Allele frequency shifts in response to climate change and physiological consequences of allozyme variation in a montane insect

Rapid changes in climate may impose strong selective pressures on organisms. Evolutionary responses to climate change have been observed in natural populations, yet no example has been documented for a metabolic enzyme locus. Furthermore, few studies have linked physiological responses to stress with allozyme genotypic variation. We quantified changes in allele frequency between 1988 and 1996 at three allozyme loci (isocitrate dehydrogenase, Idh; phosphoglucose isomerase, Pgi; and phosphoglucomutase, Pgm) for the leaf beetle Chrysomela aeneicollis in the Bishop Creek region of the Sierra Nevada of California (2900-3300 m). Beetles often experience high daytime (> 32 degrees C) and extremely low nighttime (< -5 degrees C) temperatures during summer. Bishop Creek weather station data indicated that conditions were unusually dry before 1988, and that conditions were cool and wet during the years preceding the 1996 collection. We found directional changes in allele frequency at Pgi (11% increase in the Pgi-1 allele), but not at Idh or Pgm. We also found that physiological response to thermal extremes depended on Pgi genotype. Pgi 1-1 individuals induced expression of a 70-kD heat shock protein (HSP) at lower temperatures than 1-4 or 4-4 individuals, and 1-1 individuals expressed higher levels of HSP70 after laboratory exposure to temperatures routinely experienced in nature. Survival after nighttime laboratory exposure to subzero temperatures depended on gender, previous exposure to cold, and Pgi genotype. Females expressed higher levels of HSP70 than males after exposure to heat, and recovery by female Pgi 1-1 homozygotes after exposure to cold (-5 degrees C) was significantly better than 1-4 or 4-4 genotypes. These data suggest that the cooler climate of the mid-1990s may have caused an increase in frequency of the Pgi-1 allele, due to a more robust physiological response to cold by Pgi 1-1 and 1-4 genotypes.     

Plasticity in metabolic allometry: the role of dietary stoichiometry

Metabolism involves multiple elements. While we know much about the allometry in metabolic response of organisms to energy (carbon, C) availability, little is known about how different-sized organisms respond to the relative availability of elements. I experimentally manipulated availability of phosphorus (P) relative to C, to test whether dietary C : P affects metabolism in four species of Daphnia , spanning an order of magnitude in body mass. Results indicated that the slope of the relationship between individual respiration and body mass was M ^0.83 under a balanced diet (C : P c. 150), and M ^0.67 under an imbalanced diet (C : P c. 800). Increased respiration under dietary imbalance was not due to increased ingestion. The change in the scaling exponent was due to the greater respiratory response of smaller species to altered diets. Diet-induced metabolic plasticity contributes to variation in metabolic allometry, at least at such small scales of body size.     

Genotype × environment interactions,stoichiometric food quality effects,and clonal coexistence in <Emphasis Type="Italic">Daphnia pulex</Emphasis>

The role of stoichiometric food quality in influencing genotype coexistence and competitive interactions between clones of the freshwater microcrustacean, Daphnia pulex, was examined in controlled laboratory microcosm experiments. Two genetically distinct clones of D. pulex, which show variation in their ribosomal rDNA structure, as well as differences in a number of previously characterized growth-rate-related features (i.e., life-history features), were allowed to compete in two different arenas: (1) batch cultures differing in algal food quality (i.e., high vs. low carbon:phosphorus (C:P ratio) in the green alga, Scenedesmus acutus); (2) continuous flow microcosms receiving different light levels (i.e., photosynthetically active radiation) that affected algal C:P ratios. In experiment 1, a clear genotype x environment interaction was determined with clone 1 out-competing clone 2 under high nutrient (i.e., low food C:P) conditions, while the exact opposite pattern was observed under low nutrient (i.e., high C:P) conditions. In experiment 2, clone 1 dominated over clone 2 under high light (higher C:P) conditions, but clonal coexistence was observed under low light (low C:P) conditions. These results indicate that food (nutrient) quality effects (hitherto an often overlooked factor) may play a role in microevolutionary (genotypic) responses to changing stoichiometric conditions in natural populations.     

Mitigation of adverse effects of rising CO2 on a planktonic herbivore by mixed algal diets

Putative future increase in atmospheric CO₂ is expected to adversely affect herbivore growth due to decrease in contents of key nutrients such as nitrogen and phosphorus (P) relative to carbon in primary producers including plant and algal species. However, as many herbivores are polyphagous and as the response of primary producers to elevated CO₂ is highly species-specific, effects of elevated CO₂ on herbivore growth may differ between feeding conditions with monospecific and multiproducer diets. To examine this possibility, we performed CO₂ manipulation experiments under a P-limited condition with a planktonic herbivore, Daphnia , and three algal species, Scenedesmus obliquus (green algae), Cyclotella sp. (diatoms) and Synechococcus sp. (cyanobacteria). Semibatch cultures with single algal species (monocultures) and multiple algal species (mixed cultures) were grown at ambient (360 ppm) and high CO₂ levels (2000 ppm) that were within the natural range in lakes. Both in the mono- and mixed cultures, algal steady state abundance increased but algal P : C and N : C ratios decreased when they were grown at high CO₂. As expected, Daphnia fed monospecific algae cultured at high CO₂ had decreased growth rates despite increased algal abundance. However, when fed mixed algae cultured at high CO₂, especially consisting of diatoms and cyanobacteria or the three algal species, Daphnia maintained high growth rates despite lowered P and N contents relative to C in the algal diets. These results imply that algal diets composed of multiple species can mitigate the adverse effects of elevated CO₂ on herbivore performance, although the magnitude of this mitigation depends on the composition of algal species involved in the diets.     

Temperature-dependent energy budget of an Arctic Cladoceran, Daphnia middendorffiana

1. Global change models predict the greatest impact in climate to occur in the northern polar region. Change in temperature will alter individual metabolism and has the potential to change community structure to an unknown degree.
2. The temperature-dependent energy budget of Arctic Daphnia middendorffiana was investigated by measuring respiration rates, ingestion rates and assimilation rates. The scope for growth and reproduction was determined and compared with data from the literature for a clone of Daphnia pulicaria collected in the temperate zone.
3. A difference was observed between the Arctic species and the temperate zone clone in both temperature tolerance, and the energy available for growth and reproduction at various temperatures. A low availability of energy for growth and reproduction indicated that life history patterns as well as physiological mechanisms are important in allowing D. middendorffiana to exist successfully in Arctic environments.
4. The lower available energy for growth compared to Daphnia clones from temperate zones may be detrimental to D. middendorffiana , which might have to compete with species expanding their range under the predicted temperature increase for Arctic regions.     

Oospore Germination and Formation by the Late Blight Pathogen Phytophthora infestans in vitro and under Field Conditions

The ability of the late blight pathogen Phytophthora infestans to form oospores in leaves of seven potato cultivars was examined at different incubation temperatures under controlled environmental conditions and under field conditions. At 10°C, the oospore formation in three intermediate-resistant cultivars all differed significantly from each other (P < 0.05), with the lowest amount formed in cv. Asterix. This latter cultivar did not form oospores at any other temperature. Under field conditions oospores were formed abundantly in a naturally infected field. A significant date by cultivar interaction showed that P. infestans increased the oospore formation in foliage by time in cvs Columbo, Hertha and Matilda, whereas no significant differences between dates were found for other cultivars. The genetic structure of P. infestans in the naturally infected field plot, where oospores formed abundantly, was studied by using amplified fragment length polymorphism and a high genetic diversity was revealed. Oospore germination from two Scandinavian (A1 and A2) P. infestans isolates was stimulated in visible light and in 1 : 2 and 1 : 10 soil extract. The effect of light and nutrients on oosporogenesis is discussed.     

Interspecific competition between Cephalonomia stephanoderis and Prorops nasuta (Hym.,Bethylidae), parasitoids of the coffee berry borer, Hypothenemus hampei (Col., Scolytidae)

The competition between Cephalonomia stephanoderis and Prorops nasuta was studied in the laboratory, using coffee fruits infested with the host of these parasitoids, the coffee berry borer Hypothenemus hampei . Experiments were performed under different conditions, using: (a) three temperatures; (b) five densities of infested coffee fruits; and (c) introducing the parasitoids at different times. The effect of competition was determined according to the production of the progeny. When cultured together at the same time, C. stephanoderis produced in general, more progeny than P. nasuta under conditions of 29°C and alternating temperatures of 18–29°C. Nevertheless, there were significant differences at densities of 1 : 3, fruits : parasitoids ( F _0.05=8.9; d.f.=1, 12; P < 0.05) and 1 : 5 ( F _0.05=7.56; d.f.=1, 12; P < 0.05) at 29°C. Under alternating temperatures, there were differences at the same ratios as above in favour of C. stephanoderis , 1 : 3 ( F _0.05=20.08; d.f.=1, 12; P < 0.05) and 1 : 5 ( F _0.05=20.21; d.f.=1, 12; P < 0.05). Prorops nasuta was clearly more successful in all densities at 18°C. When C. stephanoderis was introduced 10 days before P. nasuta , the progeny production was markedly higher in eight from 10 densities at temperatures of 29°C and 18–29°C. Despite being introduced 10 days later, P. nasuta showed better performance at 18°C. When P. nasuta was introduced 10 days earlier than C. stephanoderis , there were significant differences in progeny production in favour of P. nasuta in 13 of 15 fruit densities under the three temperatures. Both parasitoids avoided ovipositing on previously parasitized hosts. Aggressive behaviour or interference was not observed when they were outside coffee fruits.     

Fire effects on insect herbivores in an oak savanna: the role of light and nutrients

Abstract.  1. Environmental heterogeneity created by prescribed burning provided the context for testing whether the distribution of an oak specialist (the lace bug, Corythuca arcuata ) could be explained by stoichiometric mismatches between herbivore and host plant composition.
2. Field observations showed that lace bug density was seven-fold higher in frequently burned than in unburned units.
3. Lace bug density did not increase with leaf nutrient concentrations, but was instead associated with higher light levels, higher concentrations of leaf carbon (C), lignin and total phenolics, and lower levels of cellulose. In addition, lace bugs reared on high-light leaves had higher levels of survivorship than those fed on low-light leaves.
4. Sampling restricted to full-sun leaves was used to test whether fire-related changes in leaf nitrogen (N) and phosphorus (P) concentrations have a secondary influence on lace bug success. This sampling provided only limited evidence for nutrient limitation, as decreases in leaf N and P were associated with an increase in lace bug mass but a decrease in density.
5. It is concluded that burning probably promotes lace bug population growth by increasing canopy openness, light penetration, and the availability of C-based metabolites, and thus simple stoichoimetric mismatches between herbivores and host plants are not of primary importance in this system.     

The Pillars of Hercules as a bathymetric barrier to gene flow promoting isolation in a global deep‐sea shark (Centroscymnus coelolepis)

Knowledge of the mechanisms limiting connectivity and gene flow in deep‐sea ecosystems is scarce, especially for deep‐sea sharks. The Portuguese dogfish (Centroscymnus coelolepis) is a globally distributed and near threatened deep‐sea shark. C. coelolepis population structure was studied using 11 nuclear microsatellite markers and a 497‐bp fragment from the mtDNA control region. High levels of genetic homogeneity across the Atlantic (Φ_ST = ?0.0091, F_ST = 0.0024, P > 0.05) were found suggesting one large population unit at this basin. The low levels of genetic divergence between Atlantic and Australia (Φ_ST = 0.0744, P < 0.01; F_ST = 0.0015, P > 0.05) further suggested that this species may be able to maintain some degree of genetic connectivity even across ocean basins. In contrast, sharks from the Mediterranean Sea exhibited marked genetic differentiation from all other localities studied (Φ_ST = 0.3808, F_ST = 0.1149, P < 0.001). This finding suggests that the shallow depth of the Strait of Gibraltar acts as a barrier to dispersal and that isolation and genetic drift may have had an important role shaping the Mediterranean shark population over time. Analyses of life history traits allowed the direct comparison among regions providing a complete characterization of this shark's populations. Sharks from the Mediterranean had markedly smaller adult body size and size at maturity compared to Atlantic and Pacific individuals. Together, these results suggest the existence of an isolated and unique population of C. coelolepis inhabiting the Mediterranean that most likely became separated from the Atlantic in the late Pleistocene.     

13C‐metabolic flux analysis for batch culture of Escherichia coli and its pyk and pgi gene knockout mutants based on mass isotopomer distribution of intracellular metabolites

Since most bio‐production processes are conducted in a batch or fed‐batch manner, the evaluation of metabolism with respect to time is highly desirable. Toward this aim, we applied ¹³C‐metabolic flux analysis to nonstationary conditions by measuring the mass isotopomer distribution of intracellular metabolites. We performed our analysis on batch cultures of wild‐type Escherichia coli, as well as on Pyk and Pgi mutants, obtained the fluxes and metabolite concentrations as a function of time. Our results for the wild‐type indicated that the TCA cycle flux tended to increase during growth on glucose. Following glucose exhaustion, cells controlled the branch ratio between the glyoxylate pathway and the TCA cycle, depending on the availability of acetate. In the Pyk mutant, the concentrations of glycolytic intermediates changed drastically over time due to the dumping and feedback inhibition caused by PEP accumulation. Nevertheless, the flux distribution and free amino acid concentrations changed little. The growth rate and the fluxes remained constant in the Pgi mutant and the glucose‐6‐phosphate dehydrogenase reaction was the rate‐limiting step. The measured fluxes were compared with those predicted by flux balance analysis using maximization of biomass yield or ATP production. Our findings indicate that the objective function of biosynthesis became less important as time proceeds on glucose in the wild‐type, while it remained highly important in the Pyk mutant. Furthermore, ATP production was the primary objective function in the Pgi mutant. This study demonstrates how cells adjust their metabolism in response to environmental changes and/or genetic perturbations in the batch cultivation. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

Nitrogen and water availability interact to affect leaf stoichiometry in a semi-arid grassland

The effects of global change factors on the stoichiometric composition of green and senesced plant tissues are critical determinants of ecosystem feedbacks to anthropogenic-driven global change. So far, little is known about species stoichiometric responses to these changes. We conducted a manipulative field experiment with nitrogen (N; 17.5 g m⁻² year⁻¹) and water addition (180 mm per growing season) in a temperate steppe of northern China that is potentially highly vulnerable to global change. A unique and important outcome of our study is that water availability modulated plant nutritional and stoichiometric responses to increased N availability. N addition significantly reduced C:N ratios and increased N:P ratios but only under ambient water conditions. Under increased water supply, N addition had no effect on C:N ratios in green and senesced leaves and N:P ratios in senesced leaves, and significantly decreased C:P ratios in both green and senesced leaves and N:P ratios in green leaves. Stoichiometric ratios varied greatly among species. Our results suggest that N and water addition and species identity can affect stoichiometric ratios of both green and senesced tissues through direct and interactive means. Our findings highlight the importance of water availability in modulating stoichiometric responses of plants to potentially increased N availability in semi-arid grasslands.     

Trade-offs between male and female reproduction associated with allozyme variation in phosphoglucoisomerase in an annual plant (Clarkia unguiculata: Onagraceae)

The genotype of an individual for allozymes such as phosphoglucoisomerase (Pgi) is often not neutral with regard to fitness. Studies of several taxa have found consistent fitness differences among Pgi genotypes expressing different allozymes. We conducted a greenhouse experiment with Clarkia unguiculata to determine whether allelic variation at the Pgi-C1 locus may affect components of male and female function. We found significant differences in siring success between pollen donors homozygous for different Pgi alleles. When a mixture of pollen was applied to stigmas under conditions of gametophytic competition (more pollen deposited on stigmas than there are ovules available to fertilize), donors homozygous for the C allele of Pgi sired more seeds per fruit than B-allele donors. Differences between genotypes with respect to female fertility per fruit contrasted with the male advantage associated with the C allele. Recipients homozygous for the C allele produced fruits with more aborted seeds and fewer viable seeds than recipients homozygous for the B allele. These results suggest that allelic variation at a single locus may have opposing effects on male and female reproductive success in C. unguiculata, and that trade-offs between the two types of reproductive success could contribute to the maintenance of variation at the Pgi-C1 locus.     

Evidence for local adaptation in neighbouring Daphnia populations: a laboratory transplant experiment

1. We tested whether two neighbouring Daphnia galeata populations (from Lake Blankaart and Fish Pond), separated only by 5 m of land and with the occasional exchange of water were genetically differentiated in allozyme markers and life history traits. Allozyme electrophoresis revealed that the populations differed in allelic as well as in genotypic composition. 2. In a laboratory transplant experiment, in which animals of four clones of each of the populations were raised in the water of both ponds, survival in Blankaart water was high for both the Blankaart and Fish Pond clones, whereas survival in Fish Pond water was high for the Fish Pond clones, but low for the Blankaart clones. 3. Fish Pond clones produced fewer neonates than Blankaart clones when cultured in Blankaart water. High egg mortality was observed for animals that were raised in Blankaart water, and this egg mortality was higher for Fish Pond clones than for Blankaart clones. 4. Our results provide evidence for genetic differentiation between Daphnia populations inhabiting neighbouring water bodies and suggest local adaptation to environmental conditions other than direct predation.     

Determination of optimal growth parameters for the bioincising fungus Physisporinus vitreus by means of response surface methodology

Aim:  To evaluate the influence of water activity ( a _w), temperature and pH on the radial growth and lag phase of Physisporinus vitreus (E-642), a basidiomycete was used in the biotechnological process of bioincising.
Methods and Results:  Radial growth was monitored for 20 days on malt extract agar medium. Five levels of a _w (0·998, 0·982, 0·955, 0·928, 0·892) were combined with three incubation temperatures (10, 15, 20°C) and three pH values (4, 5, 6). Data analyses showed a highly significant effect of a _w and temperature ( P <  0·0001) and a significant effect of pH ( P <  0·05). The radial growth rate and lag phase of P. vitreus were very sensitive to a _w reduction. Although P. vitreus was able to grow at all the selected temperatures and pH values, the lag phase increased with decreasing a _w and growth became inhibited at a _w = 0·955. Optimal conditions for growth of P. vitreus were a _w = 0·998, 20°C and pH 5. The response surface model provided reliable estimates of these growth parameters and confirmed a greater dependence on a _w than on temperature or pH under in vitro conditions.
Conclusions:  Low levels of a _w can prevent growth of P. vitreus , so wood moisture content should be adjusted accordingly.
Significance and Impact of the Study:  Implementation of these results should contribute towards the optimization and efficiency of bioincising.     

Plant rhizosphere influence on microbial C metabolism: the role of elevated CO2, N availability and root stoichiometry

Microbial decomposer C metabolism is considered a factor controlling soil C stability, a key regulator of global climate. The plant rhizosphere is now recognized as a crucial driver of soil C dynamics but specific mechanisms by which it can affect C processing are unclear. Climate change could affect microbial C metabolism via impacts on the plant rhizosphere. Using continuous ¹³C labelling under controlled conditions that allowed us to quantify SOM derived-C in all pools and fluxes, we evaluated the microbial metabolism of soil C in the rhizosphere of a C4 native grass exposed to elevated CO₂ and under variation in N concentrations in soil and in plant root C:N stoichiometry. Our results demonstrated that this plant can influence soil C metabolism and further, that elevated CO₂ conditions can alter this role by increasing microbial C efficiency as indicated by a reduction in soil-derived C respiration per unit of soil C-derived microbial biomass. Moreover, under elevated CO₂ increases in soil N, and notably, root tissue N concentration increased C efficiency, suggesting elevated CO₂ shifted the stoichiometric balance so N availability was a more critical factor regulating efficiency than under ambient conditions. The root C:N stoichiometry effect indicates that plant chemical traits such as root N concentration are able to influence the metabolism of soil C and that elevated CO₂ conditions can modulate this role. Increased efficiency in soil C use was associated with negative rhizosphere priming and we hypothesize that the widely observed phenomenon of rhizosphere priming may result, at least in part, from changes in the metabolic efficiency of microbial populations. Observed changes in the microbial community support that shifting microbial populations were a contributing factor to the observed metabolic responses. Our case study points at greater efficiency of the SOM-degrading populations in a high CO₂, high N world, potentially leading to greater C storage of microbially assimilated C in soil.     

Mitochondrial DNA phylogeography of Spodoptera exigua across a broad geographic area in China

The beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae), is an important agriculture pest in China that causes serious economic losses in some of the main crop‐producing areas. To monitor and manage this pest effectively, it is necessary to investigate its phylogeographic patterns in China. In this study, we used a partial sequence of mitochondrial DNA Cytb gene consisting of 724 bps to investigate the genetic diversity of the beet armyworm. A total of 765 individuals from 47 populations across the main distribution range of the species were collected, and 112 haplotypes were identified. Moderate‐to‐high levels of genetic diversity (Hd = 0.672 ± 0.017, Pi = 0.00268 ± 0.00021) for the total populations were obtained. Phylogenetic and median‐joining network analyses indicated there was no distinct geographic distribution pattern among haplotypes. Overall, the study also revealed significant differentiation among some populations (P < 0.05). The F_ST values of Shenyang population (SY2012–SY 2014), as well as Baoding (BD), Taian (TA), Lucheng (LC), Zhengzhou (ZZ) and Wuhan (WH), were significantly different from those of the populations in most other locations. Hierarchical AMOVA showed there was no significantly genetic structure between populations located in seven geographic regions and four main bioclimatic zones. Finally, unimodal mismatch distribution combined with negative Tajima's D (D = ?2.696, P < 0.001) and Fu's F_S (F_S = ?207.228, P > 0.05) indicated recent population expansion of S. exigua at large spatial scales in China.     

A major shift in Daphnia genetic structure after the first ice‐free winter in a German reservoir

1. Climate warming may cause disruption of trophic linkages in aquatic ecosystems and lead to changes in abundance and genetic structure of zooplankton populations. We monitored the community of the Daphnia galeata‐hyalina hybrid complex in the Saidenbach Reservoir (Saxony, Germany) using allozyme electrophoresis for three consecutive years (2005–07), including one (2007) following an unusually warm winter that prevented the formation of ice cover for the first time in the history of the reservoir. 2. Genetic composition during the 2007 season differed substantially from the two preceding years that experienced the usual 3‐month ice period. Three abundance peaks in June, July and October 2007 were dominated by hybrids of Daphnia galeata x hyalina, whereas in the 2005 and 2006 seasons two peaks in June and September were dominated by Daphnia hyalina genotypes. 3. The genetic composition of the pool of diapausing eggs produced in autumn and the rate of change of genotype abundance during the following spring indicate recruitment of the D. hyalina subpopulation from ex‐ephippial animals during the spring population increase. 4. The differing potential to contribute to the overwintering animal pool or to the inoculum from diapausing eggs was confirmed by results from laboratory life‐table experiments. Daphnia galeata clones survived longer and produced parthenogenetic offspring under winter conditions, whereas D. hyalina clones showed a shorter lifespan and produced resting eggs. 5. Our results indicate a profound role of recruitment strategy in the observed shift in genetic composition. Increasing winter temperatures predicted in the context of climate change may thus favour overwintering animals, leading to an increase in the contribution of these genotypes to the population. Such microevolutionary processes may dampen possible seasonal mismatches between daphnid populations and their food or predator populations.     

Physiological traits suggest limited diapause response in false codling moth,Thaumatotibia leucotreta (Lepidoptera: Tortricidae)

The ability of a pest insect species to enter diapause, a physiological state of dormancy, has significant implications for population dynamics and pest management practises in agricultural landscapes. The false codling moth Thaumatotibia leucotreta is a major pest of deciduous and citrus fruit in southern Africa and a quarantine pest of international concern. Apart from an early field assessment that may have been compromised by taxonomic uncertainty surrounding cryptic developing life stages, no studies have investigated diapause induction within an experimental framework for this species, and none to date have used a suite of physiological traits potentially indicative of the diapause state. Here, we subjected larvae to cooling and shortening day length over a period of 14 days [Diapause Treatment (DT) group] relative to a similar‐aged control (CON) group held at optimal rearing conditions (25°C, 12 : 12 L : D) and tested if physiological traits, including resting metabolic rate, body freezing temperature (=supercooling point, equivalent to the low‐temperature mortality threshold) and body condition (body mass, body lipid and water content) varied in a direction that may be reflective of diapause induction. Mean metabolic rate in DT larvae was 0.044 ml CO₂/h (mean mass: 52.7 mg), which was significantly higher than in CON larvae [0.025 ml CO₂/h, mean mass: 51.5 mg (P = 0.04)]. Supercooling points were not statistically lower in the CON group than in DT larvae (DT:?15.6 ± 1.5°C; CON: ?16.4 ± 2.8°C; P = 0.33). Measures of body size, body condition and resting water loss rates remained similar between groups. These results support the conclusion of early field observations that T. leucotreta does not undergo diapause that has significant implications for the management of the species.     

Some features of feeding,respiration and energy conversion of Dapnia Magna

Some results of studies with Daphnia magna are presented. These results can be used as background information for toxicologists, but the techniques referred to might well be used for toxicity tests. Daphnia magna is a filter-feeder. With the Coulter Counter it was shown that the feeding mechanism is aselective for size of the food particles. It was also shown that algal cells can pass the gut of Daphnia magna several times before being completely digested. The uptake of food is proportional to the food concentration up to a critical concentration. Above this concentration the food uptake is constant. Respiration is also dependent on the food concentration, and has a maximum value at food concentrations near the critical concentration of the feeding process. Growth efficiency is independent of the food concentration. The effect of temperature on the feeding process is different for low and high food concentrations. Growth efficiency is maximal at 10°C and above 22°C growth efficiency was negative, which means that the population cannot survive under the experimental conditions used, at temperatures above 22°C.