Light pulse effect on the locomotor activity rhythm of Talitrus saltator (Montagu) (Crustacea,Amphipoda)

The locomotor activity rhythm of the sandhopper Talitrus saltator (Amphipoda Talitridae) was investigated in Madfoun beach. The rhythm was monitored in individual and group animals during 21 days at constant temperature. During the first two weeks, animals were kept under light–dark cycle (d1–d7) and constant darkness (d8–d14). Light pulses of 2 h were applied, at the end of the experimental night, during the first 3 days of the third week (d15–d18). Then, constant darkness was restored for the rest of the experiment (d19–d21). Results revealed that Talitrus saltator individuals as well as groups concentrated their activities in experimental night under light–dark cycle and in the presence of pulses; whereas, a clear drift of activity is observed under constant darkness. Periodogram analysis showed the presence of circadian component whatever the recording type. An ultradian period was revealed in individual recording whatever the regimen, while for groups, this component appeared only under nLD cycle. Furthermore, the locomotor rhythm is more defined under nLD cycle for individuals and in constant darkness for groups.     

Nuovi reperti di Trichosporon ed osservazioni interno a questo genere

Sommario Si descrivono tre ceppi di Trichosporon isolati dall' uomo, uno da pasta di cellulosa e due da formaggi, riportati rispettivamente a Trichosporon infestans (2 ceppi), T. cutaneum, T. Beigeli e T. Luchettii n. sp. (2 ceppi). Nel contempo si ristudia la sistematica del genere e delle specie ivi incluse, redigendo, a titolo provvisorio, una chiave analitica delle specie fondamentali : Trichosporon giganteum, T. proteolyticum, T. infestans, T. Luchettii, T. Balzeri, T. granulosum, T. Beigeli, T. cutaneum, T. Uffreduzzii, tutte del sottogenere Proteomyces.

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Summary Three strains of Trichosporon isolated from man, one from wood pulp, and two from cheese, are described. The strains are found to be T. infestans (2 strains), T. cutaneum, T. Beigeli and the new species T. Luchettii (2 strains). The sistematic position of the genus and the subdivision of species are discussed. A provisional analytical key of the master species is appended, including: T. giganteum, T. proteolyticum, T. infestans, T. Luchettii, T. Balzeri, T. granulosum, T. Beigeli, T. cutaneum, T. Uffreduzzii, all of the subgenus Proteomyces,

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Sumario Tres cultivos de Trichosporon aislados del hombre, uno de pasta de madera para papel, y dos del queso están descritos. Los cultivos fueron referidos al T. infestans (dos), T. cutaneum, T. Beigeli, y a la nueva especie T. Luchettii (dos). La posición sistematica del género y la subdivisión en especies fueron examinado criticamente, y una clave analítica de las especies más conocidas o clasicas ha sido instituida. Las especies consideradas (T. giganteum, T. proteolyticum, T. infestans, T. Luchettii, T. Balzeri, T. granulosum, T. Beigeli, T. cutaneum, T. Uffreduzzii) pertenecen todas al subgénero Proteomyces.

     

The annual pattern of reproduction of Talitrus saltator (Crustacea: Amphipoda: Talitridae)

The reproductive cycle and breeding biology of Talitrus saltator (Montagu), a supralittoral talitrid amphipod, were investigated over a 15 month period on a sandy beach in the Isle of Man. The species is shown to have an annual, univoltine reproductive cycle with a period of high reproductive activity between May and late August. Two generations are present throughout most of the year and the life spans of female and male T. saltator were calculated to be approximately 18 months and 21 months respectively. Initial juvenile growth was rapid, juveniles attaining sexual differentiation within three to four months of hatching. Juvenile growth rates averaged 5–5 mm in 100 days decreasing to 1–3 mm in 100 days after sexual differentiation at around 8.0 mm.
The relative brood size of incubating females was shown to be dependent on at least two factors, the length of the female and the stage of embryological development of the brood.
It is suggested that photoperiod is the major exogenous factor controlling gonadal maturation and the duration of reproductive activity in T. saltator.     

Artificial light and sun compass orientation in the sandhopper Talitrus saltator (Crustacea, Amphipoda)

Experiments on compass orientation under artificial light were conducted with adult individuals of Talitrus saltator. The aim was to reproduce in the laboratory an orientation based on the sun compass corresponding to that recorded in conditions of the true sun and sky. This was obtained by the creation within an opaque Plexiglas dome of a scenario that permitted variation of the brightness of the artificial sky and sun. The results show that it is possible to obtain sun compass orientation corresponding to the natural situation even in an artificial environment. It can be concluded that sandhoppers identify an artificial light source as the sun if the artificial sky is also illuminated and if the intensities of the artificial sun and sky exceed certain threshold values (1.13 and 10 μW cm⁻², respectively). The results of other experiments under the natural blue sky with an artificial sun and with the real sun attenuated are discussed. Accepted: 23 May 1997     

Locomotor activity rhythm of Talitrus saltator (Crustacea,Amphipoda) on a progradating sandy beach

In the Maremma Natural Park (Grosseto, Italy), the Collelungo beach exhibits a clear morphodynamics gradient, resulting in a severe erosion to a gradual accretion along the shoreline. Here, three sub-populations of the sandhopper Talitrus saltator (Montagu) (Crustacea, Amphipoda) were studied to highlight eventual intra- and inter-population variation of the endogenous locomotor rhythm. Individual activity recordings were carried out for 21 days in constant darkness and controlled temperature and humidity conditions. The variation of the free-running period was analysed at individual and sub-population levels, and the dependence on intrinsic (individual features) and extrinsic (habitat of origin and season) factors was analysed. A seasonal variation was highlighted, related to the seasonal spontaneous activity of the species. In summer and autumn, a significant correlation between the behavioural variation in the sub-populations (period and definition of the period) and beach physical parameters (slope and width) defined the dependence of the behavioural gradient on the environmental gradient. The observed relationship may represent an adaptation to the local coastline dynamics, suggesting the importance of a plastic behaviour as adaptive response to a variable environment.     

Effect of light intensity on the locomotor activity rhythm of Talitrus saltator (Montagu 1808) from Korba Beach

In this work, we investigate the locomotor behaviour of Talitrus saltator (Montagu 1808) for a population collected from the supralittoral zone of Korba beach. The locomotor activity rhythm was recorded for adult individuals during 10 summer days under continuous light with four different luminous intensities: 5 lux (N = 30), 35 lux (N = 30), 75 lux (N = 30) and 140 lux (N = 15). By the end of the experiments, 100% of the considered individuals were found alive under light intensities of 35 and 140 lux, whereas only 86 and 90% were found alive under light intensity of 5 and 75 lux, respectively. Furthermore, whatever the imposed luminous intensity is, actograms showed a clear drift to the right lengthening day after day the circadian period. Moreover, we found that by raising the light intensity, the drift becomes increasingly important. Actograms as well as activity curves, results showed that the locomotor activity profiles are mainly unimodal and their percentage increases when increasing the light intensity. Furthermore, periodogram analysis highlighted the presence of ultradian and circadian components where the longest periods were observed with the highest luminous intensity. In addition, the locomotor activity rhythm was statistically more defined and individuals of Talitrus saltator were significantly more active under the lowest luminous intensity.     

Physiological responses to hyposmotic stress in the supralittoral amphipod Talitrus saltator (Crustacea: Amphipoda)

We investigated the effect of hyposmotic stress upon osmotic capacity (OC), heart rate (HR) and heart rate variability (HRV) of an Atlantic population of the sandhopper Talitrus saltator. Strictly consecutive monitoring of cardiac activity and measurement of OC was achieved by employing a non-invasive infrared technique to monitor heart activity and direct cardiac puncture to collect the haemolymph. Body mass (range 60-160 mg) had no effect on mean HR nor the mean HRV in adult individuals of both sexes. Both OC and HR, but not HRV, were influenced by the interaction between osmotic stress and exposure time. In addition, OC and HR were coupled within a moderate range of osmotic stress, beyond which this association breaks down, and bradycardia and a positive correlation between HR and HRV occur. A possible rise in metabolic cost, indicated by HR increase, was described for hyper-osmotic regulation. This is the first assessment of the relationship OC and HR in a non-decapod crustacean, and the results indicate that, in sandhoppers, the disruptions of cardiac activity may lead to impairment in maintaining an efficient haemolymph osmotic regulation.     

Seasonality of the endogenous activity rhythm in Talitrus saltator (Montagu) from a sandy beach in northeastern Tunisia

The endogenous activity of the sandhopper Talitrus saltator (Montagu) has been investigated in a population from a relatively exposed beach in northeast Tunisia. The animals were found to exhibit a nocturnal circadian rhythm of locomotor activity, with no evidence of a circatidal component. The rhythm was monitored in individual animals over the four seasons, under constant laboratory conditions and seasonal variation in free-running period; the signal-to-noise ratio and waveform of the rhythm have been investigated, as well as the incidence of rhythmic animals in the population. The variation in these rhythm parameters is considered in relation to changes in environmental conditions prevailing at the site of collection.     

Intracerebral ocelli in an amphipod: extraretinal photoreceptors of the sandhopper Talitrus saltator (Crustacea, Amphipoda)

Abstract. No morphological clues on the amphipod head indicate the existence of ocelli. However, as in several isopod species studied so far, two rudimentary photoreceptors are integrated into the medio-dorsal part of the brain. This electron microscopical study of the photoreceptors is the first report on the presence of ocelli in amphipods. Each ocellus is made up of 3 receptor cells which contribute to the formation of a photoreceptive surface (the rhabdom) formed by tightly packed microvilli. The rhabdoms are twisted and irregular in outline. Membrane turnover is suggested by the presence of different kinds of lysosomes. Lacking dioptric lenses, these photoreceptors are not likely to be involved in image formation but may function as appraisers of ambient light intensity. Physiological and behavioral studies will, henceforth, have to take into account these unexpected ocelli, which may represent remnants of the naupliar eye.     

Endogenous activity rhythm in Talitrus saltator,Britorchestia brito (Crustacea,Amphipoda) and Tylos europaeus (Crustacea,Isopoda) from Barkoukech Beach (Tabarka,Tunisia)

The locomotor activity rhythm of three supralittoral crustacean species, Tylos europaeus (terrestrial isopod) and Britorchestia brito and Talitrus saltator (amphipod, Talitridea), was investigated in Barkoukech Beach. The rhythm was monitored in individual animals in spring under continuous darkness and constant temperature. Results revealed that whatever the species, actograms and mean activity curves showed that specimens of T. europaeus and T. saltator concentrated their activity during the subjective night; whereas, B. brito concentrated its activity during the subjective day. The three species exhibited a circadian locomotor rhythm with mean circadian period, respectively, equal to 24h41′ ± 0h44′, 24h46′ ± 0h55′ and 25h21′ ± 1h16′. The most stable locomotor rhythm was found in T. saltator (0.444 ± 0.246). Furthermore, individuals of T. europaeus were significantly more active (10h47′ ± 2h52′) than the two amphipods. Differences in the activity patterns of the three species will be discussed as an adaptative strategy to respond to interspecific competitive interactions.     

Optocardiographic recording of heart rate in Talitrus saltator (Amphipoda: Talitridae)

Abstract.  An optocardiographic non-invasive technique was used to monitor heart activity in small arthropods. Heart rate was recorded in adult individuals of the supralittoral amphipod Talitrus saltator after 3 h of immersion in marine artificial water (0, 11 and 33‰, t  = 15 ± 1 °C). Mean heart rate (± SE) ranged from 210 ± 26 beats min⁻¹ (at 33‰) to 276 ± 15 beats min⁻¹ (at 0‰) and, despite the small increase in temperature (0.5 °C) due to the infrared beam, the heart frequency remained constant for several hours. Neither the glue used to apply the sensor to the animal nor the beating of the pleopods affected heart rate. This technique could be a useful tool for the investigation of ecophysiological aspects in T. saltator , which is already well known for its ecology and behaviour.     

Experimental Change of the Orientation of Two Populations of Talitrus saltator (Crustacea Amphipoda Talitridae) from Cap Bon (North‐Eastern Tunisia)

The orientation of sandhopper populations is adapted to the direction of the shoreline of the sandy beaches where they live; this behaviour was shown to be inherited in some Mediterranean populations. The question was open whether this behaviour could be adaptively modified in case of changing shoreline or passive transfer to a new differently oriented shoreline. The Cap Bon beaches in north‐eastern Tunisia are particularly interesting because they belong to two different Mediterranean Basins, the central and the eastern one, and their supra‐tidal populations do not come together. This work verified the effect of experimental change of the shoreline direction in two populations of Talitrus saltator from Cap Bon (north‐eastern Tunisia) through a displacement experiment. We transferred samples of T. saltator from two different localities (Korba and Ratiba) from their original beach to the familiar one and tested their solar and landscape orientation on the new beach that had an almost opposite direction with respect to the previous one. The comparisons of the results on the home beach and the new one confirmed the use of the solar compass in both populations, as well as the importance of landscape view and optical local sky factor in adjusting the escape direction. In both populations, an increase of scatter was observed on the new beach, especially when individuals could see the landscape. Also, a clear behavioural difference between the two populations was recorded, being Ratiba population not significantly oriented to the shoreline when tested on the unfamiliar beach, while Korba population maintained its home direction also on the new beach.     

Locomotor activity rhythm of two sympatric species Talitrus saltator (Amphipoda) and Tylos europaeus (Oniscidea) from Tunisian beaches under continuous light

Locomotor activity rhythm of the supralittoral species Talitrus saltator and Tylos europaeus was studied under continuous light in populations of Korba and Barkoukech beaches in summer. Results showed that these two species were characterized by a nocturnal behaviour. Under the subjective night, the activity was continuous for T. saltator and interrupted in T. europaeus with the presence of a clear drift towards the right more accentuated for the second species. Whatever the site, using actograms and the waveforms, results showed the absence of bimodal profile in T. europaeus and the plurimodal one in T. saltator. Moreover, the most important activity peaks were observed around the dawn and the dusk, respectively. Furthermore, periodogram and MESA analyzes highlighted the presence of ultradian and circadian components. Whatever the component and the site, the inter-individual variability was more pronounced in T. europaeus. Moreover, whatever the site, individuals of T. europaeus were more active and the locomotor rhythm was more defined in T. saltator. With reference to environmental stability and variability, the differences of locomotor activity characteristics observed between these two species are explained as a need for plasticity to adapt to environmental changes.     

Nuove ricerche sull'orientamento e il senso del tempo di Arctosa perita (Latr.) (Araneae lycosidae)

Zusammenfassung Die Uferspinne Arctosa perita (Latr.) verfügt über einen astronomischen Orientierungsmechanismus, durch den die Tiere imstande sind, wenn sie auf dem Wasser ausgesetzt werden, in der Richtung nach dem Ufer zu fliehen. Die Spinnen orientieren sich auf Grund des Sonnenstandes und des polarisierten Himmelslichtes und haben die Fähigkeit, die Tageszeit einzukalkulieren (Papi 1955b und c).Wenn eine Gruppe von Tieren gefangengehalten wird, dann nimmt bei den Fluchtversuchen die Streuung der Fluchtrichtungen zu. Dabei ist die Streuung der gesamten Fluchtversuche — wenigstens während der ersten 16 Tage — statistisch nicht verschieden, ob die Tiere nun a) in den natürlichen Belichtungs- und Temperaturschwankungen, b) im Dauerdunkel und in den Temperaturschwankungen oder c) im Finstern unter konstanter Temperatur gehalten werden. Was die Genauigkeit der Richtungsorientierung betrifft, so bleibt, trotz der stärkeren Streuung, die durchschnittliche Fluchtrichtung bei Gruppe a) bis zu 21 Tage lang korrekt, während sie bei den Gruppen b) und c) von der theoretischen Richtung immer mehr abweicht.Tiere, die im Finstern unter konstanter Temperatur gefangengehalten werden, orientieren sich bezüglich einer unbeweglichen Lampe bei verschiedenen Tageszeiten ungefähr so, wie wenn sie die Sonne wäre.Exemplare, die 3 Tage lang einem gegen den natürlichen Tag um 6 Std verschobenen Belichtungsrhythmus ausgesetzt werden, nehmen Orientierungswinkel an, die zur Zeit ihres künstlichen Tages korrekt wären.Ein innerer Tagesrhythmus (innere Uhr) regelt die Abweichung des Orientierungswinkels der Tiere. Im Laufe des Tages ändert sich der Orientierungswinkel nicht mit einer konstanten Geschwindigkeit, sondern mit einer solchen, die die Azimutgeschwindigkeit der Sonne auszugleichen sucht.Wenn die Tiere einige Stunden bei einer Temperatur von 4–5°C oder in 2°C gehalten werden, dann orientieren sie sich so, wie es einige Stunden vorher korrekt wäre. Der Gang der inneren Uhr kann also durch sehr niedrige Temperaturen verzögert oder gestoppt werden.Unter experimentellen Bedingungen können die Tiere in 8–10 Tagen neue Fluchtrichtungen erlernen.In der Besprechung werden die Resultate mit jenen verglichen, die bei anderen, einer astronomischen Orientierung fähigen Tieren erhalten wurden.

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Dedicato al Prof. Karl von Frisch in occasione del suo 70 compleanno.     

The Local Optical Factor as an Orientation Cue for the Sandhopper Talitrus Saltator Montagu (Amphipoda,Talitridae)

The aim of the present study was to assess the influence of the local optical factor (i.e., inhomogeneity in spectral composition between the hemidomes of sky over the sea and over land at the beach) on the ability of zonal orientation of the amphipod Talitrus saltator. The experiments were conducted in the laboratory using coloured filters and an apparatus that provides for orientation in artifcial conditions comparable to that observed under natural sun and sky. The results show that T. saltator can effectively use the inhomogeneity between the two hemidomes, but only if the colour distance between them is much greater than that found in the wild. This makes the possibility of perception - and thus use - of the local optical factor rather unlikely in natural conditions.     

The effect of dusk and dawn on the locomotor activity rhythm of Talitrus saltator (Montagu) (Crustacea: Amphipoda)

Entrainment of the nocturnal, endogenous locomotor activity rhythm of Talitrus saltator (Montagu) by the natural light-dark cycle is non-parametric, the phase of the rhythm shifting only in response to changes in the time of an experimentally simulated ‘dawn’ transition. The difference in response to light at ‘dusk’ and ‘dawn’ illustrates a phase-dependent responsiveness common to endogenous rhythms. Activity begins after complete darkness, with cessation always occurring during the ‘dawn’ transition and never continuing past the onset of total experimental illumination. The point of activity cessation is taken to be the position of a synchronizing cue controlling entrainment. The ‘dawn’ cue appears to be an absolute irradiance level of approximately 1.5 × 10^?4 W/m² (1.5 lux). The implications of such a cue are discussed in relation to field behaviour.