Osmoregulatory capacity and the ability to use marine food sources in two coastal songbirds (Cinclodes: Furnariidae) along a latitudinal gradient

Cinclodes nigrofumosus and C. oustaleti are two closely related songbirds that inhabit the northern Chilean coast during the austral fall and winter.This stretch spans a dramatic north to south latitudinal gradient in rainfall and temperature. Whereas C. nigrofumosus lives exclusively on coastal environments, C. oustaleti shifts seasonally from coastal environments to inland freshwater ones. We used the δ¹³C of these two species’ tissues to investigate whether the reliance on marine versus terrestrial sources varied from the hyper-arid north to the wet south. We also investigated latitudinal variation in the renal traits that mediate how these birds cope with dehydration and a salty marine diet. Both species increased the incorporation of terrestrial carbon, as measured by δ¹³C, as terrestrial productivity increased southwards. However, C. nigrofumosus had consistently more positive (i.e. more marine) and less variable δ¹³C values than C. oustaleti. The osmoregulatory traits of both species varied with latitude as well. Urine osmolality decreased from extremely high values in the north to moderate values in the south, while C. nigrofumosus produced more concentrated urine than C. oustaleti. In both species, the proportion of kidney devoted to medullary tissue decreased from north to south, and kidney size increased significantly with latitude. Cinclodes nigrofumosus had larger kidneys with larger proportions of medullary tissue than C. oustaleti. C. nigrofumosus and C. oustaleti are terrestrial organisms subsidized by a rich marine environment where it is adjacent to an unproductive terrestrial. Variation in the reliance on marine food sources seems to be accompanied by adjustments in the osmoregulatory mechanisms used by these birds to cope with salt and dehydration.     

Osmoregulatory and metabolic costs of salt excretion in the Rufous-collared sparrow Zonotrichia capensis

Recent experiments on shorebirds have demonstrated that maintaining an active osmoregulatory machinery is energetically expensive. This may, in part, explain diet and habitat selection in birds with salt glands. However little is known about the osmoregulatory costs in birds lacking functional salt glands. In these birds, osmotic work is done almost exclusively by the kidneys. We investigated the osmoregulatory cost in a bird species lacking functional salt glands, the passerine Zonotrichia capensis. After 20 days of acclimation to fresh water (FW) and salt water (200 mM NaCl, SW), SW birds tended to be heavier than FW birds. However, this difference was not statistically significant. Total basal metabolic rate was higher in SW birds as compared with FW birds. Renal and heart masses were also higher in the SW group. We also found greater medullary development and an increase in urine osmolality in the SW group. In spite of Z. capensis' ability to tolerate a moderate salt load in the laboratory, we hypothesize that increased cost of maintenance produced by salt consumption may significantly affect energy budget, dietary, and habitat choices in the field.     

Renal physiology of two southern African Mastomys species (Rodentia: Muridae): a salt-loading experiment to assess concentrating ability

Aspects of renal physiology were examined to test the hypothesis that two cryptic species of the genus Mastomys (Mastomys natalensis and Mastomys coucha) are geographically separated by differences in aridity tolerance. Laboratory-bred females of each species were subjected to different levels of salinity in their water source (distilled water, 0.9% NaCl, and 1.5% NaCl; 10 conspecifics in each group) from weaning until sexual maturity. Individuals of the two species exhibited similar rates of water consumption and urine production. The salinity treatments caused sodium diuresis in both species, evident in increased urine volume, decreased osmolality and increased osmotic output. Urine concentration, kidney mass and kidney relative medullary area (RMA) did not differ between species. The results of our study do not support the hypothesis that differences in osmoregulatory ability separate these two cryptic species. Nor do they support the use of salt loading to elicit maximum urine concentrations in mammals.     

Kidney structure and function of obligate and facultative hibernators: the white-tailed prairie dog (Cynomys leucurus) and the black-tailed prairie dog (Cynomys ludovicianus)

The white-tailed prairie dog is an obligate hibernator that enters a heterothermic phase when maintained in the cold with low intensity light and ad libitum food and water. The black-tailed prairie dog (a facultative hibernator) will not hibernate under similar conditions. It has been suggested that the black tailed prairie dog remains active during the winter because it can conserve water more effectively due to a more efficient kidney. The present study revealed no significant differences between the species in renal morphology: relative medullary thickness, nephron heterogeneity, renal vasculature, or fornix dimensions, all of which are structures associated with the urinary concentrating mechanism. In addition, there was no difference in number of nephrons between the two species. The black-tailed prairie dog does produce a more concentrated urine when food and water deprived. However, this difference was not observed when the animals were salt loaded. The water-deprivation and salt-loading experiments suggest that the higher urine osmolality produced by the back-tailed prairie dog during fasting is a result of a higher urea load due to a greater protein catabolism and not because of a differential capacity to concentrate urine.Abbreviations C cortex - GFR glomerular filtration rate - H height - IS inner stripe - IZ inner zone of medulla - L length - OS outer stripe - PE polythylene - RMT relative medullary thickness - T _a ambient temperature - W width     

Cyclic electron flow around photosystem 1 is required for adaptation to salt stress in wild soybean species Glycine cyrtoloba ACC547

A wild soybean species Glycine cyrtoloba ACC547 was found to possess a high salinity resistance trait. It maintained higher net photosynthetic rate (PN) and maximal photochemical efficiency (F_v/F_m) than the soybean Glycine max cultivar Melrose under salt stress. Saline treatment enlarged the post-illumination transient increase in chlorophyll fluorescence in ACC547 much more than that in Melrose, indicating that its cyclic electron flow around photosystem 1 (CEF1) was accelerated more by salt stress. Additionally, ACC547 maintained higher nonphotochemical dissipation of excitation energy than Melrose under salt stress. It is suggested that the salinity resistance of ACC547 might be due to the CEF1-coupled dissipation of excess excitation energy.     

Day–night specific binding of 2-[125I]Iodomelatonin and melatonin content in gill, small intestine and kidney of three fish species

Some of melatonin’s (Mel) well-established physiological effects are mediated via high-affinity cell-membrane receptors belonging to the superfamily of G-protein-coupled receptors. Specific binding of ligand 2-[¹²⁵I]iodomelatonin, using membrane preparations from osmoregulatory tissues of flounder, rainbow trout and sea bream, together with Mel concentrations in the tissues and plasma were studied. The kidney, gill and small intestine samples were collected during the day and at night. The dissociation constants (K _d) and maximal binding densities (B _max) were calculated for each tissue at 11:00 and 23:00 h. The binding sites with K _d values in the tissues in the picomolar range indicated the high affinity. K _d and B _max values were tissue- and species-dependent. The GTP analogue [Guanosine 5′-O-(3-thiotriphosphate)] treatment significantly reduced the B _max value, indicating that the 2-[¹²⁵I]iodomelatonin-binding sites are probably coupled to a G-protein. No daily variations in K _d and B _max values were observed. These are the first studies of the presence of 2-[¹²⁵I]iodomelatonin-binding sites in the small intestine, kidney tubule and gill of fish. The data strongly suggest new potential targets for Mel action and the influence of Mel on water/ion balance in fish. The intestine seems to be a site of Mel synthesis and/or an active accumulation of the hormone.     

Urea and salt effects on enzymes from estivating and non-estivating amphibians

The effects of urea, cations (K⁺, NH₄, Na⁺, Cs⁺, Li⁺), and trimethylamines on the maximal activities and kinetic properties of pyruvate kinase (PK) and phosphofructokinase (PFK) from skeletal muscle, were analyzed in two anuran amphibians, an estivating species, the spadefoot toadScaphiopus couchii, and a semi-aquatic species, the leopard frogRana pipiens. Urea, which accumulates naturally to levels of 200–300 mM during estivation in toads, had only minor effects on the V_max, kinetic constants and pH curves of PK from either species and no effects on PFK V_max or kinetic constants. Trimethylamine oxide neither affected enzyme activity directly or changed enzyme response to urea. By contrast, high KCl (200 mM) lowered the V_max of toad PFK and of PK from both species and altered the K_m values for both substrates of frog PFK. Other cations were even more inhibitory; for example, the V_max of PK from either species was reduced by more than 80% by the addition of 200 mM NH₄Cl, NaCl, CsCi, or LiCl. High KCl also significantly changed the K_m values for substrates of toad lactate dehydrogenase and strongly reduced the V_max of glutamate dehydrogenase and NAD-dependent isocitrate dehydrogenase in both species whereas 300 mM urea had relatively little effect on these enzymes. The perturbing effect of urea on enzymes and the counteracting effect of trimethylamines that has been reported for elasmobranch fishes (that maintain high concentrations of both solutes naturally) does not appear to apply to amphibian enzymes. Rather, we found that urea is largely a non-perturbing solute for anuran enzymes (I₅₀ values were>1 M for both PK and PFK in both species) and we propose that its accumulation in high concentrations during estivation helps to minimize the increase in cellular ionic strength that would otherwise occur during desiccation and to alleviate the accompanying negative effects of high salt on individual enzyme activities and overall metabolic regulation.Abbreviations PFK 6-phosphofructo-1-kinase - PK pyruvate kinase     

Control of renal and extrarenal salt and water excretion by plasma angiotensin II in the kelp gull (Larus dominicanus)

Summary The osmoregulatory effects of intravenously (i.v.) administered angiotensin II (AII) at dose rates of 5, 15 and 45 ng · kg^–1 · min^–1 were examined in kelp gulls utilizing salt glands and/or kidneys as excretory organs.In birds given i.v. infusion of 1200 mOsmolal NaCl at 0.3 ml · min^–1 and utilizing only the salt glands to excrete the load, infusion of AII for 30 min consistently inhibited salt gland function in a dose-dependent manner.In birds given i.v. infusion of 500 mOsmolal NaCl at 0.72 ml · min^–1 and utilizing both salt glands and kidneys to excrete the load, each dose of AII given for 2 h inhibited salt gland function but stimulated the kidney, so that the overall outputs of salt and water were enhanced and showed significant (2P<0.01) positive correlations with plasma AII.In birds given i.v. infusion of 200 mOsmolal glucose at 0.5 ml · min^–1 and utilizing only the kidneys to excrete the load, low doses of AII (5 and 15 ng · kg^–1 · min^–1) caused renal salt and water retention, whereas a high dose (45 ng · kg^–1 · min^–1) stimulated salt and water output.The actions of plasma AII in kelp gulls support the concept that this hormone plays a vital role in avian osmoregulation, having effects on both salt gland and kidney function. Elevation of plasma AII consistently inhibits actively secreting salt glands, but its effects upon renal excretion depend primarily on the osmotic status as well as on the plasma AII concentration. In conditions of salt and volume loading doses of AII stimulate sodium and water excretion. With salt and volume depletion, the action of AII is bi-phasic with low doses promoting renal sodium and water retention but high circulating levels causing natriuresis and diuresis.     

Body Fineness Ratio as a Predictor of Maximum Prolonged-Swimming Speed in Coral Reef Fishes

The ability to sustain high swimming speeds is believed to be an important factor affecting resource acquisition in fishes. While we have gained insights into how fin morphology and motion influences swimming performance in coral reef fishes, the role of other traits, such as body shape, remains poorly understood. We explore the ability of two mechanistic models of the causal relationship between body fineness ratio and endurance swimming-performance to predict maximum prolonged-swimming speed (U_max) among 84 fish species from the Great Barrier Reef, Australia. A drag model, based on semi-empirical data on the drag of rigid, submerged bodies of revolution, was applied to species that employ pectoral-fin propulsion with a rigid body at U _max. An alternative model, based on the results of computer simulations of optimal shape in self-propelled undulating bodies, was applied to the species that swim by body-caudal-fin propulsion at U_max. For pectoral-fin swimmers, U_max increased with fineness, and the rate of increase decreased with fineness, as predicted by the drag model. While the mechanistic and statistical models of the relationship between fineness and U_max were very similar, the mechanistic (and statistical) model explained only a small fraction of the variance in U_max. For body-caudal-fin swimmers, we found a non-linear relationship between fineness and U_max, which was largely negative over most of the range of fineness. This pattern fails to support either predictions from the computational models or standard functional interpretations of body shape variation in fishes. Our results suggest that the widespread hypothesis that a more optimal fineness increases endurance-swimming performance via reduced drag should be limited to fishes that swim with rigid bodies.     

长江口盐沼植被生境内斑尾刺虾虎鱼食性特征

根据2015年5月至2016年4月在长江口东滩盐沼湿地水域采集的斑尾刺虾虎鱼样本数据,分析了该生境斑尾刺虾虎鱼的生物学和食性特征。结果表明:共采集到斑尾刺虾虎鱼186尾,其中6—8月采集的数量较高,而其他月份较低。约96%个体为幼体(平均体长109 mm),平均摄食等级为1.5。斑尾刺虾虎鱼主要摄食虾类(IRI(%)=69.05)、鱼类(IRI(%)=17.31)、蟹类(IRI(%)=11.51)和双壳类(IRI(%)=0.95)等11大类41小类饵料生物;虾类作为最重要的饵料类别,其生物量、数量和出现频次百分比均排列第一,以安氏白虾(Exopalaemon annandalei)、日本沼虾Macrobrachium nipponense)、长额刺糠虾(Acanthomysis longirostris)等虾类为主要饵料。鱼类饵料中,以大鳍弹涂鱼(Periophthalmus magnuspinnatus)、大弹涂鱼(Boleophthalmus valenciennes)等虾虎鱼科鱼类为主要饵料。各月平均饱满指数P(%)波动较大,6—11月呈逐渐增加趋势。随着体长的增加,饵料组成中鱼类的比例呈逐渐增高趋势,成体个体的饵料中鱼类的生物量比例达65%以上,虾类的比例则下降明显。6—8月斑尾刺虾虎鱼白天样本中鱼类饵料的重量百分比显著高于夜晚(P0.01),约是夜晚的8倍;但虾类则是夜晚显著高于白天(P0.01),约是白天的2倍,而蟹类饵料的昼夜差异不显著。从等级聚类(即组平均法)的分类方法可知,斑尾刺虾虎鱼各体长组食物组成在10%相似性水平上可分为3类,即41—60、61—180 mm和181—200 mm。从营养生态位宽度来看,41—60 mm体长组生态位宽度值为0.86,而61—120 mm体长组随着体长的增大而增大,但121—160 mm体长组生态位有所降低。盐沼生境丰富的饵料环境为斑尾刺虾虎鱼提供了良好的摄食场所,同时盐沼植被茂密的植株也可为幼体提供躲避捕食者的最佳庇护所,初步证明盐沼对于斑尾刺虾虎鱼具有重要的生境价值。     

Suitability of four different prey species for Dichochrysa tacta (Neuroptera: Chrysopidae)

The prey suitability for generalist insect predators is an important factor in efficient mass rearing. This work constitutes the first biological study of the predatory lacewing Dichochrysa tacta. We tested the effects of four different prey species on the biological parameters of the predatory lacewing D. tacta under laboratory conditions. These prey species consisted of Ephestia kuehniella (Zeller) and the aphids: Aphis fabae, Aphis punicae and Macrosiphum rosae. The results showed that prey species elicited a significant effect on preimaginal development times, survival, adult longevity and fecundity. In contrast, the progeny sex ratio, egg hatch and egg duration were not significantly affected by prey species. Eggs of E. kuehniella were the most suitable prey among those tested, and led to high survival rates, short development times for the preimaginal stages, long adult longevity, high fecundity, highest intrinsic rate of increase (r_m) and highest net reproductive rate (R₀) of D. tacta. Nymphs of both A. punicae and M. rosae were also relatively favourable prey, whereas nymphs of A. fabae were less suitable and resulted in reduced development, survival, adult longevity, fecundity, r_m and R₀. These results could be useful for optimising the mass rearing of D. tacta as an indigenous predator and for understanding its population dynamics in relation to different prey species in the field.     

Ion-poor water and dietary salt deprivation upregulate the ghrelinergic system in the goldfish (Carassius auratus)

Because the ghrelinergic system in teleost fishes is broadly expressed in organs that regulate appetite as well as those that contribute to the regulation of salt and water balance, we hypothesized that manipulating salt and water balance in goldfish (Carassius auratus) would modulate the ghrelinergic system. Goldfish were acclimated to either freshwater (FW) or ion-poor FW (IPW) and were fed either a control diet containing 1% NaCl or low-salt diet containing 0.1% NaCl. Endpoints of salt and water balance, i.e., serum Na⁺ and Cl⁻ levels, muscle moisture content and organ-specific Na⁺-K⁺-ATPase (NKA) activity, were examined in conjunction with brain, gill and gut mRNA abundance of preproghrelin and its receptor, growth hormone secretagogue receptor (ghs-r). Acclimation of fish to IPW reduced serum osmolality and Cl⁻ levels and elevated kidney NKA activity, while FW fish fed a low NaCl diet exhibited a modest reduction in muscle moisture content but otherwise no apparent osmoregulatory disturbance. In contrast, a combined treatment of IPW acclimation and low dietary NaCl content reduced serum osmolality and Cl⁻ levels, elevated muscle moisture content and increased gill, kidney and intestinal NKA activity. This intensified response to the combined effects of water and dietary ion deprivation is consistent with an increased effort to enhance ion acquisition. In association with these latter observations, a significant upregulation of preproghrelin mRNA expression in brain and gut was observed. A significant increase in ghs-r mRNAs was also observed in the gill of goldfish acclimated to IPW alone but a reduction in dietary NaCl content did not impact the ghrelinergic system of goldfish in FW. The results support the hypothesis that the ghrelinergic system is modulated in response to manipulated salt and water balance. Whether the central and peripheral ghrelinergic system contributes to ionic homeostasis in goldfish currently remains unclear and warrants further research.     

Inter- and intraspecific variation in the use of marine food resources by three Cinclodes (Furnariidae, Aves) species: carbon isotopes and osmoregulatory physiology

The avian genus Cinclodes (Furnariidae) includes species that inhabit both inland and marine shores. We compared the carbon isotopic composition and osmoregulatory capacities of field caught individuals of three Cinclodes species in Chile. Cinclodes nigrofumosus is a resident of coastal shores, whereas C. oustaleti and C. patagonicus inhabit both coastal and inland environments. The tissues of C. nigrofumosus exhibited distinctively marine delta(13)C values, whereas those of C. oustaleti and C. patagonicus were intermediate between marine and terrestrial values. The differences in carbon isotopic composition among these three species were paralleled by differences in osmoregulatory characteristics. The species that carbon isotopes revealed to be strictly marine, C. nigrofumosus, had relatively larger kidneys with a higher fraction of total renal tissue occupied by medullary cones than its congeners C. oustaleti and C. patagonicus. Cinclodes nigrofumosus individuals also produced more concentrated urine. In addition to interspecific differences in osmoregulation, we found intraspecific differences. Cinclodes nigrofumosus collected at an arid site with limited or no available fresh water exhibited larger kidneys and higher relative medullary thickness than individuals collected at a mesic site. Cinclodes nigrofumosus, like all passerines, lacks functional salt glands. This species appears to be unique among passerines in its ability to live in extreme arid coastal environments and to cope with a marine diet that imposes high osmotic loads.     

Influence of prey on developmental performance, reproduction and prey consumption of Neoseiulus californicus (Acari: Phytoseiidae)

The Spical strain of the predatory mite Neoseiulus californicus (McGregor) is used as a biological control agent, but little is known about its preferred prey and host plants in Japan. Here we studied the development, reproduction and prey consumption of the Spical strain when fed on eggs of five different spider mite species deposited on both their laboratory-rearing plant and cherry, on which all five spider mite species developed well. The developmental periods of immature N. californicus females and males were significantly affected by the prey species they fed on, but not by the plants. No difference was found between males and females. The developmental period was shorter on eggs of two Tetranychus species than on eggs of Panonychus ulmi. Immature females had a higher predation rate than immature males. Preoviposition period, oviposition period and the number of eggs laid per female were not significantly affected by either the plants or the type of prey eggs. The postoviposition period and total adult longevity were shorter on eggs of P. ulmi than of the other four prey species, but there was no effect of plant substrate. The postoviposition period of the Spical strain was much longer than that of other N. californicus strains or other predatory mite species: the postoviposition period of the Spical strain was more than three times longer than the oviposition period, accounting for more than 75% of the total adult longevity. This suggests that the females need multiple mating to reach full egg load, but this remains to be tested. Total consumption by N. californicus adults was lower for eggs of P. ulmi than for eggs of the other four species, apparently because of the shorter postoviposition period when fed on eggs of P. ulmi. The intrinsic rates of natural increase (r _m) on the rearing plant did not differ among prey species, whereas those on cherry were significantly different: the value was higher on Tetranychus urticae eggs than on eggs of other species. Only when N. californicus fed on T. urticae eggs, the r _m-values were significantly different between the rearing plant and cherry (higher on cherry). Thus, the Spical strain of N. californicus could feed on eggs of all five spider mite species, deposited on a variety of plants with similar r _m-values, suggesting that it could be successfully used to control spider mites in orchards and various crop fields of Japan.     

The growth of soybean under free air [CO<Subscript>2</Subscript>] enrichment (FACE) stimulates photosynthesis while decreasing in vivo Rubisco capacity

Down-regulation of light-saturated photosynthesis (A_sat) at elevated atmospheric CO₂ concentration, [CO₂], has been demonstrated for many C₃ species and is often associated with inability to utilize additional photosynthate and/or nitrogen limitation. In soybean, a nitrogen-fixing species, both limitations are less likely than in crops lacking an N-fixing symbiont. Prior studies have used controlled environment or field enclosures where the artificial environment can modify responses to [CO₂]. A soybean free air [CO₂] enrichment (FACE) facility has provided the first opportunity to analyze the effects of elevated [CO₂] on photosynthesis under fully open-air conditions. Potential ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation (V_c,max) and electron transport through photosystem II (J_max) were determined from the responses of A_sat to intercellular [CO₂] (C_i) throughout two growing seasons. Mesophyll conductance to CO₂ (g_m) was determined from the responses of A_sat and whole chain electron transport (J) to light. Elevated [CO₂] increased A_sat by 15–20% even though there was a small, statistically significant, decrease in V_c,max. This differs from previous studies in that V_c,max/J_max decreased, inferring a shift in resource investment away from Rubisco. This raised the C_i at which the transition from Rubisco-limited to ribulose-1,5-bisphosphate regeneration-limited photosynthesis occurred. The decrease in V_c,max was not the result of a change in g_m, which was unchanged by elevated [CO₂]. This first analysis of limitations to soybean photosynthesis under fully open-air conditions reveals important differences to prior studies that have used enclosures to elevate [CO₂], most significantly a smaller response of A_sat and an apparent shift in resources away from Rubisco relative to capacity for electron transport.Abbreviations FACE Free air [CO₂] enrichment - Rubisco Ribulose-1,5-bisphosphate carboxylase/oxygenase - RuBP Ribulose-1,5-bisphosphate - SoyFACE Soybean free air [CO₂] enrichment - VPD Vapor pressure deficit     

Paraphyly of Cinclodes fuscus (Aves: Passeriformes: Furnariidae): Implications for taxonomy and biogeography

The Andes are a hotspot of global avian diversity, but studies on the historical diversification of Andean birds remain relatively scarce. Evolutionary studies on avian lineages with Andean–Patagonian distributions have focused on reconstructing species-level phylogenies, whereas no detailed phylogeographic studies on widespread species have been conducted. Here, we describe phylogeographic patterns in the Bar-winged Cinclodes (Cinclodes fuscus), a widespread and common species of ovenbird (Furnariidae) that breeds from Tierra del Fuego to the northern Andes. Traditionally, C. fuscus has been considered a single species composed of nine subspecies, but its long and narrow range suggests the possibility of considerable genetic variation among populations. Sequences of two mitochondrial genes revealed three discrete and geographically coherent groups of C. fuscus, occupying the southern, central, and northern Andes. Surprisingly, phylogenetic analyses indicated that these groups were more closely related to other species of Cinclodes than to each other. Relationships of the southern and northern C. fuscus clades to other species of Cinclodes were straightforward; in combination with available information on plumage, behavioral, and vocal variation, this suggests that each should be recognized as a distinct biological species. The central Andean group was paraphyletic with respect to C. oustaleti, and relationships among these taxa and C. olrogi were poorly resolved. We suggest that the central Andean C. fuscus should also be considered a different species, pending new information to clarify species limits in this group. These new phylogenetic data, along with recently developed methods, allowed us to review the biogeography of the genus, confirming southern South America and the central Andes as important areas for the diversification of these birds.     

Growth and phosphate uptake kinetics of the cyanobacterium,Cylindrospermopsis raciborskii (Cyanophyceae) in throughflow cultures

• 1 Cylindrospermopsis raciborskii occupies a rapidly expanding geographical area. Its invasive success challenges eutrophication control in many lakes. To understand better the load‐dependent behaviour of this nitrogen fixing cyanobacterium under in situ conditions, we studied P‐dependent growth of a C. raciborskii strain under continuous and pulsed P supply.
• 2 The Droop model reasonably described P‐dependent growth in the continuously supplied chemostats. Large P pulses, however, caused a delay in growth and cells subject to P pulses grew slower than their counterparts with the same P quota supplied continuously.
• 3 The kinetics of P uptake indicated that C. raciborskii is opportunistic with respect to P. Its high excess P storage capacity after a saturating P pulse (Q_ex=95 µg P [mg C]^‐1) and P‐specific uptake capacity (U_max = V_max/Q_P=150–1200) are indicative of storage adaptation. At the same time, the affinity of the P uptake system (U_max/K = 800–4000) is also high.
• 4 Rate of leakage exceeded that of the steady state net P uptake by one to two orders of magnitude. Growth affinity of C. raciborskii (µ_max/K_µ≈ 20) was relatively low, presumably due to the substantial leakage.
• 5 The dynamics of the particular water body determine which trait contributes most to competitive success of C. raciborskii. In deep lakes with vertical nutrient gradients, the cyanobacterium may rely primarily on its high P storage capacity, which is coupled to a lack of short‐term feedback inhibition and efficient buoyancy regulation. In lakes without such gradients, high P uptake affinity may be vitally important.

     

Genetic mapping of the early responses to salt stress in Arabidopsis thaliana

Salt stress decreases plant growth prior to significant ion accumulation in the shoot. However, the processes underlying this rapid reduction in growth are still unknown. To understand the changes in salt stress responses through time and at multiple physiological levels, examining different plant processes within a single set-up is required. Recent advances in phenotyping has allowed the image-based estimation of plant growth, morphology, colour and photosynthetic activity. In this study, we examined the salt stress-induced responses of 191 Arabidopsis accessions from 1 h to 7 days after treatment using high-throughput phenotyping. Multivariate analyses and machine learning algorithms identified that quantum yield measured in the light-adapted state (F_v′/F_m′) greatly affected growth maintenance in the early phase of salt stress, whereas the maximum quantum yield (QY_max) was crucial at a later stage. In addition, our genome-wide association study (GWAS) identified 770 loci that were specific to salt stress, in which two loci associated with QY_max and F_v′/F_m′ were selected for validation using T-DNA insertion lines. We characterized an unknown protein kinase found in the QY_max locus that reduced photosynthetic efficiency and growth maintenance under salt stress. Understanding the molecular context of the candidate genes identified will provide valuable insights into the early plant responses to salt stress. Furthermore, our work incorporates high-throughput phenotyping, multivariate analyses and GWAS, uncovering details of temporal stress responses and identifying associations across different traits and time points, which are likely to constitute the genetic components of salinity tolerance.     

Early effects of salt stress on the physiological and oxidative status of Cakile maritima (halophyte) and Arabidopsis thaliana (glycophyte)

Early changes in physiological and oxidative status induced by salt stress were monitored in two Brassicaceae plants differing in their tolerance to salinity, Cakile maritima (halophyte) and Arabidopsis thaliana (glycophyte). Growth response and antioxidant defense of C. maritima under 400 mM NaCl were compared with those of A. thaliana exposed to 100 mM NaCl. Salinity induced early growth reduction that is less pronounced in C. maritima than in A. thaliana. Maximum hydrogen peroxide (H₂O₂) level occurred in the leaves of both species 4 h after the onset of salt treatment. A rapid decline in H₂O₂ concentration was observed thereafter in C. maritima, whereas it remained high in A. thaliana. Correlatively, superoxide dismutase, catalase and peroxidase activities increased at 4 h of treatment in C. maritima and decreased thereafter. However, the activity of these enzymes remained higher in treated plants than that in controls, regardless of the duration of treatment, in A. thaliana. The concentrations of malondialdehyde (MDA) reached maximum values at 24 h of salt stress in both species. Again, MDA levels decreased later in C. maritima, but remained high in A. thaliana. The contents of α‐tocopherol remained constant during salt stress in C. maritima and decreased during the first 24 h of salt stress and then remained low in A. thaliana. The results clearly showed that C. maritima, in contrast to A. thaliana, can rapidly evolve physiological and antioxidant mechanisms to adapt to salt and manage the oxidative stress. This may explain, at least partially, the difference in salt tolerance between halophytes and glycophytes.     

Predator–prey interactions between a planktonic ciliate Strombidium sp. (Ciliophora, Oligotrichida) and the dinoflagellate Pfiesteria piscicida (Dinamoebiales, Pyrrophyta)

The functional response of a planktonic ciliate, Strombidium sp. feeding on the dinoflagellate Pfiesteria piscicida non-toxic zoospores (NTZ) was experimentally studied with four different prey concentrations (43–3153 cells ml⁻¹). Data from direct observations (NTZ inside individual Strombidium sp.) was used to calculate predator–prey specific ingestion and clearance rates. The ingestion rates varied between 0.68 and 14.26 NTZ ind⁻¹ h⁻¹, and with the predator–prey specific handling time of 2.83 min the U_max was 21.18 NTZ ind⁻¹ h⁻¹. The increase in the prey concentration between approximately 700 and 3000 NTZ ml⁻¹ did not increase the uptake of prey, and at the lowest Pfiesteria NTZ concentrations the feeding efficiency of Strombidium sp. was lowered, possibly indicating a situation of threshold feeding. When data from direct observations of ingested Pfiesteria NTZ were compared with values of total NTZ loss from the experimental water during the experiment, ingestion was found to represent only a fraction of the total NTZ loss in the presence of ciliates. This discrepancy was concluded to be due to other grazer related factors than actual ciliate grazing. The control of the initial growth of Pfiesteria community, in a pre-bloom situation, would require only a small ciliate abundance (less than 5 ml⁻¹), but when the Pfiesteria NTZ are scarce, relatively more ciliates are needed to limit the population growth of the dinoflagellate community because of the apparent feeding threshold. It is concluded that the formation of non-toxic P. piscicida blooms require periods of low grazing pressure or a means to escape grazing.