Weight loss and survival of Biomphalaria glabrata deprived of water

Immature and mature Biomphalaria glabrata are kept out of water at relative humidities varying from 0 to 100%. When snails are submitted to a saturated atmosphere, they show a slow weight loss and survival may be long. If relative humidity (RH) decreases, weight loss becomes important and survival is short. A reduced RH (0 to 65%) produces similar effects. During desiccation, fasting has no noticeable effect; survival depends essentially on weight loss.     

Modelling the effects of microclimate on bean seed desiccation rate and seed storage ability

Bean seed storage ability is of major interest for seed firms and depends, at least partially, on the effect of desiccation microclimate and desiccation rate on the mother plant; however, their effects are contradictory and not quantified. Therefore, our aims were (a) to predict seed desiccation rate from microclimatic variables at the pod level and (b) to measure the effects of seed desiccation rate and temperature on seed storage ability. For 4 years, beans (Phaseolus vulgaris) were sown at different dates in the field and once in a greenhouse. Pods having seeds at the beginning of desiccation stage were selected according to their colour and then dried in the field or under controlled conditions. In the field, pods were dried under both natural conditions and conditions modified either by defoliation or by water spraying. Under controlled conditions, pods were dried under a wide range of temperature and relative humidity combinations. Seed water content, temperature and relative humidity were measured throughout the desiccation phase. Storage ability was measured by a standard germination test after either 11 or 15 days of controlled deterioration. Seed desiccation rate was highly correlated to air vapour pressure deficit, which measures the combined effects of temperature and relative humidity on drying. With a logit transformation, deterioration test results showed a linear decrease in storage ability as seed desiccation rate increased for either controlled or field‐dried lots. However, for controlled lots desiccated at temperatures lower than 24°C, the lower the temperature, the lower the storage ability at a given desiccation rate. Moreover, the relationship between the results of the two deterioration periods differed between controlled and field‐dried lots. Finally, the high correlation between seed storage ability, desiccation rate and vapour pressure deficit in the field has given new insights for building a crop decision‐oriented model for optimising harvesting.     

Shell Temperature, Activity and Resistance to Desiccation in the Polymorphic Land Snail Cepaea Vindobonensis

Shell temperature during the morning hours, and the 24-houractivity pattern have been studied in the two distinct morphsof the polymorphic land snail Cepaea vindobonensis. Shell temperaturesbetween the two morphs differed significantly when snails wereplaced in the sun and the temperature difference was about 1°C. Activity observations in the field and in the laboratory revealedthat adult dark-banded snails were in general less active thanboth morphs of juveniles and adult faint-banded snails during sunnymornings or under severe heat load. In the field and duringcloudy mornings no statistically significant differences betweenmorphs were seen. Resistance to desiccation was studied among the two morphs ofthe same population in which activity was observed and anotherpopulation coming from a more northern and more humid habitat.A clear intraspecific difference was found in resistance todesiccation. Snails from the southern population living in amore arid habitat were more resistant than snails from the northernpopulation. Within the same population percentage water lossdid not differ significantly between the two morphs but thefaint-banded snails seemed better adapted to aridity since onlyin these snails was no difference detected in relative bodywater after desiccation. (Received 28 July 1997; accepted 20 June 1998)     

Evaluation of the desiccation tolerance of blastospores of Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes) using a lab-scale, air-drying chamber with controlled relative humidity

The stabilization of living microbial agents for use as biological control agents is often accomplished through desiccation. Our air-drying studies with the entomopathogenic fungus Paecilomyces fumosoroseus have shown that the relative humidity (RH) of the drying air significantly affects the desiccation tolerance and the storage stability of blastospores. Drying air with a RH of more than 40% supported significantly higher rates of initial blastospore survival (68-82%) after drying compared to drying with lower relative humidity air. Drying air with a RH above 50% improved the shelf-life of the air-dried blastospore preparations. Adjustment of the pH or replacement of the spent medium with deionized water (d-H₂O) in the blastospore suspension had no significant impact on blastospore desiccation tolerance or storage stability. We have developed and describe a lab-scale, air-drying chamber that delivers air flow over the sample and that can be operated at controlled relative humidity.     

Low rates of change enhance effect of humidity on the activity of insect hygroreceptors

The inability to measure humidity during stimulation has so far prevented us from understanding the contribution of moist cells and dry cells to orientation in a gradient of humidity. The problem was solved in the present study by means of a UV-absorption hygrometer that made it possible to monitor humidity at a rate of 100 Hz. The antennal moist and dry cells of the cockroach were exposed to humidities alternatively falling or rising at low rates between -1% RH s(-1) and +1% RH s(-1) (relative humidity). Impulse frequency of both types of cells depended simultaneously on instantaneous humidity and its rate of change. High frequencies of the moist cells signal high humidity. But at a given humidity, the response frequency is higher still when humidity is also rising. Conversely, high frequencies of the dry cell signal low humidity, and frequency is higher still at a given humidity when humidity is also falling. These responses ensure that the cockroach spent a minimum time in environments where desiccation or hydration occur and may thus protect the animal from emerging accidentally from under cover into moving air. In the constant-humidity retreat of the cockroach, fluctuating or even drifting discharge frequencies could serve as an early warning: return!     

Some Factors Affecting Survival of Desiccation by Infective Juveniles of Orrina phyllobia

The survival of desiccation by J4 Orrina phyllobia was examined at controlled relative humidities. When nematodes were transferred from water to air at 10% relative humidity (rh), 80% died within 30 minutes. When nematodes were transferred from water to air with rh at 70% or greater for ca. 15 minutes prior to being transferred to 10% rh, more than 90% of them survived desiccation. This phenomenon is referred to as preconditioning and occurred at much faster rates (2-30 minutes) than has been observed for other nematode species (24 hours). Differences in preconditioning rates may be due to technique-dependent variations in boundary layer resistance around nematodes during desiccation.     

Desiccation,Moisture Content and Germination of Zostera marina L. Seed

Zostera marina is the only seagrass species whose seeds have been successfully used in large‐scale restoration. Although progress has been made in refining Z. marina restoration protocols, additional information on Z. marina seed physiology is necessary as the science of seagrass restoration evolves. We tested the germination rates of Z. marina seeds under different relative humidities and temperatures for different periods of time. Z. marina seed moisture content (MC) and germination rates were also tested when seeds were exposed to a temperature of 25°C and relative humidity of 50%. Z. marina seeds suffered higher mortality when exposed to lower relative humidity and higher temperature for longer period of exposure time. A significant negative correlation was detected between seed germination rate and MC. Z. marina seeds are sensitive to desiccation exposure and long periods of exposure to air should be prevented to minimize seed mortality when seeds are used in restoration projects.     

Changes in body melanisation and desiccation resistance in highland vs. lowland populations of D. melanogaster

Wild caught samples of Drosophila melanogaster from five highland localities showed parallel changes in melanisation and desiccation resistance in darker versus lighter phenotypes, i.e. darker flies (>45% melanisation) showed significantly higher desiccation resistance than lighter flies (<30% melanisation). In order to find an association between body melanisation and desiccation resistance, highland and lowland populations from tropical and subtropical regions (11.15-31.06 degrees N) of the Indian subcontinent were raised and investigated at 21 degrees C for four physiological traits, i.e. per cent body melanisation, desiccation resistance, rate of water loss and rate of water absorption. On the basis of mother-offspring regression, body melanisation and desiccation resistance showed higher heritability (0.58-0.68) and thus these traits are suitable for laboratory analyses. Significantly higher melanisation as well as desiccation resistance were observed in highland populations as compared with lowland populations. The rates of water loss as well as absorption were negatively correlated with body melanisation, i.e. darker flies from highlands showed a reduced rate of water loss as well as a lower rate of water absorption while the reverse trend was observed in lighter flies from lowlands. On the basis of multiple regressions, significant effects due to combined altitude and latitude were observed for all the four physiological traits. Local climatic conditions (i.e. annual average temperature and relative humidity) helped in explaining parallel changes in body melanisation and desiccation resistance in D. melanogaster.     

Desiccation tolerance in fully developed embryos of two cicadas, Cryptotympana facialis and Graptopsaltria nigrofuscata

In two Japanese cicadas, Cryptotympana facialis and Graptopsaltria nigrofuscata , with different habitat distributions, fully developed embryos hatch in response to high humidity due to rainfall. Despite the advantage of hatching on rainy days, this trait burdens embryos with an extra period of desiccation until the unpredictable advent of rain. We compared the ability of the fully developed embryos of these cicadas to endure periods of low humidity. Eggs were exposed to a combination of different humidities (43% and 75% relative humidity, RH) and durations (0–15 days), and then transferred to an environment with 100% RH to stimulate hatching. In both species, total hatching rates decreased as duration increased, although there was no significant effect of humidity. In C. facialis , a considerable proportion of the eggs hatched during the desiccation period, and the hatching rate was higher at 75% RH than at 43% RH. After transfer to 100% RH, most hatching occurred within a day regardless of the desiccation level. In G. nigrofuscata , no nymphs hatched during the desiccation periods. However, more eggs required more than a day after transfer to 100% RH to hatch after desiccation at 43% RH than at 75% RH. Consequently, the overall proportion of timely hatching of eggs (eggs hatching within a day of moisture supply) was higher after desiccation at 43% RH in C. facialis , but it was higher after desiccation at 75% RH in G. nigrofuscata . These different physiological responses of the two species may reflect adaptation to habitat dryness.     

Ecology of the intertidal snail Littorina acutispira Smith

Littorina acutispira Smith, a minute gastropod of < 3 mm shell height, lives at great densities in pools and on rock-surfaces at the highest levels of sea-shores in New South Wales. Populations from pools and dry areas were sampled on two shores for 18 months to investigate seasonal changes in density, size-structure, rates of growth and reproductive biology of the snails. Densities of snails increased between February and May, due to an influx of juveniles, and then declined until the following February, when they increased again. The decrease in density was due to the death of the largest snails at the end of summer, and the mortality of medium-sized snails between June and January. Longevity was estimated as 1–2 yr, but most individuals died by ≈ 16 months from settlement on the shore. Newly-settled snails grew to merge in size with those of the previous year's population by winter. During the summer months, the rate of growth of snails from a sheltered shore was greater than that of snails on a shore exposed to wave-action. Laboratory experiments revealed that this could be attributed to the presence of better quality food, or food in greater abundance on the sheltered shore, compared with the exposed shore.During winter months, but not during the summer, snails from dry areas grew more slowly than those from pools. An experiment demonstrated that some snails from dry areas might be able to compensate for reduced periods of feeding by being able to feed faster when submersed. This could not explain the differences in natural rates of growth.L. acutispira bred from October–November to March–April. Spawning in the laboratory was greatest during late summer (January to March). The percentage of mature oocytes in the gonads was small in winter and increased in early summer. Among the largest-sized snails, females outnumbered males. Two experiments, on unsexed and pre-sexed snails, demonstrated that the biased sex-ratio of the largest snails was due to faster growth by females.There was a greater density of snails on the exposed shore, which was correlated with the presence of barnacles. When barnacles were removed from experimental areas, the density of the snails declined within 24 h. This suggested that barnacles provided a refuge from wave-shock, rather than shelter from desiccation or high temperature. In laboratory experiments, snails were exposed to higher temperatures and less humidity than they would normally encounter on the shore. There was negligible mortality of small or large snails after 24 h of these conditions.This minute species grows quickly, recruits annually and has a short life-span. This type of life-history is discussed in comparison with similar small species from other habitats.     

Moisture relationships of the high arctic collembolan Onychiurus arcticus

Abstract. Rates of desiccation, rehydration and survival, under conditions of 0 and 100% relative humidity, were investigated in the high arctic collembolan Onychiurus arcticus (Tullberg) over a range of temperatures from -3 to 10C. Desiccation, measured over 4h in a dry environment, was rapid and highly significantly correlated with saturated vapour pressure deficit (SVPD). At 10C animals lost over 60% of body moisture in under 1h. Under moist conditions body weight remained constant. Survival, measured over 4h under dry conditions, showed a highly significant negative correlation with SVPD across the range of temperatures. Survival in moist controls was 100%. Partially desiccated animals were able to rehydrate using free water or moisture from a saturated atmosphere, but uptake of the former was faster. Rates of water uptake were around 30 times slower than rates of loss through desiccation. Animals given free water regained initial weights in 24-144h, dependent on temperature. Uptake rates of free water, measured over the time necessary fully to rehydrate, were highly significantly correlated with temperature, whereas those for atmospheric moisture were not. Over the time scales used in the experiments, three linear regression equations accurately predict rates of desiccation, rehydration and survival from SVPD or temperature. Ecological adaptation by O.arcticus to the highly contrasting climatic environments of the arctic summer and winter seasons is discussed in the context of climate change.     

EFFECT OF LIGHT QUALITY ON POLYSACCHARIDE YIELD AND COMPOSITION OF TWO RED ALGAE

Porphyra perforata is a common seaweed inhabiting the upper intertidal zone, and as a consequence it experiences great fluctuations in tissue temperature and desiccation. The objective of this work was to evaluate the effect of ambient temperature and the tissue desiccation status on the photosynthetic performance of P. perforata. Photosynthetic performance was evaluated polarographically after the temperature or desiccation treatments. Maximum photosynthesis (P_max) occurred between 25 and 30° C and decreased at higher and lower temperatures, however, no significant differences were observed in the initial slope of photosynthesis (α) from 10 to 30° C. This suggests that the photosynthetic efficiency of this species does not decrease as a result of fluctuating temperatures during tidal emergence/submergence. P_max and α were relatively constant in tissue of P. perforata with 5 to 100% relative water content. This also suggests that natural desiccation rates during low tides do not decrease photosynthetic rates in this species. Variations in the synthesis of specific proteins as a result of fluctuations in temperature and relative water content in the tissue of P. perforata are being studied.     

Relative humidity affects the intercellular spaces and cell contacts of the kidney epithelium of the terrestrial snail Helix aspersa müller

The effects of relative humidity on hemolymph osmolarity and on kidney ultrastructure are explored in Helix aspersa. The snails are active at 95% relative humidity and less active at 50% relative humidity. The hemolymph osmotic pressure increases with the decrease of relative humidity. Pericardial fluid and hemolymph collected from the heart contain similar amounts of total proteins, and both fluids display hemocyanin molecules in negatively stained preparations. When the snails are kept in an atmosphere of 95% relative humidity, numerous wide intercellular spaces are observed in the single-layered-kidney epithelium. The spaces are almost absent when the snails are kept at 50% relative humidity. It is suggested that prourine is formed through a paracellular junctional pathway across the single-layered kidney epithelium, and that the pericardial cavity is not the site of prourine formation. The septate junctions joining the kidney epithelial cells form a continuous belt of intimate contact in the paracellular pathway of prourine. Long septate junctions with many septa are present in the kidneys of snails from the atmosphere of 50% relative humidity, whereas short septate junctions with fewer septa are found in the kidneys of snails from the atmosphere of 95% relative humidity. It is possible that the longer septate junctions with many septa reduce prourine formation across the kidney sac epithelium.     

Water balance and resistance to desiccation in rock-dwelling snails

We have examined the resistance to desiccation among rock-dwelling land snails of various phylogenetic groups:Cristataria genezarethana (Clausiliidae),Rupestrella rhodia (Chondrinidae) andLevantina caesareana (Helicidae), all from the same location in Israel.L. caesareana was the most resistant andR. rhodia the least resistant to desiccation andC. genezarethana was of intermediate resistance. Differences in the rates of water loss during desiccation were determined mainly by rate of water loss during the first 2 days of desiccation. The high rates of water loss in rock-dwelling species exceed those of other snails in the Mediterranean habitat of Israel. However, snails collected in the field at the end of aestivation were in only a mild state of dehydration, suggesting that the rocky habitat protects its occupants against desiccation. We also suggest that among the rock-dwelling species, the protective role of the rock is more important in the more evolutionarily primitive genera (the chondrinidRupestrella and the clausiliidCristataria) and that physiological capacities are more effective in the more highly evolved helicidLevantina.     

Influence of shell colour on the mortality rate of the land snail Arianta arbustorum under different microclimatic regimes

The mortality of phenotypic shell colour morphs and age classes of the snail Arianta arbustorum in several microclimatic conditions was recorded. An analysis of variance was performed on five factors: adaptation temperature, relative humidity, shell colour, age class and test temperature. There were no significant differences in the mortality between different adaptation temperatures or relative humidities, but the interaction of these two factors was highly significant. There were significant differences in mortality rate between test temperature and age class. The mortality of the brown morph was higher than the yellow one at all adaptation temperatures (overall, P < 0.05). There were no significant differences between the mortality rates of the two morphs at different relative humidities. The mortality of the brown morph was higher than that of the yellow at six out of seven test temperatures. Juvenile snails survived significantly better than adults at all test temperatures.     

中国东南高海拔黄山松生长对气候的响应——以浙江省九龙山和安徽省牯牛降为例

利用中国浙江省西南部九龙山自然保护区和安徽省南部牯牛降的高海拔黄山松树轮径向宽度资料,分别建立了2个树轮宽度差值年表(RES).由子样本信号强度(SSS)>0.8判定,九龙山年表(JLS01)的可靠时段为1884—2010年,牯牛降年表(GNJ01)的可靠时段为1837—2008年.将采样点周围气象站气象数据做算术平均代表区域气候状况,利用相关函数检验了两年表与区域气象数据的月降水量、月平均温度、月平均相对湿度、月总云量和月日照时数的关系.结果表明： 2个高海拔点树木径向生长主要受夏季(上年6、7月,当年6月)水热条件的影响.九龙山年表与上年6、7月温度呈显著正相关,与上年6、7月和当年6月降水及相对湿度呈显著负相关,与上年7月总云量呈显著负相关,与上年6、7月日照时数呈显著正相关;牯牛降年表与上年7月温度呈显著正相关,与上年7月和当年6月降水及相对湿度呈显著负相关,与上年6月总云量呈显著负相关,与上年7月、当年6月日照时数呈显著正相关.由于高海拔地区温度较低,夏季温度的升高有利于该地区树木生长,同时较多降水对应的高相对湿度、高云量和低日照时数,限制了光合作用产物的合成,导致树木的径向生长受到抑制.
     

Thermal and hygric physiology of Australian burrowing mygalomorph spiders (Aganippe spp.)

This study investigated the standard metabolic rate (SMR) and evaporative water loss (EWL) responses of three Australian trapdoor-constructing mygalomorph spider species, two undescribed arid-zone species (Aganippe ‘Tropicana A’ and A. ‘Tropicana B’) and a mesic-dwelling species (A. rhaphiduca) to acute environmental regimes of temperature and relative humidity. There were significant effects of species, temperature, and relative humidity on SMR. SMR was lower for A. raphiduca than both A. ‘Tropicana’ spp. with no difference between the two A. ‘Tropicana’ spp. Metabolic rate increased at higher temperature and relative humidity for all three species. There were significant effects of species, temperature, and relative humidity on EWL. The mesic Aganippe species had a significantly higher EWL than either arid Tropicana species. EWL was significantly higher at lower relative humidity. Our results suggest an environmental effect on EWL but not SMR, and that mygalomorphs are so vulnerable to desiccation that the burrow provides a crucial refuge to ameliorate the effects of low environmental humidity. We conclude that mygalomorphs are highly susceptible to disturbance, and are of high conservation value as many are short-range endemics.     

Tests of the contribution of acclimation to geographic variation in water loss rates of the West Indian lizard <Emphasis Type="Italic">Anolis cristatellus</Emphasis>

Phenotypic plasticity can contribute to the process of adaptive radiation by facilitating population persistence in novel environments. West Indian Anolis lizards provide a classic example of an adaptive radiation, in which divergence has occurred along two primary ecological axes: structural microhabitat and climate. Adaptive plasticity in limb morphology is hypothesized to have facilitated divergence along the structural niche axis in Anolis, but very little work has explored plasticity in physiological traits. Here, we experimentally ask whether Puerto Rican Anolis cristatellus from mesic and xeric habitats differ in desiccation rates, and whether these lizards exhibit an acclimation response to changes in relative humidity. We first present microclimatic data collected at lizard perch sites that demonstrate that abiotic conditions experienced by lizards differ between mesic and xeric habitat types. In Experiment 1, we measured desiccation rates of lizards from both habitats maintained under identical laboratory conditions. This experiment demonstrated that desiccation rates differ between populations; xeric lizards lose water more slowly than mesic lizards. In Experiment 2, lizards from each habitat were either maintained under the conditions of Experiment 1, or under extremely low relative humidity. Desiccation rates did not differ between lizards from the same habitat maintained under different treatments and xeric lizards maintained lower desiccation rates than mesic lizards within each treatment. Our results demonstrate that A. cristatellus does not exhibit an acclimation response to abrupt changes of hydric conditions, and suggest that tropical Anolis lizards might be unable to exhibit physiological plasticity in desiccation rates in response to varying climatic conditions.     

Temperature and humidity acclimation increase desiccation resistance in the butterfly Bicyclus anynana

Desiccation resistance, that is, the ability to reduce water loss, is an ecologically important trait relevant to all terrestrial organisms, which may constrain species distributions. Nevertheless, relatively few studies have investigated plastic capacities in desiccation resistance. We here investigate plastic responses in body mass change, used as a proxy of desiccation resistance, to variation in temperature and relative humidity in the tropical butterfly Bicyclus anynana (Butler) (Lepidoptera: Nymphalidae). Our results indicate that butterflies acclimated to a higher (27 °C) compared with a lower temperature (18 °C) and a lower (50%) compared with a higher (90%) relative humidity displayed a decreased loss of body mass, and therefore likely a loss of body water (27 °C: 11%, 18 °C: 15%; 50% r.h.: 14%, 90% r.h.: 18%). Thus, mass loss was reduced under conditions indicating increased desiccation risk, suggesting adaptive phenotypic plasticity. Effects were most pronounced during the first 24 h after acclimation, indicating quick and transient responses to environmental conditions. As anthropogenic climate change is predicted to increase the magnitude and frequency of heat and drought periods, we argue that more studies on plastic capacities in traits relating to desiccation resistance are needed to better understand species responses.     

EFFECT OF TEMPERATURE AND DESICCATION ON THE PHOTOSYNTHETIC PERFORMANCE OF PORPHYRA PERFORATA

Porphyra perforata is a common seaweed inhabiting the upper intertidal zone, and as a consequence it experiences great fluctuations in tissue temperature and desiccation. The objective of this work was to evaluate the effect of ambient temperature and the tissue desiccation status on the photosynthetic performance of P. perforata. Photosynthetic performance was evaluated polarographically after the temperature or desiccation treatments. Maximum photosynthesis (P_max) occurred between 25 and 30° C and decreased at higher and lower temperatures, however, no significant differences were observed in the initial slope of photosynthesis (α) from 10 to 30° C. This suggests that the photosynthetic efficiency of this species does not decrease as a result of fluctuating temperatures during tidal emergence/submergence. P_max and α were relatively constant in tissue of P. perforata with 5 to 100% relative water content. This also suggests that natural desiccation rates during low tides do not decrease photosynthetic rates in this species. Variations in the synthesis of specific proteins as a result of fluctuations in temperature and relative water content in the tissue of P. perforata are being studied.