Environmental influence on the locomotor activity rhythm of Talitrus saltator (Crustacea: Amphipoda)

The persistence and precision of the endogenous, nocturnal, circadian locomotor rhythm of the sand-beach amphipod Talitrus saltator is characterised, and the influence of substrate availability, photoperiod, temperature and relative humidity as potential environmental synchronizers of the rhythm is assessed. Individual, cyclic light-dark and temperature regimes synchronize and modify the laboratory activity pattern, but substrate availability and relative humidity have no significant long-term effect. Under simulateneous experimental regimes simulating field conditions of photoperiod, temperature and relative humidity the rhythm is entrained solely by photoperiod. The implications are discussed in relation to field behaviour.     

Ontogenetic differences in the circadian locomotor activity rhythm of the talitrid amphipod crustacean Orchestoidea tuberculata

 Adult talitrid amphipods often display a nocturnal activity pattern, which has been shown in a number of cases to be partly controlled by an endogenous rhythm of circadian period. Juvenile talitrids have been little studied in the past, but evidence from field studies indicates that they may display a different diel pattern of locomotor activity from that of adults. This study presents evidence from the field in south–central Chile that juvenile Orchestoidea tuberculata Nicolet show crepuscular activity peaks, contrasting with the nocturnal peaks shown by adult conspecifics. Under constant conditions in the laboratory, both juveniles and adults exhibit endogenous rhythms of circadian periodicity. However, the phasing of activity differs in juveniles and adults, corresponding to the differences observed in the field. It is suggested that differing phasing of peak locomotor activity may be a mechanism to reduce contact between juvenile and adult talitrids. Experimental evidence indicates a significant negative influence on survival of juveniles in the presence of adult conspecifics by intraspecific predation. Other factors influencing the timing of surface activity are also discussed. Received: 3 August 1999 / Accepted: 26 May 2000     

The effect of male calling on female locomotor activity of Teleogryllus commodus

Summary The calling song of the -cricket, Teleogryllus commodus, attracts for mating. Both calling and -locomotor activity are under circadian control and the behaviors occur approximately at the same time. Daily playback of calling songs for 3–12 h in constant light failed to entrain -running. Instead, calling acts as an external stimulus which can release -locomotion at any time of the 24-h period, while the clock-induced activity continues to run freely. The stimulatory effect of the calling song causes flexible extension of -locomotor activity, but a subsequent restorative period is necessary. The ecological consequences of acoustical stimulation are discussed.     

Effects of dusk and dawn on locomotor activity rhythms in the norway lobster Nephrops norvegicus

The endogenous locomotor activity rhythm of Nephrops norvegicus (L.) shows peaks during darkness, around 3 h after dusk. At the peaks, activity occurs mainly within the burrow, although the prawns repeatedly vacate the burrows during the same periods. The phase of the rhythm shifts with a change of light-dark regime and in response to changed timing of dusk when dawn is fixed. Activity is suppressed immediately at dawn, but recommences before complete darkness during gradually reduced light at simulated dusk. This difference in response to light at dusk and dawn indicates phase responsiveness which is characteristic of endogenous rhythms entrained by light. The light-entrained endogenous rhythm is complementary to the rhythm of emergence which, reflected in commercial catches, appears to be controlled by exogenous factors.     

Is there any influence of magnetic or astrophysical fields on the circadian rhythm of honeybees?

Summary While honeybees use magnetic fields as references to orient in space, there is no unequivocal evidence that honeybees use magnetic cues to orient in time. In this report, it is demonstrated that magnetic fields usually have no influence on the time sense of honeybees, and the bees' rhythmicity is not driven exclusively by exogenous factors. All the variations of the forager bees' behavior are explicable by an endogenous control of rhythmicity; differences are due to individually different periods of the forager bees and dependent on the season. The coincidence of curves calculated from the constellation of sun and moon and the behavior of bees is shown to be an artifact and not a causal relationship.     

The eye and some effects of light on locomotor activity in Nephrops norvegicus

The compound eye of Nephrops norvegicus (L.) is of the superposition type, well-adapted to the low levels of light prevailing at the sea bed during the activity periods of the species. Only the proximal retinal shielding pigment responds to light, the distal retinal shielding pigment being in the dark-adapted position at all times. The response of the proximal pigment appears to vary seasonally. Field observations compared light intensity at the sea bed with the numbers of N. norvegicus caught by trawl at various times of day in the Irish Sea in summer and winter. Laboratory experiments were combined with these field data to indicate that light is an important modulator of locomotor activity in this species.     

Seasonal changes of locomotor activity patterns in ruin lizards Podarcis sicula

The daily pattern of locomotor activity of the ruin lizard Podarcis sicula in its natural environment changes from unimodal in spring (with only one activity peak per day) to bimodal in summer (with two well-separated activity peaks per day) and it becomes unimodal again in autumn. In order to establish whether such seasonal changes in pattern might be at least in part controlled by endogenous temporal programs, lizards were collected at different times of the year and immediately after capture their locomotor behavior was tested in the laboratory under constant temperature (29°C) and in darkness. For some individuals tested in the laboratory the locomotor pattern previously expressed in the field was known. Seasonal differences in pattern have been unequivocally found to have an endogenous component, as most lizards in constant conditions retained the locomotor pattern shown in the field during the same season. Besides, in the bimodal lizards the freerunning period of locomotor rhythms () was significantly shorter and circadian activity time (a) longer than in the unimodal ones. Altogether the data are compatible with the idea that both the interdependent changes of and a and the changes in locomotor pattern occurring seasonally in the circadian activity rhythms of P. sicula would depend on changes in the phase relationship between mutually coupled oscillators which drive these rhythms. Correspondence to: A. Foà     

Seasonal changes of locomotor activity patterns in ruin lizards Podarcis sicula

Seasonal differences in the locomotor activity pattern of Podarcis sicula held in constant conditions in the laboratory were found to be associated with systematic differences in both the freerunning period of locomotor rhythms () and the circadian activity time (). In order to establish whether the pineal played a role in the control of seasonal changes in circadian parameters, we examined the effects of pinealectomy in constant conditions on the locomotor behavior of lizards displaying the bimodal activity pattern typical of summer. In most lizards pinealectomy lengthened , shortened and abolished the bimodal activity pattern. Pinealectomy induced a sudden transition from the typical locomotor behavior of summer, characterized by a marked bimodal pattern, short and long , to the typical locomotor behavior of autumn, characterized by a unimodal pattern, a long and short . These results demonstrate that the pineal plays a central role in the seasonal reorganization of the circadian system that occurs in P. sicula.     

Effects of environmental manipulation on the locomotor activity and agonistic behavior of cultured juvenile American lobsters,Homarus americanus

The locomotor activity patterns and agonistic encounters of cultured juvenile (IX–XIII stage) American lobsters, Homarus americanus (Milne-Edwards) held in 8 experimental environments were investigated to examine their relative contribution to aggressive level. Three variables: (1) lobsters individually or communally maintained, (2) shelters present or absent, and (3) open or closed seawater system were tested in a set of factorial experiments. Locomotor activity of lobsters held in a 12 h: 12 h light: dark regime was recorded for individually separated lobsters for the first 5 days and for communally held lobsters for the next 5 days of a 10-day experimental period. All lobsters maintained individually had similar levels of activity. When the same individuals were communally maintained, there appeared to be social inhibition of activity. In addition, communally held lobsters without shelter were twice as active as those provided with shelter. The activity levels of groups of communally held lobsters with shelter progressively decreased over the experimental period. All lobsters became somewhat entrained to the light: dark cycle and were nocturnally active. However, the degree of entrainment was strongly influenced (P<0.001) by the presence or absence of shelter and other lobsters. Individually maintained lobsters all showed good entrainment, although those provided with shelter were slightly better entrained. The presence of conspecifics desynchronized activity patterns when shelter was not provided. Aggressive level, as measured by the frequency of agonistic encounters per 15-min observation period and the number and types of displays per encounter, decreased over an 8-day period for groups of 3 lobsters in all experimental environments. Lobsters maintained in a closed system initially showed higher frequencies of agonistic encounters than those held in an open system. The observed decrease in aggressive level with time primarily resulted from decreased activity levels. When two lobsters met, the probability of an agonistic encounter was about 0.8 throughout the experimental period, but decreasing activity levels resulted in progressively fewer encounters. The results suggest several approaches for limiting aggression among communally maintained lobsters in culture systems by environmental manipulation.     

Effect of uranium on growth and reproduction of the marine amphipod Allorchestes compressa

Experiments on growth of the marine amphipod Allorchestes compressa Dana were carried out over four weeks, and both growth and reproduction were studied over three generations, each of which was exposed to uranium for approximately 10 wk. At 0.1 mg l^-1 the uranium increased growth by 23%, as measured by the mean weight after 4 wk, and at 2 mg l^-1 growth was reduced by 28% compared with the control. A. compressa accumulated uranium from sea water with a concentration factor of 10. There was no effect of uranium on the survival of amphipods or their progeny in the multiple-generation experiment, but the numbers of males, the sex ratio, and the respiration rate (measured on males only) at 1mg l^-1 were significantly lower than the control. A. compressa is shown to be a convenient species for the study of toxic effects on growth and reproduction using multiple-generation experiments.     

Behaviour and distribution of the sand-beach amphipod Orchestoidea corniculata

The field distribution of Orchestoidea corniculata Stont a talitrid amphipod inhabiting the upper intertidal zone of sandy beaches, was measured by pitfall trap and subsurface core transects. Variations in the distribution of juveniles and adults were recorded. At Coal Oil Point (Goleta, California, USA), the population was concentrated on the leeward side of the Point and, with increasing distance from the Point, both the number and size of beachhoppers decreased. The amphipods burrowed in a 5 to 7 m wide band during the day, and were active over a 15 to 25 m area at night. When they emerged from their burrows, a net seaward movement of 3 m was observed for the population. Behavioural tests suggested that sand penetrability is an important factor determining the location of burrow sites. Diurnal orientation was investigated, and it was found that the amphipods oriented in a landward direction despite overcast sky conditions, beach slope, moisture gradients, or displacement to a new beach.     

Modelling the effects of extreme events on the dynamics of the amphipod Corophium orientale

The brackish water amphipod Corophium orientale is the dominant macroinvertebrate species in the upper Mira estuary, a small mesotidal system located in the southwest coast of Portugal. As climate changes will increase the frequency and intensity of extreme events such as floods and droughts, these will have a negative effect on benthic estuarine invertebrates, namely C. orientale. In order to understand the effects of these events on C. orientale, a dynamic model, based on published information and calibrated with field data, was developed and different scenarios were tested.For model construction, the annual development of three cohorts of C. orientale, their growth rates, and the establishment of the timing of each cohort rise and extinction are introduced. This structure can be repeated indefinitely, for years, and few parameters are required. The model simulations highlight the need for refuge areas that enable a fast recovery of the amphipod population after an extreme event and the recolozination of the affected areas.     

Bioturbation effects of the amphipod Corophium volutator on microbial nitrogen transformations in marine sediments

Microcosms containing different densities of Corophium volutator, ranging from 0 to 6000 ind m^-2, were incubated in a flow-through system. Benthic fluxes of CO₂, O₂, NO₃ ^- and NH₄ ⁺ were measured regularly. Thirteen days after setup the microcosms were sacrificed and sediment characteristics, pore water NO₃ ^-, NH₄ ⁺ and exchangeable NH₄ ⁺ concentrations, and potential nitrification activity were measured. The presence of C. volutator increased overall mineralization processes due to burrow construction and irrigation. The amphipods increased the ratio CO₂/O₂ fluxes from 0.73 to 0.86 in microcosms inhabited by 0 and 6000 ind m^-2, respectively. Burrow ventilation removed NH₄ ⁺ from the sediment, which was nitrified in the oxic layer and transported NO₃ ^- to the burrow sediment, where denitrification potential was enhanced. Nitrification and total denitrification rates (denitrification of NO₃ ^- coming from the overlying water and of NO₃ ^- generated within the sediment) were calculated and discussed. Bioturbation by C. volutator increased both nitrification and denitrification, but denitrification was stimulated more than nitrification. Denitrification of NO₃ ^- coming from the overlying water was stimulated 1.2- and 1.7-fold in microcosms containing 3000 and 6000 ind m^-2 relative to control microcosms. The presence of C. volutator (6000 ind m^-2) stimulated nitrogen removal from the system, as dinitrogen, 1.5-fold relative to non-bioturbated microcosms. C. volutator individuals used in our study were collected from Norsminde Fjord, Denmark, in 1990.     

Circadian rhythm of swimming activity in juvenile pink salmon (Oncorhynchus gorbuscha)

The circadian rhythm of swimming activity and the role of the daily illumination cycle in the synchronization of this rhythm were studied in individual juvenile pink salmon. Sixty eight percent of all fish examined (n=38) were day-active when exposed to a 12 h L:12 h D cycle; the remaining fish were nocturnally active. One half of the fish tested under laboratory conditions of continuous, constant light intensity (LL) and constant temperature showed unambiguously endogenous activity rhythms with circadian periods for up to 10 d. The remaining fish were arrhythmic. Mean period length of the free-running activity rhythms for diurnal fish in LL shortened with constant light intensity increasing from 6 to 600 lx, as predicted by the circadian rule. In contrast, mean free-running period for nocturnal fish did not vary significantly with similarly increasing constant light intensity. Mean swimming speed (activity level) of both diurnal and nocturnal fish increased significantly with increasing light intensity. This is suggestive of a positive photokinetic response. When subjected to a phase-delayed LD cycle, the fish resynchronized their daily rhythms of activity with this new LD cycle after only one transient cycle in most instances. Hence, the timing of the daily activity rhythms appeared to occur through the direct masking action of the illumination cycle on activity, rather than through entrainment of an endogenous circadian system.     

Contrasting diel patterns in vertical movement and locomotor activity of whale sharks at Ningaloo Reef

Activity patterns of animals often relate to environmental variables such as food availability and predation pressure. Technological advances are providing us with new tools to monitor and better understand these activity patterns. We used animal-attached data loggers recording acceleration and depth to compare activity patterns and vertical habitat use of whale sharks (Rhincodon typus) at Ningaloo Reef, Western Australia. Whale sharks showed a moderate reverse diel vertical migration but exhibited a clear crepuscular pattern in locomotory activity. Peak activity occurred at sunset, whereas vertical movement peaked prior to this. Typical ram surface filter feeding could be identified and occurred primarily during sunset and the first hours of night. At such times, direct observations indicated whale sharks were feeding on tropical krill swarms. Kinematic analysis of postural data and data from vertical movement suggests that whale sharks at Ningaloo spend ~8 min per day actively ram surface filter feeding. Considering the high biomass present in krill schools, it is estimated that whale sharks at Ningaloo have a similar energy intake as those at other aggregation sites. Diel patterns in activity and diving behaviour suggest that whale sharks have tuned their diving behaviour in anticipation of the formation of these high-density patches which appear to only be periodically, but predictably available at sunset. Our results confirm that diel patterns in vertical habitat selection and vertical movements do not necessarily reflect patterns in activity and foraging behaviour. Direct quantification of activity and behaviour is required in gaining accurate representation of diel activity patterns.     

Survival and bioturbation of the amphipod Monoporeia affinis in sulphide-rich sediments

Laboratory experiments were conducted to investigate the survival rate of Monoporeia affinis in sulphide-rich sediment with oxic overlying water, and the effect of amphipod bioturbation on sulphide and oxygen profiles. As long as the oxygen content in the water is high, the amphipods seem to avoid quite high concentrations (>200 μmol l⁻¹) of sulphide in the sediment by creating microhabitats where sulphide is rapidly oxidised. In cores with amphipods, a decrease of sulphide concentration was found in upper layers, while an increase of sulphide was found in deeper layers. Aggregation of amphipods generated pockets of light-brown sediment, characterised by high oxygen concentrations and no sulphide, and their depth was clearly dependent on amphipod density. This indicates that M. affinis has a potential to recolonise sulphide-rich sediments, devoid of macroscopic life, after the overlying water column has become oxygenated. Received: 13 April 2000 / Accepted: 8 September 2000