The influence of stomach distention on feeding in the nudibranch mollusk Melibe leonina

Although research on satiation has revealed much about the effect of sensory inputs on motivational state, we have yet to fully understand exactly how satiating signals influence the neural circuits underlying specific behaviors. One organism that is well suited for addressing this question is the nudibranch Melibe leonina, because its feeding activity is easily quantified, it has translucent skin that makes the stomach easy to observe, and it has large, identifiable neurons that are very suitable for subsequent analysis of the neural correlates of satiation. In this study our goal was to document the time course of satiation in Melibe, and determine if stomach distention contributes to satiation. When exposed to brine shrimp (Artemia), Melibe immediately commenced stereotypic oral hood movements to capture prey, and continued to do so for approximately five hours. Individuals eventually stopped, despite the continued presence of food, and the slowing and eventual termination of oral hood closures was correlated with distension of the stomach caused by the ingested Artemia. We obtained further evidence that stomach distension is one of the underlying causes of satiation by injecting artificial non-nutritive food into the stomach, and by cutting open part of the stomach wall to prevent it from filling and distending. The first treatment caused satiation to occur more rapidly, while the second treatment delayed satiation. Both results demonstrate that in Melibe stomach distention has a major impact on the motivation to feed. These findings provide the framework for subsequent studies designed to determine precisely how stomach distention influences feeding circuits.     

Passive drag is still a good evaluator of swimming aptitude

The passive drag (Dp) of 218 competitive swimmers was studied and related to their performance level. To study this relationship, specific attention was given to anthropometric and joint laxity (JL) variations. The Dp was measured at 1.40 m.s-1, using a mechanical winch and a strain gauge with a load cell connected to a strain bridge. Swimmers were towed in a prone position holding their breath after a maximal inspiration. Buoyancy was evaluated by the hydrostatic lift (HL), i.e., the maximal weight just necessary to maintain the swimmer in a balanced position under the water after a maximal inspiration. The JL was assessed by a standard scoring system. The Dp was related mainly to the surface area (SA) (r = 0.73 and 0.53; P less than 0.01, for males and females, respectively). For a given SA, Dp was inversely related to the performance level. The JL explained 7% of the variability of Dp. On average, Dp measured after a maximal expiration, increases of about 22% SD 3% (P less than 0.01). This increase was related to individual vital capacities (r = 0.86, P less than 0.01). As Dp was mainly related to SA and HL, it is suggested that the body exerts a large pressure effect on the water. The contribution to performance might be related to the gliding phase of swimming.     

Epigenetic Regulator CoREST Controls Social Behavior in Ants

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Twins are more different than commonly believed,but made less different by compensating behaviors

Twin studies are popular, because twins are believed to be the same/similar in genes and environmental exposures. It is well documented, however, that the firstborns are healthier at birth. We use the entire U.S. record of twin births during 1995–2000 to show that the survival duration parameters differ between twins depending on the birth order. We also find that wiser (i.e., older or educated) or married (i.e., resource-richer) mothers take more care of the weaker, which is a “compensating” behavior reducing the twin difference, as opposed to “reinforcing (the twin difference)” behavior. The systematic survival pattern difference and the mother's intervention against nature send cautions to twin studies that regard twins homogeneous to interpret their findings accordingly. Since the survival duration in our data is 97% right-censored in one year, we devise a quantile-based ‘fixed-effect’ semiparametric estimator that can handle heavy censoring, which is our methodological contribution.     

The occurrence and frequency of 2n pollen in 2x, 4x,and 6x wild,tuber-bearing Solanum species from Mexico,and Central and South America

Summary The occurrence of 2n pollen-producing plants was investigated in 187 plant introductions (PIs) of 38 wild species of tuber-bearing Solanum. These 2x, 4x, and 6x species are from Mexico, and Central and South America. The determination of 2n pollen-producing plants was conducted using acetocarmine glycerol. Plants with more than 1% large-size pollen were regarded as 2n pollen-producing plants. 2n pollen-producing plants were identified in the following species: 10 out of 12 Mexican 2x species, seven of nine South American 2x species, seven of seven Mexican and Central American 4x species, five of five South American 4x species, and five of five Mexican 6x species. The frequency of 2n pollen-producing plants varied among species at the same ploidy level, but the range of frequency, generally between 2 and 10% among species, was similar over different ploidy levels. The general occurrence of 2n pollen in both 2x and polyploid species, which are evolutionarily related, is evidence that the mode of polyploidization in tuber-bearing Solanums is sexual polyploidization. Furthermore, the frequencies of 2n pollen-producing plants in autogamous disomic polyploid species were not markably different from those of their related diploid species. It is thought that the frequent occurrence of 2n gametes with autogamy tends to disturb the fertility and consequently reduce fitness of polyploids. Thus, we propose that the breeding behavior of polyploids and the occurrence of 2n gametes may be genetically balanced in order to conserve high fitness in polyploid species in tuberbearing Solanum.Paper No. 3114 from the Laboratory of Genetics. Research supported by the College of Agriculture and Life Sciences; International Potato Center; USDA, SEA, CGRO 84-CRCR-1-1389; and Frito Lay, Inc.     

Long-time behavior of continuous time models in genetic algebras

In [2] the solutions of Andreoli's differential equation in genetic algebras with genetic realization were shown to converge to equilibria. Here we derive an explicit formula for these limits.     

Influence of Different Abutment Designs on the Biomechanical Behavior of One-Piece Zirconia Dental Implants and Their Surrounding Bone: A 3D-FEA

BackgroundIn a dental implant/bone system, the design factors affect the value and distributions of stress and deformations that plays a pivotal role on the stability, durability and lifespan of the implant/bone system.ObjectiveThe aim of this study was to compare the influence of different abutment designs on the biomechanical behavior of one-piece zirconia dental implants and their surrounding bone tissues using three-dimensional finite element analysis.MethodsA three-dimensional geometrical model of a zirconia dental implant and its surrounding bone tissue were created. The occlusal loading force applied to the prosthetic abutments was a combination of 114.6 N in the axial direction, 17.1 N in the lingual direction and 23.4 N toward the mesial direction where these components represent masticatory force of 118.2 N in the angle of approximately 75° to the occlusal plane.ResultsThe system included implant abutment Model 01 showed a decrease of 9.58%, 9.92% and 3.62% at least in the average value of maximum von Mises stress compared to Model 02, Model 03 and Model 04 respectively. The results also showed that the system included implant abutment Model 01 decreases the average value of maximum deformation of 16.96%, 7.17% and 9.47% at least compared to Model 02, Model 03 and Model 04 respectively.ConclusionThe one-piece zirconia dental implant abutment Model 01 presents a better biomechanical behavior in the peri-implant bone than others. It can efficiently distribute the applied load and present more homogeneous behavior of stress distribution and has less deformation than others, which will enhance the stability of implant/bone system and prolong its lifespan.     

Changes in the acoustic behavior of resident bottlenose dolphins near operating vessels

Maritime traffic is an issue of major ecological concern, and vessel noise may be an important source of disturbance for coastal cetaceans. In the Sado estuary, Portugal, core habitat areas of a small resident population of bottlenose dolphins (Tursiops truncatus) overlap with routes of intense maritime traffic, which presents an opportunity to assess vocal responses of these dolphins to specific vessel noise sources. Field recordings of dolphin vocalizations were made from April to November 2011, using a calibrated system. Dolphin behavior and group size were recorded, as well as the operating boat condition (no boats or specific boat type) in a 1,000 m radius. Spectral analyses of vocalizations allowed the categorization and quantitative analysis of echolocation click trains and social calls, including whistles. Mean overall call rates decreased significantly in the presence of operating vessels. Creaks (fast click trains) were significantly reduced in the presence of ferry boats. Significant differences were also observed in the whistles' minimum, maximum, and start frequencies. These changes in call emission rates and temporary shifts in whistles characteristics may be a vocal response to the proximity of operating vessels, facilitating communication in this busy, noisy estuary.     

Central Place Foraging in Nonpatchy Habitats

This paper deal with a model of optimal foraging in a habitat with arbitrary food distribution. It takes into account an arbitrary risk cost related to the distance to the animal's nest. Food acquisition and risk cost are accounted for in common units of fitness. The resulting problem is solved in the context of Calculus of Variations. The optimal duration of absence from the nest and the optimal spatial allocation of foraging time are obtained: the optimal strategy leads to separate the habitat into a region to exploit and a region to ignore. The definition of these two distinct regions depends on the relative importance of risk and food availability. With realistic risk costs, the resulting strategy indicates a highly selective behaviour when far from the nest, as observed in field studies. The model is also extended to take account of the need of returning to the nest to guard it or to feed the young.