Parasites driving host diversity: Incidence of disease correlated with Daphnia clonal turnover.

According to the Red Queen hypothesis, clonal diversity in asexual populations could be maintained by negative frequency-dependant selection by coevolving parasites. If common clones are selected against and rare clones gain a concomitant advantage, we expect that clonal turnover should be faster during parasite epidemics than between them. We tested this hypothesis exploring field data of the Daphnia-Caullerya host-parasite system. The clonal make-up and turnover of the Daphnia host population was tracked with high temporal resolution from 1998 until 2013, using first allozyme and later microsatellite markers. Significant differences in the clonal composition between random and infected subsamples of Daphnia populations were detected on six of seven tested occasions, confirming genetic specificity of the host-parasite interaction in this system. We used time series analysis to compare the rates of host clonal turnover to the incidence of parasitism, and found that Caullerya prevalence was significantly associated with microsatellite-based clonal turnover. As alternate hypotheses, we further tested whether turnover was related to a variety of biotic, abiotic, and host demographic parameters. Other significant correlates of turnover were cyanobacterial biomass and (weakly) temperature. Overall, parasitism seems to be a strong driver of host clonal turnover, in support of the Red Queen hypothesis.

Bacterial chitin hydrolysis in two lakes with contrasting trophic statuses.

Chitin, which is a biopolymer of the amino sugar glucosamine (GlcN), is highly abundant in aquatic ecosystems, and its degradation is assigned a key role in the recycling of carbon and nitrogen. In order to study the significance of chitin decomposition in two temperate freshwater lakes with contrasting trophic and redox conditions, we measured the turnover rate of the chitin analog methylumbelliferyl-N,N'-diacetylchitobioside (MUF-DC) and the presence of chitinase (chiA) genes in zooplankton, water, and sediment samples. In contrast to the eutrophic and partially anoxic lake, chiA gene fragments were detectable throughout the oligotrophic water column and chiA copy numbers per ml of water were up to 15 times higher than in the eutrophic waters. For both lakes, the highest chiA abundance was found in the euphotic zone--the main habitat of zooplankton, but also the site of production of easily degradable algal chitin. The bulk of chitinase activity was measured in zooplankton samples and the sediments, where recalcitrant chitin is deposited. Both, chiA abundance and chitinase activity correlated well with organic carbon, nitrogen, and concentrations of particulate GlcN. Our findings show that chitin, although its overall contribution to the total organic carbon is small (~0.01 to 0.1%), constitutes an important microbial growth substrate in these temperate freshwater lakes, particularly where other easily degradable carbon sources are scarce.

Near-infrared spectroscopy measurements of cerebral oxygenation in newborns during immediate postnatal adaptation.

OBJECTIVE: In view of growing concerns regarding the optimal supplementation of oxygen at birth, we measured cerebral oxygenation during the first minutes of life. STUDY DESIGN: Using near-infrared spectroscopy, changes in cerebral oxygenated hemoglobin (O(2)Hb), dexoxygenated hemoglobin (HHb), and tissue oxygenation index (TOI) were measured during the first 15 minutes of life in 20 healthy newborn infants delivered at term by elective cesarean section. RESULTS: O(2)Hb and TOI increased rapidly within the first minutes of life (median slope for O(2)Hb, 3.4 micromol/L/min; range, 1.4 to 20.6 micromol/L/min; median slope for TOI, 4.2 %/min; range, -0.4 to 27.3%/min), and cerebral HHb decreased (median slope, -4.8 micromol/L/min; range, -0.2 to -20.6 micromol/L/min). O(2)Hb, TOI, and HHb all reached a plateau within 8 minutes. CONCLUSIONS: A significant increase in cerebral O(2)Hb and TOI and a significant decrease in HHb occur during immediate adaptation in healthy term newborns, reaching a steady plateau at around 8 minutes after birth.

Slow blood sampling from an umbilical artery catheter prevents a decrease in cerebral oxygenation in the preterm newborn.

OBJECTIVE: Blood sampling from an umbilical artery catheter (UAC) placed in a high position (thoracal 6-9) has the potential to produce clinically significant changes in cerebral blood flow and, thereby, in cerebral oxygenation. This may contribute to cerebral impairment in preterm newborn infants. Therefore, we set up a study to determine the effects of different sampling speeds through a UAC on cerebral oxygenation in preterm infants. METHODS: Thirty pairs of measurements were conducted on 20 preterm infants (median gestational age: 30.14 weeks; median birth weight: 1170 g). For each infant, 2 blood samplings (both 2.3 mL, including flush volume) through the UAC in high position were taken at 2 different speeds (20 and 40 seconds) in alternating sequence. Cerebral oxygenation was measured noninvasively by near-infrared spectroscopy. Concentration changes in cerebral oxygenated hemoglobin (O2Hb) and deoxygenated hemoglobin (HHb), along with the tissue oxygenation index (TOI; O2Hb/[O2Hb + HHb] x 100), were recorded while blood was withdrawn and subsequently reinfused. RESULTS: A significant decrease in O2Hb and TOI occurred during blood sampling within 20 seconds (median DeltaO2Hb: -1.5 micromol/L; range: -4.1-2.3; median DeltaTOI: -0.6%; range: -6.3-2.3), whereas HHb increased (median DeltaHHb: 0.4 micromol/L, range: -1.1-3.9). No significant change was found in O2Hb, HHb, and TOI when sampling time was extended to 40 seconds. CONCLUSION: Our results show that blood withdrawal over 20 seconds from a UAC in high position significantly decreases cerebral O2Hb and TOI in preterm infants. Prolonging sampling time to 40 seconds can prevent this phenomenon.