Selective Learning in a Marsupial

Behavioural plasticity allows animals to adjust rapidly to local environmental conditions, but at the risk of erroneously changing behaviour in response to irrelevant events. Adaptive biases or predispositions constrain learning and reduce such potential costs. Preferential learning about complex biologically‐meaningful stimuli, such as predators, has been investigated in only a few systems and there have been no experimental tests for the presence of adaptive biases in a marsupial. We have previously shown that tammar wallabies (Macropus eugenii) became fearful of a model fox (Vulpes vulpes) after it was repeatedly paired with an aversive event. Tammars generalized their acquired response to a cat (Felis catus), but not to a non‐predator (juvenile goat, Capra hircus), suggesting that they might have a bias to associate predators with frightening events. The present study tested this idea directly. We used an experimental design identical to that of earlier predator‐training experiments, but substituted a model goat for the fox as the stimulus predicting a capture attempt. A control group had the same total experience of the goat and of a human with a net, but without any predictive relationship between these two events. We detected no change in behaviour towards the goat, or to any of an array of control stimuli, as a consequence of training. This finding contrasts strongly with the effects of the same pairing procedure using a fox model. Taken together, these studies provide the first evidence for an adaptive predisposition to acquire a fear of predators in marsupials. Learning processes in this group are thus evolutionarily convergent with those previously described in eutherian mammals.     

Proximal Femoral Density Patterns are Consistent with Bicentric Joint Loads

We developed an alternate method for density-based load estimation and applied it to estimate hip joint load distributions for two femora. Two-dimensional finite element models were constructed from single energy quantitative computed tomography (QCT) data. Load estimation was performed using five loading regions on the femoral head. Within each loading region, individual nodal loads, normal to the local surface, were supplied as input to the load estimation. An optimization procedure independently adjusted individual nodal load magnitudes in each region, and the magnitudes of muscle forces on the greater trochanter, such that the applied tissue stimulus approached the reference stimulus throughout the model. Dominant estimated load resultant directions were generally consistent with published experimental data for loads during gait. The estimated loads also suggested that loads near the extremes of the articulating surface may be important (even required) for development and maintenance of normal bone architecture. Estimated load distributions within nearly all regions predicted bicentric loading patterns, which are consistent with observations of hip joint incongruity. Remodeling simulations with the estimated loads predicted density distributions with features qualitatively similar to the QCT data sets. This study illustrates how applications of density-based bone load estimation can improve understanding of dominant loading patterns in other bones and joints. The prediction of bicentric loading suggests a very fine level of local adaptation to details of joint loading.     

Bipedalism and quadrupedalism in Megatheriurn: an attempt at biomechanical reconstruction

Biomechanical reconstruction is increasingly being applied to the study of the mode of life of fossil animals. Different footprints from the fossil mammal Megatherium sp., the giant ground sloth, seem to indicate that it was able to use either bipedal or quadrupedal locomotion. By means of the estimation of the body mass of the type of the species Megatherium americanum , and using the published tracks, different mechanical parameters, such as speed, Froude number, indicators of athletic ability and bending and resistance moments of the vertebral column were calculated in both bipedal and quadrupedal conditions. Results on leg parameters are not conclusive as to the kind of locomotion to which Megatherium sp. was better adapted, but the calculations on the moments of resistance of the vertebral column and on the bending moment at breaking of the femur seem to indicate that Megatherium sp. presented adaptations to bipedalism. MEGATHERIUM, mammals, legs, vertebral column, locomotion, biomechanics, reconstruction .     

Community Rates of IgG4 Antibodies to Ascaris Haemoglobin Reflect Changes in Community Egg Loads Following Mass Drug Administration

BackgroundConventional diagnostic methods for human ascariasis are based on the detection of Ascaris lumbricoides eggs in stool samples. However, studies of ascariasis in pigs have shown that the prevalence and the number of eggs detected in the stool do not correlate well with exposure of the herd to the parasite. On the other hand, an ELISA test measuring antibodies to Ascaris suum haemoglobin (AsHb) has been shown to be useful for estimating transmission intensity on pig farms. In this study, we further characterized the AsHb antigen and screened samples from a population-based study conducted in an area that is endemic for Ascaris lumbricoides in Indonesia to assess changes in AsHb antibody rates and levels in humans following mass drug administration (MDA).Conclusion/SignificanceIgG4 antibody levels to AsHb appear to reflect recent exposure to Ascaris. The antibody prevalence rate may be a useful indicator for Ascaris transmission intensity in communities that can be used to assess the impact of control measures on the force of transmission.     

Illuminating the Impact of Habitual Behaviors in Depression

Researchers have hypothesized that habitual behaviors are zeitgebers for the circadian clock. However, few studies have examined the relationship between habitual behaviors and light, the strongest zeitgeber. Depression is an ideal model in which to explore this relationship because depression is a disorder associated with disruptions in circadian biological activity, sleep, and social rhythms (or patterns of habitual behaviors). We hypothesized that individuals with fewer habitual behaviors have less average exposure to light from morning rise time to evening bedtime and that a reduction in light exposure increases the likelihood of depression. Thirty‐nine depressed and 39 never‐depressed participants wore an ambulatory light monitor and completed the Social Rhythm Metric over the course of 2 weeks. Linear and logistic regression techniques were used to calculate regression coefficients, and confidence limits based on the distribution of the product of two normal random variables were computed to test the significance of the mediation effect. Infrequent habitual behaviors were associated with a decrease in average levels of light exposure, and low levels of light increased the likelihood of depression. This mediation effect was partial; the overall number of habitual behaviors had a direct relationship with depression above and beyond the association with light exposure. Longitudinal studies are needed to empirically demonstrate the direction of relationships between each of the variables tested.     

Natal Dispersal and Philopatry in the Carnivorous Marsupial Phascogale tapoatafa (Dasyuridae)

The proximate and ultimate causes of dispersal in semelparous carnivorous marsupials (Phascogalinae) have previously been hypothesized to be maternal aggression and inbreeding avoidance, respectively. This study tests these hypotheses by exposing 26 litters of Phascogale tapoatafa to a diverse range of social and environmental conditions that potentially affect dispersal (e.g. supplemental feeding, post-weaning desertion by the mother, orphaning, and release of subadults into unoccupied habitat). The mean dispersal age was 162 ± 5.6 d, which is about 3 wk after weaning is complete. Juvenile dispersal was strongly male biased under all conditions, suggesting that extrinsic proximate causes do not adequately account for male emigration. Home range establishment by males was contingent on the presence of females. Half of the monitored daughters were philopatric, and others typically settled adjacent to the natal site, thus possibly enhancing their reproductive potential by occupying an area of known resource quality. Because philopatry increases the risk of incest, females may be selected to preferentially mate with unrelated males (immigrants), when they are available, to avoid inbreeding. If so, the presence of immigrant males would reduce the probability of locally born, related males reproducing at their natal site. Thus inbreeding avoidance by females may create local mate competition among males and select for male dispersal. Emigration also ensured that males avoided inbreeding, but, if they dispersed into unoccupied habitat, male P. tapoatafa often returned to the natal area. This 'boomerang strategy' of returning to mate with related females suggests that, in the absence of conspecifics along the dispersal path of a male, mate competition will be weak at the natal site and female mate choice will not preclude related males. Thus while inbreeding avoidance by either or both sexes is perhaps the most parsimonious explanation of male-biased emigration, dispersal patterns were apparently strongly influenced by additional factors, so that the ultimate causation of the dispersal regime may be more complex.     

Marsupial light chains: IGK with four V families in the opossum Monodelphis domestica

 A full-length and several partial cDNAs encoding IGK light chains from the marsupial South American opossum, Monodelphis domestica, were isolated and characterized. Using these clones as a starting point, the expressed IGKV repertoire was sampled by anchored polymerase chain reaction using an IGKC-specific primer. Based on nucleotide sequences of twenty unique, expressed IGKV-J combinations, there are at least four IGKV families and two J segments. Southern blot analysis revealed each IGK-V family contains multiple gene segments totaling at least thirty-five IGKV in the opossum genome. No evidence for particular, recurrent IGKV-J combinations in the opossum IGK repertoire was seen, rather the V-J combinations appeared random and diverse. Each of the four IGKV families appear more closely related to V segments from placental mammals than to each other, suggesting the duplication of the IGKV families prior to the separation of marsupials and placental mammals more than one-hundred-million years ago. Overall, the complexity of opossum light chain V segments appears greater than that found in the heavy chain, and light chains are likely to contribute significantly to Ig diversity in this species.With this report, the homologues encoding all three classes of eutherian Ig chains, IGH, IGL, and IGK, have been described in a non-placental mammal. Received: 5 April 1999 / Revised: 3 June 1999     

The role of photoperiod in the timing of reproduction in the Dasyurid Marsupial Antechinus stuartii

Summary Antechinus stuartii has one highly synchronized mating period which occurs at the same time each year. An analysis of the time of reproduction in 162 populations of A. stuartii shows that the onset of the mating period is correlated with the rate of change of photoperiod, rather than with critical photoperiodic length. The rate of change of photoperiod is different for two designated forms of this species and can be used as a predictor of these animals' reproductive timing. A rate of change model further explains the rigid and highly sunchronized nature of the mating period and, by providing a mechanism for reproductive isolation, offers an explanation for the evolution of the two forms of this species.     

石油作业习惯性流产女性细胞遗传毒性研究

目的：研究石油作业环境对女性习惯性流产的遗传毒性。方法：随机选择习惯性流产的石油作业女性38人和正常的育龄女性20人,检测其外周血淋巴细胞姐妹染色单体互换,记数SCE发生率。结果：观察组的外周血淋巴细胞SCE发生率为8．81＋0．35,明显高于对照组（P〈0．05）。结论：SCE的发生可作为石油作业习惯性流产女性染色体结构稳定性的检测指标。石油作业环境对女性生育具有遗传毒性。     

Habitual level of physical activity and cardiorespiratory endurance capacity in children

A total of 257 healthy children (140 boys, 117 girls) varying in age from 5.7 to 18.5 years underwent graded exercise tests on a treadmill. Cardiorespiratory endurance capacity was assessed by determination of the ventilatory threshold, which was defined as the highest exercise intensity before a disproportionate increase occurred in pulmonary ventilation (VE) relative to oxygen uptake (VO2). The purpose of the present study was to investigate the relationship between the habitual level of physical activity (HLPA) and the cardiorespiratory endurance capacity in children. The HLPA was assessed by a standardized questionnaire. In boys and girls HLPA increased gradually with advancing age. For the group as a whole, the boys reached the highest values for HLPA. The most active boys reached the highest value for ventilatory threshold and the lowest value was found in the less active ones, except for the age span of 12-16 years. It is concluded that more active boys showed a higher cardiorespiratory endurance capacity, as assessed by the ventilatory threshold, compared to less active ones, except during puberty. It can be postulated that during puberty this effect may be overruled by the influence of other more dominant growth-related factors. In girls, because HLPA was rather low, there was no discriminative effect of HLPA on exercise performance, as would be expected.     

习惯化用药及其策略转换的神经环路调控机制

目标导向和习惯化行为策略转换缺陷是习惯化觅药行为形成的主要原因.以往认为,前额叶皮层对负责目标导向系统的背内侧纹状体控制能力的减弱介导了习惯化行为.然而,最新研究发现,背外侧纹状体(DLS)的直接通路和间接通路可选择性调控目标导向和习惯化系统.并且,运动皮层对DLS的投射可通过双向调节多巴胺D1受体(D1DR)和D2受体(D2DR)神经元突触可塑性,调控直接通路和间接通路间的协同或拮抗作用.近期研究还发现,杏仁核作为调控情绪的关键脑区,可通过中央杏仁核与基底外侧杏仁核间的功能迁移,从而介导习惯化觅药行为中伏隔核与DLS间的功能连接.此外,纹状体内D1DR和D2DR神经元对习惯化觅药行为的调控存在竞争关系.鉴于此,本文将重点讨论伴随习惯化用药形成发生行为策略转换缺陷相关的细胞特异性和环路特异性的脑功能异常机制.     

乌本苷免疫活性物和组织中钠泵容量的关系

依赖于Na+、K+的Na+-K+-ATP酶(EC3.6.1.3,钠泵),广泛存在于哺乳类动物细胞质膜上,是催化Na+、K+跨膜主动运输的质膜酶,除维持正常的细胞内外离子浓度梯度外,对细胞能量代谢也有重要影响,许多疾病的发生是由于钠泵活性异常引起.研究证明有2种特异性的内源性钠泵抑制因子在?..     

Artificial Sweeteners in a Large Canadian River Reflect Human Consumption in the Watershed

Artificial sweeteners have been widely incorporated in human food products for aid in weight loss regimes, dental health protection and dietary control of diabetes. Some of these widely used compounds can pass non-degraded through wastewater treatment systems and are subsequently discharged to groundwater and surface waters. Measurements of artificial sweeteners in rivers used for drinking water production are scarce. In order to determine the riverine concentrations of artificial sweeteners and their usefulness as a tracer of wastewater at the scale of an entire watershed, we analyzed samples from 23 sites along the entire length of the Grand River, a large river in Southern Ontario, Canada, that is impacted by agricultural activities and urban centres. Municipal water from household taps was also sampled from several cities within the Grand River Watershed. Cyclamate, saccharin, sucralose, and acesulfame were found in elevated concentrations despite high rates of biological activity, large daily cycles in dissolved oxygen and shallow river depth. The maximum concentrations that we measured for sucralose (21 µg/L), cyclamate (0.88 µg/L), and saccharin (7.2 µg/L) are the highest reported concentrations of these compounds in surface waters to date anywhere in the world. Acesulfame persists at concentrations that are up to several orders of magnitude above the detection limit over a distance of 300 km and it behaves conservatively in the river, recording the wastewater contribution from the cumulative population in the basin. Acesulfame is a reliable wastewater effluent tracer in rivers. Furthermore, it can be used to assess rates of nutrient assimilation, track wastewater plume dilution, separate human and animal waste contributions and determine the relative persistence of emerging contaminants in impacted watersheds where multiple sources confound the usefulness of other tracers. The effects of artificial sweeteners on aquatic biota in rivers and in the downstream Great Lakes are largely unknown.     

Transient Mitochondrial Depolarizations Reflect Focal Sarcoplasmic Reticular Calcium Release in Single Rat Cardiomyocytes

Digital imaging of mitochondrial potential in single rat cardiomyocytes revealed transient depolarizations of mitochondria discretely localized within the cell, a phenomenon that we shall call “flicker.” These events were usually highly localized and could be restricted to single mitochondria, but they could also be more widely distributed within the cell. Contractile waves, either spontaneous or in response to depolarization with 50 mM K⁺, were associated with propagating waves of mitochondrial depolarization, suggesting that propagating calcium waves are associated with mitochondrial calcium uptake and consequent depolarization. Here we demonstrate that the mitochondrial flicker was directly related to the focal release of calcium from sarcoplasmic reticular (SR) calcium stores and consequent uptake of calcium by local mitochondria. Thus, the events were dramatically reduced by (a) depletion of SR calcium stores after long-term incubation in EGTA or thapsigargin (500 nM); (b) buffering intracellular calcium using BAPTA-AM loading; (c) blockade of SR calcium release with ryanodine (30 μM); and (d) blockade of mitochondrial calcium uptake by microinjection of diaminopentane pentammine cobalt (DAPPAC), a novel inhibitor of the mitochondrial calcium uniporter. These observations demonstrate that focal SR calcium release results in calcium microdomains sufficient to promote local mitochondrial calcium uptake, suggesting a tight coupling of calcium signaling between SR release sites and nearby mitochondria.