Outcomes and Risk Factors in Microsurgical Forefoot Reconstruction.

BACKGROUND: Defects at the forefoot frequently require microsurgical reconstruction; however, reconstructive failure can lead to results inferior to primary amputation. The purpose of this study was to identify independent factors affecting surgical outcomes and hospitalization time in these patients. METHODS: All patients that underwent free flap reconstruction of the forefoot between 2008 and 2019 were reviewed retrospectively. Statistical evaluation included binary logistic regression and correlation analysis. RESULTS: A total of 93 free flap procedures were performed in 87 patients. The most common defect etiologies were acute trauma (30 cases; 32.3%), diabetic foot syndrome (20 cases; 21.5%), and infection (17 cases; 18.3%). Muscle flaps were used in 50 cases (53.8%) and fasciocutaneous flaps were used in 43 cases (46.2%). Major complications occurred in 24 cases (25.8%) including 11 total flap losses and 2 partial flap losses. Minor complications occurred in 38 cases (40.9%). Patients aged 60 years or above were at significant higher risk of major complications (p = 0.029). Use of fasciocutaneous flaps (odds ratio [OR]: 14.341; p = 0.005), arterial hypertension (OR: 18.801; p = 0.014), and operative time (min) (OR: 1.010; p = 0.029) were identified as individual risk factors for major complications. Two venous anastomoses significantly reduced the risk of major complications (OR: 0.078; p = 0.022). Multiresistant bacterial wound colonization (OR: 65.152; p < 0.001) and defect size (OR: 1.007; p = 0.045) were identified as independent risk factors for minor complications. The median hospital stay was 28 days (7-85 days). Age significantly correlated with the length of hospital stay (r = 0.405, p < 0.01). CONCLUSION: Our study identified independent risk factors that might help to make individual decisions whether to target microsurgical forefoot reconstruction or primary amputation. Two venous anastomoses should be performed whenever feasible, and muscle free flaps should be preferred in patients at higher risk of major surgical complications.

A sterol-mediated gleaner-opportunist trade-off underlies the evolution of grazer resistance to cyanobacteria.

The human-caused proliferation of cyanobacteria severely impacts consumers in freshwater ecosystems. Toxicity is often singled out as the sole trait to which consumers can adapt, even though cyanobacteria are not necessarily toxic and the lack of nutritionally critical sterols in cyanobacteria is known to impair consumers. We studied the relative significance of toxicity and dietary sterol deficiency in driving the evolution of grazer resistance to cyanobacteria in a large lake with a well-documented history of eutrophication and oligotrophication. Resurrecting decades-old Daphnia genotypes from the sediment allowed us to show that the evolution and subsequent loss of grazer resistance to cyanobacteria involved an adaptation to changes in both toxicity and dietary sterol availability. The adaptation of Daphnia to changes in cyanobacteria abundance revealed a sterol-mediated gleaner-opportunist trade-off. Genotypes from peak-eutrophic periods showed a higher affinity for dietary sterols at the cost of a lower maximum growth rate, whereas genotypes from more oligotrophic periods showed a lower affinity for dietary sterols in favour of a higher maximum growth rate. Our data corroborate the significance of sterols as limiting nutrients in aquatic food webs and highlight the applicability of the gleaner-opportunist trade-off for reconstructing eco-evolutionary processes.

Feeding in the frequency domain: coarser-grained environments increase consumer sensitivity to resource variability, covariance and phase.

Theory predicts that resource variability hinders consumer performance. How this effect depends on the temporal structure of resource fluctuations encountered by individuals remains poorly understood. Combining modelling and growth experiments with Daphnia magna, we decompose the complexity of resource fluctuations and test the effect of resource variance, supply peak timing (i.e. phase) and co-limiting resource covariance along a gradient from high to low frequencies reflecting fine- to coarse-grained environments. Our results show that resource storage can buffer growth at high frequencies, but yields a sensitivity of growth to resource peak timing at lower ones. When two resources covary, negative covariance causes stronger growth depression at low frequencies. However, negative covariance might be beneficial at intermediate frequencies, an effect that can be explained by digestive acclimation. Our study provides a mechanistic basis for understanding how alterations of the environmental grain size affect consumers experiencing variable nutritional quality in nature.

The relative importance of plant-soil feedbacks for plant-species performance increases with decreasing intensity of herbivory.

Under natural conditions, aboveground herbivory and plant-soil feedbacks (PSFs) are omnipresent interactions strongly affecting individual plant performance. While recent research revealed that aboveground insect herbivory generally impacts the outcome of PSFs, no study tested to what extent the intensity of herbivory affects the outcome. This, however, is essential to estimate the contribution of PSFs to plant performance under natural conditions in the field. Here, we tested PSF effects both with and without exposure to aboveground herbivory for four common grass species in nine grasslands that formed a gradient of aboveground invertebrate herbivory. Without aboveground herbivores, PSFs for each of the four grass species were similar in each of the nine grasslands-both in direction and in magnitude. In the presence of herbivores, however, the PSFs differed from those measured under herbivory exclusion, and depended on the intensity of herbivory. At low levels of herbivory, PSFs were similar in the presence and absence of herbivores, but differed at high herbivory levels. While PSFs without herbivores remained similar along the gradient of herbivory intensity, increasing herbivory intensity mostly resulted in neutral PSFs in the presence of herbivores. This suggests that the relative importance of PSFs for plant-species performance in grassland communities decreases with increasing intensity of herbivory. Hence, PSFs might be more important for plant performance in ecosystems with low herbivore pressure than in ecosystems with large impacts of insect herbivores.

Environmental concentrations of pharmaceuticals directly affect phytoplankton and effects propagate through trophic interactions.

Pharmaceuticals are found in freshwater ecosystems where even low concentrations in the range of ng L-1 may affect aquatic organisms. In the current study, we investigated the effects of chronic exposure to three pharmaceuticals on two microalgae, a potential modulation of the effects by additional inorganic phosphorus (Pi) limitation, and a potential propagation of the pharmaceuticals' effect across a trophic interaction. The latter considers that pharmaceuticals are bioaccumulated by algae, potentially metabolized into more (or less) toxic derivates and consequently consumed by zooplankton. We cultured Acutodesmus obliquus and Nannochloropsis limnetica in Pi-replete and Pi-limited medium contaminated with one of three commonly human used pharmaceuticals: fluoxetine, ibuprofen, and propranolol. Secondly, we tested to what extent first level consumers (Daphnia magna) were affected when fed with pharmaceutical-grown algae. Chronic exposure, covering 30 generations, led to (i) decreased cell numbers of A. obliquus in the presence of fluoxetine (under Pi-replete conditions) (ii) increased carotenoid to chlorophyll ratios in N. limnetica (under Pi-limited conditions), and (iii) increased photosynthetic yields in A. obliquus (in both Pi-conditions). In addition, ibuprofen affected both algae and their consumer: Feeding ibuprofen-contaminated algae to Pi-stressed D. magna improved their survival. We demonstrate, that even very low concentrations of pharmaceuticals present in freshwater ecosystems can significantly affect aquatic organisms when chronically exposed. Our study indicates that pharmaceutical effects can cross trophic levels and travel up the food chain.

Covariance modulates the effect of joint temperature and food variance on ectotherm life-history traits.

Understanding animal performance in heterogeneous or variable environments is a central question in ecology. We combine modelling and experiments to test how temperature and food availability variance jointly affect life-history traits of ectotherms. The model predicts that as mean temperatures move away from the ectotherm's thermal optimum, the effect size of joint thermal and food variance should become increasingly sensitive to their covariance. Below the thermal optimum, performance should be positively correlated with food-temperature covariance and the opposite is predicted above it. At lower temperatures, covariance should determine whether food and temperature variance increases or decreases performance compared to constant conditions. Somewhat stronger than predicted, the covariance effect below the thermal optimum was confirmed experimentally on an aquatic ectotherm (Daphnia magna) exposed to diurnal food and temperature variance with different amounts of covariance. Our findings have important implications for understanding ectotherm responses to climate-driven alterations of thermal mean and variance.

Bridging factorial and gradient concepts of resource co-limitation: towards a general framework applied to consumers.

Organism growth can be limited either by a single resource or by multiple resources simultaneously (co-limitation). Efforts to characterise co-limitation have generated two influential approaches. One approach uses limitation scenarios of factorial growth assays to distinguish specific types of co-limitation; the other uses growth responses spanned over a continuous, multi-dimensional resource space to characterise different types of response surfaces. Both approaches have been useful in investigating particular aspects of co-limitation, but a synthesis is needed to stimulate development of this recent research area. We address this gap by integrating the two approaches, thereby presenting a more general framework of co-limitation. We found that various factorial (co-)limitation scenarios can emerge in different response surface types based on continuous availabilities of essential or substitutable resources. We tested our conceptual co-limitation framework on data sets of published and unpublished studies examining the limitation of two herbivorous consumers in a two-dimensional resource space. The experimental data corroborate the predictions, suggesting a general applicability of our co-limitation framework to generalist consumers and potentially also to other organisms. The presented framework might give insight into mechanisms that underlie co-limitation responses and thus can be a seminal starting point for evaluating co-limitation patterns in experiments and nature.

Photosynthetic sensitivity of phytoplankton to commonly used pharmaceuticals and its dependence on cellular phosphorus status.

Recently pharmaceuticals have become significant environmental pollutants in aquatic ecosystems, that could affect primary producers such as microalgae. Here we analyzed the effect of pharmaceuticals on the photosynthesis of microalgae commonly found in freshwater-two species of Chlorophyceae and a member of the Eustigmatophyceae, via PAM fluorometry. As pharmaceuticals, three medicines often consumed in households were chosen: (i) fluoxetine, an antidepressant, (ii) propranolol, a ß-blocker and (iii) ibuprofen, an anti-inflammatory and analgesic medicine. The EC50 for the quantum yield of photosystem II in phytoplankton acclimated to inorganic phosphorus (Pi)-replete and Pi-limited conditions was estimated. Acute toxicity experiments over a 5 h exposure revealed that Nannochloropsis limnetica was the least sensitive to pharmaceuticals in its photosynthetic yield out of all species tested. Although the estimation of sub-lethal effects can be vital in contrast to that of LC50s, the EC50 values in all species and for all medicines were orders of magnitude higher than concentrations found in polluted surface water. Chlamydomonas reinhardtii was the most sensitive to fluoxetine (EC50 of 1.6 mg L(-1)), and propranolol (EC50 of 3 mg L(-1)). Acutodesmus obliquus was most sensitive to ibuprofen (EC50 of 288 mg L(-1)). Additionally, the sensitivity to the pharmaceuticals changed under a Pi-limitation; the green algae became less sensitive to fluoxetine and propranolol. In contrast, Pi-limited algal species were more sensitive to ibuprofen. Our results suggest that the sensitivity of algae to pharmaceuticals is (i) highly compound- and species-specific and (ii) dependent on the cellular P status.

Interspecific competition in phytoplankton drives the availability of essential mineral and biochemical nutrients.

The underlying mechanisms and consequences of competition and diversity are central themes in ecology. A higher diversity of primary, producers often results in higher resource use efficiency in aquatic and terrestrial ecosystems. This may result in more food for consumers on one hand, while, on the other hand, it can also result in a decreased food quality for consumers; higher biomass combined with the same availability of the limiting compound directly reduces the dietary proportion of the limiting compound. Here we tested whether and how interspecific competition in phytoplankton communities leads to changes in resource use efficiency and cellular concentrations of nutrients and fatty acids. The measured particulate carbon: phosphorus ratios (C:P) and fatty acid concentrations in the communities were compared to the theoretically expected ratios and concentrations of measurements on simultaneously running monocultures. With interspecific competition, phytoplankton communities had higher concentrations of the monounsaturated fatty acid oleic acid and also much higher concentrations of the ecologically and physiologically relevant long-chain polyunsaturated fatty acid eicosapentaenoic acid than expected concentrations based on monocultures. Such higher availability of essential fatty acids may contribute to the positive relationship between phytoplankton diversity and zooplankton growth, and may compensate limitations by mineral nutrients in higher trophic levels.

Daphnia's dilemma: adjustment of carbon budgets in the face of food and cholesterol limitation.

We studied the carbon (C) metabolism in Daphnia when the amount of C (food quantity) and/or the content of biochemical nutrients (food quality) was limiting. Growth performances and C budgets of Daphnia magna (assimilation, faeces egestion, excretion and respiration measured by [(14)C]-tracing) were analysed when animals were raised on different food quantities and concentrations of cholesterol, an essential biochemical food compound. Cholesterol is of special interest because it not only acts as limiting nutrient but also contributes to the overall C pool of the animals. As the tissue cholesterol concentration in Daphnia is quite low, we hypothesized the selective exclusion of cholesterol from C budgeting and tested this using radiolabelled cholesterol. Somatic growth rates of D. magna were highest at high quantity and quality and were reduced to a moderate value if either the food quantity or the cholesterol concentration was low. Growth was lowest at low food quantity and quality. The measurements of C budgets revealed high regulative response to low food quality at high food quantity only. Here, low dietary cholesterol caused bulk C assimilation efficiency (AE) to decrease and assimilated (excess) C to be increasingly respired. Additionally, Daphnia enhanced efficient adjustment of C budgets when facing cholesterol limitation by (1) increasing the AE of the cholesterol itself and (2) not changing cholesterol respiration, which was still not detectable. In contrast, at low food quantity, Daphnia is unable to adjust for low food quality, emphasizing that food limitation could overrule food quality effects.

Longevity of Daphnia and the attenuation of stress responses by melatonin.

BACKGROUND: The widespread occurrence of melatonin in prokaryotes as well as eukaryotes indicates that this indoleamine is considerably old. This high evolutionary age has led to the development of diverse functions of melatonin in different organisms, such as the detoxification of reactive oxygen species and anti-stress effects. In insects, i.e. Drosophila, the addition of melatonin has also been shown to increase the life span of this arthropod, probably by reducing age-related increasing oxidative stress. Although the presence of melatonin was recently found to exist in the ecological and toxicological model organism Daphnia, its function in this cladoceran has thus far not been addressed. Therefore, we challenged Daphnia with three different stressors in order to investigate potential stress-response attenuating effects of melatonin. i) Female and male daphnids were exposed to melatonin in a longevity experiment, ii) Daphnia were confronted with stress signals from the invertebrate predator Chaoborus sp., and iii) Daphnia were grown in high densities, i.e. under crowding-stress conditions. RESULTS: In our experiments we were able to show that longevity of daphnids was not affected by melatonin. Therefore, age-related increasing oxidative stress was probably not compensated by added melatonin. However, melatonin significantly attenuated Daphnia's response to acute predator stress, i.e. the formation of neckteeth which decrease the ability of the gape-limited predator Chaoborus sp. to handle their prey. In addition, melatonin decreased the extent of crowding-related production of resting eggs of Daphnia. CONCLUSIONS: Our results confirm the effect of melatonin on inhibition of stress-signal responses of Daphnia. Until now, only a single study demonstrated melatonin effects on behavioral responses due to vertebrate kairomones, whereas we clearly show a more general effect of melatonin: i) on morphological predator defense induced by an invertebrate kairomone and ii) on life history characteristics transmitted by chemical cues from conspecifics. Therefore, we could generally confirm that melatonin plays a role in the attenuation of responses to different stressors in Daphnia.

Thresholds for sterol-limited growth of Daphnia magna: a comparative approach using 10 different sterols.

Arthropods are incapable of synthesizing sterols de novo and thus require a dietary source to cover their physiological demands. The most prominent sterol in animal tissues is cholesterol, which is an indispensable structural component of cell membranes and serves as precursor for steroid hormones. Instead of cholesterol, plants and algae contain a variety of different phytosterols. Consequently, herbivorous arthropods have to metabolize dietary phytosterols to cholesterol to meet their requirements for growth and reproduction. Here, we investigated sterol-limited growth responses of the freshwater herbivore Daphnia magna by supplementing a sterol-free diet with increasing amounts of 10 different phytosterols and comparing thresholds for sterol-limited growth. In addition, we analyzed the sterol composition of D. magna to explore sterol metabolic constraints and bioconversion capacities. We show that dietary phytosterols strongly differ in their potential to support somatic growth of D. magna. The dietary threshold concentrations obtained by supplementing the different sterols cover a wide range (3.5-34.4 µg mg C(-1)) and encompass the one for cholesterol (8.9 µg mg C(-1)), indicating that certain phytosterols are more efficient in supporting somatic growth than cholesterol (e.g., fucosterol, brassicasterol) while others are less efficient (e.g., dihydrocholesterol, lathosterol). The dietary sterol concentration gradients revealed that the poor quality of particular sterols can be alleviated partially by increasing dietary concentrations, and that qualitative differences among sterols are most pronounced at low to moderate dietary concentrations. We infer that the dietary sterol composition has to be considered in zooplankton nutritional ecology to accurately assess potential sterol limitations under field conditions.

Nutritional indicators and their uses in ecology.

The nutrition of animal consumers is an important regulator of ecological processes due to its effects on their physiology, life-history and behaviour. Understanding the ecological effects of poor nutrition depends on correctly diagnosing the nature and strength of nutritional limitation. Despite the need to assess nutritional limitation, current approaches to delineating nutritional constraints can be non-specific and imprecise. Here, we consider the need and potential to develop new complementary approaches to the study of nutritional constraints on animal consumers by studying and using a suite of established and emerging biochemical and molecular responses. These nutritional indicators include gene expression, transcript regulators, protein profiling and activity, and gross biochemical and elemental composition. The potential applications of nutritional indicators to ecological studies are highlighted to demonstrate the value that this approach would have to future studies in community and ecosystem ecology.

Photoperiodic adaptation of aanat and clock gene expression in seasonal populations of Daphnia pulex.

Changes in day-length entrain the endogenous clock of organisms leading to complex responses to photoperiod. In long-lived organisms experiencing several seasons this response of the clock to photoperiod is phenotypically plastic. However, short-lived organisms often experience a single season without pronounced changes in day-length. For those, a plastic response of the clock to different seasons would not necessarily be adaptive. In aquatic ecosystems, zooplankton species like Daphnia live only for some weeks, i.e. one week up to ca. two months. However, they often show a succession of clones that are seasonally adapted to environmental changes. Here, we found that 16 Daphnia clones per each of three seasons ( = 48 clones) from the same pond and year differed in clock gene expression with a homogenous gene expression pattern in ephippia-hatched spring clones and a bimodal expression pattern in summer and autumn populations indicating an ongoing adaptation process. We clearly demonstrate that spring clones were adapted to a short, and summer clones to a long photoperiod. Furthermore, we found that gene expression of the melatonin-synthesis enzyme AANAT was always lowest in summer clones. In the Anthropocene, Daphnia's clock might be disturbed by light-pollution and global warming. Since Daphnia is a key-organism in trophic carbon transfer, a disruption of its clock rhythm would be devastating for the stability of freshwater ecosystems. Our results are an important step in understanding the adaptation of Daphnia's clock to environmental changes.

Omega-3 versus Omega-6: Are We Underestimating the Ecological Significance of Arachidonic Acid in Aquatic Systems?

The long-chain polyunsaturated fatty acids (PUFA) eicosapentaenoic acid (EPA, ω-3, or n-3) and arachidonic acid (ARA, ω-6 or n-6) are known to have distinct physiological functions, yet can both support growth and reproduction of consumers, raising the question of whether EPA and ARA are ecologically substitutable dietary resources. We explored the relative importance of EPA and ARA for the growth and reproduction of the freshwater keystone herbivore Daphnia in a life-history experiment. Both PUFA were supplemented in a concentration-dependent manner to a PUFA-free diet, separately and in combination (50% EPA: 50% ARA mixture). The growth-response curves obtained with EPA, ARA, and the mixture were virtually congruent and the thresholds for PUFA limitation did not differ, indicating that EPA (n-3) and ARA (n-6) were substitutable dietary resources under the applied experimental conditions. The actual requirements for EPA and ARA might change with growth conditions, e.g., under the influence of parasites or pathogens. The higher retention of ARA in Daphnia suggests that EPA and ARA are subject to different turnover rates, which also implies different physiological functions. Studies on the ARA requirements of Daphnia could provide valuable information on the presumably underestimated ecological importance of ARA in freshwater food webs.

Growth and fatty acid composition of pikeperch (Sander lucioperca L., 1758) larvae under altered feeding protocol including the copepod Apocyclops panamensis (Marsh, 1913).

Alternative live feeds for small and sensitive fish early life stages such as pikeperch (Sander lucioperca L., 1758) can improve the larval quantity, quality and performance in aquaculture. Therefore, this study evaluated the cyclopoid copepod Apocyclops panamensis (Marsh, 1913) as live feed for pikeperch larviculture from day 11 post hatch (dph) in two independent experiments. In both experiments, pikeperch larvae had the highest specific growth rate (SGR) when they fed on Brachionus plicatilis until dph 11 and A. panamensis until dph 16-18. SGR was related to a decrease in total fatty acids (FAs), saturated FAs and monounsaturated FAs in pikeperch larvae, indicating their use as energy for growth. Within the polyunsaturated FAs, docosahexaenoic acid (DHA) increased in larvae fed with A. panamensis and coincided with the highest SGR suggesting that DHA is accumulated in larvae as structural FA. Our study demonstrated a suitable pikeperch larval fatty acid composition for growth after feeding A. panamensis compared with Artemia sp. from dph 11 until dph 16 and previously fed with B. plicatilis. Moreover, it highlighted the importance of the dietary PUFAs in pikeperch rearing, specifically of linoleic acid (LA) from dph 4 until dph 11 and of DHA from dph 11 onwards.

Multiple resource limitation theory applied to herbivorous consumers: Liebig's minimum rule vs. interactive co-limitation.

There is growing consensus that the growth of herbivorous consumers is frequently limited by more than one nutrient simultaneously. This understanding, however, is based primarily on theoretical considerations and the applicability of existing concepts of co-limitation has rarely been tested experimentally. Here, we assessed the suitability of two contrasting concepts of resource limitation, i.e. Liebig's minimum rule and the multiple limitation hypothesis, to describe nutrient-dependent growth responses of a freshwater herbivore (Daphnia magna) in a system with two potentially limiting nutrients (cholesterol and eicosapentaenoic acid). The results indicated that these essential nutrients interact, and do not strictly follow Liebig's minimum rule, which consistently overestimates growth at co-limiting conditions and thus is not applicable to describe multiple nutrient limitation of herbivorous consumers. We infer that the outcome of resource-based modelling approaches assessing herbivore population dynamics strongly depends on the applied concept of co-limitation.

CD137 ligand mediates opposite effects in human and mouse NK cells and impairs NK-cell reactivity against human acute myeloid leukemia cells.

Natural killer (NK) cells play an important role in the immunosurveillance of leukemia. Their reactivity is governed by a balance of activating and inhibitory receptors including various members of the tumor necrosis factor receptor (TNFR) family. Here we report that human NK cells acquire expression of the TNFR family member CD137 upon activation, and NK cells of acute myeloid leukemia (AML) patients display an activated phenotype with substantial CD137 expression. CD137 ligand (CD137L) was detectable on leukemic cells in 35% of 65 investigated AML patients, but not on healthy CD34(+) cells, and expression was associated with monocytic differentiation. Bidirectional signaling following CD137-CD137L interaction induced the release of the immunomodulatory cytokines interleukin-10 and TNF by AML cells and directly diminished granule mobilization, cytotoxicity, and interferon-gamma production of human NK cells, which was restored by blocking CD137. Cocultures of NK cells with CD137L transfectants confirmed that human CD137 inhibits NK-cell reactivity, while activating signals were transduced by its counterpart on NK cells in mice. Our data underline the necessity to study the function of seemingly analog immunoregulatory molecules in mice compared with men and demonstrate that CD137-CD137L interaction enables immune evasion of AML cells by impairing NK-cell tumor surveillance in humans.

Dietary lipid quality affects temperature-mediated reaction norms of a freshwater key herbivore.

Temperature-mediated plasticity in life history traits strongly affects the capability of ectotherms to cope with changing environmental temperatures. We hypothesised that temperature-mediated reaction norms of ectotherms are constrained by the availability of essential dietary lipids, i.e. polyunsaturated fatty acids (PUFA) and sterols, as these lipids are involved in the homeoviscous adaptation of biological membranes to changing temperatures. A life history experiment was conducted in which the freshwater herbivore Daphnia magna was raised at four different temperatures (10, 15, 20, 25°C) with food sources differing in their PUFA and sterol composition. Somatic growth rates increased significantly with increasing temperature, but differences among food sources were obtained only at 10°C at which animals grew better on PUFA-rich diets than on PUFA-deficient diets. PUFA-rich food sources resulted in significantly higher population growth rates at 10°C than PUFA-deficient food, and the optimum temperature for offspring production was clearly shifted towards colder temperatures with an increased availability of dietary PUFA. Supplementation of PUFA-deficient food with single PUFA enabled the production of viable offspring and significantly increased population growth rates at 10°C, indicating that dietary PUFA are crucial for the acclimation to cold temperatures. In contrast, cumulative numbers of viable offspring increased significantly upon cholesterol supplementation at 25°C and the optimum temperature for offspring production was shifted towards warmer temperatures, implying that sterol requirements increase with temperature. In conclusion, essential dietary lipids significantly affect temperature-mediated reaction norms of ectotherms and thus temperature-mediated plasticity in life history traits is subject to strong food quality constraints.

Photosynthetic activity in both algae and cyanobacteria changes in response to cues of predation.

A plethora of adaptive responses to predation has been described in microscopic aquatic producers. Although the energetic costs of these responses are expected, with their consequences going far beyond an individual, their underlying molecular and metabolic mechanisms are not fully known. One, so far hardly considered, is if and how the photosynthetic efficiency of phytoplankton might change in response to the predation cues. Our main aim was to identify such responses in phytoplankton and to detect if they are taxon-specific. We exposed seven algae and seven cyanobacteria species to the chemical cues of an efficient consumer, Daphnia magna, which was fed either a green alga, Acutodesmus obliquus, or a cyanobacterium, Synechococcus elongatus (kairomone and alarm cues), or was not fed (kairomone alone). In most algal and cyanobacterial species studied, the quantum yield of photosystem II increased in response to predator fed cyanobacterium, whereas in most of these species the yield did not change in response to predator fed alga. Also, cyanobacteria tended not to respond to a non-feeding predator. The modal qualitative responses of the electron transport rate were similar to those of the quantum yield. To our best knowledge, the results presented here are the broadest scan of photosystem II responses in the predation context so far.