Adaptive foraging by predators as a cause of predator-prey cycles

Summary When foraging has costs, it is generally adaptive for foragers to adjust their foraging effort in response to changes in the population density of their food. If effort decreases in response to increased food density, this can result in a type-2 functional response; intake rate increases in a negatively accelerated manner as prey density increases. Unlike other mechanisms for type-2 responses, adaptive foraging usually involves a timelag, because foraging behaviours do not often change instantaneously with changes in food density or risks. This paper investigates predator-prey models in which there are explicit dynamics for the rate of adaptive change. Models appropriate to both behavioural and evolutionary change are considered. Both types of change can produce cycles under similar circumstances, but under some evolutionary models there is not sufficient genetic variability for evolutionary change to produce cycles. If there is sufficient variability, the remaining conditions required for cycles are surprisingly insensitive to the nature of the adaptive process. A predator population that approaches the optimum foraging strategy very slowly usually produces cycles under similar conditions as does a very rapidly adapting population.     

Changes in diet,prey size and feeding habit in Bagrus bayad,and possible interactions with B. docmac in a Nile canal

Synopsis Bagrids in Bahr Shebeen Nilotic canal depend mainly on fish, insects and shrimp as well as fish embryos for food and their stomachs included runoff materials (e.g. plant foliage, glass, black crystals, coloured gravel). B. bayad maximised its efficiency of catching prey catfish by face to face attack to avoid damage by the prey's pectoral and dorsal spines. In the size classes of 10 to 30 cm standard length, B. bayad and B. docmac show diet overlap and interact with each other especially with respect to tilapias as prey. After this length, B. docmac, aided by its relatively larger mouth, shifted to larger size of tilapias to coexist with B. bayad.     

对冷适应大鼠棕色脂肪和肝脏在非寒颤产热机制中作用的评价

本实验主要观察并比较了大鼠冷适应前后直肠温度(RT)、血清游离脂肪酸(SFFA)浓度、肩胛间棕色脂肪组织(IBAT)和肝脏cAMP含量的变化及其对去甲肾上腺素(NE)反应性的改变。结果表明:①冷适应28d大鼠在冷环境中RT稳定,NE刺激后RT上升幅度大于常温对照组(P<0.005);②冷适应1d组SFFA升高,冷适应28d组SFFA接近对照组,且对NE刺激无反应,对照组给NE后SFFA与RT一致性升高;③冷适应28d组IBAT的cAMP升高,而肝脏的cAMP含量三组间无显著性差异。NE刺激后,冷适应28d组IBAT和肝脏cAMP均升高,与RT反应一致,而对照组不变。结果提示,在5±3℃适应28d的大鼠已建立冷适应机制,非寒颤产热(NST)容量增加,在冷适应的不同时期,肝脏和IBAT调节NST的机制不同。     

Influence of salt concentration and temperature on the fatty acid compositions of Ectothiorhodospira and other halophilic phototrophic purple bacteria

Influences of the salt concentration on the fatty acid composition of Ectothiorhodospira species and other phototrophic purple bacteria have been analysed. Major fatty acids in bacteria of the genera Rhodobacter, Rhodopseudomonas, Chromatium, and Ectothiorhodospira were straight chain saturated and monounsaturated C-16 and C-18 fatty acids. Salt-dependent responses of all investigated bacteria revealed relations to their salt optima. Minimum values of C-16 and saturated fatty acids and maximum values of C-18 and unsaturated fatty acids were found at or close to the salt optima. Responses of Ectothiorhodospira mobilis upon changes in salinity were nearly identical, whether cells were grown in batch culture or in continuous culture with identical dilution rates at all salt concentrations. With increasing temperature, the fatty acid composition of Ectothiorhodospira mobilis and Ectothiorhodospira halophila strains showed decreasing portions of C-18 and of unsaturated fatty acids, while the contents of C-16 and saturated fatty acids increased. The results are discussed with respect to bilayer stabilisation and membrane fluidity.Abbreviations PC phosphatidylcholine - PG phosphatidylglycerol - CL cardiolipin - PE phosphatidylethanolamine     

Seasonal change in photoperiodic response of the larvae of the lacewing Nineta pallida

Larvae of the lacewing Nineta pallida (Schneider), collected in the field during two seasons, from September to July, were reared in the laboratory under short- or long-day light conditions at 21°C. In autumn and winter, artificial short days delayed the first ecdysis. The influence on the duration of the first instar was maximal (3.4 times longer) when the short days began at hatching time, and later regularly diminished. In spring, the second and third instars showed a reversed response so that the long days now increased the duration of development, although development took no more than 1.4 time as long as in short days. A similar effect appeared in field-collected third instars on and after mid June, reaching its maximum (1.8 time until the cocoon spinning) in July. This sort of photoperiodic effect on the larval development is new to the seasonal adaptation of the life cycle in insects.

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Résumé Des formes préimaginales (oeufs, puis larves) de N. pallida sont récoltées sur des conifères de montagne (Pyrénées), chaque mois depuis septembre jusqu'en juillet en deux saisons (1983/84 et 1985/86). Elles sont ensuite élevées au laboratoire à 21°C, soit en jours longs (JL=L16:D8), soit en jours courts (JC=L8:D16).Le développement embryonnaire est légèrement plus long s'il se fait en JC. Pour les larves de premier stade récoltées en automne et en hiver, les JC retardent considérablement la première mue et prolongent aussi le deuxième stade qui en provient. L'influence retardatrice est maximale (3,4 fois) lorsque les JC agissent dès l'éclosion. Elle diminue ensuite progressivement et devient insignificante pour les larves récoltées à artir de février.Au printemps, les larves récoltées au deuxième stade ainsi que les troisièmes stades qui en découlent présentent une réaction inverse: ce sont alors les JL qui augmentent la durée du dévelopement, toutefois, pas plus de 1,4 fois par rapport aux JC. Un effet de même ordre se manifeste sur les larves de troisième stade récoltées à partir de juin, atteignant son maximum (1,8 fois) dans le lot de larves de juillet, c'est-à-dire peu avant la fin de la croissance pondérale larvaire et le coconnage.Un tel retardement du développement larvaire hivernal, prolongé au printemps et au début de l'été par une inversion de la réponse à la photopériode, est nouveau comme élément d'adaptation saisonnière du cycle naturel chez les insectes.

     

多鳞铲颌鱼的生态适应性及地理分布成因的探讨

本文根据对多鳞铲颔鱼的分布、生物学特性及栖居河段的生态环境等所做的调查和研究,探讨了多鳞铲颌鱼的生态适应性及分布成因等问题。做为对北方寒冷气候的适应,多鳞铲颌鱼有蛰伏泉穴越冬的习性,越冬期近6个月;推测多鳞铲颌鱼是由原始鲃类演化来的,形成于更新世早期;现代分布状况可能是受第四纪冰期的影响而造成的。     

Mouse lymphoma L1210 cells acquire a new cystine transport activity upon adaptation in vitro

Summary Mouse lymphoma L1210 cells maintained in vitro at a high cell density for a certain time period adapted themselves to the in vitro environment and were able to grow indefinitely. From these adapted cells, more than 30 clones were isolated. They all had much higher activity to take up cystine than the original L1210 cells, supporting a previous view that the deficiency of the cystine uptake limits the survival and growth of L1210 cells in vitro. The cystine uptake of one cloned cell line was characterized. The enhanced uptake of cystine in these cells was mainly mediated by a Na⁺-independent, saturable system and was potently inhibited by glutamate and some other anionic amino acids, but less by aspartate. Such activity of cystine uptake was not observed in the original L1210 cells. The results suggest that, upon adaptation in vitro, L1210 cells acquire a new cystine transport activity necessary for survival and growth in vitro.     

明适应条件下鲤属鱼L-型外水平细胞反应的给光-瞬变成分

在明适应条件下鲤属鱼 L-型外水平细胞的反应显示明显的给光-瞬变成分(on-transient)、它与刺激波长有关——对蓝、绿光的反应比对红光的反应有更明显的瞬变成分,其光谱特性提示它与绿敏锥细胞的输入信号有关。与已报道的其它动物 L 型水平细胞的给光-瞬变成分不同,它的出现在一定范围内与网膜受照射的面积无关。绿色(502nm)和红色(706nm)闪光同时照射所引起反应的给光-瞬变成分比各自单独刺激时要显著得多,提示它也与绿敏锥细胞和红敏锥细胞输入的相互作用有关。     

Primary cultures of rat pancreatic acinar cells in serum-free medium

Summary Rat pancreatic acinar cells were isolated and cultured in Ham's F12 medium with 15% bovine calf serum. Caerulein, insulin, somatostatin, and dexamethasone (DEX) had no effect on intracellular or secreted amylase in these cultured cells. A serum-free medium, using Waymouth's MB 752/1 supplemented with albumin, epidermal growth factor (EGF), DEX, and HEPES, was then developed to avoid serum factors that might mask hormonal effects. In this SF medium, pancreatic acinar, cells maintained the morphological and ultrastructural characteristics of freshly isolated cells and secreted amylase in response to the secretagogue, carbamyl choline. Insulin, at a concentration of 1 μg/ml, significantly increased intracellular and secreted amylase activity after 3 d. This model cell system can be used to study the regulation of the synthesis of amylase and other pancreatic enzymes in vitro.