An entrainment model for semilunar rhythmic swimming behaviour in the marine isopod Eurydice pulchra Leach

Entrainment experiments have been carried out with geographically widely separated populations of the sand beach isopod Eurydice pulchra Leach subjected to periods of simulated tidal agitation imposed concurrently with a 24-h light: dark (L: D) cycle. Circatidal swimming rhythms of greatest amplitude were induced when agitation was applied with the subjective timing, within the L: D cycle, of local spring high tides. This occurred in a normal L: D regime and also when the L: D regime was phase shifted through 90°. Animals previously maintained in constant darkness (D: D) and subsequently exposed to simulated tidal disturbance at various times in constant darkness were unable to modulate the amplitude of circatidal swimming activity. Isopods previously maintained in a normal L: D cycle and subsequently subjected to artificial tidal agitation in constant darkness were, however, able to modulate circatidal activity. This indicates that E. pulchra is capable of detecting tidal agitation and daily light cues and using them in conjunction with its circadian “clock” to modulate its endogenous circatidal rhythmicity. The free-running semilunar rhythm of swimming activity entrained only when the timing of agitation within the day/night cycle mimicked the pattern of local spring high tides. Agitation with the timing of neap high tides entrained no free-running circa-semilunar activity pattern.     

中国重要海洋动物遗传多样性的研究进展

海洋动物遗传多样性的研究不仅可以揭示物种的起源与进化历史,而且为遗传资源的保存、海水养殖动物育种和遗传改良及整个海洋生态环境的修复和稳定等工作提供理论依据.本文概述了近十几年来我国重要海洋动物(主要包括鱼类、虾蟹类和贝类)遗传多样性研究所取得的成果,具体阐述其在种质鉴定、系统进化、群体遗传结构分析和良种培育等方面的应用,以期进一步推动海洋动物遗传多样性研究,加快优良种质的培育,促进海水养殖业的健康发展,实现海洋生物资源的合理开发和可持续利用.     

Circadian range of entrainment in the semilunar eclosion rhythm of the marine insect clunio marinus

The semilunar eclosion of the intertidal chironomid Clunio is controlled by a semilunar timing of pupation in combination with a daily timing of emergence. This results in reproductive activities of a laboratory population every 15 days at a distinct time of day (in nature mostly in correlation with the afternoon low water time on days with spring tides). The entrainment of the timing processes has been tested under various periods of the daily light-dark cycle in order to check the circadian organization of the timing mechanisms as suggested for the perception of the semilunar zeitgeber situation (a distinct phase relationship between the 24 h light-dark cycle and the 12.4 h tidal cycle recurring after every 15th light-dark cycle, named semimonthly zeitgeber cycle) as well as for the daily zeitgeber (the 24 h light-dark cycle). With respect to the semilunar timing, a strong entrainment was only possible in semimonthly zeitgeber cycles with light-dark cycle periods close to the 24-h day (light-dark cycles of 10:10 to 14:14). This limited circadian range of entrainment of an endogenous circasemilunar long-term rhythm (syn. oscillator) conforms with the hypothesis for a circadian clock component as an intrinsic part of the semilunar zeitgeber perception.The range of entrainment for the daily timing was obviously wider which may be discussed either in relation to a multioscillatory circadian organization of the midges or in relation to different coupling characteristics of one circadian oscillator during semilunar and daily timing.     

The effect of pollutants on sensory systems and behaviour of aquatic animals

A wide variety of pollutants (for example, heavy metals, organic compounds such as pesticides, hydrocarbons and oil dispersants, radioactive materials, excessive nutrients, acids, litter, silt, temperature and explosions) can influence the function of sense organs, and so influence behaviour by reducing or changing sensory information reaching the brain. Experiments show that so-called sublethal effects of pollutants occur at much lower concentration thresholds than lethal effects, yet subethal effects may well be lethal in the long term. Although a considerable amount of work has been done on marine invertebrates, practically all the work on fish is on freshwater species.     

Non-parametric photic entrainment of Djungarian hamsters with different rhythmic phenotypes

To investigate the role of non-parametric light effects in entrainment, Djungarian hamsters of two different circadian phenotypes were exposed to skeleton photoperiods, or to light pulses at different circadian times, to compile phase response curves (PRCs). Wild-type (WT) hamsters show daily rhythms of locomotor activity in accord with the ambient light/dark conditions, with activity onset and offset strongly coupled to light-off and light-on, respectively. Hamsters of the delayed activity onset (DAO) phenotype, in contrast, progressively delay their activity onset, whereas activity offset remains coupled to light-on. The present study was performed to better understand the underlying mechanisms of this phenomenon. Hamsters of DAO and WT phenotypes were kept first under standard housing conditions with a 14:10 h light–dark cycle, and then exposed to skeleton photoperiods (one or two 15-min light pulses of 100 lx at the times of the former light–dark and/or dark–light transitions). In a second experiment, hamsters of both phenotypes were transferred to constant darkness and allowed to free-run until the lengths of the active (α) and resting (ρ) periods were equal (α:ρ = 1). At this point, animals were then exposed to light pulses (100 lx, 15 min) at different circadian times (CTs). Phase and period changes were estimated separately for activity onset and offset. When exposed to skeleton-photoperiods with one or two light pulses, the daily activity patterns of DAO and WT hamsters were similar to those obtained under conditions of a complete 14:10 h light–dark cycle. However, in the case of giving only one light pulse at the time of the former light–dark transition, animals temporarily free-ran until activity offset coincided with the light pulse. These results show that photic entrainment of the circadian activity rhythm is attained primarily via non-parametric mechanisms, with the “morning” light pulse being the essential cue. In the second experiment, typical photic PRCs were obtained with phase delays in the first half of the subjective night, phase advances in the second half, and a dead zone during the subjective day. ANOVA indicated no significant differences between WT and DAO animals despite a significantly longer free-running period (tau) in DAO hamsters. Considering the phase shifts induced around CT0 and the different period lengths, it was possible to model the entrainment patterns of both phenotypes. It was shown that light-induced phase shifts of activity offset were sufficient to compensate for the long tau in WT and DAO hamsters, thus enabling a stable entrainment of their activity offsets to be achieved. With respect to activity onsets, phase shifts were sufficient only in WT animals; in DAO hamsters, activity onset showed increasing delays. The results of the present paper clearly demonstrate that, under laboratory conditions, the non-parametric component of light and dark leads to circadian entrainment in Djungarian hamsters. However, a stable entrainment of activity onset can be achieved only if the free-running period does not exceed a certain value. With longer tau values, hamsters reveal a DAO phenotype. Under field conditions, therefore, non-photic cues/zeitgebers must obviously be involved to enable a proper circadian entrainment.     

Light and temperature entrainment of a locomotor rhythm in honeybees

Abstract. The circadian locomotor (walking) rhythms of forager honeybees (Apis mellifera ligustica L.) were entrained to eight different 24 h light-dark cycles. The phases of activity onset, peak activity, and offset were correlated with the lights-off transition, suggesting lights-off as the primary zeitgeber for the rhythm. Further support for this hypothesis was provided by LD 1:23 experiments, in which entrainment occurred when the light pulse was situated at the end, but not at the beginning, of the subjective photophase. Steady-state entrainment of the locomotor rhythm was achieved with square-wave temperature cycles of 10^oC amplitude under constant dark: most of the activity occurred within the early thermophase. Smaller amplitude temperature cycles yielded relative coordination of the rhythm. Interactions of temperature and light-dark cycles resulted in entrainment patterns different from those elicited in response to either cycle alone or those formed by a simple combination of the two separate responses. Furthermore, temperature cycles having amplitudes insufficient for entrainment of the rhythm nevertheless modified the pattern of entrainment to light - dark cycles, suggesting a synergism of light and temperature effects on the underlying circadian clock system.     

Variability of entrainment of cohesive sediments in freshwater

Estimates of sediment entrainment are required for models of particle transport in lakes and estuaries but are difficult to make because of the multiplicity of factors affecting cohesiveness of surficial sediments. We present results of sediment resuspension studies performed in an annular flume calibrated with laser-Doppler velocimetry. In our experiments, using sediments collected from two sites in the R. Raisin which flows into L. Erie and from one site in the western basin of L. Erie near the mouth of the R. Raisin, we applied shear stresses at the sediment-water interface in steps from 2 to 12 dyne/cm². Percent water content at the surface of the sediments was either 77 or 74%, and trials were run with and without oxygenating the water overlying the sediments. Entrainment rates as a function of shear stress at the sediment-water interface were best described by a power-law relationship. All but 14% of the variability in the power law expression was due to shear stress and percent water content; the variability not accounted for was due to differences in particle size distributions, chemical properties, and biological activity in the sediments.     

Light and feeding entrainment of the molecular circadian clock in a marine teleost (Sparus aurata)

Daily light and feeding cycles act as powerful synchronizers of circadian rhythmicity. Ultimately, these external cues entrain the expression of clock genes, which generate daily rhythmic behavioral and physiological responses in vertebrates. In the present study, we investigated clock genes in a marine teleost (gilthead sea bream). Partial cDNA sequences of key elements from both positive (Bmal1, Clock) and negative (Per2, Cry1) regulatory loops were cloned before studying how feeding time affects the daily rhythms of locomotor activity and clock gene expression in the central (brain) and peripheral (liver) oscillators. To this end, all fish were kept under a light-dark (LD) cycle and were divided into three experimental groups, depending on the time of their daily meal: mid-light (ML), mid-darkness (MD), or at random (RD) times. Finally, the existence of circadian control on gene expression was investigated in the absence of external cues (DD?+?RD). The behavioral results showed that seabream fed at ML or RD displayed a diurnal activity pattern (>91% of activity during the day), whereas fish fed at MD were nocturnal (89% of activity during the night). Moreover, seabream subjected to regular feeding cycles (ML and MD groups) showed food-anticipatory activity (FAA). Regardless of the mealtime, the daily rhythm of clock gene expression in the brain peaked close to the light-dark transition in the case of Bmal1 and Clock, and at the beginning of the light phase in the case of Per2 and Cry1, showing the existence of phase delay between the positive and negative elements of the molecular clock. In the liver, however, the acrophases of the daily rhythms differed depending on the feeding regime: the maximum expression of Bmal1 and Clock in the ML and RD groups was in antiphase to the expression pattern observed in the fish fed at MD. Under constant conditions (DD?+?RD), Per2 and Cry1 showed circadian rhythmicity in the brain, whereas Bmal1, Clock, and Per2 did in the liver. Our results indicate that the seabream clock gene expression is endogenously controlled and in liver it is strongly entrained by food signals, rather than by the LD cycle, and that scheduled feeding can shift the phase of the daily rhythm of clock gene expression in a peripheral organ (liver) without changing the phase of these rhythms in a central oscillator (brain), suggesting uncoupling of the light-entrainable oscillator (LEO) from the food-entrainable oscillator (FEO). These findings provide the basis and new tools for improving our knowledge of the circadian system and entraining pathways of this fish species, which is of great interest for the Mediterranean aquaculture. (Author correspondence: javisan@um.es).     

Environmental constraints on the foraging behaviour of a dwarf antelope (Madoqua kirkii)

Dik-diks (Madoqua sp.) inhabit semi-arid regions and experience very different conditions of food availability and quality between wet and dry seasons. By comparing the behaviour of dik-diks between these two seasons, we identified environmental constraints affecting their feeding strategies. In both seasons foraging time was limited by high mid day temperatures. In the wet season a high intake rate compensates for the loss in foraging time, but in the dry season water and protein become limiting. To meet minimum daily water requirements in the dry season dik-diks fed on plant species that they avoided during the wet season. Analysis at the plant species level showed higher species selectivity in the wet season than in the dry season. In a multiple regression analysis food species preferences were best explained by relative abundance and water content in the dry season, and by dry matter content in the wet season. In the wet season the daily dry-matter intake of dik-diks in the field was only about 10% higher than the theoretically predicted minimum for a ruminant of this body weight, while protein and water intake were about 3 times as high. This suggests that the most limiting dietary component in the wet season is energy. In the dry season the daily intake of all dietary components is lower than the theoretical minimum required, and also lower than the values suggested by laboratory studies of dik-diks. This dry season deficit is presumably met from body reserves. Dry season water intake was approximately 30% of the intake observed in laboratory studies indicating that dikdiks are even better adapted to arid conditions than suggested by physiological experiments.     

Optimal diving behaviour for foraging in relation to body size

Overall, large animals dive longer and deeper than small animals; however, after the difference in body size is taken into account, smaller divers often tend to make relatively longer dives. Neither physiological nor theoretical explanations have been provided for this paradox. This paper develops an optimal foraging diving model to demonstrate the effect of body size on diving behaviour, and discusses optimal diving behaviour in relation to body size. The general features of the results are: (1) smaller divers should rely more heavily on anaerobic respiration, (2) larger divers should not always make longer dives than smaller divers, and (3) an optimal body size exists for each diving depth. These results explain the relatively greater diving ability observed in smaller divers, and suggest that if the vertical distribution of prey in the water column is patchy, there is opportunity for a population of diving animals to occupy habitat niches related to body size.     

Navigation of marine, freshwater and coastal animals: concepts and current problems

The animals from the environments focused on here share the same navigational mechanisms with terrestrial animals. However, some of them seem to rely on additional ways of detecting and/or processing navigational cues, some of which are perhaps still unknown. A classification of the mechanisms of navigation is given. This is based on the source of information that animals use to head for their targets. A selected series of phenomena of current interest is presented, starting with olfactory beaconing in oceanic birds, which allows the detection of patchily distributed food and productive areas from long distances. Animals of sandy beaches rely on an array of mechanisms of orientation, which have an adaptive value for their ecotonal system. As some species are capable of using both the moon and sun compass in orientation, attention and experiments are focused on the significance of these celestial cues in the navigational process. Two clocks of different periods, one of which would appear to regulate both the activity rhythm and the sun compass, are presumed to underlie the two compass mechanisms. The feats of global navigators in and over the oceans are especially puzzling considering their ability of homing to the natal and nesting sites after long lasting, extended wandering in the open ocean, and of pinpointing tiny, isolated oceanic islands. The existent literature allows comparison of the navigational capabilities of oceanic birds with those of sea turtles. Their performances in natural conditions seem to be similar, but sea turtles exhibit a reduced capacity of compensation for experimental relocation. Capacity of positioning based on geomagnetic parameters has been indicated for sea turtles through laboratory experiments, but this is not confirmed by the routes of magnetically disturbed turtles tracked while migrating or attempting to compensate for relocation. Also albatrosses with fitted magnets are not disturbed in their homing.     

SMS seal: A new technique to measure haul-out behaviour in marine vertebrates

Many marine vertebrates, including pinnipeds, turtles and birds, spend periods of time ashore during their life cycles. Quantification of time spent ashore is important for estimating population parameters such as abundance and productivity in some species, but can prove to be a difficult task. Here we describe a novel telemetry system based on Global Systems for Mobile Communications (GSM), to provide detailed information on the haul-out behaviour of tagged animals. We tested the system on harbour seals in southwest Ireland. The GSM telemetry system proved an effective means of obtaining information on the haul-out activity of harbour seals in the study area and of providing crude movement information that was less labour intensive than VHF telemetry and provides an alternative means of data acquisition offering some advantages over satellite telemetry. The GSM tag with its internal antennae is more robust than a satellite tag. The GSM networks allow more information to be relayed, so the “cost per bit of data” is reduced. Moreover, the large global investment in GSM networks have resulted in a telemetry technology with low running costs and therefore with significantly lower costs of data acquisition via GSM relative to Argos systems. With the ever-expanding global GSM network coverage the system has significant potential applications in behavioural studies of amphibious vertebrates, such as estimating clutch frequency in sea turtles.     

Modeling temperature entrainment of circadian clocks using the Arrhenius equation and a reconstructed model from Chlamydomonas reinhardtii

Endogenous circadian rhythms allow living organisms to anticipate daily variations in their natural environment. Temperature regulation and entrainment mechanisms of circadian clocks are still poorly understood. To better understand the molecular basis of these processes, we built a mathematical model based on experimental data examining temperature regulation of the circadian RNA-binding protein CHLAMY1 from the unicellular green alga Chlamydomonas reinhardtii, simulating the effect of temperature on the rates by applying the Arrhenius equation. Using numerical simulations, we demonstrate that our model is temperature-compensated and can be entrained to temperature cycles of various length and amplitude. The range of periods that allow entrainment of the model depends on the shape of the temperature cycles and is larger for sinusoidal compared to rectangular temperature curves. We show that the response to temperature of protein (de)phosphorylation rates play a key role in facilitating temperature entrainment of the oscillator in Chlamydomonas reinhardtii. We systematically investigated the response of our model to single temperature pulses to explain experimentally observed phase response curves.     

Ocean acidification erodes crucial auditory behaviour in a marine fish

Ocean acidification is predicted to affect marine ecosystems in many ways, including modification of fish behaviour. Previous studies have identified effects of CO(2)-enriched conditions on the sensory behaviour of fishes, including the loss of natural responses to odours resulting in ecologically deleterious decisions. Many fishes also rely on hearing for orientation, habitat selection, predator avoidance and communication. We used an auditory choice chamber to study the influence of CO(2)-enriched conditions on directional responses of juvenile clownfish (Amphiprion percula) to daytime reef noise. Rearing and test conditions were based on Intergovernmental Panel on Climate Change predictions for the twenty-first century: current-day ambient, 600, 700 and 900 μatm pCO(2). Juveniles from ambient CO(2)-conditions significantly avoided the reef noise, as expected, but this behaviour was absent in juveniles from CO(2)-enriched conditions. This study provides, to our knowledge, the first evidence that ocean acidification affects the auditory response of fishes, with potentially detrimental impacts on early survival.     

早期环境经验对雏鸡啄羽行为发育的影响

本试验是验证印记敏感期和早期经验对雏鸡啄羽行为的影响。试验包括8个处理组：一组鸡（OF组）在整个试验期（0—14周）饲养在沙质底层;一组（0P组）饲养在贫瘠底层;三组分别在贫瘠底层饲养为期2周（3P组）、4周（5P组）、6周（7P组）,然后转入沙质底层直至14周;其它三组分别饲养在沙质底层为期2周（3F组）、4周（5F组）、6周（7F组）,然后转入贫瘠底层直至14周。观察啄羽、啄地、啄物和盯物等四种行为。结果显示：啄羽行为印记的最重要时期为雏鸡出生后的头4周,尤其是3—4周;早期环境经验可以修饰雏鸡后续的啄羽行为,但不能根本改变它。另外,环境条件似乎对啄物和盯物行为无影响[动物学报54（6）：955-963,2008]。     

Thermal and digestive constraints to foraging behaviour in marine mammals

While foraging models of terrestrial mammals are concerned primarily with optimizing time/energy budgets, models of foraging behaviour in marine mammals have been primarily concerned with physiological constraints. This has historically centred on calculations of aerobic dive limits. However, other physiological limits are key to forming foraging behaviour, including digestive limitations to food intake and thermoregulation. The ability of an animal to consume sufficient prey to meet its energy requirements is partly determined by its ability to acquire prey (limited by available foraging time, diving capabilities and thermoregulatory costs) and process that prey (limited by maximum digestion capacity and the time devoted to digestion). Failure to consume sufficient prey will have feedback effects on foraging, thermoregulation and digestive capacity through several interacting avenues. Energy deficits will be met through catabolism of tissues, principally the hypodermal lipid layer. Depletion of this blubber layer can affect both buoyancy and gait, increasing the costs and decreasing the efficiency of subsequent foraging attempts. Depletion of the insulative blubber layer may also increase thermoregulatory costs, which will decrease the foraging abilities through higher metabolic overheads. Thus, an energy deficit may lead to a downward spiral of increased tissue catabolism to pay for increased energy costs. Conversely, the heat generated through digestion and foraging activity may help to offset thermoregulatory costs. Finally, the circulatory demands of diving, thermoregulation and digestion may be mutually incompatible. This may force animals to alter time budgets to balance these exclusive demands. Analysis of these interacting processes will lead to a greater understanding of the physiological constraints within which the foraging behaviour must operate.