between the NS and BS causes a barrier to gene flow in many marine species. In P. elegans, low, but significant, differentiation was detected between the NS and BS (3.34% in AMOVA), but no clear transition zone was observed, indicating that larvae are not hampered by the change in salinity.     

云斑尖塘鳢仔鱼摄食节律的研究

对自然光照条件下云斑尖塘鳢仔鱼的昼夜摄食节律和在夜间增加不同强度外光源条件下仔鱼的摄食发生率进行了研究。结果表明,云斑尖塘鳢仔鱼具有明显的昼夜摄食节律,晚上摄食发生率是著高于白天,其摄食主要集中在光线较弱的16:00～00:00;5日龄仔鱼在100～500Lx,8日龄和12日龄仔鱼在10～100Lx光照条件下的摄食发生率要明显高于黑暗或更高光照条件下的摄食发生率。     

THE GENETIC BASIS OF LIFE-HISTORY CHARACTERS IN A POLYCHAETE EXHIBITING PLANKTOTROPHY AND LECITHOTROPHY

The polychaete Streblospio benedicti is unusual in that several field populations consist of individuals that exhibit either planktotrophic or lecithotrophic larval development. Planktotrophy in this species involves production of many small ova that develop into feeding larvae with a two- to three-week planktonic period. Lecithotrophy involves production of fewer, larger ova that develop into nonfeeding larvae that are brooded longer and have a brief planktonic stage. Reciprocal matings were performed to investigate genetic variance components and the correlation structure of life-history traits associated with planktotrophy and lecithotrophy. Our objective was to better understand persistence of this developmental dichotomy in Streblospio benedicti, and among marine invertebrates in general. Substantial additive genetic variation (75–98% of total) was detected for the following characters at first reproduction: female length; position of the first gametogenic setiger and first brood pouch; ovum diameter; three traits related to fecundity (numbers of ova per ovary, larvae per brood pouch, and larvae per brood); median larval planktonic period and the presence of larval swimming setae; but not for total number of brood pouches; larval length; larval feeding; and larval survivorship. Based on the unusual geographic distribution of development modes in this species, we hypothesize that the developmental traits have evolved in allopatry and have only recently come into contact in North Carolina. The high additive contribution to variance observed for many traits may be inflated due to (a) nonrandom breeding in nature, and (b) examination of only one component of an age-structured population at one time. Nuclear interaction variance and maternal variance accounted for 84% of the total variation in larval survivorship. This observation supports other empirical studies and theoretical predictions that nonadditive components of variance will increase in importance in individual traits that are most closely tied to fitness. A network of life-history trait correlations was observed that defines distinct planktotrophic and lecithotrophic trait complexes. Negative genetic correlations were present between fecundity and egg size, between fecundity and position of the first gametes, and between larval survivorship and median planktonic period. Positive genetic correlations were detected between fecundity and female size at first reproduction and between planktonic period and the presence of swimming setae. Intergenerational product-moment correlations were negative for larval length and fecundity, planktonic period and egg size, female size and larval survivorship, and fecundity and larval survivorship. If the genetic correlation structure observed in the laboratory persists in the field, it may constrain responses of individual characters to directional selection, and indirectly perpetuate the dichotomies associated with planktotrophy and lecithotrophy.     

Analysis of brood development in the ant Amblyopone silvestrii, with special reference to colony bionomics

There are five larval instars in the temperate, subterranean ponerine ant, Amblyopone silvestrii (Wheeler). An examination of the seasonal developmental patterns of immatures collected from more than 100 colonies collected in the field revealed that most or all of the newly hatched individuals overwintered as second to fifth instar larvae and emerged as adults in the next summer. The fifth instar larvae were most abundant in the colony's larval population all year round. The number of eggs present in the nest diminished temporarily in midsummer, although queens collected during this period maintained fully developed ovaries with mature oocytes. When the larvae matured, they were usually moved to temporary nests away from the nest area of the colony and finished pupation and eclosion there, while accompanied by a small number of workers. Pupation of sexuals occurred in the more distant cocoon chambers compared with pupation of workers.     

Temporal Organization in Locomotor Activity of the Hypogean Loach, Nemacheilus Evezardi, and its Epigean Ancestor

Locomotor activity rhythm in the hypogean population of Nemacheilus evezardi was recorded first under light-to-dark (LD) 12 : 12 h cycle and then DD. The results were compared with that of its epigean counterpart held under comparable regimes. In LD 12 : 12, while hypogean loach exhibited a distinct bimodality in its locomotor activity rhythm, it was altogether absent in the case of epigean population. In hypogean loach, dark-to-light transition peak in LD was observed to free-run under DD. The same was not discernible in case of epigean loach. The locomotor activity rhythm in epigean fish was noticed to free-run in DD either from the dawn peak or dusk peak in LD. It is hypothesized that the hypogean fish still possesses a functional oscillator underlying its overt circadian rhythm in locomotor activity. The ecophysiological significance of these findings is yet to be fully understood.     

A circadian rhythm in spontaneous locomotor activity in the larvae and pupae of the mosquito, Culiseta incidens

ABSTRACT. The spontaneous locomotor activity of the larvae of Culiseta incidens was monitored with acoustic actographs. Individuals, in water resting on the cones of the speakers, displayed an activity rhythm in LD 12:12 with peak activity in the light phase. A similar rhythm occurred in DD following rearing in either LD 12:12 or LL, with free-running periods of 23.5–24 h. No evidence was found of any consistent differences between the periods of the larvae and pupae. The amplitude of the pupal rhythm gradually increased as metamorphosis progressed. It is suggested that rhythmicity might also be found in those behavioural responses of mosquito larvae and pupae which have been the subject of previous studies.     

Lack of gas bladder inflation by the larvae of zebrafish in the absence of an air-water interface

Compared to a control gas bladder inflation rate of 95·1±1·9%, zebrafish Danio rerio larvae 72 h post-fertilization maintained in closed chambers had an inflation rate of just 19·1±7·7%. Larval survivorship through 10 days in closed chambers (32%) was significantly less than that in open chambers (76%), and the extent of spinal curvature was significantly higher among larvae maintained in closed chambers. Larvae which failed to inflate their gas bladder showed very little change in body length, and had a final dry weight c. 14% of that for control larvae. The small number of larvae with inflated gas bladders found in closed chambers might be attributed to the inadvertent introduction of small bubbles into two replicates. These results indicate that access to an air-water interface is critical for the normal development of zebrafish larvae, but also that a small, submerged, spherical gas volume may to a limited extent be used for initial gas bladder inflation.     

A hemicord locomotor network of excitatory interneurons: a simulation study

Locomotor burst generation is simulated using a full-scale network model of the unilateral excitatory interneuronal population. Earlier small-scale models predicted that a population of excitatory neurons would be sufficient to produce burst activity, and this has recently been experimentally confirmed. Here we simulate the hemicord activity induced under various experimental conditions, including pharmacological activation by NMDA and AMPA as well as electrical stimulation. The model network comprises a realistic number of cells and synaptic connectivity patterns. Using similar distributions of cellular and synaptic parameters, as have been estimated experimentally, a large variation in dynamic characteristics like firing rates, burst, and cycle durations were seen in single cells. On the network level an overall rhythm was generated because the synaptic interactions cause partial synchronization within the population. This network rhythm not only emerged despite the distributed cellular parameters but relied on this variability, in particular, in reproducing variations of the activity during the cycle and showing recruitment in interneuronal populations. A slow rhythm (0.4–2 Hz) can be induced by tonic activation of NMDA-sensitive channels, which are voltage dependent and generate depolarizing plateaus. The rhythm emerges through a synchronization of bursts of the individual neurons. A fast rhythm (4–12 Hz), induced by AMPA, relies on spike synchronization within the population, and each burst is composed of single spikes produced by different neurons. The dynamic range of the fast rhythm is limited by the ability of the network to synchronize oscillations and depends on the strength of synaptic connections and the duration of the slow after hyperpolarization. The model network also produces prolonged bouts of rhythmic activity in response to brief electrical activations, as seen experimentally. The mutual excitation can sustain long-lasting activity for a realistic set of synaptic parameters. The bout duration depends on the strength of excitatory synaptic connections, the level of persistent depolarization, and the influx of Ca²⁺ ions and activation of Ca²⁺-dependent K⁺ current.     

Rhythmic signalling and entrainment inVespa orientalis larvae: Characterization of the underlying interactions

Rhythmic “circa-second” contrations of larvae of the hornetVespa orientalis, believed to serve as hunger signals, were studied. A considerable degree of coordination among individual larvae, both in frequency and phase of these contractions, has been observed. The oscillations of singly isolated larvae are of short duration, non-constant, with increasing intervals in between and there is a substantial variability in the patterns shown by different larvae. In contrast, the association of two or more larvae leads to enhancement of their periodic behaviour and to (partial) entrainment. Communication among larvae may perhaps be mediated by the sound pulses (“scratching” noises) which are generated by these contractions. We have subjected individual and grouped larvae to external sound pulses and were able to demonstrate: (a) enhancement of rhythmic activity; (b) phase resetting; (c) entrainment to an external oscillator within a range of frequencies; (d) the existence of a subharmonic mode of entrainment. We propose a simple phenomenologic model to account for these larvae responses. Our model assumes the existence of an “energy” variable which declines with time but is upgraded, in a phase-dependent way, by external stimuli. Based in part on work performed by V. Barenholz-Paniry in partial fulfillment of the requirements for the M.Sc. degree from the Sackler Faculty of Medicine, Tel Aviv University, 1986.     

心肌单细胞兴奋模式转迁规律和转迁过程中延迟后去极化、早后去极化的生成

实验观察了培养心肌单细胞自发性兴奋节律的不同模式以及兴奋模式的转迁规律。结果表明,单细胞在正常灌流条件下可处于不同的兴奋状态,产生不同的兴奋节律,包括延迟后去极化、早后去极化现象。不同的兴奋模式在膜电流改变条件下可规律地相互转迁。随外向电流的逐渐减弱、内向电流的逐渐加强,同一细胞顺序历经“极化”静息状态、含延迟后去极化电位的节律、连续兴奋节律、含早后去极化电位的节律和“去极化”静息状态的兴奋节律动态转迁过程,形成心肌单细胞自发兴奋的哗律谱系”。其中延迟后去极化节律介于“极化”静息状态和连续放电节律之间,是连续放电节律向“极化”静息过渡的一种表现形式。而早后去极化节律则介于连续放电节律和“去极化”静息状态之间,是连续放电向“去极化”静息过渡的一种表现形式。哗律谱系”的概念在延迟后去极化、早后去极化现象和正常节律之间建立了内在联系。     

Geographical patterns of genetic structure in marine species with contrasting life histories

Aim  Phylogeographical breaks may reflect historical or present-day impediments to gene flow, and the congruence of these breaks across multiple species lends insight into evolutionary history and connectivity among populations. In marine systems, examining the concordance of phylogeographical breaks is challenging due to the varied sampling scales in population genetics studies and the diverse life histories of marine organisms. A quantitative approach that considers the effects of sampling scale and species life history is needed.
Location  The south-east and south-west coasts of the United States.
Methods  We quantitatively analysed previously published datasets of marine fauna to look for concordance among phylogeographical breaks. We used a bootstrap approach to determine the regions where phylogeographical breaks are more common than expected by chance among species with planktonic dispersal as well as those with restricted dispersal.
Results  On the south-west coast, breaks were clustered near Point Conception among planktonic dispersers and near Los Angeles among restricted dispersers. On the south-east coast, breaks were most common near the southern tip of Florida for planktonic dispersers and near Cape Canaveral for restricted dispersers.
Main conclusions  Dispersal ability is an important determinant of phylogeographical patterns in marine species. Breaks among planktonic dispersers on both coasts are congruent with present-day flow-mediated barriers to dispersal, suggesting that phylogeographical structure in species with planktonic larvae may reflect contemporary oceanography, while breaks in restricted dispersers reflect historical processes. These results highlight the importance of explicitly considering sampling scale and life history when evaluating phylogeographical patterns.     

Entrainment of the larval release rhythm of the crab Rhithropanopeus harrisii (Brachyura: Xanthidae) by cycles in hydrostatic pressure

This study investigated the entrainment of a larval release rhythm by determining whether a tidal cycle in hydrostatic pressure could entrain the circatidal rhythm in larval release by the crab Rhithropanopeus harrisii (Gould). Ovigerous females were collected from a non-tidal estuary. The time of larval release by individual crabs was monitored under constant conditions with a time-lapse video system. Crabs with mature embryos at the time of collection had a pronounced circadian rhythm in larval release with a free running period of 25.1 h. Crabs with immature embryos that were maintained under constant conditions from the time of collection until larval release retained a weak circadian rhythm. Other crabs with immature embryos were exposed to a tidal cycle in step changes in hydrostatic pressure equivalent to 1 m of water. This cycle entrained a circatidal rhythm in larval release. The free-running period was 12.1 h and larvae were released at the time of the transition from low to high pressure. Although past studies demonstrated that a tidal cycle in hydrostatic pressure could entrain activity rhythms in crustaceans, this is the first study to show that pressure can entrain a larval release rhythm.     

The Measurement of Electron Transport System Activity in Freshwater Benthic and Planktonic Samples

The measurement of electron transport system (ETS) activity in freshwater benthic and planktonic samples was examined. Significant improvements in sensitivity were obtained by increasing the concentration of substrates and of Triton X-100 in the extraction buffer and by changing the buffer system. The mechanical homogenization procedures which have been used previously to extract the enzymes were shown to be inadequate yielding, at best, 25% of the activity obtained by ultrasonication. The yield of enzymes from sediments was greatly affected by the degree of dilution used and previously published methods would appear to be inadequate. ETS activity correlated well with biological oxygen uptake and, in individual water and sediment profiles, with microbial numbers and biomass. At a more general level, however, the ETS: biomass ratio showed considerable variation.     

Biological studies on adult water snipe fly,Atherix ibis (Fabricius, 1798) (Diptera: Athericidae): old myths and new facts

The water snipe fly, Atherix ibis, is known for its eggbearing females aggregating in clusters. They are most frequently found as flat crusts under the outer parts of bridge ceilings above the water. There is no persistent pattern in the cluster distribution either in relation to the current direction or to the sun. Females aggregate in early summer in short periods of warm and calm weather only. Females are attracted to an aggregation site, probably by pheromones. The flies fasten to the surface and to each other by minute Velcro-like structures on their feet. The eggs are shed inside the cluster. After 9–12 days the eggs hatch, and the larvae leave clusters and drop into the water. There is no increased temperature inside the cluster. There are no signs of larval feeding on either dead flies or siblings in the cluster. The majority of larvae leave the cluster during night time, also when the normal day–night rhythm is eliminated by experimental black-out.     

Activity in the ferret: oestradiol effects and circadian rhythms

The present study was conducted to determine whether oestradiol increases activity in the European ferret (Mustela furo), whether this effect is sexually dimorphic, and whether a 24-h rhythm is present in the ferret's daily activity. The activity of male and female adult, postpubertally gonadectomized ferrets was monitored while they were maintained singly on a 13:11 light-dark cycle, before and after implantation with oestradiol-17β. Gonadectomized male and female ferrets exhibited equal levels of activity, and neither sex exhibited a significant change in activity following oestradiol implantation. None of the ferrets exhibited a strong circadian rhythm, although weak 24-h rhythms and shorter harmonic rhythms were present. Golden hamsters (Mesocricetus auratus), monitored in an identical manner, exhibited strong circadian rhythms. It was concluded that oestradiol administration may not cause an increase in activity in the ferret, and that this species lacks a strong circadian activity rhythm.