Daylight Period Research Articles

CO2 fluxes among different vegetation types during the growing season in Marguerite Bay (Antarctic Peninsula)

The Antarctic Peninsula has experienced a strong climate warming trend of +0.53°C (mean annual air temperature) over the last 50years. In the Polar Regions, changes in vegetation and permafrost due to a warming climate are expected to produce strong feedbacks to climate and, despite their relatively small areal extent, ice-free areas in Antarctica provide unique natural environments for studying these effects.Off the Antarctic Peninsula, close to Rothera Research Station on Adelaide Island, we used in situ measurements to assess whether spatial variation of CO2 fluxes exists a) among three important and typical vegetation types at Rothera Point during the daylight period; b) across four different ecosystem types (from Antarctic vascular tundra to barren soil) on neighbouring Anchorage Island during the peak of the growing season (January–February 2009). We aimed to assess whether Net Ecosystem Exchange (NEE), Ecosystem Respiration (ER) and Gross Ecosystem Photosynthesis (GEP) change among the selected ecosystem types and determine which environmental factors (soil moisture, soil temperature and PAR) influence NEE and ER.The data obtained at Rothera Point confirmed the presence of spatial variation of CO2 fluxes related to vegetation type, and temporal variation of the CO2 cycle during the daylight period for moss and barren soil ecosystems. At Anchorage Island the spatial variation of CO2 fluxes was mainly influenced by vegetation type at inter-community level. Deschampsia and Sanionia showed higher NEE and ER values (−0.03/0.43μmol CO2 m−2s−1 for Deschampsia NEE; 0/0.62μmol CO2 m−2s−1Sanionia NEE; 0.27/2.03μmol CO2 m−2s−1Deschampsia ER; 0.31/1.7μmol CO2 m−2s−1Sanionia ER) than the other vegetation types studied. We measured generally positive NEE values probably due to high soil respiration.Our data suggest that ecosystems such as those studied may act as a source for CO2 release to the atmosphere and that this source effect is likely to continue and/or to increase until the “legacy” of organic matter and nutrients stored in the soils is largely decomposed.

Diurnal variations in the phagocytic activity of zebrafish kidney leukocytes can be influenced by melatonin in a time-of-day dependent manner. (117.13)

Abstract Diurnal variations in immune system function result from rhythmic expression of clock genes. Their relationship with neuroendocrine regulators such as melatonin is not well understood. We explored the influence of melatonin on variations of phagocytic activity of zebrafish leukocytes. The percentage of kidney myeloid cells that phagocytosed pHrodo-labeled E. coli varied substantially throughout the day. The greatest increase in activity was between 6 AM and 10 AM, spanning the daily dark-to-light transition, a time when endogenous melatonin levels are falling to their daytime low. To determine whether extending the perceived night by prolonging the presence of melatonin would reduce the peak participation in phagocytosis observed at 10 AM, fish were exposed to exogenous melatonin for two hours beyond the beginning of the daily light period. Treatment with melatonin resulted in significantly lower participation in phagocytosis, similar to the normal 6 AM (dark phase) levels. The opposite effect was observed when fish received melatonin later in the day, prior to the evening light-to-dark transition. Fish exposed to melatonin prior to assay at 6 PM (late day) displayed a significant increase in phagocytosis over control fish, with participation levels surpassing normal 10 PM (early dark phase) levels. At both times of day, pre-treatment with the melatonin receptor antagonist luzindole prevented the changes in phagocytosis associated with extended melatonin presence.

The Arabidopsis E3 Ubiquitin Ligase HOS1 Negatively Regulates CONSTANS Abundance in the Photoperiodic Control of Flowering

The Arabidopsis thaliana early in short days6 (esd6) mutant was isolated in a screen for mutations that accelerate flowering time. Among other developmental alterations, esd6 displays early flowering in both long- and short-day conditions. Fine mapping of the mutation showed that the esd6 phenotype is caused by a lesion in the high expression of osmotically responsive genes1 (HOS1) locus, which encodes a RING finger-containing E3 ubiquitin ligase. The esd6/hos1 mutation causes decreased flowering locus C expression and requires CONSTANS (CO) protein for its early flowering phenotype under long days. Moreover, CO and HOS1 physically interact in vitro and in planta, and HOS1 regulates CO abundance, particularly during the daylight period. Accordingly, hos1 causes a shift in the regular long-day pattern of expression of flowering locus T (FT) transcript, starting to rise 4 h after dawn in the mutant. In addition, HOS1 interacts synergistically with constitutive photomorphogenic1, another regulator of CO protein stability, in the regulation of flowering time. Taken together, these results indicate that HOS1 is involved in the control of CO abundance, ensuring that CO activation of FT occurs only when the light period reaches a certain length and preventing precocious flowering in Arabidopsis.

Eelgrass survival in two contrasting systems: role of turbidity and summer water temperatures

Eelgrass Zostera marina L. distribution patterns in the mid-Atlantic region of the USA have shown complex changes, with recovery from losses in the 1930s varying between the coastal lagoons and Chesapeake Bay. Restoration efforts in the coastal bays of Virginia introduced Z. marina back to this system, and expansion since 2005 has averaged 66% yr �1 . In contrast, Chesapeake Bay has experienced 2% expansion and has undergone 2 significant die-off events, in 2005 and 2010. We used a temperature-dependent light model to show that from 2005 to 2010 during daylight periods in the summer, coastal bay beds received at least 100% of their light requirements 24% of the time, while beds in the lower Chesapeake Bay only met this 6% of the time. Summer light attenuation (Kd) and temperatures from continuous monitoring at 2 additional Chesapeake Bay sites in 2010 suggest that the greater tidal range and proximity of the coastal bays to cooler ocean waters may ameliorate influences of exposure to stressful high water temper- ature conditions compared to Chesapeake Bay. A temperature difference of 1°C combined with a Kd difference of 0.5 m �1 at 1 m depth results in a 30% difference in available light as a proportion of community light requirements. These differences are critical between survival and decline in these perennial populations growing near the southern limits of their range. Without an increase in available light, Chesapeake Bay populations may be severely reduced or eliminated, while coastal bay populations, because of their proximity to cooler Atlantic waters, may become the refuge populations for this region.

The use of artificial spawning substrates in order to understand the factors influencing the spawning site selection, depth of egg strands deposition and hatching time of perch (Perca fluviatilis L.)

The distribution of egg strands of perch Perca fluviatilis and factors affecting this distribution, in terms of spawning sites and spawning depths used, was studied in spring 2010 in Chabařovice Lake, Czech Republic, using areas with an artificial spawning substrate (A.S.S.) and control areas outside the A.S.S. Perch significantly preferred a calm shore instead of a windward shore for spawning. The depths at which perch egg strands were found increased significantly during the spawning period in both A.S.S. areas and in areas outside the A.S.S. (on average from 4.9 m at the beginning to 12.3 m at the end of the spawning period). With increasing depth of deposition the size of the egg strands decreased significantly. The mean depth of egg strands on individual dates corresponded to the position of 10-12°C water layers. From the third week onward, however, egg strands were deposited in much deeper and colder water. A strong relationship was found between the depth at which egg strands were deposited and the duration of the daylight period, indicating that, at the end of the spawning season, perch do not react to the actual temperature of the water column but that they follow their inner clock, assuming that normally the shallower depth layers are too warm for successful embryo development. Factors influencing the depth distribution of egg strands were identified as waves, temperature and duration of the daylight period. Factors influencing the selection of spawning sites were identified as wind inducing current, internal seiches and temperature instability of the water column. The first perch larvae were present in the open water of Chabařovice Lake before mid-May, and the latest larvae not earlier than the beginning of July, since warming of the water in deeper layers was very slow. It appears that with prolonged spawning and hatching periods and with spawning occurring at various depths and temperatures, perch have evolved a powerful mechanism to protect their population against the vagaries of the weather and temporary bad biological conditions in the lake.

Routine Oxygen Consumption Rate of the Black Sea Trout (Salmo trutta labrax Pallas, 1811)

Aim of this study is to determinate oxygen consumption rate of Black Sea trout, (Salmo trutta labrax Pallas, 1811) in the sea water (18‰ salinity) in tanks at farm condition. Two different fish size were used as small size and big size which average weights 54.1 ±3.06 (n=300) and 507.0 ±17.71 (n=32) g, average total lengths 17.7 ±0.36 and 35.5 ±0.44 cm respectively. Water temperature averaged 10.0 ±0.01°C during the experiment. The amount of dissolved oxygen was measured during 3 days inlet and outlet of each tank. Oxygen consumption rate was found to be in the range of 95.2-140.0 mgO2kg/h according to fish size. It was observed that O2 con-sumption increased in the daylight period.

Solar Energy Optimization through Seasons: Case Study in Jordan

Solar energy in Jordan is recognized high amongst in the world. The solar energy cultivation needs to be magnified by optimizing the angle of inclination of solar cells. The angle of inclination in this work is not fixed but variable throughout the year, and consequently the angle is optimized for seasons. In this research, the optimized angles for seasons in Jordan are obtained as: 60? for Winter (November to February), 30? for Spring (March and April), 10? for Summer (May to August), and 30? for Fall (September and October). The optimized cultivated energy throughout all seasons in the year equals about 2490 kWh/m2. The residential customer consumption of electricity is 2475 kWh/customer per year. Therefore, according to Jordan, if the sun energy is converted efficiently to electricity, it will be worthy to apply for residential building for which each customer should have some area of solar cells to overcome the needs of energy. In addition, with some wise management of electricity in the daylight period, fossil fuel consumption will be minimized. Hence, combining solar energy concept in the design of building is an important step in sustainable development of green energy.

Persistent bimodal activity patterns in wild and captive black-tailed godwit Limosa limosa under different environmental conditions

There is a large literature dealing with daily foraging routines of wild birds during the non-breeding season. While different laboratory studies have showed that some bird activity patterns are a persistent property of the circadian system, most of field studies preclude the potential role of an endogenous circadian rhythm in controlling bird’s foraging routines. In this study we compared the patterns of diurnal foraging activity and intake rates of migrating black-tailed godwits, Limosa limosa (radio-tagged and non-tagged individuals) at two stopover sites (habitats) with different environmental characteristics, aiming at identifying proximate factors of bird activity routines. To gain insights into the role of food availability in control of such foraging routines, we also estimated foraging activity patterns in captive godwits subjected to constant food availability. Captive and wild black-tailed godwits showed a persistent bimodal activity pattern through daylight period. Food availability had a significant effect on the intake rates, but had a subtler effect on foraging and intake rate rhythms. Temperature and wind speed (combined in a weather index) showed non-significant effects on both rhythms. Although we could not discard a role for natural diurnal changes in light intensity, an important timing cue, our findings support the idea that an endogenous circadian rhythm could be an important proximate factor regulating foraging activity and food items taken per unit time of wild black-tailed godwits during migration.

Evidence for Time-of-Day Dependent Effect of Neurotoxic Dorsomedial Hypothalamic Lesions on Food Anticipatory Circadian Rhythms in Rats

The dorsomedial hypothalamus (DMH) is a site of circadian clock gene and immediate early gene expression inducible by daytime restricted feeding schedules that entrain food anticipatory circadian rhythms in rats and mice. The role of the DMH in the expression of anticipatory rhythms has been evaluated using different lesion methods. Partial lesions created with the neurotoxin ibotenic acid (IBO) have been reported to attenuate food anticipatory rhythms, while complete lesions made with radiofrequency current leave anticipatory rhythms largely intact. We tested a hypothesis that the DMH and fibers of passage spared by IBO lesions play a time-of-day dependent role in the expression of food anticipatory rhythms. Rats received intra-DMH microinjections of IBO and activity and body temperature (T b) rhythms were recorded by telemetry during ad-lib food access, total food deprivation and scheduled feeding, with food provided for 4-h/day for 20 days in the middle of the light period and then for 20 days late in the dark period. During ad-lib food access, rats with DMH lesions exhibited a lower amplitude and mean level of light-dark entrained activity and T b rhythms. During the daytime feeding schedule, all rats exhibited food anticipatory activity and T b rhythms that persisted during 2 days without food in constant dark. In some rats with partial or total DMH ablation, the magnitude of the anticipatory rhythm was weak relative to most intact rats. When mealtime was shifted to the late night, the magnitude of the food anticipatory activity rhythms in these cases was restored to levels characteristic of intact rats. These results confirm that rats can anticipate scheduled daytime or nighttime meals without the DMH. Improved anticipation at night suggests a modulatory role for the DMH in the expression of food anticipatory activity rhythms during the daily light period, when nocturnal rodents normally sleep.

Nitrogen uptake and growth by the opportunistic macroalga Ulva lactuca (Linnaeus) during the internal tide

To determine if an opportunistic macroalga could increase its tissue nitrogen content in response to nutrient pulses forced by the internal tide, independent samples of the green alga Ulva lactuca (Linnaeus), previously cultured in nutrient-poor tanks, were outplanted in the nearshore ocean for 12 h deployment periods (8 daylight periods, 7 night periods), at three different depths (1, 5, and 10 m), during stratified water column conditions and spring tides. Algal tissue nitrogen and growth weight (before and after each deployment), water-column temperature (continuous), and inorganic water-column nutrient concentrations (taken on 3 days during the experiment) were measured. Abrupt drops in temperature (up to 3 °C in an hour) occurred twice daily, at 10 m and occasionally at 5 m depth, associated with the internal tide. Date and deployment depth had significant effects on U. lactuca tissue nitrogen, showing a significant increase for deeper deployments and a positive correlation with the duration of cool water (< 15.8 °C, > 1 μM NO 3 −) at the deployment depth. On days when temperature remained above 15.8 °C at all depths (15.8 °C was established as the temperature below which nitrate was above 1 μM), no significant increase in tissue nitrogen was detected at any depth. Growth and tissue nitrogen were significantly and inversely correlated for mid-water (5 m) and bottom (10 m) deployments, but not at the surface. The data support the hypothesis that U. lactuca can increase tissue nitrogen in response to the cold phase of the semidiurnal internal tide.

Inhibition of hippocampal neurogenesis by sleep deprivation is independent of circadian disruption and melatonin suppression

Procedures that restrict or fragment sleep can inhibit neurogenesis in the hippocampus of adult rodents, although the underlying mechanism is unknown. We showed that rapid-eye-movement (REM) sleep deprivation (RSD) by the platform-over-water method inhibits hippocampal cell proliferation in adrenalectomized rats with low-dose corticosterone clamp. This procedure also greatly disrupts daily behavioral rhythms. Given recent evidence for circadian clock regulation of cell proliferation, we asked whether disruption of circadian rhythms might play a role in the anti-neurogenic effects of sleep loss. Male Sprague-Dawley rats were subjected to a 4-day RSD procedure or were exposed to constant bright light (LL) for 4 days or 10 weeks, a non-invasive procedure for eliminating circadian rhythms of behavior and physiology in this species. Proliferating cells in the granule cell layer of the dentate gyrus were identified by immunolabeling for the thymidine analogue 5-bromo-2-deoxyuridine. Consistent with our previous results, the RSD procedure suppressed cell proliferation by ∼50%. By contrast, although LL attenuated or eliminated daily rhythms of activity and sleep-wake without affecting daily amounts of REM sleep, cell proliferation was not affected. Melatonin, a nocturnally secreted neurohormone that is inhibited by light, has been shown to promote survival of new neurons. We found that 3-weeks of LL eliminated daily rhythms and decreased plasma melatonin by 88% but did not significantly affect either total cell survival or survival of new neurons (doublecortin+). Finally, we measured cell proliferation rates at the beginning and near the end of the daily light period in rats entrained to a 12:12 light/lark (LD) cycle, but did not detect a daily rhythm. These results indicate that the antineurogenic effect of RSD is not secondary to disruption of circadian rhythms, and provide no evidence that hippocampal cell proliferation and survival are regulated by the circadian system or by nocturnal secretion of pineal melatonin.

Increase in Rubisco activity and gene expression due to elevated temperature partially counteracts ultraviolet radiation–induced photoinhibition in the marine diatom Thalassiosira weissflogii

We performed outdoor experiments to evaluate the effect of temperature on photoinhibition properties in the cosmopolitan diatom Thalassiosira weissflogii. Cultures were exposed to solar radiation with or without ultraviolet radiation (UVR, 280–400 nm), UV‐A (320–400 nm), and UV‐B (280–320 nm) at both 20°C and 25°C. Four possible cellular mechanisms involved in UVR stress were simultaneously addressed: carbon incorporation, chlorophyll a fluorescence of photosystem II, xanthophyll cycle activity, and ribulose‐1,5‐biphosphate carboxylase : oxygenase (Rubisco) activity and gene expression. Experiments consisted of daily cycles (i.e., the daylight period) and short‐term incubations (i.e., 1 h centered on local noon). Samples incubated at 25°C had significantly less UVR‐induced inhibition of carbon fixation and effective photochemical quantum yield compared to those incubated at 20°C. At 25°C Rubisco activity and gene expression were significantly higher than at 20°C. The higher Rubisco activity and gene expression were correlated with less dissipation of excess energy, evaluated via non‐photochemical quenching, and the de‐epoxidation state of the xanthophyll pigments, as more photons could be processed. An increase in temperature due to climate change would partially counteract the negative effects of UVR by increasing the response of metabolic pathways, such as those involved in Rubisco. This, in turn, may have important consequences for the ecosystem, as higher production (due to more Rubisco activity) could be expected under a scenario of global warming.

Cloud properties derived from two lidars over the ARM SGP site

Active remote sensors such as lidars or radars can be used with other data to quantify the cloud properties at regional scale and at global scale. Relative to radar, lidar remote sensing is sensitive to very thin and high clouds but has a significant limitation due to signal attenuation in the ability to precisely quantify the properties of clouds with a cloud optical thickness larger than 3. The cloud properties for all levels of clouds are derived and distributions of cloud base height (CBH), top height (CTH), physical cloud thickness (CT), and optical thickness (COT) from local statistics are compared. The goal of this study is (1) to establish a climatology of macrophysical and optical properties for all levels of clouds observed over the ARM SGP site and (2) to estimate the discrepancies between the two remote sensing systems (pulse energy, sampling, resolution, etc.). Our first results tend to show that the MPL, which are the primary ARM lidars, have a distinctly limited range within which all of these cloud properties are detectable, especially cloud top and cloud thickness, but this can include cloud base particularly during summer daytime period. According to the comparisons between RL and MPL, almost 50% of situations show a signal to noise ratio too low (smaller than 3) for the MPL in order to detect clouds higher than 7km during daytime period in summer. Consequently, the MPL-derived annual cycle of cirrus cloud base (top) altitude is biased low, especially for daylight periods, compared with those derived from the RL data, which detects cloud base ranging from 7.5 km in winter to 9.5 km in summer (and tops ranging from 8.6 to 10.5 km). The optically thickest cirrus clouds (COT > 0.3) reach 50% of the total population for the Raman lidar and only 20% for the Micropulse lidar due to the difference of pulse energy and the effect of solar irradiance contamination. A complementary study using the cloud fraction derived from the Micropulse lidar for clouds below 5 km and from the Raman lidar for cloud above 5 km allows for better estimation of the total cloud fraction between the ground and the top of the atmosphere. This study presents the diurnal cycle of cloud fraction for each season in comparisons with Long et al.'s (2006) cloud fraction calculation derived from radiative flux analysis. Copyright © 2011 by the American Geophysical Union.

Microclimate in coffee plantation grown under grevillea trees shading

Measurements of solar global radiation, wind speed, temperature and relative humidity of air were made in a coffee plantation (Coffea Arabica L. variety Icatu Vermelho- IAC 4045), grown under conditions of shading levels caused by grevillea trees (Grevillea robusta) in Mococa-SP region (21&deg; 28’ S, 47&deg; 01’ W, altitude 665m), between January and December 2005, aiming to show the effects of shading crop system on the microclimate. The results showed that there was a reduction of about 26% of solar global radiation in the shaded systems, with a monthly variation of 24-30%. It has been highlighted some differences in the transmittance of global radiation in the shaded coffee trees due to the spatial variation of grevillea canopy. There was a reduction of about 35% in the five days-averaged wind speed in the shaded system that also presented reduced maximum air temperature and a reduction in the vapor pressure deficit during day-light period, especially in the point sampled near to the grevillea trees.

Advancing Oil Spill Preparedness and Response Techniques for Arctic Conditions

ABSTRACTIndustrial and commercial activities in Arctic and sub-Arctic regions, including oil exploration, have increased in recent years. The 2008 circumpolar analysis by the US Geological Survey highlighted the large quantities of undiscovered oil and gas (O&amp;G) estimated to be present. Governments of Arctic coastal states require industry to ensure a high level of environmental protection while operating in these areas. There are unique considerations which must be addressed such as: prolonged periods of darkness and daylight, cold temperatures, environmental sensitivities, indigenous peoples and their culture, distant infrastructure and remoteness, presence of seasonal/dynamic sea ice offshore, and a generally higher cost of doing business. Oil spill response (OSR) in the ice-free season can be comparable to the response in others parts of the world, with the exception of lower temperatures and extended daylight hours. The latter is a distinct advantage for OSR operations.Prevention of spills remains a top priority for industry. To address spills, if prevention is unsuccessful, the O&amp;G industry has made significant progress over the last decades on addressing the technical challenges of operating in the Arctic. The O&amp;G industry has also performed work to evaluate and validate OSR response measures under Arctic conditions. Oil spill response is a demanding task in any environment, but responding to spills in Arctic regions can present different challenges, especially with presence of sea ice, than to spills found in more temperate regions and opportunities exist to improve upon this existing capability. Some response techniques have been modified or specially developed for use in the Arctic. The O&amp;G industry will undertake a joint industry research program to further address the challenges of Arctic Oil Spill Response. This paper describes the background, planning, and scope for this Joint Industry Program (JIP).

Diurnal trends in methylmercury concentration in a wetland adjacent to Great Salt Lake, Utah, USA

A 24-h field experiment was conducted during July 2008 at a wetland on the eastern shore of Great Salt Lake (GSL) to assess the diurnal cycling of methylmercury (MeHg). Dissolved (< 0.45 μm) MeHg showed a strong diurnal variation with consistently decreasing concentrations during daylight periods and increasing concentrations during non-daylight periods. The proportion of MeHg relative to total Hg in the water column consistently decreased with increasing sunlight duration, indicative of photodegradation. During the field experiment, measured MeHg photodegradation rates ranged from 0.02 to 0.06 ng L − 1 h − 1 . Convective overturn of the water column driven by nighttime cooling of the water surface was hypothesized as the likely mechanism to replace the MeHg in the water column lost via photodegradation processes. A hydrodynamic model of the wetland successfully simulated convective overturn of the water column during the field experiment. Study results indicate that daytime monitoring of selected wetlands surrounding GSL may significantly underestimate the MeHg content in the water column. Wetland managers should consider practices that maximize the photodegradation of MeHg during daylight periods.

Factors Affecting Sleep/vigilance Behaviour in Incubating Mallards

Vigilance is a behavioural tactic that allows individuals to control their surroundings and to assess predation risk. In contrast, sleep is unique behavioural state with widely hypothesized restorative and energy-saving functions, but reducing attentiveness and increasing susceptibility to predation. Sleeping birds resolve this conflict by interrupting sleep with short periods of eye opening (termed ‘scans’) during vigilant sleep. Miscellaneous environmental factors and sleeping postures may affect the perception of risk and corresponding vigilance level. Here, we investigated the influence of nest vegetation concealment, time of day and sleeping postures on the sleep/vigilance trade-off in incubating Mallards (Anas platyrhynchos). We found that incubating females increased their vigilance with increasing nest vegetation cover facing the vigilant eye during both the day and the night periods; however, mean nest vegetation concealment did not affect female vigilance. Females also reduced their total vigilance along with scan frequency during the night period, while displaying the opposite pattern during the daylight. The rest-sleeping position was preferred more during the night compared with the daylight period, and females were more vigilant in this position at night. Our data show that the nest vegetation concealment regardless of visual abilities during different light conditions, time of day and sleeping posture play an underlying role in antipredator vigilance during sleep in this cryptic ground-nesting bird.

Reproduction of the Siberian salamander, Salamandrella keyserlingii (Amphibia, Caudata, Hynobiidae), in water bodies on permafrost in Northeastern Asia

The possibility for Siberian salamanders to reproduce in the permafrost zone of Eurasia is due to specific thermal conditions in small water bodies (pools) freezing to the bottom, rather than to the adaptive properties of the species. These conditions are as follows: (1) meltwater in freezing marshland pools appears relatively early; (2) the rate of water warming increases in the south-north direction due to the lengthening of the daylight period; (3) water temperature is higher than air temperature but does not reach the values critical for S. keyserlingii eggs and larvae; and (4) the thawed silt layer prevents water cooling by the underlying permafrost bed. Reproduction of Siberian salamanders in different parts of the species range begins under similar thermal conditions, which are formed 1.5–2 months earlier in the south (the Jewish Autonomous Region) than in the north (the Chaun Bay coast). In any region, the onset of spawning may vary by up to 30 days. The existence of Siberian salamanders in the tundra zone is facilitated by continuous daylight during the polar day, which provides for rapid water warming to relatively high temperatures and creates additional opportunities for larval feeding. These factors may account for the acceleration of amphibian ontogeny in the North, noted by Shvarts and Ishchenko (1971). The northern boundary of the Siberian salamander range in Eastern Siberia is defined by the sum of water temperatures over the warm season, which should be no less than 850–900°/day. This boundary in the tundras of Europe, Western Siberia, and the Chukchi Peninsula is shifted southward, with its location being apparently dependent on some other factors.

Group sizes and resting locations of free range pigs when grazing in a natural environment

A herd of 86 Iberian pigs aged 13 ± 0.5 months and with an average live weight of 110 ± 1.3 kg at the start of the study was followed to monitor their social organisation (spontaneous group size: GS) and resting preferences when free ranging on natural pastures in a dehesa of evergreen oaks ( Quercus ilex rotundifolia) of 111 ha (average of 27.4 adult oaks/ha) with 2 adjacent shelters for resting. Oaks were considered as activity centres and resource patches (characterized by unpredictability in the distribution of resources). 60 complete “pig grazing days”, distributed over 6 different observation days, were studied (10 pigs per day). Every observation session was carried out for 10.5 h, covering >90% of the daylight period. Results show that pigs split into small subgroups to forage and maintained this division during daylight rests, however animals regrouped to rest during the night in a common area and behaved as a united flock. The mean daylight GS (from 9:00 to 18:00) was 8.6 ± 0.3 pigs; however GS was larger when pigs were resting than when they were grazing (13.8 ± 0.6 vs. 5.6 ± 0.3 pigs, P < 0.001). GSs were significantly different when pigs were grazing in open pasture or under an oak crown (5.0 vs. 5.8, P < 0.001). The most frequent GS when grazing under an oak were ≤4 pigs, whereas GS of pigs eating acorns was ≤2 pigs for 26.4 ± 3.0% of observations. The behaviour of these pigs could be called “Chase Optimal Foraging”, to refer to those animals which are exploiting the remains of a preferred patch (oak mast) whilst paying attention to the discovery of another close preferred patch by their group mates. When eating acorns, subgrouping would be conditioned by the space requirements to avoid competition when foraging, hence the mean grazing surface when foraging acorns could be considered an indication of the space required to avoid social stress (mean was 8.9 m 2 and median was 5.2 m 2 per pig). GSs of resting pigs increased as the day progressed. In spite of the temperature at sunset (19:00) (8.4 ± 0.1 °C outside vs. 11.9 ± 0.1 °C inside, P < 0.001), 28.6 ± 3.3% of pigs rested outside the shelters in smaller subgroups (9.5 ± 0.9 pigs outside vs. 28.0 ± 0.7 pigs inside, P < 0.001). Pigs inside each shelter constituted a single subgroup. There was no significant difference in the body weight or sex of pigs resting inside or outside the shelters at sunset. The mean surface for pigs resting inside the shelter at sunset was 6.8 ± 0.1 m 2 per pig. The results suggest a reconsideration of the lower critical temperature for rustic and non-lean porcine breeds, in terms of comfort and the minimum space allowance per pig for preferred resting distribution.

Morning or evening exercise: effects on the heart rate circadian rhythm above the Arctic Circle

The potency of exercise as a nonphotic time cue compared to the solar cycle in influencing entrainment (organism synchronization within the 24-h period) has yet to be defined. Above the Arctic Circle during winter the sun remains below the horizon for several weeks and during summer remains above the horizon for several weeks. The goal of the present study was to investigate the effects related to exercising time on the circadian structure under conditions of lack of daylight and continuous daylight. The experiments were carried out at 70° North, above the Arctic Circle. Ten healthy females (age 24±5 years) were divided into two groups: an exercise and a control group. The subjects in the exercise group performed the same exercise routine at two different times of day (0900 and 1800 hours) both in January (twilight period) and in May (continuous daylight period). Continuous heart rate data were collected and analysed by the cosinor method. The acrophase values were significantly modified in the exercise group during evening exercise in January showing a delay compared with morning exercise and compared with the control group (3 h and 1.5 h, respectively), while in May this effect was not seen. The results indicate that in continuous daylight, the potency of exercise in modulating the circadian phase seems to be suppressed. However, these findings need to be verified in a larger poulation.