Spatial and Temporal Variation of Cestode Infection and its Effects on Two Small Barbs (Barbus humilis and B. tanapelagius) in Lake Tana, Ethiopia

Pseudophyllidean cestodes as Ligula have a complex life cycle with cyclopoid copepods as first intermediate host, zooplanktivorous fish as second, and piscivorous birds as final host. We studied the effects of diet, season and habitat occupation on the prevalence of plerocercoid larvae of the tapeworm Ligula intestinalis in two closely related small barbs and the effects of the parasites on the barbs life histories in Lake Tana (Ethiopia) during 1 year. In all affected barbs L. intestinalis caused retardation in gonad development, maturation at reduced size and lower absolute fecundity. Infection rate, averaged over all habitats was significantly higher in B. tanapelagius (10%) than in B. humilis (6%). Below a threshold of 48 mm the infection rate was zero for both barbs, this coincided with a very low proportion of copepods in their diets, increasing up to 90 and 55%, respectively, for their largest size class (81–90 mm). The relatively high infection rate in B. tanapelagius is explained by its obligatory zooplanktivorous feeding behaviour, ingesting a relatively high proportion of infected cyclopoid copepods. This is in contrast with B. humilis, which is a polyphagous species, feeding both on zooplankton and benthic invertebrates. Significant seasonal effects in infection rates were observed. In both barb species infection rates were lower during the breeding season. Only for B. tanapelagius a significant negative correlation was observed between rain fall and infection rate, probably caused by an increased turbidity that decreases feeding efficiency on zooplankton. Habitat type had also a significant effect on infection rate. Barbus humilis showed a much higher infection rate in shallow clear water (10%) than in shallow turbid water (3%), whereas B. tanapelagius showed much higher infection rates in the shallow sublittoral (13%) than in the deeper pelagic (7%). Most likely, birds predate more efficiently on barbs in shallow clear waters than in shallow turbid and deep waters.     

Computerized morphometric analysis of pathological prion protein deposition in scrapie-infected hamster brain.

Transmissible spongiform encephalopathies (TSEs or prion diseases) are characterized by a constellation of typical though variable pathological changes in the brain. Deposition of disease-associated abnormal prion protein (PrP(Sc)) is the pathological feature of TSEs most consistent and accessible for quantification. However, the evaluation of PrP(Sc) deposits detected by immunohistochemical techniques has been traditionally based on arbitrarily assigned semiquantitative scores. This approach is limited by its subjectivity and bias, yielding considerable variability. In this study, we used MetaMorph 6.1 image analysis software for quantitative analysis of immunostained PrP(Sc) deposits in the CNS of hamsters infected with the 263K strain of scrapie agent. Computerized morphometric analysis (CMA) allowed unambiguous detection of even minimal amounts of immunostained PrP(Sc). CMA values for intensity of staining and area stained correlated well with semiquantitative scores, providing reproducible quantitative data and objective criteria for analyzing PrP(Sc) deposition. CMA provides a simple and reliable method for improved and consistent diagnosis of TSEs that may also be used to quantify other immunostained biomarkers.     

How to measure top–down vs bottom–up effects: a new population metric and its calibration on Daphnia

Research on the role of top–down (predation) and bottom–up (food) effects in food webs has led to the understanding that the variability of these effects in space and time is a fundamental feature of natural systems. Consequently, our measurement tools must allow us to evaluate the effects from a dynamical perspective. A population‐dynamics approach may be appropriate to the task. More specifically, because food and predators both affect birth rate, birth rate dynamics may be a key to understanding their impact on the population of interest. Based on the Edmondson–Paloheimo model for birth rate, we propose a new population metric to assess the relative strength of top–down vs bottom–up effects. The metric is the ratio of contributions of changes in proportion of adults and fecundity to change in birth rate. Proportion of adults reflects a top–down effect (predators are assumed to be size‐selective), fecundity reflects a bottom–up effect, and birth rate appears as a common currency with which to compare the former and the latter. Using microcosm experiments and computer simulations on the cladoceran Daphnia, we calibrate the metric and show that, in both types of tests, the ratio of contributions is typically 0.5–0.7 under a strong bottom–up effect and 2.0–2.2 under a strong top–down effect. This provides experimental evidence that the ratio of contributions may allow one to distinguish a strong top–down effect from a strong bottom–up effect.     

Genomic DNA hypomethylation by histone deacetylase inhibition implicates DNMT1 nuclear dynamics

Histone deacetylase inhibitors (HDACi) are promising antitumor drugs acting through reactivation of silenced tumor suppressor genes. Several HDACi are currently in clinical trials both for hematological and solid tissue malignancies. Cooperative action of HDACi and DNA methylation inhibitors (DNMTi) has been reported, making combined treatment an attractive choice for cancer therapy. There is some evidence that synergistic effects of HDACi and DNMTi are achieved by their action on common targets, including DNA methyltransferase 1 (DNMT1). To further analyze this interaction, we investigated the effect of the HDACi trichostatin A on global and gene-specific DNA methylation and applied methods with single molecule sensitivity, confocal laser scanning microscopy with avalanche photodiode detectors (APD imaging) and fluorescence correlation spectroscopy (FCS), to study its effect on the nuclear dynamics of DNMT1 in live cells. Our data show that trichostatin A treatment reduces global DNA methylation and the DNMT1 protein level and alters DNMT1 nuclear dynamics and interactions with chromatin. The mechanisms underlying these effects are apparently distinct from the mechanisms of action of the DNMT inhibitor 5-azacytidine. Our study sheds light on the molecular mechanisms underlying the synergistic action of HDACi and DNMTi and may also help to define improved policies for cancer treatment.     

Earliest Mexican Turkeys (Meleagris gallopavo) in the Maya Region: Implications for Pre-Hispanic Animal Trade and the Timing of Turkey Domestication

Late Preclassic (300 BC-AD 100) turkey remains identified at the archaeological site of El Mirador (Petén, Guatemala) represent the earliest evidence of the Mexican turkey (Meleagris gallopavo) in the ancient Maya world. Archaeological, zooarchaeological, and ancient DNA evidence combine to confirm the identification and context. The natural pre-Hispanic range of the Mexican turkey does not extend south of central Mexico, making the species non-local to the Maya area where another species, the ocellated turkey (Meleagris ocellata), is indigenous. Prior to this discovery, the earliest evidence of M. gallopavo in the Maya area dated to approximately one thousand years later. The El Mirador specimens therefore represent previously unrecorded Preclassic exchange of animals from northern Mesoamerica to the Maya cultural region. As the earliest evidence of M. gallopavo found outside its natural geographic range, the El Mirador turkeys also represent the earliest indirect evidence for Mesoamerican turkey rearing or domestication. The presence of male, female and sub-adult turkeys, and reduced flight morphology further suggests that the El Mirador turkeys were raised in captivity. This supports an argument for the origins of turkey husbandry or at least captive rearing in the Preclassic.     

Contrasting migration behaviour of Daphnia pulicaria and D. galeata x hyalina, in avoidance of predation by 0+perch (Perca fluviatilis)

In spring and early summer, a small population of the large-bodied Daphnia pulicaria coexists with a much larger population of the medium-sized hybrid Daphnia galeata × hyalina in the epilimnion of Lake Maarsseveen (The Netherlands). When large shoals of juvenile perch (Perca fluviatilis) appear in the open water, both species start to migrate vertically. Since D. pulicaria has a larger body-size than D. galeata × hyalina, and is therefore competitive dominant over the hybrid, it is unlikely that both species interact via their common food resource, but they react both to fish predation. However, since they differ in size, and therefore in vulnerability for fish predation, both species adopt different strategies. The smaller bodied, and less vulnerable D. galeata × hyalina exhibits diel vertical migration ascending to the surface at dusk, and staying there during the night. In this way, benefiting from the higher temperatures of the surface layers. In contrast, the large-bodied, and more vulnerable D. pulicaria selects the deep cold hypolimnion water layers as refuge against fish predation. In this way it benefits from a safe habitat, free from fish predators, but on the other hand suffers from low water temperatures, which decrease its fitness. It is likely that the relatively higher temperature in the upper water layers serves as a proximate factor for the downward migration of D. pulicaria.     

Low tryptophan diet increases stress-sensitivity, but does not affect habituation in rats

Cerebral dysfunction of 5-HT (serotonin) has been associated with stress response and with affective disorders. Stress alone is insufficient to induce depression, since only a minor proportion of subjects that have experienced stressful life events develop depressive episodes. We investigated whether long-term brain 5-HT depletion induced in rats by a diet with low content of its precursor tryptophan affects stress-responsiveness in rats. Stress-sensitivity was measured through various physiological parameters and by measuring the rats' response to acoustic stimuli. One group of rats was subjected to daily acoustic stimulus sessions for 5 days. Other groups received both immobilization stress and acoustic stimulus sessions daily for either 9 days (chronic experiment) or 1 day (acute experiment). A low tryptophan diet led to decreases in plasma tryptophan levels, low ratio of tryptophan/large neutral amino acid, whole blood 5-HT, and neuronal 5-HT content in the Dorsal and Median Raphe Nuclei, as well as altered c-fos expression in the brain. Without concomitant immobilization, the diet alone did not affect reactivity and habituation to acoustic stimuli, although plasma corticosterone levels, but not the adrenal weights, were increased on day 5. Low tryptophan and chronic immobilization stress together with the acoustic testing procedure increased adrenal weight, plasma corticosterone levels and reactivity to the acoustic stimuli, but not the rate of habituation to acoustic stimuli. These results show that cerebral dysfunction of serotonin achieved through a low tryptophan diet, increases the sensitivity of rats to external and stressful stimuli, but does not impair the capacity to adapt to these stimuli. Accordingly, brain-serotonin modulates reactivity to stress, but not stress coping.     

The effects of food and temperature regimes on life-history responses to fish kairomones in Daphnia hyalina × galeata*

Life-history responses to two concentrations of fish released info-chemicals at two temperature and food regimes were investigated for one clone of Daphnia hyalina × galeata. The presence of fish kairomones had a negative impact on size at maturity, carbon allocation to individual eggs and size of neonates in all treatments. Food concentration and temperature had positive effects on size of adult stages, independent of kairomone treatment. However, kairomone treatment were not found to interact with food or temperature. Age at maturity was positively influenced by increased temperature and food concentrations, whereas no direct kairomone effects were detected for this trait. Clutch size was not directly influenced by kairomone treatment, whereas both food concentration and temperature had strong, positive effects.