Astronomical, landscape and climatic factors influencing oriented movements of Talitrus saltator in nature

 The present study was conducted on a Mediterranean beach (Burano, southern Tuscany, Italy) to examine the timing, orientation, and motivating and directing factors of the spontaneous movements of the sandhopper Talitrus saltator (Montagu, 1808). In April 1994, October 1994 and June 1995, during different moon phases, traps were positioned in the eulittoral zone, which intercepted sandhoppers when walking on the sand surface. At the same time environmental parameters were registered. Contemporaneously, orientation tests were carried out on active individuals using two arenas, one of which permitted a view of both sky and landscape and one which prohibited the landscape view. The results show landward migration after sunset, for juveniles later than for adults, nonoriented activity for 2 or 3 h after midnight and seawards zonal recovery before and after sunrise. The main microclimatic factor modulating activity was sand temperature, while the nonoriented activity between the two migratory movements seems to be endogenously determined. Both sky and landscape cues are used by sandhoppers for orienting their course, but the landscape view is sufficient and necessary on new moon nights. These results contribute to solution of the controversy on the mechanisms actually motivating sandhoppers in nature. Received: 24 September 1996 / Accepted: 25 October 1996     

The use of slope and visual information in sandhoppers: innateness and plasticity

Mediterranean sandhoppers of the species Talitrus saltator (Montagu) from the Tyrrhenian population of Burano (Grosseto, Italy) were tested by rearing under different conditions in order to enquire into the innateness and modifiability of orientation with respect to substrate slope and landscape features. Tests were conducted from November 1990 to November 1991. The results were as follows: the sandhoppers responsed to slope only by orienting themselves downslope on dry substrate and upward on a wet one. These responses appeared to be innate but modifiable by experience. Visual dishomogeneity (half horizon covered with a black strip), with a horizontal substrate, elicited an innate orientation towards the black shape, again modifiable by experience. When a black strip was positioned around the upper half of the inclined arena, the sandhoppers responded differently, dependent upon their prior experience: wild individuals responded to the visual stimulus, amphipods reared in optical homogeneity did not make a choice and those reared in conditions identical to those of the test arena responded to slope by orienting downwards and away from the balck strip. With a black strip around the lower half of the inclined arena and with a dry substrate identical responses were shown by wild-caught and laboratory-reared sandhoppers, i.e., downslope and towards the black strip.     

Multiple regression analysis of the sources of variation in orientation of two sympatric sandhoppers, <Emphasis Type="Italic">Talitrus saltator</Emphasis> and <Emphasis Type="Italic">Talorchestia brito</Emphasis>, from an exposed Mediterranean beach

Two sympatric species from an exposed sandy beach in north-western Tunisia, the sandhoppers Talitrus saltator (Montagu) and Talorchestia brito Stebbing, were compared as regards orientation under natural conditions. Sets of experiments were carried out on the beach using two experimental arenas, one permitting the view of both the sky and landscape and the other of the sky only. Replicates were made at different hours of the day, in different days and period of the year and with various climatic conditions. Multiple regression models were fitted to the angular data obtained. These models allow an estimate of the trends of variation depending on a combination of factors. The simultaneous effects of environmental factors influencing orientation were quantified for each species. The sun was confirmed as the major orientation cue in these populations, but the concentration of directional choices was enhanced by the landscape vision. The climatic factors affected orientation in different ways depending on the time of day and year. When the two species were compared, Talitrus saltator showed a higher flexibility of response than Talorchestia brito under the same environmental conditions, supporting the hypothesis of a higher level of terrestrialization of the former species.     

Variation in zonal recovery in four Talitrus saltator populations from different coastlines: a comparison of orientation in the field and in an experimental arena

Under stressful conditions (e.g. finding themselves on dry or moisture-saturated substrates) littoral talitrids (Crustacea, Amphipoda) demonstrate zonal orientation, in which they must promptly reach the optimal zone of the beach, the wet fringe near the shoreline. A relationship might therefore exist between the use of orientation and the frequency of such stressful conditions in the natural environment. Moreover, the efficiency of orientation toward the sea could be related to the possibility of using strategies other than zonal orientation in order to avoid stress. This study analysed the actual use and efficiency of orientation under natural conditions of four Talitrus saltator (Montagu, 1808) populations from Mediterranean and northern European Atlantic coasts with different ecological features. Orientation tests were carried out on the beach with all natural cues available. Then the same individuals underwent control experiments to study their sun orientation far from the sea in an experimental arena. The following results emerge from the comparison of the circular distributions: (1) marked differences among populations in the precision of zonal recovery under natural conditions; (2) a common solar orientation capacity in the control tests far from the sea; (3) different orientation choices of the same individuals according to the test conditions, natural or controlled. The habitat diversity of the four populations (amount, distribution and kind of detritus and wrack on the beach, degree of coastal erosion, orientation of the shoreline, human use of the beach) provides an ecological interpretation for the differences in orientation observed among populations. Received: 13 October 1997 / Accepted after revision: 26 April 1998     

Moon orientation in sandhoppers: effects of lighting treatments on the persistence of orientation ability

The moon orientation rhythm persists in sandhoppers removed from environmental entrainments relative to moon periodicity. In order to investigate the underlying mechanism, the crustacean amphipods Talorchestia capensis and Talitrus saltator were collected at new moon and exposed in the laboratory to an artificial light during the day, but to a variety of lighting treatments during the night: (1) continuous dark, (2) dim light in phase with the natural moon, (3) continuous dim light. The animals were tested under the moon 9–21 days later by using a new type of arena. The ability to orientate in a direction perpendicular to the shore persisted in sandhoppers under treatments 1 and 2, but not under treatment 3. A disturbance due to a phototactic tendency in Talorchestia was also observed in animals captured on the day of the test when exposed to unnatural lighting, but not when they were kept under natural light. The present findings show that the timing mechanism allowing compensation for changes in the moon’s position also persists in animals that have been long removed from entraining factors. The dependence of this orientation ability on nocturnal lighting and the disturbing effect of sudden changes in light intensity support the idea that the phasal lighting of the moon, and perhaps sunrise and sunset act as resetting factors for the moon’s orientation rhythm.     

Biomonitoring of polychlorinated byphenyls contamination in the supralittoral environment using the sandhopper Talitrus saltator (Montagu)

We evaluated the use of Talitrus saltator as biomonitor of polychlorinated byphenyls (PCBs) contamination of the supralittoral zone of Mediterranean sandy shores, an area not yet investigated about the presence of these pollutants. Twenty of 22 PCB congeners analysed were detected and quantified in sand and sandhoppers' samples collected in 6 different sites along the Tyrrhenian coast of Central Italy. Among the congeners analysed, PCB 153 and PCB 138 were the most abundant both in amphipods and sand samples and, regarding the congener pattern analysis, hexa-, hepta- and penta-PCBs were the most abundant congeners in sandhoppers. Though hydrophobic compounds, such as PCBs, bind strongly to sand and sediments, PCB concentrations were higher in T. saltator than in the sand revealing a good ability of this species to accumulate this class of contaminants. The concentration of each PCB congener recorded in tissues of sandhoppers showed significant differences among sampling sites revealing a good ability of these species to accumulate PCBs at different concentrations depending on the contamination levels of the sampling site. Therefore, our results suggest the possible utilisation of T. saltator as a biomonitor of PCB contamination of the supralittoral zone of Mediterranean sandy shores.     

Orientation of juvenile barn swallows (<Emphasis Type="Italic">Hirundo rustica</Emphasis>) tested in Emlen funnels during autumn migration

Although hirundines have been used extensively in homing experiments, to date no investigation of their migratory orientation has been carried out, despite the well-known migratory habits of many species of this family. This paper reports on a study of the orientation of the barn swallow (Hirundo rustica), a typical diurnal trans-Saharan migrant. Modified Emlen funnels were used to verify the suitability of this species for cage experiments and investigate the role of visual and magnetic cues during the birds first migratory journey. Juvenile swallows were mist-netted at a roost site in central Italy and then tested in a site 19 km apart. Orientation experiments were performed under four experimental conditions: natural clear sky and simulated overcast, in both local and shifted magnetic fields (magnetic North=geographical West). Under clear sky, the swallows tended to orient phototactically toward the best-lit part of the funnel and failed to respond to the magnetic field shift. Under overcast conditions, they oriented northward and modified their directional choices as expected in response to the shifted magnetic North. On the whole, our data indicate that swallows can use magnetic information for compass orientation. Possible explanations for the northward orientation of birds tested under overcast conditions are discussed.Communicated by W. Wiltschko     

Genetic determination and plasticity in the sun orientation of natural populations ofTalitrus saltator

As has been previously shown, talitrid crustaceans have an inherited compass which causes them to head in a direction appropriate to their original shoreline (even after several generations in the laboratory), while learnt components can improve the correctness of orientation in natural conditions. In order to extend this analysis to a greater range of populations and to show differences in the determination of direction finding behaviour, seven natural populations ofTalitrus saltator (Montagu) from differently oriented shores of the Ligurian (Marina di Vecchiano, Pisa), Tyrrhenian (Castiglione della Pescaia and Tombolo di Feniglia, Grossetto) and Adriatic (Casal Borsetti, Ravenna; Torre Fantine, Marina di Lesina and Lido di Siponta, Foggia). Italian coasts were compared for their rigidity-plasticity in sun orientation. The study was conducted from 1982 to 1985. Differences were given in relation to the dynamics of the shorelines, the stability of which changes over the years due to natural and artificial causes. Furthermore, in order to reveal something about the genetic determination of the compass, mass-crosses between geographically distant populations (Ligurian-Tyrrhenian on one side and Adriatic on the other) were performed, and the F1 and F2 inexpert offspring tested for sun orientation. The results show a partial or total disruption of the compass in cross offspring which is discussed in the light of oligogenic and polygenic transmission mechanisms.     

Orientation of sandhoppers at different points along a dynamic shoreline in southern Tuscany

Orientation experiments were carried out on Talitrus saltator (Crustacea Amphipoda) at four points along 3 km on a dynamic sandy beach inside the Maremma Regional Park (Grosseto, Italy) to highlight behavioural variation related to distance from a river mouth, to erosion or accretion of shoreline, and to human trampling on the beach. Tests were performed using circular transparent Plexiglas arenas, contemporaneously at the four points. Replicates were made in 2 different months (September 2002 and May 2003), on 2–3 successive days, in the morning and afternoon. The distributions of the angles of orientation were compared for the different points and seasons, and multiple regression analysis was performed to test the effects of environmental and intrinsic variables on orientation. Sandhoppers showed the highest scatter at the eroded shoreline, intermediate scatter at the accreting beach most distant from the river mouth, and consistent orientation seaward at the least disturbed point. Orientation of sandhoppers was significantly affected by season, global radiation, time of day, distance from the river mouth, and human trampling. Sex and air humidity were of minor significance in the multiple regression model. The results, on the one hand, confirm plasticity in orientation of sandhoppers living on a dynamic shoreline, and on the other hand, show that variation in orientation could potentially be used as a bioindicator of shoreline changes.Communicated by R. Cattanevo-Vietti, Genova     

Sunset orientation of robins,Erithacus rubecula,with different fields of sky vision

Summary Migratory orientation of robins (Erithacus rubecula) at sunset was recorded using orientation cages, under clear autumn skies. The aim of the experiments was to examine the importance of different visible sky sections for the orientation of robins. I obtained the following results: (1) Robins tested with the visible sky section limited to 90° around zenith (45° above the horizon) showed a mean orientation that coincided with the average sunset azimuth, with little scatter around the mean angle (Fig. 2). (2) When the birds were allowed a more extensive field of sky vision (maximum 160°), they chose headings on an approximate north-south axis, significantly different from tests with a restricted view of the sky (Fig. 3). (3) Experiments were also performed in which the response of robins to a mirror deflection (about 120° counterclockwise) of visual cues in the lower parts of the sunset sky was examined. The outcome indicated that visual information in the lower part of the sky may be critical for the orientation of robins (Fig. 5). These results, together with recent findings that robins captured and tested at two nearby sites show distinctly different orientation behavior in relation to experimental manipulations of the magnetic field, suggest that priorities among orientation cues may differ depending on the migratory situation encountered.     

Sunset and the orientation of a nocturnal bird migrant: A mirror experiment

Summary If savannah sparrows, (Passerculus sandwichensis), a North American night migrant, select a migratory heading based upon the setting sun, a shift in the position of that cue should produce a predictable shift in the migrant's nocturnal orientation. I tested this hypothesis by shifting the sunst position with mirrors and by recording the bird's orientation in Emlen funnels. The control group displayed directionality appropriate for spring migration (=342°). The mean heading of experimentals (=272°), which were exposed to a cue-shifted situation, was in the expected westerly direction relative to the control mean (P<0.05, V-test). The setting sun appears to be a sufficient source of directional information for this avian migrant.     

Distribution patterns of different age classes and sexes in a Tyrrhenian population of <Emphasis Type="Italic">Talitrus saltator</Emphasis> (Montagu)

Temporal and spatial distribution patterns of a population of Talitrus saltator living on the Tyrrhenian coast of Tuscany (Italy) were studied. Bimonthly surveys were performed from March 1991 to January 1992 along transects using a standard system of pitfall traps and sieves for surface-active and burrowed individuals, respectively. Captured individuals were subdivided into sex and age classes (on the basis of the number of articles of the flagellum of the second antenna). Abundances were calculated for each sampling period and sex ratios were determined. For each sampling period the mean hour of surface activity was calculated together with the mean zonation of both surface-active and burrowing sandhoppers belonging to the different sex and age classes. Shifts in mean zonation between the resting and active phase were also determined. For each category of sex, age, and reproductive phase, simple and multiple regression analyses were used to find relationships of the mean zonation of surface-active animals with climatic data, and of the number of burrowed individuals with surface sand parameters recorded in correspondence to the sieves. On the whole, the results show that this Tyrrhenian population of T. saltator exhibited a bivoltine reproductive cycle and that the sex ratios of active sandhoppers were male or female biased according to the season. The variations in the mean hour of surface activity and in the zonation patterns of sandhoppers depended more on the age than on the sex. Furthermore distribution patterns were generally related to seasonal changes in the local climatic and substrate parameters. The observed differences between burrowing and activity zonations were interpreted on the basis of the nocturnal migrations of the different categories.     

Influence of weak electric and magnetic fields on turning behavior in elvers of the American eel Anguilla rostrata

The turning behavior of elvers of the American eel Anguilla rostrata was studied in an arena in which a horizontal electric or a vertical magnetic field could be manipulated. The objectives were to determine if the strength and polarity of a weak direct-current (dc) electric field influenced elver orientation, and to determine if any such influence was due to electric fields generated by the elvers' own swimming movements. As electric current density increased from 10^-2 A cm^-2 to 10² A cm^-2, elvers turned increasingly more toward the anode, regardless of whether the anode was on the left or right side of the arena. Elvers in the lowest field turned more toward the cathode than control elvers, and elvers in the highest field turned more toward the anode than controls. There were no differences in mean turning angles of groups of elvers swimming in four different vertical magnetic field conditions (0.54 gauss, <0.02 gauss, 0.52 gauss reversed direction, and 2.00 gauss), suggesting that elvers were not influenced by internally generated electric fields. However, swimming speeds were such that the generated fields would have been of the order of 10^-4 A cm^-2 or less. Elver orientation apparently could be influenced by electric fields of the magnitude generated in major ocean current systems, but probably are not influenced by electric fields generated by their own swimming in the geomagnetic field.     

The effect of a “permanent” clock-shift on the orientation of experienced homing pigeons

Summary A group of experienced homing pigeons vas subjected to a 6 h slow shift of their internal clock and kept under these conditions for more than 2 months. During the overlap time between the natural and artificial photoperiods they were released for training flights to familiarize them with an area while living in a permanent shift.Tested outside the permanent shift training range, the experimentals always deviated about 30° clockwise from the mean of their controls, markedly less than in a regular 6 h slow shift. Inside the permanent shift training range, however, they oriented like the controls (Fig. 2). When their internal clock was returned to normal, the birds showed a larger counterclockwise deflection on their first flight, which was roughly comparable to the effect of a regular 6 h fast shift (Fig. 3). On later flights after normalization, this large shift was no longer found; instead we observed a roughly 30° counterclockwise deflection when they were released inside the permanent shift training range in the morning. This deflection did not seem to occur in the afternoon or outside the permanent shift training range (Figs. 4, 5), and it disappeared when the birds were repeatedly released from the same site (Fig. 6).The occurrence or non-occurrence of the deflection was independent of the duration of the shift or the time passed after normalization; it seemed to depend solely on whether the birds had become familiar with a given site in the situation of the permanent shift. This argues against an effect based on the sun compass. We tend to assume that the still unknown navigational map is involved. In this case, however, as the deflection is independent of the home direction and the type of release site bias, the factors in question would act very differently from the gradients on which the traditional concepts of the navigational map are based. The processes establishing and updating the map and their possible differences are discussed.Died on August 17, 1980     

Vertical distribution of phytoplankton during investigations of a natural surface film

An interdisciplinary research program (Kombiniertes Oberflächenfilmprojekt KOFF), in the North Sea area about 75 km west of the Island of Sylt, is directed towards gaining further knowledge on the biological importance of the natural surface film. The investigations include the water body below the film as well as dynamic processes at the surface. Persistence of calm weather conditions (cloudless sky) before and during the investigations permitted observations of the diurnal species-specific vertical migration of Dinophyceae. Two groups could be distinguished: (1) Prorocentrum micans and Ceratium furca; (2) C. horridum, C. macroceros and C. fusus. The active accumulation of P. micans in the slick was verified by a significant correlation coefficient—linearly correlated with the time of day. The results presented reveal continuity between surface film and underlying water column.This work was supported by the Sonderforschungsbereich (SFB) 94, Hamburg, of the Deutsche For-schungsgemeinschaft.     

Turbulence and waves inside flexible-wall systems designed for biological studies

Simultaneous flow measurements were performed by hot-wire anemometry inside and outside (a) a closed bag, and (b) a flow-through system designed for metabolic experiments of Fucus vesiculosus communities. Since water movement is considered an important parameter in such biological studies, the walls of the systems were flexible in order to establish flow conditions within the enclosed water body comparable to those in the natural environment. In situ experiments in the Baltic Sea at a water depth of 2 m showed that energy spectra inside the systems were comparable to those outside for a variety of flow and wave conditions. Thus, biological data from glexible wall systems, carefully designed to meet specific natural flow requirements, can be taken as reliable input data for natural ecosystem modeling.Contribution No. 147 of the Joint Research Programme 95 Interaction Sea-Sea Bottom, Kiel University, Kiel (FRG), and Hawaii Institute of Geophysics Contribution No. 803.     

Pigeon homing: the effect of a clock-shift is often smaller than predicted

This analysis is based on 103 releases with 6-h clock-shifted pigeons of various ages and experiences. Resetting the internal clock normally leads to a significant change in initial orientation; however, in half of the cases, the induced deflections are significantly smaller than predicted by the sun compass hypothesis. The relative size of the deflections decreases with increasing age and experience (Fig. 3). Only young pigeons with limited experience respond as expected, while old birds show deflections which are, on the average, only slightly more than half of the predicted size, except at extremely familiar sites (Table 2). There is no difference between fast and slow shifts (Fig. 4). It is not possible to clearly specify under what circumstances smaller deflections occur; previous clock-shifts (Fig. 5), familiarity with the release site (Table 4) and duration of the shifting procedure (Table 5) do not seem to be the reasons. Clock-shifting also tends to decrease the vector lengths and has a marked effect on homing performance (Table 7). Nevertheless, considerable numbers of clock-shifted birds return on the day of release before their internal clock has begun to be reset back to normal. The general role of the sun compass in bird orientation is considered and theoretical implications of our findings are discussed in view of the map and compass-model and the possibility that an alternative, non-time-compensating compass is used in parallel with the sun compass.     

Solar orientation in the snail Nerita plicata (Prosobranchia: Neritacea) on a beach near Watamu,Kenya

Investigations carried out under natural conditions suggest that Nerita plicata Linné is capable of orientating to the sun. Behaviour is predominatly photonegative during the morning, and photopositive during the afternoon. Accuracy of orientation improves as the brightness of the sun increases. At Watamu (Kenya), snails tended to orientate away from the sea at all times of the day. Orientatory performance is not affected by the temporal proximity of high or low water, and locomotory speeds seem to be unaffected by the strength of the sun, the time of day, or the state of the tide.     

Thermal behaviour of a small spider (Araneae : Araneidae : Araneinae) on horizontal webs in semi-arid Western Australia

Summary The solar orientation response of a small spider (gen. nov.: Araneae: Araneidae: Araneinae) is examined at a semi-arid location in tropical Western Australia. The spiders rest beneath horizontal dome-shaped webs close to the ground surface on spinifex (Triodia sp.). The spiders are small (c. 5 mm long) and robust, being only twice as long as wide. Spider orientation, elevation, wind velocity, radiation and wet and dry bulb temperatures together with spider and egg-sac temperatures were measured throughout the day. The spiders orientated their long axis to the solar azimuth through much of the day and postured to the solar elevation; in so doing they tracked the apparent movement of the sun throughout the day with considerable precision, far exceeding that of other spiders studied. Stepwise regression indicated that the solar position was the most important environmental factor associated with the posturing and orientation. The variance in the orientation of the population was associated with a suite of environmental variables related to wind velocity and temperature. Spider (abdominal) temperature had a curvilinear relationship with ambient temperature, with a plateau at c. 35° C, whereas egg-sac temperature had a strictly linear relationship with ambient temperature. Stepwise regression indicates that both the spider and egg-sac temperatures are related mainly to net radiation and ambient temperature. The spiders can alter the incident radiation to which they are exposed by c. 2.2 times which represent the limits of the exposed silhouette area between full dorsal sunlight and the posterior (or anterior) aspect. Under hot conditions the spiders posture and orientate such that the long axis of the body is orientated abdomen towards the sun.