Behavioral rhythms of the Japanese newts, Cynops pyrrhogaster, under a semi-natural condition

 Locomotor activity rhythms of the Japanese newt, Cynops pyrrhogaster, were recorded under a semi-natural condition using phototransistor systems. The daily activity rhythm showed a seasonal change: the locomotor activity was mainly diurnal (active during the daytime) from spring to early summer; mainly nocturnal (active during the night-time) from summer to autumn; and showed either a diurnal or nocturnal pattern, depending on the ambient temperature, in winter. To analyze the daily activity in detail, we observed the behavior of a group of newts (three males, three females) throughout 24 h. Four types of behavior (respiration, feeding, mating, and resting on the land) were observed. Each behavior had daily rhythms and showed a seasonal change. The behavior on land showed mainly a nocturnal or bimodal pattern (activity rhythms with two peaks) throughout the year and was more frequently observed in summer. Mating behavior also showed a seasonal change: high activity in spring, with peaks in the early morning and evening, but no activity in summer. Except in winter, feeding and respiratory behavior showed no seasonal changes in either activity period or frequency. Coupling between behavior and the clock seems to be weak in the Japanese newt because of indistinct daily rhythms and frequent phase changes of locomotor activity in water. Physical factors such as humidity and temperature seem to affect strongly the daily activity of the newts. Received: 21 April 1997 / Accepted: 1 September 1997     

Seasonal Variation of Temporal Niche in Wild Owl Monkeys (Aotus azarai azarai) of the Argentinean Chaco: A Matter of Masking?

Among the more than 40 genera of anthropoid primates (monkeys, apes, and humans), only the South American owl monkeys, genus Aotus, are nocturnal. However, the southernmostly distributed species, Aotus azarai azarai, of the Gran Chaco may show considerable amounts of its 24-h activity during bright daylight. Due to seasonal changes in the duration of photophase and climatic parameters in their subtropical habitat, the timing and pattern of their daily activity are expected to show significant seasonal variation. By quantitative long-term activity recordings with Actiwatch AW4 accelerometer data logger devices of 10 wild owl monkeys inhabiting a gallery forest in Formosa, Argentina, the authors analyzed the seasonal variation in the temporal niche and activity pattern resulting from entrainment and masking of the circadian activity rhythm by seasonally and diurnally varying environmental factors. The owl monkeys always displayed a distinct bimodal activity pattern, with prominent activity bouts and peaks during dusk and dawn. Their activity rhythm showed distinct lunar and seasonal variations in the timing and daily pattern. During the summer, the monkeys showed predominantly crepuscular/nocturnal behavior, and a crepuscular/cathemeral activity pattern with similar diurnal and nocturnal activity levels during the cold winter months. The peak times of the evening and morning activity bouts were more closely related to the times of sunset and sunrise, respectively, than activity-onset and -offset. Obviously, they were better circadian markers for the phase position of the entrained activity rhythm than activity-onset and -offset, which were subject to more masking effects of environmental and/or internal factors. Total daily activity was lowest during the two coldest lunar months, and almost twice as high during the warmest months. Nighttime (21:00–06:00?h) and daytime (09:00–18:00?h) activity varied significantly across the year, but in an opposite manner. Highest nighttime activity occurred in summer and maximal daytime activity during the cold winter months. Dusk and dawn activity, which together accounted for 43% of the total daily activity, barely changed. The monkeys tended to terminate their nightly activity period earlier on warm and rainy days, whereas the daily amount of activity showed no significant correlation either with temperature or precipitation. These data are consistent with the dual-oscillator hypothesis of circadian regulation. They suggest the seasonal variations of the timing and pattern of daily activity in wild owl monkeys of the Argentinean Chaco result from a specific interplay of light entrainment of circadian rhythmicity and strong masking effects of various endogenous and environmental factors. Since the phase position of the monkeys' evening and morning activity peaks did not vary considerably over the year, the seasonal change from a crepuscular/nocturnal activity pattern in summer to a more crepuscular/cathemeral one in winter does not depend on a corresponding phase shift of the entrained circadian rhythm, but mainly on masking effects. Thermoregulatory and energetic demands and constraints seem to play a crucial role. (Author correspondence: hans.erkert@t-online.de)     

Nocturnally retained zeaxanthin does not remain engaged in a state primed for energy dissipation during the summer in two Yucca species growing in the Mojave Desert

Differently oriented leaves of Yucca schidigera and Yucca brevifolia were characterized in the Mojave Desert with respect to photosystem II and xanthophyll cycle activity during three different seasons, including the hot and dry summer, the relatively cold winter, and the mild spring season. Photosynthetic utilization of a high percentage of the light absorbed in PSII was observed in all leaves only during the spring, whereas very high levels of photoprotective, thermal energy dissipation were employed both in the summer and the winter season in all exposed leaves of both species. Both during the summer and the winter season, when energy dissipation levels were high diurnally, xanthophyll cycle pools (relative to either Chl or other carotenoids) were higher relative to the spring, and a nocturnal retention of high levels of zeaxanthin and antheraxanthin (Z + A) occurred in all exposed leaves of both species. Although this nocturnal retention of Z + A was associated with nocturnal maintenance of a low PSII efficiency (F_v/F_m) on a cold winter night, pre‐dawn F_v/F_m was high in (Z + A)‐retaining leaves following a warm summer night. This indicates nocturnal engagement of Z + A in a state primed for energy dissipation throughout the cold winter night – while high levels of retained Z + A were not engaged for energy dissipation prior to sunrise on a warm summer morning. Possible mechanisms for a lack of sustained engagement of retained Z + A for energy dissipation at elevated temperatures are discussed.     

Changes in distribution and behaviour of two congeneric mayflies in a boreal river and its seasonal tributaries

Both Parameletus chelifer and P. minor had univoltine life-cycles. For a period of 6–10 months almost no nymphs of either species were found. The first nymphs appeared near midstream in winter and later in spring when the ice had broken up, they were found in great numbers close to the bank of the main river. During spring, nymphs of P. chelifer colonized the newly flooded littoral faster, and a seasonal stream in an alluvial meadow in greater numbers, than did nymphs of P. minor. Both species also colonized 10 seasonal tributaries which showed that the springtime upstream colonization was a common behaviour. During the colonization of the seasonal stream in the alluvial meadow, the diel activity pattern changed in nymphs of both species. In the main river small nymphs showed a nocturnal activity, while large nymphs were active during day-time. In the seasonal stream, both small and large nymphs showed a diurnal activity. However, when the stream was flooded, small nymphs of both species showed nocturnal activity again. In both species, diurnal activity of mature nymphs continued during emergence. Reasons for shifts in diel activity are discussed.     

Nocturnal variation of prolactin secretion in the Mouflon (Ovis gmelini musimon) and domestic sheep (Ovis aries): seasonal changes

Seasonal changes in nocturnal prolactin secretion and their relationship with melatonin secretion were monitored in wild (Mouflon, Ovis gmelini musimon) and domesticated sheep (breed Manchega, Ovis aries). Two groups of eleven adult females each, were maintained outdoors under natural photoperiod. Plasma concentrations of prolactin and melatonin were determined during the summer and winter solstices and the autumn and spring equinoxes. Blood samples were collected every 3h during the night hours, and 1h before and after the onset of darkness and sunrise. Maximum mean plasma concentrations of prolactin during the dark-phase in Mouflons were observed in the summer solstice, (P<0.001) and in the summer solstice and spring equinox in Manchega ewes (P<0.001). Mean plasma concentrations of prolactin were higher in the wild species (P<0.001) during the summer solstice. In contrast, during the spring equinox, mean levels of prolactin were higher in Manchega ewes than in Mouflons (P<0.05). Plasma prolactin concentrations showed a nocturnal rhythm in both breeds, with seasonal variations (P<0.001). The increase in plasma melatonin levels during the first hour after sunset was accompanied to increasing concentrations of PRL 1h after the onset of darkness, only in the autumn and spring equinox for the Mouflon, and in the summer solstice and spring equinox for the Manchega ewes. In Mouflons, the fall of plasma PRL concentrations about the middle dark-phase in all the periods studied, coincided with high levels of melatonin. A similar relation was observed in Manchega ewes only in the winter solstice and spring equinox. The current study shows that the nocturnal rhythm of prolactin secretion exhibits seasonal variation; differences in the patterns of prolactin secretion between Mouflon and Manchega sheep are taken to represent the effects of genotype.     

The effect of environmental factors on the activity ofGammarus pseudolimnaeus (Amphipoda)

Various environmental parameters which may affect the activity ofGammarus pseudolimnaeus were examined in the laboratory. The animals' responses were monitored automatically using an ultraviolet beam interruption technique. The basic diel activity pattern in the fall showed high rates of drifting at night but in the summer showed uniform drift throughout the light/dark cycle. Upstream activity was greater in the summer when it compensated approximately 11% of the number of animals drifting downstream. A large-sized gravel substrate (31.5 mm diameter) produced significantly lower night-time drift than either a medium-sized gravel (11.0 mm diameter) or a small-sized gravel (3.4 mm diameter). Animals drifted more at current speeds of 5 to 15 cm/s than at 20 to 25 cm/s. The introduction of rainbow trout to the tanks in the day or night caused almost total cessation of drift and upstream activity within minutes. Trials with fish water suggested that the amphipods detect some form of labile exudate produced by the fishes. Additions of toxicants, in the form of sulphuric acid and NaCl, produced changes in activity levels before lethal concentrations were reached.     

Seasonal variation of temporal niche in wild owl monkeys (Aotus azarai azarai) of the Argentinean Chaco: a matter of masking?

Among the more than 40 genera of anthropoid primates (monkeys, apes, and humans), only the South American owl monkeys, genus Aotus, are nocturnal. However, the southernmostly distributed species, Aotus azarai azarai, of the Gran Chaco may show considerable amounts of its 24-h activity during bright daylight. Due to seasonal changes in the duration of photophase and climatic parameters in their subtropical habitat, the timing and pattern of their daily activity are expected to show significant seasonal variation. By quantitative long-term activity recordings with Actiwatch AW4 accelerometer data logger devices of 10 wild owl monkeys inhabiting a gallery forest in Formosa, Argentina, the authors analyzed the seasonal variation in the temporal niche and activity pattern resulting from entrainment and masking of the circadian activity rhythm by seasonally and diurnally varying environmental factors. The owl monkeys always displayed a distinct bimodal activity pattern, with prominent activity bouts and peaks during dusk and dawn. Their activity rhythm showed distinct lunar and seasonal variations in the timing and daily pattern. During the summer, the monkeys showed predominantly crepuscular/nocturnal behavior, and a crepuscular/cathemeral activity pattern with similar diurnal and nocturnal activity levels during the cold winter months. The peak times of the evening and morning activity bouts were more closely related to the times of sunset and sunrise, respectively, than activity-onset and -offset. Obviously, they were better circadian markers for the phase position of the entrained activity rhythm than activity-onset and -offset, which were subject to more masking effects of environmental and/or internal factors. Total daily activity was lowest during the two coldest lunar months, and almost twice as high during the warmest months. Nighttime (21:00-06:00 h) and daytime (09:00-18:00 h) activity varied significantly across the year, but in an opposite manner. Highest nighttime activity occurred in summer and maximal daytime activity during the cold winter months. Dusk and dawn activity, which together accounted for 43% of the total daily activity, barely changed. The monkeys tended to terminate their nightly activity period earlier on warm and rainy days, whereas the daily amount of activity showed no significant correlation either with temperature or precipitation. These data are consistent with the dual-oscillator hypothesis of circadian regulation. They suggest the seasonal variations of the timing and pattern of daily activity in wild owl monkeys of the Argentinean Chaco result from a specific interplay of light entrainment of circadian rhythmicity and strong masking effects of various endogenous and environmental factors. Since the phase position of the monkeys' evening and morning activity peaks did not vary considerably over the year, the seasonal change from a crepuscular/nocturnal activity pattern in summer to a more crepuscular/cathemeral one in winter does not depend on a corresponding phase shift of the entrained circadian rhythm, but mainly on masking effects. Thermoregulatory and energetic demands and constraints seem to play a crucial role.     

Diurnal variations in plasma testosterone concentrations in the male lesser mouse lemur (Microcebus murinus)

In 6 isolated adult male lesser mouse lemurs, concentrations of testosterone in plasma were determinated at 6-h intervals over a 24-h period. Blood samples were collected at monthly intervals and for a period of 12 months under natural photoperiod. In this nocturnal prosimian, there were no apparent diurnal changes in testosterone concentrations during the non-breeding season (autumn). During seasonal sexual activity (January-August), diurnal changes in testosterone concentrations were characterized by a significant rise during the light phase. The daily testosterone peak occurred about 8.5 h after sunrise from February to July, but at the beginning (January) or at the end (August) of the breeding season, the daily testosterone peak was displaced to the morning. A circannual testosterone rhythm occurred with the highest testosterone values in May/June and the lowest values 6 months later. The dramatic fall in testosterone concentrations after the summer solstice may be associated with a change in the peripheral metabolism of testosterone.     

Daily cycles in plasma and ocular melatonin in demand-fed sea bass, Dicentrarchus labrax L.

Melatonin is regarded as an internal zeitgeber, involved in the synchronization to light of the daily and seasonal rhythms of vertebrates. To date, plasma and ocular melatonin in fish have been extensively surveyed almost solely in freshwater species – with the exception of some migrating species of salmonids. In the present paper, melatonin levels of a marine species (sea bass, Dicentrarchus labrax L) were examined. In addition, the daily rhythms of the demand-feeding activity of sea bass, a fish species characterized by a dual phasing capacity (i.e. the ability to switch between diurnal and nocturnal behaviour), were investigated before sampling. Sea bass, distributed in 12 groups of four fish and kept under constant water temperature and salinity, were exposed to a 12 h light:12 h dark cycle (200:0 lx, lights on at 0800 hours). After 4 weeks recording, the animals were killed at 0900, 1200, 1400, 1600, 1900, 2100, 2400, 0200, 0400, 0700 and 0900 hours. Actograms of demand-feeding records revealed a nocturnal feeding behaviour, with some cases of spontaneous inversions in phasing. Melatonin levels in plasma peaked in the middle of the dark phase, dropping after lights on. Melatonin in the eye, on the contrary, exhibited an inverse profile, with high levels during daytime and low levels at night. These results suggest that melatonin in the plasma and the eye may act independently on the flexible circadian system of sea bass. Accepted: 30 January 1997     

Carbon dioxide output and mating in adult cabbage looper moths exposed to discrete light régimes

Carbon dioxide discharge and the number of spermatophores transferred were recorded from populations of adult cabbage loopers, Trichoplusia ni, maintained under various wavelengths and intensities of light. Nocturnal CO₂ output was enhanced by retaining 1 per cent of the diurnal intensity of near-u.v. and blue lights during the scotophase. However, addition of < 10 per cent of the diurnal intensities of u.v., blue, and white lights suppressed CO₂ production. Exposure to gold light resulted in the lowest 24 hr CO₂ accumulations, and red was intermediate. Similarly, maximum levels of mating occurred when cabbage loopers were exposed to nocturnal intensities of 1 per cent of the diurnal u.v., blue, or white lights, even though higher intensities were inhibitory. Considering all nocturnal intensities ranging from 0 to 100 per cent of diurnal levels, u.v. and red yielded the highest mating frequencies, blue and gold were intermediate, and white was lowest. Thus, relatively unique action spectra resulted from each régime.     

140 Ecophysiology of The Red Alga Porphyra Umbilicalis Kützing (Rhodophyta,Bangalies): Responses to Abiotic Stress

The effects of tidal elevation, emersion, sun exposure, and season on several antioxidant enzymes (ascorbate peroxidase, glutathione reductase, and catalase), pigments (phycoerythrin, phycocyanin, chlorophyll a and total carotene) and photosynthetic efficiency of photosystem II (Fv/Fm) in Porphyra umbilicalis were evaluated. Plants were collected monthly from sun‐exposed and shaded locations in the high, mid, and low intertidal following periods of tidal emersion ranging from 0–6 hours. Glutathione reductase activity was greatly affected by emersion during summer months, while ascorbate peroxidase and catalase activities showed no seasonal patterns. Differences in glutathione reductase and catalase levels occurred between sun‐exposed and shaded plants in the high and mid intertidal during summer. At all elevations, photosynthetic pigments showed a strong seasonal trend, with the effect of sun exposure being most apparent during summer. While total carotene increased with emersion during summer months, the combined effects of emersion and season were inconsistent for phycoerythrin, phycocyanin and chl a. Photosynthetic efficiency (Fv/Fm) decreased following emersion in summer and fall. During most months, sun exposed plants had lower Fv/Fm values compared to plants growing in the shade. This study emphasizes the importance of examining the effects of abiotic stresses simultaneously in order to reveal interactive relationships.     

Suppression of nocturnal increases in levels of melatonin elicits an anticipatory behavior in male quail

Abstract

During the reproductive development of male Japanese quail the duration of daily activity is prolonged and the onset of the rhythm of activity is advanced relative to the light‐dark cycle. The neuroendocrine basis for these changes was investigated with focusing on plasma levels of melatonin and testosterone. By means of 4 additional hours of photic stimulation of the brain, after the environmental lights (8L: 16D, lights on at 1000 hr) were turned off, the increase in levels of melatonin after lights‐off was suppressed for a few days. Thereafter the early onset of daily locomotor activity was observed and the gonads began to develop. Similar behavioral changes occurred in castrated quail following direct brain‐illumination or testosterone implants. The testosterone implants also suppressed the increases in levels of melatonin after lights‐off, for a few days. Treatment with an antiserum raised against melatonin (anti‐M) for the first 3 days, to suppress the increases in levels of melatonin after lights‐off, elicited such an anticipatory behavior. These results suggest that suppression of the nocturnal rise in melatonin levels is important for the first steps toward reproductive activity in male Japanese quail.     

Species composition and nocturnal activity of phlebotomine sand flies (Diptera: Psychodidae) inhabiting a limestone cave in Thailand

We investigated the nocturnal activity of cave‐dwelling sand flies at different time intervals and determined their species composition and seasonal variation. Sand flies were captured on one night each month using CDC light traps from 18:00–06:00 with the collecting bag being changed every two h between February, 2010 and January, 2011. A total of 18,709 individuals, including 10,740 males and 7,969 females, was collected. The overall ratio between male and female specimens was 1:0.74. The collected specimens included 14 species from four genera, Chinius, Idiophlebotomus, Phlebotomus, and Sergentomyia. Sergentomyia phadangensis was the most abundant species (comprising 31.9% of the collected individuals), followed by Se. anodontis (22.8%) and Ph. mascomai (18.2%). The highest number of specimens was collected in July (15.6%), followed by May (15.5%) with the peak of collection recorded at the time interval of 00:01–02:00, followed by 22:01–00:00. However, there were no significant differences observed among time intervals of sand fly collections (p=0.154). Observations of the nocturnal activity of male and female sand flies throughout the night suggest that phlebotomine sand flies show the greatest activity level after midnight.     

Drift and upstream movement in Yuccabine Creek,an Australian tropical stream

Drift and upstream movement were monitored over 14 months in a seasonal upland tropical stream in northeastern Australia. There were distinct seasonal pulses in the drift with variable peak levels in the summer wet season and low more stable levels during the dry season. Drift density ranged from 0.36 to 3.98 animals per m³ (monthly mean = 1.26). There was no correlation between drift density and either benthic density or stream discharge. In the absence of catastrophic drift, drift was dispersive, not depletive in the wet season. A total of 121 taxa were caught in the 14 drift samples. Most taxa had nocturnal maximum drift levels with a peak immediately after sunset, a pattern apparently related to level of light and not temperature. Compensation for drift by upstream-moving nymphs and larvae was least during the wet season and increased during the dry season to a peak of 27% by numbers. Mean compensation was 8.2%. It is suggested that apart from in the wet season when an animal may drift substantial distances, most riffle animals will spend their larval lives in one small stretch of stream.     

Melatonin implantation during spring and summer does not affect the seasonal rhythm of feeding in anadromous Arctic charr (Salvelinus alpinus)

Plasma melatonin levels in the high-latitude teleost Arctic charr (Salvelinus alpinus) are constantly low during summer when feeding activity is high, and high during the dark winter when they eat little and loose weight. The question arises if melatonin is involved in the phase-setting of annual rhythms of feeding and growth and if low summer melatonin production is permissive for high summer growth in this species. The present study was therefore set out to compare the seasonal appetite and growth rhythms in Arctic charr with constantly high plasma melatonin levels from February throughout the Arctic summer (melatonin implanted, average mid-day plasma melatonin levels 1,106 ± 147 pg/ml) with those of fish with natural plasma melatonin levels (vehicle implanted and untreated fish with average mid-day plasma melatonin levels of 94 ± 13 and 58 ± 6 pg/ml, respectively). Feed intake, body mass or body length, as well as the timing of the seasonal growth rhythm, were not affected by the high summer plasma melatonin level. Further, Arctic charr fasted for 3 months had a 24 h plasma profile of melatonin which was consistently higher throughout the scotophase compared to fed charr. Although the daily melatonin production seems to be affected by the energy status of the fish, melatonin does not seem to be directly involved in regulation of the seasonal feeding and growth rhythm in the high-latitude, anadromous Arctic charr.     

Observations on the Nocturnal Activity and Feeding Behavior of Anguilla japonica Glass Eels Under Laboratory Conditions

Glass eels of the temperate anguillid species, Anguilla japonica, clearly showed a nocturnal activity rhythm under laboratory conditions. Light–dark cycle was a determinant factor affecting their photonegative behavior, nocturnal locomotor activity, and feeding behavior. Under natural light conditions, glass eels remained in shelters with little daytime feeding, but came out to forage during darkness. They moved and foraged actively in the following dark, and then their activity gradually declined possibly because of food satiation. They finally buried in the sand or stayed in tubes immediately after the lights came on. Under constant light, glass eels often came out of the shelters to forage in the lights but spent little time moving outside the shelters (e.g. swimming or crawling on the sand). Glass eels took shelter to avoid light and preferred tubes to sand for shelter possibly because tubes were much easier for them to take refuge in than sand. Feeding and locomotor activities of the glass eels were nocturnal and well synchronized. They appeared to depend on olfaction rather than vision to detect and capture prey in darkness. Feeding was the driving force for glass eels to come out of sand under constant light. However, in the dark, some glass eels swam or crept actively on sand even when they were fully fed. The lunar cycles of activity rhythms of glass eels that have been observed in some estuarine areas were not detected under these laboratory conditions.     

FITNESS CONSEQUENCES OF SEASONAL POLYPHENISM IN WESTERN WHITE BUTTERFLIES

The western white butterfly, Pontia occidentalis, has distinctly different wing phenotypes during spring and summer generations as a result of phenotypic plasticity (seasonal polyphenism). We experimentally generated different seasonal phenotypes in the lab by altering photoperiodic conditions during rearing, and released the resulting butterflies in the field. Mark-recapture studies were then used to estimate the effects of the polyphenism on activity patterns and adult survival in both late-spring (one study) and summer (two studies) conditions. There were no significant effects of rearing treatment on temporal patterns of behavioral activity during either the late-spring or the summer field studies. Recapture probabilities were consistently higher for males than females in all three field studies; in the summer 1992 study, recapture probabilities were higher for long-day (LD) than for short-day (SD) treatment groups. During the late-spring 1992 study, there were no significant differences between LD and SD treatment groups for survival probabilities. In the two summer studies, there were significant effects of photoperiodic treatment on survival probabilities; in the summer 1992 study, LD individuals consistently had higher survival probabilities than SD individuals; in the summer 1991 study, there was a significant interaction between treatment and time period on survival probabilities, such that survival probabilities were higher for LD than for SD individuals in two of four time periods. The consistent differences in survival probabilities between treatment groups in the summer 1992 study can be accounted for by the differences in wing traits between the treatment groups. Micrometeorological data from the study site showed that midday ambient temperatures averaged ~3°C hotter during the 1992 than the 1991 summer study and that ambient conditions during the late-spring 1992 study were relatively warm and sunny for the season. These results document the varying relationships between phenotype and fitness in the temporally fluctuating environments experienced by this population.     

Seasonal changes in diel activity of juvenile European catfish Silurus glanis (Linnaeus, 1758) in Byšická Lake,Central Bohemia

Dualism in activity has been described in many fish species, including larger individuals of European catfish (Silurus glanis), which are able to switch their activities from nocturnal to diurnal in winter and spring. During the multi‐year telemetry study, seasonal changes in diel activity of 45 juvenile European catfish were investigated. These juveniles exhibited no dualism in movement and were strictly nocturnal and crepuscular with no period of diurnal activity. During winter, the same juvenile European catfish were completely inactive throughout the 24‐hr cycle. Also investigated was the impact of temperature, dissolved oxygen levels and water clarity on fish movement, relocation of resting places and home range size. The only significant correlations were that relocation and home range size increased with rising water temperatures.     

Seasonal changes in entrainment cues for the circadian rhythm of the supratidal amphipod Talorchestia longicornis

The supratidal amphipod Talorchestia longicornis Say has a circadian rhythm in activity, in which it is active on the substrate surface at night and inactive in burrows during the day. The present study determined: (1) the circadian rhythms in individual versus groups of amphipods; (2) the range of temperature cycles that entrain the circadian rhythm; (3) entrainment by high-temperature cycles versus light?:?dark cycles, and (4) seasonal substrate temperature cycles. The circadian rhythm was determined by monitoring temporal changes in surface activity using a video system. Individual and groups of amphipods have similar circadian rhythms. Entrainment occurred only to temperature cycles that included temperatures below 20°C (10–20, 15–20, 17–19, 15–25°C) but not to temperatures above 20°C (20–25, 20–30°C), and required only a 2°C temperature cycle (17–19°C). Diel substrate temperatures were above 20°C in the summer and below 20°C during the winter. Upon simultaneous exposure to a diel high-temperature cycle (20–30°C) and a light?:?dark cycle phased differently, amphipods entrained to the light?:?dark cycle. Past studies found that a temperature cycle below 20°C overrode the light?:?dark cycle for entrainment. The functional significance of this change in entrainment cues may be that while buried during the winter, the activity rhythm remains in phase with the day?:?night cycle by the substrate temperature cycles. During the summer, T. longicornis switches to the light?:?dark cycle for entrainment, perhaps as a mechanism to phase activity precisely to the short summer nights.     

The seasonal distribution and characteristics of bush fly Musca vetustissima Walker populations in south-western Australia

In the agricultural region of south-western Australia the bush fly Musca ventustissima Walker was found to occur permanently in the north-eastern half but it died out during winter in the south-west. The abundance of bush flies increased rapidly throughout the overwintering zone in early spring as a result of local breeding. Flies then dispersed south-westwards, completely repopulating the region during October. Immigrant flies were large and therefore highly fecund, and of advanced reproductive maturity. Local breeding then rapidly increased the population. Maximum abundance occurred in mid-spring in the north and east and in early summer in the south and west. Abundance was greatest in the north where large overwintering populations occurred, and in the far south where repopulation occurred early in the seasonal cycle of pasture growth so that the more favourable cattle dung produced flies that were more fecund than their immigrant parents. The abundance of bush flies declined throughout the region in summer, to negligible levels near the south-west coast but, paradoxically, higher levels occurred inland where there were fewer cattle. On average, flies were smaller and reproductively younger in summer. In areas where irrigated pastures produced more favourable dung in summer, the patterns of abundance and other characteristics of flies did not differ substantially from those in comparable non-irrigated areas. The abundance and other characteristics of a bush fly population 10 km from a cattle-grazing breeding site were similar to those at the site, indicating that constant dispersal is the basis of the bush fly's ubiquity.