How do migrating daphnids cope with fish predation risk in the epilimnion under anoxic conditions in the hypolimnion?

The vertical distribution of Daphnia in experimental tubes is influenced by fish kairomone concentration in the ‘epilimnion' and oxygen conditions in the ‘hypolimnion'. Daphnids trade off reduced predation mortality in a refuge against disadvantages due to unfavourable oxygen condition

Hatching with the enemy: Daphnia diapausing eggs hatch in the presence of fish kairomones

Summary.: Infochemicals are known to play a key role in mediating predator-prey interactions, both in aquatic and terrestrial communities. However, state-dependent variation may exist in how effectively individuals can use this information, depending on genotype, life stage and experience. For our study, we used the predator-prey model system fish-waterflea Daphnia magna Straus (Cladocera, Daphniidae). Adult Daphnia use fish-derived infochemicals, so-called kairomones, as indicators of predation risk, and exhibit a spectrum of morphological, behavioural and life-history responses to the presence of fish kairomones. Here, we investigate whether diapausing eggs, an embryonic resting stage in the life cycle of D. magna, also use fish kairomones and tune their hatching to the risk of fish predation, as reported for diapausing stages of dinoflagellates. In two laboratory experiments, we studied hatching proportion and time until hatching of D. magna diapausing eggs in the absence and presence of fish kairomones. D. magna families differed significantly in their response to the presence of fish kairomones; some families reduced hatching proportion, whereas others increased it. Our results imply genotype-dependent differences in the hatching reactions to fish kairomones as observed for other traits in adult Daphni

Converging seasonal prevalence dynamics in experimental epidemics

Background Regular seasonal changes in prevalence of infectious diseases are often observed in nature, but the mechanisms are rarely understood. Empirical tests aiming at a better understanding of seasonal prevalence patterns are not feasible for most diseases and thus are widely lacking. Here, we set out to study experimentally the seasonal prevalence in an aquatic host-parasite system. The microsporidian parasite Hamiltosporidium tvärminnensis exhibits pronounced seasonality in natural rock pool populations of its host, Daphnia magna with a regular increase of prevalence during summer and a decrease during winter. An earlier study was, however, unable to test if different starting conditions (initial prevalence) influence the dynamics of the disease in the long term. Here, we aim at testing how the starting prevalence affects the regular prevalence changes over a 4-year period in experimental populations.Results In an outdoor experiment, populations were set up to include the extremes of the prevalence spectrum observed in natural populations: 5% initial prevalence mimicking a newly invading parasite, 100% mimicking a rock pool population founded by infected hosts only, and 50% prevalence which is commonly observed in natural populations in spring. The parasite exhibited similar prevalence changes in all treatments, but seasonal patterns in the 100% treatment differed significantly from those in the 5% and 50% treatments. Populations started with 5% and 50% prevalence exhibited strong and regular seasonality already in the first year. In contrast, the amplitude of changes in the 100% treatment was low throughout the experiment demonstrating the long-lasting effect of initial conditions on prevalence dynamics.Conclusions Our study shows that the time needed to approach the seasonal changes in prevalence depends strongly on the initial prevalence. Because individual D. magna populations in this rock pool metapopulation are mostly short lived, only few populations might ever reach a point where the initial conditions are not visible anymore

Adiponutrin Functions as a Nutritionally Regulated Lysophosphatidic Acid Acyltransferase

SummaryNumerous studies in humans link a nonsynonymous genetic polymorphism (I148M) in adiponutrin (ADPN) to various forms of fatty liver disease and liver cirrhosis. Despite its high clinical relevance, the molecular function of ADPN and the mechanism by which I148M variant affects hepatic metabolism are unclear. Here we show that ADPN promotes cellular lipid synthesis by converting lysophosphatidic acid (LPA) into phosphatidic acid. The ADPN-catalyzed LPA acyltransferase (LPAAT) reaction is specific for LPA and long-chain acyl-CoAs. Wild-type mice receiving a high-sucrose diet exhibit substantial upregulation of Adpn in the liver and a concomitant increase in LPAAT activity. In Adpn-deficient mice, this diet-induced increase in hepatic LPAAT activity is reduced. Notably, the I148M variant of human ADPN exhibits increased LPAAT activity leading to increased cellular lipid accumulation. This gain of function provides a plausible biochemical mechanism for the development of liver steatosis in subjects carrying the I148M variant

Different mechanisms of transmission of the microsporidium Octosporea bayeri: a cocktail of solutions for the problem of parasite permanence

Periods of low host density impose a constraint on parasites with direct transmission, challenging their permanence in the system. The microsporidium Octosporea bayeri faces such constraint in a metapopulation of its host, the cladoceran Daphnia magna, where ponds frequently lose their host population due to ponds drying out in summer and freezing in winter. We conducted experiments aimed to investigate the mechanisms of transmission of O. bayeri, and discuss how these mechanisms could contribute to the parasite's permanence in the system. Spores accumulate in the fat cells and the ovaries of the host, and vary in morphology, possibly corresponding to 3 different spore types. Horizontal transmission occurred through the release of spores from dead hosts, with the proportion of infected hosts depending on the spore dose. Further, spores are able to persist outside the host both in dry and wet conditions. Vertical transmission occurred to both parthenogenetic and sexual offspring. The former were invariably infected, while the sexually produced resting eggs (=ephippia) had a less efficient transmission. The parasite may be carried by the ephippia, and thus disperse to new ponds together with the host. Together, these mechanisms may allow the parasite to endure periods of harsh environmental conditions both outside and inside the host

Hatching with the enemy: Daphnia diapausing eggs hatch in the presence of fish kairomones

Infochemicals are known to play a key role in mediating predator-prey interactions, both in aquatic and terrestrial communities. However, state-dependent variation may exist in how effectively individuals can use this information, depending on genotype, life stage and experience. For our study, we used the predator-prey model system fish-waterflea Daphnia magna Straus (Cladocera, Daphniidae). Adult Daphnia use fish-derived infochemicals, so-called kairomones, as indicators of predation risk, and exhibit a spectrum of morphological, behavioural and life-history responses to the presence of fish kairomones. Here, we investigate whether diapausing eggs, an embryonic resting stage in the life cycle of D. magna, also use fish kairomones and tune their hatching to the risk of fish predation, as reported for diapausing stages of dinoflagellates. In two laboratory experiments, we studied hatching proportion and time until hatching of D. magna diapausing eggs in the absence and presence of fish kairomones. D. magna families differed significantly in their response to the presence of fish kairomones; some families reduced hatching proportion, whereas others increased it. Our results imply genotype-dependent differences in the hatching reactions to fish kairomones as observed for other traits in adult Daphnia

Octosporea bayeri: fumidil B inhibits vertical transmission in Daphnia magna, Exp Parasitol 109

Abstract Microsporidia are a highly successful and ecologically diverse group of parasites, and thus represent interesting model systems for research on host-parasite interactions. However, such research often requires the ability to cure hosts of infections, a difficult task, given the short lifespan of most invertebrates and the efficient vertical transmission of some parasites. To our knowledge, few treatments are available to cure microsporidiosis in invertebrate hosts, and protocols have not yet been developed to inhibit vertical transmission and thereby cure host lines. We present a protocol for inhibiting vertical transmission of the microsporidian parasite Octosporea bayeri in the freshwater crustacean Daphnia magna. We used 100 mg/L Fumidil B dissolved in the culture medium of the host. This technique allowed Daphnia to survive and reproduce and inhibited vertical transmission of the parasite. The method presented here may be of general interest for other aquatic host-parasite systems involving microsporidia

In Vitro Activities of Amphotericin B and Voriconazole against Aleurioconidia from Aspergillus terreus

This study used aleurioconidia as inoculum and compared the MICs of amphotericin B and voriconazole to those obtained for conidia of 31 Aspergillus terreus strains. For conidia and aleurioconidia, the MIC at which 90% of strains were inhibited was 2.5 μg/ml and 5 μg/ml with amphotericin B and 1 μg/ml and 2 μg/ml with voriconazole