Harsh nutritional environment has positive and negative consequences for family living in a burying beetle

Harsh environmental conditions in form of low food availability for both offspring and parents alike can affect breeding behavior and success. There has been evidence that food scarce environments can induce competition between family members, and this might be intensified when parents are caring as a pair and not alone. On the other hand, it is possible that a harsh, food-poor environment could also promote cooperative behaviors within a family, leading, for example, to a higher breeding success of pairs than of single parents. We studied the influence of a harsh nutritional environment on the fitness outcome of family living in the burying beetle Nicrophorus vespilloides. These beetles use vertebrate carcasses for reproduction. We manipulated food availability on two levels: before and during breeding. We then compared the effect of these manipulations in broods with either single females or biparentally breeding males and females. We show that pairs of beetles that experienced a food-poor environment before breeding consumed a higher quantity of the carcass than well-fed pairs or single females. Nevertheless, they were more successful in raising a brood with higher larval survival compared to pairs that did not experience a food shortage before breeding. We also show that food availability during breeding and social condition had independent effects on the mass of the broods raised, with lighter broods in biparental families than in uniparental ones and on smaller carcasses. Our study thus indicates that a harsh nutritional environment can increase both cooperative as well as competitive interactions between family members. Moreover, our results suggest that it can either hamper or drive the formation of a family because parents choose to restrain reproductive investment in a current brood or are encouraged to breed in a food-poor environment, depending on former experiences and their own nutritional status.     

Soft-start polymerization of fissure sealant: retention after three years

The aim of this study was to investigate retention of composite fissure sealant polymerized with standard and soft-start technique after a three year clinical trial. One hundred teeth were divided into two groups (A&B) of teeth and sealed with composite material (Visioseal, 3M Espe) using split mouth design. Sealants were polymerized using standard (Group A) and soft-start (Group B) techniques with commercial polymerization unit (Elipar Highlight, 3M Espe). Retention rate in Group A was 72%. In 14 teeth sealant was partially or completely missing. Group B showed retention rate of 80%. Sealant was partially or completely missing in 10 teeth. Six new caries lesions in Group A (3) and B (3) were detected. Mann-Whitney test did not reveal significant differences between the polymerization techniques. After three years complete retention of sealants, regardless of the group, was 76% (76 teeth) with six new caries lesions. Soft-start polymerization showed a comparable retention rate as the standard polymerization technique.     

Operant generalization in quail neonates after intradimensional training: Distinguishing positive and negative reinforcement

Operant generalization has been demonstrated in neonates only recently. To investigate the development of intradimensional stimulus control immediately after hatching, northern bobwhite chicks (Colinus virginianus) pecked for brief heat presentations while hearing a high-pitched sound repeated at two constant rates: an S+ tempo signaling a rich reinforcement schedule, alternating with an S− tempo signaling a leaner schedule. Tempo generalization was then assessed in extinction. The expected excitatory gradients were produced after a threshold number of training sessions; unexpectedly, below that threshold, gradients were inhibitory. The chicks’ rapidly developing thermoregulatory capability may have resulted in a change from perceived negative reinforcement initially to positive reinforcement later. Given past research showing excitatory gradients after negative reinforcement, we suggest that these results demonstrate that all negative reinforcement is not equivalent, and, further, that classical conditioning effects require consideration.     

Thirty years after Chernobyl accident: Evaluation of consequences by biologists and medical scientists

This survey paper contains a brief analysis of publications summarizing the results of cell biological, molecular genetics, and population genetic studies devoted to the assessment of the damages inflicted on biological systems by acute radiation and chronic radioactive contamination as a result of the 1986 accident at the Chernobyl NPP.     

Critical years and stages of puberty for radial bone mass apposition during adolescence.

The acquisition of radial mineral density was evaluated in relation to anthropometric characteristics, menarche status, calcium intake and physical activity in a healthy young female population (200 girls and 100 women, respectively aged 11-16 yrs and 20-24 yrs) living in an area of Southern Italy. We performed bone mineral density (BMD) by dual energy X-ray absorptiometry on the ultradistal and middistal radius. Dietary calcium intake was evaluated by a detailed Food Frequency Questionnaire and confirmed by a 3-day record. A questionnaire on energy expenditure was used to assess physical activity in each participant. Morning blood samples were drawn from fasting girls to measure 25-hydroxycalciferol (25 OH-D). We found current calcium above the levels reported by Recommended Dietary Allowances (RDA) in only 31% of women and 6% of girls. BMD steadily increased up to the age of 16 and was increased in postmenarcheal girls compared to premenarcheals of the same pubertal stage. Bone density was also significantly related to age, weight and height in postmenarcheal adolescents, while in girls before and after menarche, no relation was observed between radial BMD and calcium intake or physical activity. In the presence of comparable calcium-intake values recorded in pre- and in postmenarcheal girls, the latter subgroup displayed a marked increase of 25 OH-D serum levels. Our study revealed a calcium intake lower than the RDA in a large percentage of healthy girls and young women, and emphasized the importance of menarche occurrence in bone mass acquisition during pubertal development.     

The indirect consequences of a mutualism: comparing positive and negative components of the net interaction between honeydew-tending ants and host plants

1. In ecological webs, net indirect interactions between species are composed of interactions that vary in sign and magnitude. Most studies have focused on negative component interactions (e.g. predation, herbivory) without considering the relative importance of positive interactions (e.g. mutualism, facilitation) for determining net indirect effects. 2. In plant/arthropod communities, ants have multiple top-down effects via mutualisms with honeydew-producing herbivores and harassment of and predation on other herbivores; these ant effects provide opportunities for testing the relative importance of positive and negative interspecific interactions. We manipulated the presence of ants, honeydew-producing membracids and leaf-chewing beetles on perennial host plants in field experiments in Colorado to quantify the relative strength of these different types of interactions and their impact on the ant's net indirect effect on plants. 3. In 2007, we demonstrated that ants simultaneously had a positive effect on membracids and a negative effect on beetles, resulting in less beetle damage on plants hosting the mutualism. 4. In 2008, we used structural equation modelling to describe interaction strengths through the entire insect herbivore community on plants with and without ants. The ant's mutualism with membracids was the sole strong interaction contributing to the net indirect effect of ants on plants. Predation, herbivory and facilitation were weak, and the net effect of ants reduced plant reproduction. This net indirect effect was also partially because of behavioural changes of herbivores in the presence of ants. An additional membracid manipulation showed that the membracid's effect on ant activity was largely responsible for the ant's net effect on plants; ant workers were nearly ten times as abundant on plants with mutualists, and effects on other herbivores were similar to those in the ant manipulation experiment. 5. These results demonstrate that mutualisms can be strong relative to negative direct interspecific interactions and that positive interactions deserve attention as important components of ecological webs.     

Static respiratory muscle work during immersion with positive and negative respiratory loading.

Upright immersion imposes a pressure imbalance across the thorax. This study examined the effects of air-delivery pressure on inspiratory muscle work during upright immersion. Eight subjects performed respiratory pressure-volume relaxation maneuvers while seated in air (control) and during immersion. Hydrostatic, respiratory elastic (lung and chest wall), and resultant static respiratory muscle work components were computed. During immersion, the effects of four air-delivery pressures were evaluated: mouth pressure (uncompensated); the pressure at the lung centroid (PL,c); and at PL,c +/-0.98 kPa. When breathing at pressures less than the PL,c, subjects generally defended an expiratory reserve volume (ERV) greater than the immersed relaxation volume, minus residual volume, resulting in additional inspiratory muscle work. The resultant static inspiratory muscle work, computed over a 1-liter tidal volume above the ERV, increased from 0.23 J. l(-1), when subjects were breathing at PL,c, to 0.83 J. l(-1) at PL,c -0.98 kPa (P < 0.05), and to 1.79 J. l(-1) at mouth pressure (P < 0.05). Under the control state, and during the above experimental conditions, static expiratory work was minimal. When breathing at PL,c +0.98 kPa, subjects adopted an ERV less than the immersed relaxation volume, minus residual volume, resulting in 0.36 J. l(-1) of expiratory muscle work. Thus static inspiratory muscle work varied with respiratory loading, whereas PL,c air supply minimized this work during upright immersion, restoring lung-tissue, chest-wall, and static muscle work to levels obtained in the control state.     

Integration of positive and negative growth signals during ras pathway activation in vivo

Expression of RAS proteins can have either positive or negative effects on cell growth, differentiation and death. New technologies are being developed for the generation of animal models to address the questions of where, when and how much Ras is expressed during tumorigenesis, and how these disparate signals are integrated during multistage carcinogenesis.     

Food web manipulation in Lake Zwemlust: Positive and negative effects during the first two years

The hypertrophic Lake Zwemlust, a small water body used as a swimming pool, was characterized by algal blooms in summer, reducing the Secchi disk transparency to less than 0.3 m. Since in The Netherlands a Secchi disk transparency of 1 m is obligatory for swimming waters, corrective measures were called for to improve the light climate of the lake. In March, 1987, as an experiment, the lake was drained by pumping out the water to facilitate fish elimination. Planktivorous and benthivorous fish species, which were predominant, were removed by seine- and electro-fishing. After the lake had refilled by seepage it was restocked by a new simple fish community comprising pike (Esox lucius) and rudd (Scardinius erythrophthalmus) only. Stacks of willow twigs (Salix) and macrophytes (roots ofNuphar lutea and seedlings ofChara globularis) were introduced into the lake as spawning grounds and refuges for the pike against cannibalism and as shelter for the zooplankton. The effects of this food web manipulation on the light climate, phytoplankton, zooplankton, fish, macrophytes, macrofauna and on the nutrient concentrations were monitored during 1987 and 1988. In summer 1987, despite of high nutrient concentrations, the phytoplankton density was low, due to control by zooplankton, causing a Secchi disk transparency of 2.5 m, the maximum depth. Chlorophyll-a concentrations were low (<5 g Chl.l^–1), blooms of cyanobacteria did not occur and a shift from rotifers to cladocerans took place. In 1988, however, also some negative effects were noticed. Macrophytes and filamentous green algae reached a much higher biomass (50–60% cover of the lake bottom) than in 1987; some species, growing through the entire water column, interfered with the lake's recreational use. Associated with the macro-vegetation and possibly with the absence of larger cyprinids, the diet of which also comprises snails, a large scale development of the snail population, among themLymnaea peregra var.ovata took place. This species is known to act as an intermediate host of the bird-parasitizing trematodeTrichobilharzia ocellata, the cercariae of which cause an itching sensation at the spot of penetration of the human skin, accompanied by rash (schistosome dermatitis or swimmers' itch); in July, 1988, about 40% of the bathers complained about this itching. A positive effect of the macrophytes and filamentous green algae was the high uptake of nitrogen, resulting in a low nitrogen concentration in the lake and growth limitation of the phytoplankton population by nitrogen in the summer of 1988. In 1988 the cladocerans were abundant in April only; and unlike in 1987, in the summer of 1988 there was a shift from cladocerans to rotifers. Therefore, only in early spring (April) zooplankton grazing controlled phytoplankton growth and in summer nitrogen limitation was the major controlling factor, keeping chlorophyll-a concentrations low.     

TGF-beta signaling: positive and negative effects on tumorigenesis.

TGF-beta binding to the cell surface triggers activation of multiple signal transduction pathways that are connected in intricate ways with each other, and with other response networks involved in sensing cellular information input. Recent data indicate that changes in signal intensity and connectivity of these pathways may underlie the complex transition of the TGF-beta pathway from tumor suppressor to oncogene during tumorigenesis.