Population dynamics of stable flies Stomoxys calcitrans (Diptera: Muscidae) at an organic dairy farm in Denmark based on mark-recapture with destructive sub-sampling

A population of stable flies, Stomoxys calcitrans (L.), was studied on a Danish cattle farm in two successive years. Flies were captured monthly by sweep nettings and marked with fluorescent dust. Absolute population size, dilution rate, loss rate, and adult longevity were estimated by means of a modified version of Bailey's triple catch method. In both years, the abundance of flies peaked in July. Using a statistical model, we were able to explain 86.6% of the variation in the per capita growth rate r as a function of current temperature, precipitation, and population size. Omitting precipitation from the model, it still explained 69.3%. The model predicts that stable flies have a temperature optimum at 21.8°C, and that no development will take place when temperatures inside the stable are below 10.2°C or above 33.5°C. At the optimal temperature the intrinsic rate of natural increase is 0.070 d(-1). The per capita dilution rate increased with temperature and decreased with population size, whereas no effect of these factors on the per capita loss rate could be shown. Mean adult survival time was estimated to 6.3 d with 95% CL ranging from 4.3 to 11.1 d. The study points at the possibility of developing predictive models as tools for achieving better, and more environmentally sound, control of stable flies.     

Metabolic rates of tsetse flies in the field as measured by the excretion of injected caesium

ABSTRACT Teneral tsetse flies, Glossina morsitans morsitans Westw., were injected with labelled caesium (¹³⁷Cs) <18 h after emergence and released in the Zambezi Valley of Zimbabwe between May 1983 and June 1984, and again in February 1985. Radioactivity in flies recaptured time t days after injection indicated a three-stage exponential loss of caesium, identical for both sexes. For t≫4 the estimated rate constant (-0.119 per day) was significantly lower than for 4≫t≫12 (–0.252 per day). By day 15 about 97% of the isotope had been excreted; thereafter the loss rate fell by an order of magnitude. The data for t>4 days were well fitted by the sum of two exponentials but no smooth function was found to fit all three phases. The loss rate from the rapidly metabolized pool increased exponentially with temperature at the same rate as for male tsetse kept in the dark in the laboratory. However, the loss rate in the field was lower at every temperature, suggesting that these flies live at 2–6^oC lower than the average Stevenson screen temperature. Published estimates of hunger cycle and daily flight durations, made on the basis of measured rates of caesium excretion, are invalid because they use the assumption that flies are living in the field at screen temperatures. The data suggest that both sexes have the same metabolic rate up to the age of about 15 days, which implies that the females (being larger and having to nourish a larva in the latter stages of this period) must be less active and/or live at even lower temperatures than the males.     

Ascaris sp.: water loss during desiccation of embryonating eggs

The ability of embryonating eggs of Ascaris lumbricoides to avoid desiccation by reducing the loss of water through the egg shell was investigated. When exposed to desiccation the eggs lost water at a rate dependent upon the relative humidity and ambient temperature, eventually resulting in the collapse of the eggs and the death of the enclosed embryo. The eggs are small with a large surface to volume ratio. A low permeability to gaseous exchange thus restricts water loss while still ensuring an adequate supply of oxygen for embryonic development. Relative humidity did not appear to affect the rate of development. In eggs exposed to desiccation at various constant temperatures, the rate of water loss increased as an exponential function of increasing temperature. When eggs were exposed to various temperatures before exposure to desiccation at 22 C, the rate of water loss increased as a function of increasing pretreatment temperature. After exposure to 63–65 C, the ability of the egg shell to slow down the loss of water was destroyed. These phenomena suggest that there is not a simple “critical” or “transition” temperature, but a gradual melting of the complex mixture of components forming the lipid layer.     

Differences in transpiration rates between tropical and temperate grasses under controlled conditions

Summary Two experiments were conducted to determine the transpiration rates of tropical and temperate grasses under a range of environmental conditions. In dense populations, three temperate grasses lost considerably more water per unit leaf area than did four tropical grasses, though tropical grasses tended to produce more dry matter per unit leaf area. The efficiency of production in relation to water use was thus greater in tropical than in temperate grasses. Wheat, a temperate grass, lost water at an average rate 2.25 times that of sorghum, a tropical grass, on a unit leaf area basis when single leaves were exposed to temperatures from 17 to 32° and light intensities from 1.7 to 4.4×10⁴ ergs cm^-2 sec^-1 at 0.55 (1,100 to 2,800 ft.-c.). The measurement of transpiration and leaf temperature indicated that latent heat loss was much more important in wheat, and sensible heat loss was more important in sorghum as means of dissipating excess energy absorbed. These findings were attributed to the greater resistance to gas diffusion offered by sorghum than by wheat stomata in each environment.     

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.     

Measuring thermal behavior in smaller insects: A case study in Drosophila melanogaster demonstrates effects of sex,geographic origin,and rearing temperature on adult behavior

Measuring thermal behavior in smaller insects is particularly challenging. In this study, we describe a new horizontal thermal gradient apparatus designed to study adult thermal behavior in small insects and apply it using D. melanogaster as a model and case study. Specifically, we used this apparatus and associated methodology to examine the effects of sex, geographic origin, and developmental rearing temperature on temperature preferences exhibited by adults in a controlled laboratory environment. The thermal gradient established by the apparatus was stable over diurnal and calendar time. Furthermore, the distribution of adult flies across thermal habitats within the apparatus remained stable following the period of acclimation, as evidenced by the high degree of repeatability across both biological and technical replicates. Our data demonstrate significant and predictable variation in temperature preference for all 3 assayed variables. Behaviorally, females were more sensitive than males to higher temperatures. Flies originating from high latitude, temperate populations exhibited a greater preference for cooler temperatures; conversely, flies originating from low latitude, tropical habitats demonstrated a relative preference for higher temperatures. Similarly, larval rearing temperature was positively associated with adult thermal behavior: low culture temperatures increased the relative adult preference for cooler temperatures, and this response was distinct between the sexes and for flies from the temperate and subtropical geographic regions. Together, these results demonstrate that the temperature chamber apparatus elicits robust, predictable, and quantifiable thermal preference behavior that could readily be applied to other taxa to examine the role of temperature-mediated behavior in a variety of contexts.     

A comparison of the responses of tropical and temperate flies (Diptera: Sarcophagidae) to cold and heat stress

Summary Two flesh fly species from the tropical lowlands (Peckia abnormis and Sarcodexia sternodontis) were more susceptible to both cold-shock and heatshock injury than temperate flies (Sarcophaga crassipalpis and S. bullata) and a fly from a tropical high altitude (Blaesoxipha plinthopyga). A brief (2-h) exposure to 0°C elicits a protective response against subsequent cold injury at–10°C in the temperate flies and in B. plinthopyga but no such response was found in the flies from the tropical lowlands. However, both tropical and temperate flies could be protected against heat injury (45°C) by first exposing them to a mild heat shock (2 h at 40°C). The supercooling point is not a good indicator of cold tolerance: supercooling points of pupae were similar in all species, ranging from–18.9 to–23.0°C, and no differences were found between the tropical and temperate species. Among the temperate species, glycerol, the major cryoprotectant, can be elevated by short-term exposure to 0°C, but glycerol could not be detected in the tropical flies. Low-temperature (0°C) exposure also increased hemolymph osmolality of the temperate species, but no such increase was observed in the tropical lowland species. Adaptations to temperature stress thus differ in tropical and temperate flesh flies: while flies from both geographic areas share a mechanism for rapidly increasing heat tolerance, only the temperate flies appear capable of responding rapidly to cold stress. The presence of a heat shock response in species that lack the ability to rapidly respond to cold stress indicates that the biochemical and physiological bases for these two responses are likely to differ.     

Respiration rate of arctic plants as related to the production process

This work deals with two intertwined questions: (1) what are the factors underlying equally high respiration rates of arctic plants at low temperature and of temperate zone plants at 20–25°C and (2) whether this respiration feature would explain small size of the northern plants. In an attempt to answer these questions, we collected various hypotheses scattered in the current literature and experimentally examined the respiration- growth relationships by analyzing plant productivity characteristics in three representative species inhabiting Wrangel Island (lat. 71°N). The results show that the components of the production process stay in accord in the arctic plants so that their productivity characteristics at low temperatures are nearly the same as in the temperate zone plants at higher temperatures. Hence, respiration cannot account for small size of the northern plants. Upon the experimental results and general concepts for regulation of respiration, we conclude that the intense respiration of plants inhabiting cold climate regions is caused by higher metabolic demands for energy and intermediates under the northern conditions. The enhanced metabolic demands of plants at low temperature represent the main factor of intense respiration.     

The impact of diapause on the evolution of other life history traits in flesh flies

Summary Flesh flies (Sarcophagidae) collected in Costa Rica and Panama lack the pupal diapause that is characteristic of flesh flies from the temperate zone and tropical Africa. The absence of a diapause capacity in the neotropical species correlates with several other life history traits: in most species the post feeding wandering phase of the third larval instar is longer and duration is more variable, adult life is longer, clutch size is smaller, and more clutches are produced. Among species that have the capacity for diapause, risk is invested primarily in the diapausing stage and other life stages are brief. Though diapausing species are short-lived, they produce as many or more progeny than nondiapausing species by increasing clutch size. The slower and more variable developmental rate and increased adult longevity desynchronizes development and permits the nondiapausing species to spread an environmental risk over different stages of the life cycle, thus offering an alternative to diapause. Other traits such as body size, developmental velocity, thermal constant thresholds, thermal constants, age at first reproduction, and the interval between clutches do not appear related to the capacity for diapause.     

The effects of acclimation and rearing conditions on the response of tropical and temperate populations ofDrosophila melanogaster andD. simulans to a temperature gradient (Diptera: Drosophilidae)

The effects of rearing and acclimation on the response of adultDrosophila to temperature were investigated in a gradient.D. melanogaster flies preferred a higher mean temperature and were distributed over a wider range of temperatures thanD. simulans flies. Acclimating adults at different temperatures for a week did not influence the response of either species. Adults reared at 28°C as immatures had a lower mean preference than those reared at cooler temperatures, suggesting that flies compensated for the effects of rearing conditions. Adults from tropical and temperate populations ofD. melanogaster andD. simulans did not differ in the mean temperature they preferred in a gradient, suggesting little genetic divergence for this trait within species. The species differences and environmental responses may be related to changes in optimal physiological conditions for the flies.     

Testing the plant stress hypothesis: stressed plants offer better food to an insect herbivore

Temperature and nutrition are among the most important environmental factors affecting ectotherm growth. As temperature and host‐plant quality often co‐vary in nature, the interaction between the two is of potentially high ecological importance for herbivorous insects. We here use the temperate‐zone butterfly Pieris napi L. (Lepidoptera: Pieridae) to investigate interactive effects of larval rearing temperature and host‐plant quality (by manipulating water availability) on larval growth. As growth rates have been hypothesized to govern stress tolerance, we additionally assessed adult starvation resistance. Butterflies followed the ‘temperature‐size rule’, which states that body size increases at lower developmental temperatures, proximately caused by differences in growth increment, which resulted from increased consumption at the lower temperature. Larvae benefitted from feeding on stressed plants from the low‐water regime by having higher body mass, growth rate, and food conversion efficiency, thus supporting the plant stress hypothesis, which predicts that plant quality for herbivores should increase if stress is imposed on plants. Some effects of host‐plant quality on larval growth parameters were as strong as or even stronger than effects of temperature, whereas interactive effects between temperature and food quality were scarce. At the low temperature, adult starvation resistance was higher than at the higher temperature and females were more resistant than males, whereas plant water regime had no clear impact. No evidence was found for a trade‐off between growth rate and starvation resistance. This study illustrates the importance of considering effects of host‐plant quality along with variation in other environmental factors for estimating the impact of environmental changes on herbivorous species.     

A model for blood meal digestion and fat metabolism in male tsetse flies (Glossinidae)

Abstract. Fat and haematin levels of mature male Glossina morsitans morsitans Westwood were estimated at different times after feeding at temperatures between 15 and 30°C. Flies were kept (largely inactive) in 7.5 × 2.5 cm tubes, or in actograph cages, where flight activity increased with time after feeding. Haematin excretion was modelled as a series of three first order reactions, all with the same rate parameter. The model accounted for > 98% of the variance in mean haematin in each of seven experiments; the rate parameter increased linearly with temperature and activity level. A similar approach was adopted for modelling fat metabolism. The rate coefficients of lipogenesis increased with temperature, and that for lipolysis with temperature, activity level and their interaction. All experiments were analysed simultaneously to provide equations predicting haematin or fat levels for all times, for active or inactive flies, and for temperatures between 15 and 30°C. Haematin exhibited large variations between individuals, but for active flies the expected haematin content at a given time varied little between flies kept at 25 and at 30°C. In inactive flies kept at 25°C, lipogenesis peaked at ≈ 24 h and lipolysis at ≈ 48 h. For active flies the times were 12 and 24 h, respectively; both rates were about twice as high as in inactive flies. Active flies produced (up to 1 mg) more fat out of a given size of blood meal than inactive flies. Curves of fat content against logarithm of haematin content differed little with temperature, and can therefore be useful for comparative studies of field populations of tsetse.     

Age-related changes in the rate of water loss and survival time in dry air of active Drosophila melanogaster

By continuously monitoring the weight loss in dry air at 24.5°C of active individual male Drosophila melanogaster, it was shown that: (i) during the active period, weight loss is a linear function of time, but once the body water content is reduced to below a critical level, activity ceases and the rate of weight loss increases rapidly; the time at which the rate of weight loss increases probably coincides with the time of death; (ii) the sudden change in the rate of weight loss can be prevented by blocking the spiracles; (iii) the rate of weight loss in the active period is positively correlated with age; (iv) young flies can tolerate a greater reduction in total body water than old flies. It is suggested that the age-related decrease in survival time in dry air is a consequence of changes in the initial water content of the flies, in their rate of water loss, in their activity, and in their tolerance of low water content.     

Time-dependent changes in the size distribution of distearoylphosphatidylcholine vesicles.

The results of transmission electron microscopic and ultracentrifugal studies of the size distributions of sonicated distearoylphosphatidylcholine vesicles are reported. Small vesicles (d approximately 300 A) were prepared by sonication of pure 1,2-distearoyl-3-sn-phosphatidylcholine in water and incubated at 4, 21, 40, 53, and 65 degrees C. The vesicle size distributions changed as a function of time at all temperatures below the phase-transition temperature but remained constant at the transition temperature and above. The sizes of structures to which the small vesicles are converted are the same at all temperatures, although the rates of conversion differ. The primary structures formed are identified as larger vesicles. The rate of loss of small vesicles is found to increase with decreasing temperature. At 4 and 21 degrees C small vesicles are converted to amorphous material, possibly irregular fragments of neat phase, in addition to being converted to larger vesicles. Trace amounts of an impurity commonly produced in the synthesis of 1,2-distearoyl-3-sn-phosphatidylcholine, 1,3-distearoyl-2-sn-phosphatidylcholine, are found to dramatically reduce the rate of loss of small vesicles at 21 degrees C.     

Effects of temperature on growth, development and diapause in the yellow dung fly – against all the rules?

The effects of rearing temperature (and photoperiod) on growth, development, body size, and diapause induction and termination in the yellow dung fly, Scathophaga stercoraria, were investigated by allowing replicate families of larvae to develop in the field along a time sequence approaching the onset of winter. This was supplemented with extensive laboratory rearing. At constant laboratory temperatures, growth rates were maximal between 15°C and 20°C and decreased at higher (25°C) and lower (10°C) temperatures, while the development rate was maximal at 25°C. Perhaps related to this, yellow dung flies reached a given size faster at naturally variable, as opposed to constant, temperatures. In the field, lower temperatures towards the end of the season resulted in larger individuals that grew faster. Adult body size increased as development time, expressed in calendar days, increased, a positive relationship commonly taken for granted in life history theory, but decreased as development time expressed in degree-days increased. The effect of temperature on growth, development and body size can thus change or even reverse if individuals can alter their growth rate independently of development time, and if the physiological effects of temperature are factored out by converting development time into degree-days above a lower development threshold. Therefore, supposedly well-established trends possibly need to be re-examined along these lines. Pupal winter diapause towards the end of the season was highly reversible by temperature. Pre- and post-winter emergence patterns together suggest that the minimum time for yellow dung flies to successfully complete development, at any time of the year, is about 230–250 degree-days. Received: 2 September 1996 / Accepted: 26 February 1997     

高寒地区根田鼠的体温调节与蒸发失水

对栖息于青藏高原地区的草食性小型哺乳动物根田鼠的代谢率、热传导、体温和蒸发失水等生理生态特征随环境温度的变化进行了测定,结果表明：根田鼠代谢水平较高,热传导率也较高,但体温相对较低;蒸发失水在体温调节中占十分重要的地位;这些特点对于栖居于日温差较大,年温差相对较小的环境中具重要的适应意义,说明动物在长期适应进化过程中,面临的主要选择压力是寒冷。结合同域分布的其它物种的生理生态特征,提出了高寒地区草食性小型兽拥有较高的代谢水平,较高的热传导率和相对较低的体温的观点。     

A generalized,lumped-parameter model of photosynthesis,evapotranspiration and net primary production in temperate and boreal forest ecosystems

Summary PnET is a simple, lumped-parameter, monthlytime-step model of carbon and water balances of forests built on two principal relationships: 1) maximum photosynthetic rate is a function of foliar nitrogen concentration, and 2) stomatal conductance is a function of realized photosynthetic rate. Monthyly leaf area display and carbon and water balances are predicted by combining these with standard equations describing light attenuation in canopies and photosynthetic response to diminishing radiation intensity, along with effects of soil water stress and vapor pressure deficit (VPD). PnET has been validated against field data from 10 well-studied temperate and boreal forest ecosystems, supporting our central hypothesis that aggregation of climatic data to the monthly scale and biological data such as foliar characteristics to the ecosystem level does not cause a significant loss of information relative to long-term, mean ecosystem responses. Sensitivity analyses reveal a diversity of responses among systems to identical alterations in climatic drivers. This suggests that great care should be used in developing generalizations as to how forests will respond to a changing climate. Also critical is the degree to which the temperature responses of photosynthesis and respiration might acclimate to changes in mean temperatures at decadal time scales. An extreme climate change simulation (+3° C maximum temperature, –25% precipitation with no change in minimum temperature or radiation, direct effects of increased atmospheric CO₂ ignored) suggests that major increases in water stress, and reductions in biomass production (net carbon gain) and water yield would follow such a change.     

Life history strategies of cladocerans: comparisons of tropical and temperate taxa

We review recent works on different life history variables of cladoceran taxa in tropical and temperate freshwater bodies, comparing the strategies that cladocerans have evolved to adapt to contrasting environmental conditions in the two geographical regions. These life-history parameters relate to age and size at maturity, survival, fecundity, life-expectancy at birth, lifespan, gross, and net reproductive rates, generation time, the rate of population increase, peak population density and day of peak abundance. We also discuss the role of photoperiod and temperature on some of these life history parameters. We found a general paucity of experimental work and field data in tropics on cladocerans. There is very limited information on the few Daphnia species found in the tropics. The misconception of low species diversity of cladocerans in the tropics arose due to several reasons including lack of extensive and intensive field collections. Higher water temperatures apparently promote permanent infestation of tropical waters with toxic cyanobacteria, which reduce the zooplankton diversity. In addition to higher temperatures in the tropics, the year-round high predation pressure of planktivorous fish probably causes the tropical species, particularly in pelagic habitats, to reach maturity earlier (< 3 days) than in temperate regions. Species of Daphnia in temperate regions are particularly adapted to living at food concentrations that are much lower and seasonably more variable than those for tropical genera such as Diaphanosoma. This is further corroborated by the more than an order of magnitude higher threshold food concentration (TFC) for tropical Cladocera than for their temperate counterparts. Fecundity patterns differ between tropical and temperate cladoceran taxa: cultured under optimal temperature regimes, tropical taxa have fewer eggs than temperate species of a comparable body size. Predation pressure may act differently depending on the size of the cladoceran neonates and thus on their population size structure. Global warming and climate changes seem to affect the behaviour (migration), distribution, and abundance of cladocerans. Apparently, in direct response to these changes, the possibility of encountering the tropical cladocerans in the northern, temperate hemisphere (bioinvasions) is on the rise.     

横断山区中华姬鼠的体温调节和蒸发失水

为探讨中华姬鼠的生理生态适应特征,对该鼠的代谢率、热传导、体温和蒸发失水等生理生态指标随环境温度从-5℃ ～ 35℃ 的变化进行了测定。结果表明:中华姬鼠的热中性区(TNZ)为20℃ ～ 30℃ ,平均体温为37. 2 ±0.3℃ ,体温在20℃ ～30℃ 范围内维持恒定;基础代谢率为3.17 ±0.08 ml O₂ / g· h,最大非颤抖性产热为5.99 ±0.58 ml O₂ / g· h,非颤抖性产热范围(最大非颤抖性产热与基础代谢率的比率)为1. 90,平均最小热传导(Cm )为0.16 ± 0.02 ml O₂ / g· h℃ ,热中性区内,中华姬鼠的F 值(RMR /Kleiber 期望RMR)/ (C /Bradley 期望C)为1.58 ±0.10,中华姬鼠的蒸发失水随着温度增高而增加,蒸发失水在35℃ 达到峰值,为0.10 ±0.02 mgH₂ O/ g· h。这些结果表明中华姬鼠对林地的适应特征是:基础代谢率较高,体温相对较低,最小热传导率与期望值相当,热中性区较宽,下临界温度较低;较高的最大非颤抖性产热和非颤抖性产热范围;蒸发失水在体温调节中占一定地位;这些特征与该物种的生活习性和栖息生境等因素密切相关,也可能是该物种对横断山区的适应对策。     

PHENOTYPIC PLASTICITY AND REACTION NORMS IN TEMPERATE AND TROPICAL POPULATIONS OF DROSOPHILA MELANOGASTER: OVARIAN SIZE AND DEVELOPMENTAL TEMPERATURE

The plasticity of ovariole number relative to developmental temperature was studied in three populations of Drosophila melanogaster at both ends of the cline: a temperate French population and two equatorial Congolese. Ovary size was much greater in the French flies, in agreement with an already known latitudinal cline. Among isofemale lines, significant differences in genetic variability were observed between populations with a maximum variability at intermediate temperatures. Parameters of phenotypic variability (CV and FA) were not statistically different among lines or populations, but a significant increase at low temperature was demonstrated for both. The shapes of the response curves (i.e., the norm of reaction) were analyzed by adjusting the data to a quadratic equation. The parameters of the equation were highly variable among lines. On the other hand, the temperature for maximum value of ovarioles (TMV) was much less variable and exhibited only a slightly significant difference between temperate and tropical flies (22.2°C vs. 22.7°C). During its geographic extension toward colder places, D. melanogaster underwent a large, presumably adaptative, increase in ovariole number but very little change in the norm of reaction of that trait.