How<Emphasis Type="Italic"> Daphnia</Emphasis> copes with excess carbon in its food

Animals that maintain near homeostatic elemental ratios may get rid of excess ingested elements from their food in different ways. C regulation was studied in juveniles of Daphnia magna feeding on two Selenastrum capricornutum cultures contrasting in P content (400 and 80 C:P atomic ratios). Both cultures were labelled with ¹⁴C in order to measure Daphnia ingestion and assimilation rates. No significant difference in ingestion rates was observed between P-low and P-rich food, whereas the net assimilation of ¹⁴C was higher in the treatment with P-rich algae. Some Daphnia were also homogeneously labelled over 5 days on radioactive algae to estimate respiration rates and excretion rates of dissolved organic C (DOC). The respiration rate for Daphnia fed with high C:P algae (38.7% of body C day^-1) was significantly higher than for those feeding on low C:P algae (25.3% of body C day^-1). The DOC excretion rate was also higher when animals were fed on P-low algae (13.4% of body C day^-1) than on P-rich algae (5.7% of body C day^-1) . When corrected for respiratory losses, total assimilation of C did not differ significantly between treatments (around 60% of body C day^-1). Judging from these experiments, D. magna can maintain its stoichiometric balance when feeding on unbalanced diets (high C:P) primarily by disposing of excess dietary C via respiration and excretion of DOC.     

Contribution analysis of body mass dynamics in <Emphasis Type="Italic">Daphnia</Emphasis>

The concept of body mass dynamics can be viewed as part of life history theory, but its potential has remained largely untapped due to a lack of analytical methodology. We therefore propose a method, called contribution analysis, which enables us to decompose a change in body mass into contributions associated with variations in individual egg mass, clutch size, and standard somatic mass (somatic mass adjusted to body length). The advantage of contribution analysis is that various contributions are expressed in the same units (units of mass) and show the amount of resources committed to changes in the individual traits, while the traits themselves are measured in different units and thus incomparable on their own. The method is tuned to study zooplankton, and is applied to examine body mass dynamics in Daphnia galeata. We found that when recovering from a poor-resource environment just above the threshold food concentration, Daphnia primarily increase their standard somatic mass, that is, restore body condition. When the trophic environment improves further but remains below the incipient limiting level, resources are invested equally to enhance body condition and reproduction in terms of clutch size. Finally, when food is no longer a limiting factor, almost all resources are committed to increase clutch size. While individual egg mass also varies, it never attracts more resources than the shift in the most prioritized trait. We suggest that the significance of this shift in resource allocation priorities is to keep an adult female alive in a poor environment and thus to allow her to retain her reproductive potential for better conditions in the future. Contribution analysis of body mass dynamics may allow us to detect flexible allocation strategies in a changing natural environment.     

Filamentous cyanobacteria,temperature and <Emphasis Type="Italic">Daphnia</Emphasis> growth: the role of fluid mechanics

Viscosity increases significantly with a fall in water temperature, thus temperature change affects not only the metabolic rates of aquatic suspension feeders, but also the physical properties of the surrounding fluid. This mechanistic effect of water temperature change on growth was separated from the effect of metabolism by using culture media with modified viscosity, while the temperature was kept constant. The effect of water viscosity on growth rate and feeding of four Daphnia species (D. magna, D. pulicaria, D. hyalina, D. galeata) was investigated. Increased viscosity decreased the growth rate significantly for three species, with the exception of D. galeata. Changing viscosity also affects growth qualitatively: the filamentous blue-green Cylindrospermopsis raciborskii reduces the growth rate of D. pulicaria at low viscosity, but its negative effect disappears when viscosity is higher. The findings are consistent with the hypothesis that it is the Reynolds number of the filtering appendages that determines the qualitative features of Daphnia filtration. The edibility of C. raciborskii at high water viscosity is most probably caused by lack of interference with filtering combs, and explains the coexistence of D. pulicaria with filamentous blue-green species in the field, and also the observed temperature dependence of growth inhibition of filaments.Electronic Supplementary Material Supplementary material is available for this article at     

The impact of diel vertical migration of <Emphasis Type="Italic">Daphnia</Emphasis> on phytoplankton dynamics

Diel vertical migration (DVM) of large zooplankton is a very common phenomenon in the pelagic zone of lakes and oceans. Although the underlying mechanisms of DVM are well understood, we lack experimental studies on the consequences of this behaviour for the zooplankton’s food resource—the phytoplankton. As large zooplankton species or individuals migrate downwards into lower and darker water strata by day and upwards into surface layers by night, a huge amount of herbivorous biomass moves through the water column twice a day. This migration must have profound consequences for the phytoplankton. It is generally assumed that migration supports an enhanced phytoplankton biomass and a change in the composition of the phytoplankton community towards smaller, edible algae in the epilimnion of a lake. We tested this assumption for the first time in field experiments by comparing phytoplankton biomass and community assemblage in mesocosms with and without artificially migrating natural stocks of Daphnia hyalina. We show that DVM can enhance phytoplankton biomass in the epilimnion and that it has a strong impact on the composition of a phytoplankton community leading to an advantage for small, edible algae. Our results support the idea that DVM of Daphnia can have strong effects on phytoplankton dynamics in a lake.     

Feeding behaviour,efficiency and food preference in yabbies <Emphasis Type="Italic">Cherax</Emphasis><Emphasis Type="Italic"> destructor</Emphasis>

The influence of body size on the consumption of live zooplankton (Daphnia spp.) by freshwater crayfish was examined using yabbies (Cherax destructor) ranging from 5 to 45 g. Food preference between live zooplankton and inert pellets was also assessed under experimental conditions. In experimental tanks, yabbies of four size classes (<15, 15–24.9, 25–34.9 and 35–45 g) were presented with live Daphnia. All yabbies were held in separate tanks with five animals per size class. In yabbies less than 15 g, the feeding mode on zooplankton involved rapid searching and probing with the first two pairs of walking legs. Once a prey was located, the chelae on the end of these walking legs would grasp the zooplankton and then rapidly move it towards the mouthparts. Yabbies larger than 25 g tended to use their walking legs to push the Daphnia nearer to their third maxilliped which would then force or scoop the zooplankton towards the mouthparts. A short-term feeding trial showed that there was no significant difference between size classes in regards to zooplankton consumption (P > 0.05). Capture efficiency of live Daphnia by yabbies less than 15 g was significantly lower (76%, P = 0.008) than the three larger size classes (93.6%). Yabbies less than 15 g consumed a significantly (P < 0.001) higher percentage (5.2%) of their body weight than the other size classes (1.1%, 0.8%, and 0.6%, respectively). In the presence of both live zooplankton and a pellet diet, yabbies spent significantly (P = 0.005) more time feeding on zooplankton (85%) than on inert pellets (15%). This was the first study to quantify zooplankton consumption by yabbies and the results provide insights into understanding the trophic role of freshwater crayfish in structuring zooplankton communities and the husbandry management of crayfish farming. Handling editor: S. I. Dodson     

Foraging behavior by <Emphasis Type="Italic">Daphnia</Emphasis> in stoichiometric gradients of food quality

Mismatches in the elemental composition of herbivores and their resources can impact herbivore growth and reproduction. In aquatic systems, the ratio of elements, such as C, P, and N, is used to characterize the food quality of algal prey. For example, large increases in the C:P ratio of edible algae can decrease rates of growth and reproduction in Daphnia. Current theory emphasizes that Daphnia utilize only assimilation and respiration processes to maintain an optimal elemental composition, yet studies of terrestrial herbivores implicate behavioral processes in coping with local variation in food quality. We tested the ability of juvenile and adult Daphnia to locate regions of high-quality food within a spatial gradient of algal prey differing in C:P ratio, while holding food density constant over space. Both juveniles and adults demonstrated similar behavior by quickly locating (i.e., <10 min) the region of high food quality. Foraging paths were centred on regions of high food quality and these differed significantly from paths of individuals exposed to a homogeneous environment of both food density and food quality. Ingestion rate experiments on algal prey of differing stoichiometric ratio show that individuals can adjust their intake rate over fast behavioral time-scales, and we use these data to examine how individuals choose foraging locations when presented with a spatial gradient that trades off food quality and food quantity. Daphnia reared under low food quality conditions chose to forage in regions of high food quality even though they could attain the same C ingestion rate elsewhere along a spatial gradient. We argue that these aspects of foraging behavior by Daphnia have important implications for how these herbivores manage their elemental composition and our understanding of the dynamics of these herbivore–plant systems in lakes and ponds where spatial variation in food quality is present. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Phylogenetic relationships in the genera<Emphasis Type="Italic"> Zostera</Emphasis> and<Emphasis Type="Italic"> Heterozostera</Emphasis> (Zosteraceae) based on<Emphasis Type="Italic"> matK</Emphasis> sequence data

Phylogenetic analysis of the plastid (chloroplast) DNA matK gene of Zosteraceae species was undertaken. A molecular phylogenetic tree based on matK sequence data showed the monophyly of Heterozostera tasmanica and subgenus Zosterella and did not support the separation of Heterozostera from the genus Zostera. The tree based on matK supported the monophyly of the subgenus Zostera, and showed that Zosteraceae consist of three main groups: Phyllospadix, which is clearly defined by being dioecious; the subgenus Zosterella and Heterozostera; and the subgenus Zostera. Character-state reconstruction of chromosome number and geographic distribution for our molecular phylogenetic tree showed that 2n=12 is a plesiomorphic character for Zostera and Heterozostera, that the chromosome number was doubled or tripled in two lineages, and that the initial speciation of Zostera and Heterozostera occurred in the Northern Hemisphere. The matK tree showed the close affinity of Z. noltii and Z. japonica, which have disjunct distributions. Zostera marina, which is the only widely distributed species in the subgenus Zostera, also occurring in the northern Atlantic, was shown to be embedded within other subgenus Zostera species.     

Arbuscular mycorrhizal fungi colonize decomposing leaves of<Emphasis Type="Italic"> Myrica parvifolia</Emphasis>,<Emphasis Type="Italic"> M. pubescens</Emphasis> and<Emphasis Type="Italic"> Paepalanthus</Emphasis> sp.

Hyphae and vesicles of arbuscular mycorrhizal fungi (AMF) were found within the decomposing leaves of Myrica parvifolia, M. pubescens and Paepalanthus sp. at three montane sites in Colombia. Hyphae, vesicles, and arbuscule-like structures were also found within scale-like leaves of the rhizomes of Paepalanthus sp. The litter found in the vicinity of the roots was divided into three decomposition layers. The highest AMF colonization occurred in the most decomposed leaves, which were in close association with roots. In contrast, there were no differences in AMF colonization of roots present in the different decomposition layers. Colonization of decomposing leaves by AMF did not differ between the two closely related species M. parvifolia and M. pubescens, nor between two sites (Guatavita and Zipacón, Colombia) differing in soil fertility. Occurrence of vesicles in decomposing leaves was correlated with abundant AMF extraradical hyphae among the leaves. We propose that AMF enter decomposing leaves mechanically through vascular tissue. As a consequence, AMF are well positioned to obtain and efficiently recycle mineral nutrients released by decomposer microorganisms before their loss by leaching or immobilization in soil.     

wFleaBase: the <Emphasis Type="Italic">Daphnia</Emphasis> genome database

Background  

wFleaBase is a database with the necessary infrastructure to curate, archive and share genetic, molecular and functional genomic data and protocols for an emerging model organism, the microcrustacean Daphnia. Commonly known as the water-flea, Daphnia's ecological merit is unequaled among metazoans, largely because of its sentinel role within freshwater ecosystems and over 200 years of biological investigations. By consequence, the Daphnia Genomics Consortium (DGC) has launched an interdisciplinary research program to create the resources needed to study genes that affect ecological and evolutionary success in natural environments.     

Effects of arbuscular mycorrhizal fungi and a non-pathogenic<Emphasis Type="Italic"> Fusarium oxysporum</Emphasis> on<Emphasis Type="Italic"> Meloidogyne incognita</Emphasis> infestation of tomato

Arbuscular mycorrhizal (AM) fungi and non-pathogenic strains of soil-borne pathogens have been shown to control plant parasitic nematodes. As AM fungi and non-pathogenic fungi improve plant health by different mechanisms, combination of two such partners with complementary mechanisms might increase overall control efficacy and, therefore, provide an environmentally safe alternative to nematicide application. Experiments were conducted to study possible interactions between the AM fungus Glomus coronatum and the non-pathogenic Fusarium oxysporum strain Fo162 in the control of Meloidogyne incognita on tomato. Pre-inoculation of tomato plants with G. coronatum or Fo162 stimulated plant growth and reduced M. incognita infestation. Combined application of the AM fungus and Fo162 enhanced mycorrhization of tomato roots but did not increase overall nematode control or plant growth. A higher number of nematodes per gall was found for mycorrhizal than non-mycorrhizal plants. In synergisms between biocontrol agents, differences in their antagonistic mechanisms seem to be less important than their effects on different growth stages of the pathogen.     

Inhibition of <Emphasis Type="Italic">Zizania latifolia</Emphasis> growth by <Emphasis Type="Italic">Phragmites australis</Emphasis>: an experimental study

The influence of Phragmites australis on the growth of Zizania latifolia, and the morphological characteristics of both species, were investigated at two nutrient levels. The experiment was carried out over three growing seasons between May 2003 and December 2005. The experimental plot was longitudinally divided into two equal halves, one of which was planted with Zizania latifolia (Zizania zone) and the other one with Phragmites australis (Phragmites zone). Four weeks after transplantation, the plot was again divided horizontally, perpendicular to the previous division, and subject to low (LN) and high nutrient (HN) treatments. Measured growth indices of the two species were more developed in the HN than in the LN treatments. Both species were observed to invade each other’s zone, but Phragmites latifolia seemed to out-compete Zizania latifolia individuals. This was evident from the decrease in below ground biomass of Zizania latifolia in the third growing season and deterioration in above ground organs with time. It was concluded that Phragmites australis out-competes Zizania latifolia due to better developed root and rhizome system.     

Composition of<Emphasis Type="Italic">Casuarina</Emphasis> leaf litter and its influence on<Emphasis Type="Italic">Frankia-Casuarina</Emphasis> symbiosis in soil

Plant needles ofCasuarina equisetifolia were collected and analyzed in parallel with soil analysis. In three strains ofFrankia—symbionts ofCasuarina—their infectivity and plant performance was determinedin vitro after soil amendment with different leaf litter concentrations. Only one strain was able to nodulate the plant at all litter concentrations (0.5, 3 and 5%) although the nodules were very small. However, all treated plants grew poorly; their growth was reduced by approximately 90% (for 5% litter concentration) compared to plants grown on untreated soil, on the basis of total dry mass. Inhibition of nodulation can be attributed to high concentrations of some elements and compounds that were either found inC. equisetifolia litter or originally found in soil (i.e. chloride, cyanide, copper, manganese and phenols). In general, plant growth decreased as more litter was added. Plant total nitrogen content was also reduced after increasing the litter concentration. The inhibitory effect of high litter concentrations was mainly on plant growth and to a lesser extent on plant nodulation byFrankia strains.     

<Emphasis Type="Italic">Ty</Emphasis>1<Emphasis Type="Italic">/copia</Emphasis>- and <Emphasis Type="Italic">Ty</Emphasis>3<Emphasis Type="Italic">/gypsy</Emphasis>-like DNA sequences in <Emphasis Type="Italic">Helianthus </Emphasis>species

Two repeated DNA sequences isolated from a partial genomic DNA library of Helianthus annuus, p HaS13 and p HaS211, were shown to represent portions of the int gene of a Ty3 /gypsy retroelement and of the RNase-Hgene of a Ty1 /copia retroelement, respectively. Southern blotting patterns obtained by hybridizing the two probes to BglII- or DraI-digested genomic DNA from different Helianthus species showed p HaS13 and p HaS211 were parts of dispersed repeats at least 8 and 7 kb in length, respectively, that were conserved in all species studied. Comparable hybridization patterns were obtained in all species with p HaS13. By contrast, the patterns obtained by hybridizing p HaS211 clearly differentiated annual species from perennials. The frequencies of p HaS13- and p HaS211-related sequences in different species were 4.3x10(4)-1.3x10(5) copies and 9.9x10(2)-8.1x10(3) copies per picogram of DNA, respectively. The frequency of p HaS13-related sequences varied widely within annual species, while no significant difference was observed among perennial species. Conversely, the frequency variation of p HaS211-related sequences was as large within annual species as within perennials. Sequences of both families were found to be dispersed along the length of all chromosomes in all species studied. However, Ty3 /gypsy-like sequences were localized preferentially at the centromeric regions, whereas Ty1/ copia-like sequences were less represented or absent around the centromeres and plentiful at the chromosome ends. These findings suggest that the two sequence families played a role in Helianthusgenome evolution and species divergence, evolved independently in the same genomic backgrounds and in annual or perennial species, and acquired different possible functions in the host genomes.     

Stoichiometry in an ecological context: testing for links between <Emphasis Type="Italic">Daphnia</Emphasis> P-content,growth rate and habitat preference

We used laboratory experiments with ten Daphnia taxa to test for links between Daphnia P-content, growth rate and habitat preference. The taxa represent a wide range of body sizes and most show distinct preferences for one of three habitats: shallow lakes, deep, stratified lakes or fishless ponds. Previous studies show that taxa from shallow lakes and fishless ponds experience high predation risk and rich food resources, whereas taxa from deep lakes experience low predation risk, strong food limitation and potentially P-deficient resources. Thus, we predicted higher P-content and higher maximal growth rates in taxa from ponds and shallow lakes and lower P-content, lower maximal growth but reduced sensitivity to P-limitation in taxa preferring stratified lakes. In each of 25 experiments, a clonal Daphnia cohort was cultured for 4 days on a P-sufficient (molar C:P ratio 70) or a P-deficient (C:P 1,000) diet of a green alga at a high concentration (1 mg C l^–1). The P-content of adult Daphnia fed the P-sufficient diet ranged from 1.52 to 1.22% mass. Small-bodied taxa from shallow lakes had higher P-content than larger-bodied taxa from deep lakes or fishless ponds. However, we found a nonsignificant negative correlation between P-content and growth on the P-sufficient diet, rather than the positive relationship predicted by the growth rate hypothesis. The P-deficient diet resulted in declines in both growth rate and P-content compared with the P-sufficient controls and the extent of the declines differed between taxa. Taxa from ponds showed a marginally greater decline in growth with the P-deficient diet compared with taxa from shallow or deep lakes. However, contrary to stoichiometric theory, no relationship was found between a species P-content and growth depression on the P-deficient diet. Although we found evidence for habitat adaptations, our results show that factors other than Daphnia P-content are important in determining differences between Daphnia species in both maximal growth rate and sensitivity to P-limited growth.     

Expression of <Emphasis Type="Italic">cspH</Emphasis> upon nutrient up-shift in <Emphasis Type="Italic">Salmonella enterica</Emphasis> serovar Typhimurium

The gene cspH , which encodes one of the cold-shock proteins in Salmonella enterica serovar Typhimurium, has previously been reported to be induced during early exponential phase at 37°C. In the present study, the expression of cspH upon nutrient up-shift at 37°C was investigated and found to be affected by DNA gyrase and DNA-binding protein Fis. When cells at stationary phase were subcultured into a rich medium, the mRNA level of cspH increased dramatically prior to the first cell division. However, when the cells were treated with DNA gyrase inhibitors, cspH mRNA was not induced upon nutrient up-shift. The low level of DNA superhelical density at the cspH promoter in part affected the expression of cspH mRNA in vitro. In addition, a fis-deficient strain had a lower level of cspH mRNA than the wild-type upon nutrient up-shift. Finally, a cspH–lacZ construct, in which the putative binding region for Fis was deleted in the cspH promoter, expressed a low level of LacZ, in contrast to the native cspH–lacZ construct.This revised version was published online in July 2004 with corrections to Fig. 4.     

Incidence of <Emphasis Type="Italic">Wolbachia</Emphasis> and <Emphasis Type="Italic">Cardinium</Emphasis> endosymbionts in the <Emphasis Type="Italic">Osmia</Emphasis> community in Korea

Sex ratio distorting endosymbionts induce reproductive anomalies in their arthropod hosts. They have recently been paid much attention as firstly texts of evolution of host-symbiont relationships and secondly potential biological control agents to control arthropod pests. Among such organisms, Wolbachia and Cardinium bacteria are well characterized. This study aims at probing such bacteria in the Osmia community to evaluate their potential utilization to control arthropod pests. Among 17 PCR tested species, Osmia cornifrons and a parasitic fly are infected with Wolbachia and a mite species is infected with Cardinium. Phylogenetic tree analyses suggest that horizontal transfer of the bacteria occurred between phylogenetically distant hosts.     

Taxonomic notes on<Emphasis Type="Italic">Linaria</Emphasis> mill. (<Emphasis Type="Italic">Scrophulariaceae</Emphasis>) for Flora Iberica

Taxonomic considerations and nomenclatural adjustments as a part of a revision ofLinaria Mill. undertaken within the “Flora iberica” project are presented. Data on morphology, seed coat surface, chorology, ecology, synonymy and variability of 11 accepted taxa are reported. The following new combinations are proposed:Linaria aeruginea subsp. cardonica (Font Quer)L. Sáez etM. Sainz,Linaria depauperata subsp.ilergabona (M.B. Crespo etV.J. Arán)L. Sáez, andLinaria saturejoides subsp.angustealata (Willmott)L. Sáez etM.B. Crespo.     

Sex allocation in the polydomous leaf-cutting ant <Emphasis Type="Italic">Acromyrmex</Emphasis><Emphasis Type="Italic">balzani</Emphasis>

Logistic regression analysis was used to analyse sex allocation in a population of the leaf-cutting ant Acromyrmex balzani occurring in a pasture in southern Brazil. The field sample consisted of 151 fungus-garden chambers (18 queenright and 133 queenless), belonging to 50 nests with three vertically stacked chambers per nest on average. Taking nest chamber as the unit of analysis, seven predictor variables were considered: sampling date, chamber depth, chamber volume, weight of fungus garden, presence of a queen, number of large workers, and number of small to medium workers. The population-level numerical proportion of females was 0.548 and the inferred proportional energetic investment in females 0.672. The former was not significantly different from 0.5 (P=0.168), but the latter was (P=0.0003). The proportional investment in females per fungus garden increased with the number of large workers present (P=0.0002) and decreased with the dry weight of the fungus garden (P=0.012). This implies that resource acquisition through foraging is likely to be a major proximate determinant of sex allocation. The negative correlation between female bias and fungus garden weight might be due to developing adult females requiring more food than males, but this hypothesis could not be confirmed by direct statistical evidence.