Ontogeny and evolution of salinity tolerance in anadromous salmonids: Hormones and heterochrony

Use of estuaries and oceans by salmonids varies greatly, from no use in nonanadromous species, to movement toward the sea soon after hatching and emergence in some Pacific salmon. This variation is accompanied by large differences in the ontogeny of salinity tolerance among salmonids. Some species acquire increased salinity tolerance early in development, whereas others develop this characteristic much later, indicating there is a heterochrony (change in timing) in the development of salinity tolerance in salmonids. The basic physiological mechanisms for ion regulation in seawater (such as increased gill chloride cells, gill Na⁺,K⁺-ATPase activity, membrane permeability, and drinking rate) are common to all salmonids. What determines the differences in salinity tolerance among the salmonids is not the basic mechanisms for salt secretion but the environmental and ontogenetic control of these mechanisms. In salmonids such as pink and chum salmon that enter seawater soon after emergence, acclimation to seawater may be controlled largely by internal (ontogenetic) information. In smolting salmonids that acquire increased salinity tolerance 1–2 yr after hatching, photoperiod is the dominant environmental cue. In nonsmolting species that migrate 2–3 yr after hatching, salinity itself may be the primary stimulus for salt secretory mechanisms. Physiological changes triggered by developmental and environmental cues are mediated by endocrine factors. Treatments with cortisol, growth hormone, and insulin-like growth factor I have been shown to increase seawater tolerance of salmonids, whereas prolactin is inhibitory. Differences in developmental patterns of endocrine activity (such as secretion, binding proteins, and receptors) are hypothesized to be responsible for the differences in timing (heterochrony) of increased salinity tolerance among and within salmonid species.     

Comparative compressibility of end-member feldspars

The compressibilities of the three end-member feldspars have been determined between 1 bar and 50 kbar by single crystal X-ray diffraction techniques, using a Merrill-Bassett type diamond anvil cell with three crystals loaded simultaneously. Low albite (ordered aluminium-silicon distribution) and high sanidine (disordered Al-Si) show similar behaviour on compression, with bulk moduli (linear fit to volume-pressure data) of 0.70 and 0.67 Mbar respectively. The most compressible cell axis of all three feldspars studied is a, indicating that the major change in the feldspar framework with pressure is a shortening of the overall length of the “crankshaft chains” by reduction of T-O-T angles. Anorthite shows anomalous behaviour in that we have observed a previously unreported reversible phase transition at a pressure between 25.5 and 29.5 kbar. This transition is marked by large discontinuities in the unit cell angles and a small decrease of 0.2 percent in the cell volume with increasing pressure. The high-pressure phase is less compressible than the low-pressure phase, the bulk moduli being 0.94 and 1.06 Mbar respectively. There was no evidence of a monoclinic to triclinic inversion in sanidine that was expected to occur between 20 and 30 kbar on the basis of previous work on intermediate alkali feldspars.     

内蒙古鸡冠山斑岩钼矿床成矿时代和成矿流体研究

内蒙古鸡冠山钼矿床是西拉沐伦钼成矿带上的典型斑岩矿床。矿床产于火山侵入杂岩中,矿化类型以细脉浸染状矿化为主。对矿床5件辉钼矿样品进行了铼-锇同位素分析,获得了151.1±1.3Ma的等时线年龄,表明成矿作用发生在晚侏罗世。成矿作用可划分为三个阶段:早阶段为石英-黄铁矿阶段,发育乳白色石英和粗粒浸染状黄铁矿;中阶段包括早期石英-多金属硫化物亚阶段和晚期石英-萤石-金属硫化物亚阶段;晚阶段为石英-碳酸盐细脉,穿切早、中阶段脉体和矿物组合。鸡冠山钼矿床流体包裹体岩相学研究表明,与成矿有关的包裹体主要有六种类型:富液相、富气相、含子晶多相、含CO2三相、纯CO2及纯液相包裹体。其中,早阶段以富气和富CO2包裹体为主,中阶段多种包裹体共存,晚阶段则主要为富液包裹体。冷热台显微测温和激光拉曼显微探针(LRM)成分分析结果表明,早阶段石英中原生包裹体的均一温度480℃,盐度最高66.75%NaCleqv,包裹体气相成分富含水和CO2,液相成分则以水为主,子晶矿物有石盐、黄铜矿以及指示氧化条件的赤铁矿等,同时也说明成矿流体是富含成矿金属元素的。中阶段早期石英中的流体包裹体均一温度为320～480℃,晚期石英和萤石中的流体包裹体的均一温度为180～320℃。中阶段流体盐度介于4.65%～56.76%NaCleqv。中阶段包裹体含石盐、方解石、黄铜矿、赤铁矿等子矿物,富气相、富液相与含子晶多相包裹体共存,且具有相近的均一温度,而盐度相差悬殊,指示流体发生了沸腾。晚阶段流体的温度降低至100～180℃,盐度则低于10.86%NaCleqv,流体包裹体成分主要为水。鸡冠山钼矿成矿流体演化从早至晚为:从早阶段高温、高盐度、高氧逸度、富CO2、富成矿物质以岩浆热液为主成矿流体,演化至晚期低温、低盐度、无子晶、贫CO2、以大气降水为主的流体。沸腾作用是鸡冠山钼矿形成的重要机制。     

西秦岭勉略带陆内构造变形研究

秦岭造山带勉略缝合带是古特提斯洋盆向北俯冲形成的华北与华南最后拼接带。这个主缝合带俯冲-碰撞过程中以由北向南的一系列韧性逆冲推覆构造为特征,形成由前泥盆系、泥盆-石炭系和蛇绿混杂岩等不同构造岩片叠置的复杂构造带,碰撞时代从245Ma一直延续到230Ma左右。最近,作者对勉略缝合带内发育的韧性和脆性左行走滑剪切变形进行了研究,结果表明这些顺造山带的左行韧性走滑剪切变形带的变形时代为223±2Ma,与碰撞后花岗岩所确定的碰撞后构造环境的起始时间(225Ma)一致,显示这些韧性走滑剪切变形带是勉略带陆内变形初期变形产物。亦即华北、扬子大陆碰撞之后很快就转入陆内变形阶段,并且是以顺造山带的侧向走滑位移为主要变形方式。勉略带内顺造山带的脆性左行走滑断层的发育,表明这种顺造山带的侧向位移过程从深部到地壳浅层是一致的。因此,大陆碰撞在直接碰撞之后很快转变为顺造山带的侧向走滑位移为主的陆内变形,这种位移可能表现为两个大陆碰撞后的相对走滑,或是碰撞带中强烈变形部分顺造山带的侧向挤出,从而消减了正向碰撞所造成的地壳缩短和增厚。     

Multiple relativistic outbursts of GRS 1915+105: radio emission and internal shocks

We present 5-GHz Multi-Element Radio-Linked Interferometer Network (MERLIN) radio images of the microquasar GRS 1915+105 during two separate outbursts in 2001 March and July, following the evolution of the jet components as they move outwards from the core of the system. Proper motions constrain the intrinsic jet speed to be  >0.57 c   , but the uncertainty in the source distance prevents an accurate determination of the jet speed. No deceleration is observed in the jet components out to an angular separation of ∼300 mas. Linear polarization is observed in the approaching jet component, with a gradual rotation in position angle and a decreasing fractional polarization with time. Our data lend support to the internal shock model whereby the jet velocity increases leading to internal shocks in the pre-existing outflow before the jet switches off. The compact nuclear jet is seen to reestablish itself within 2 d, and is visible as core emission at all epochs. The energetics of the source are calculated for the possible range of distances; a minimum power of 1–10 per cent of the Eddington luminosity ( L _Edd) is required to launch the jet.     

Spatial and Temporal Variation in Brackish Wetland Seedbanks: Implications for Wetland Restoration Following <Emphasis Type="Italic">Phragmites</Emphasis> Control

Chesapeake Bay tidal wetlands are experiencing a broad-scale, aggressive invasion by the non-native, clonal grass Phragmites australis. The grass is often managed with herbicides in efforts to restore native plant communities and wildlife habitat. Management efforts, however, can act as a disturbance, resulting in increased light availability, potentially fostering reinvasion from soil seedbanks. If native vegetation establishes quickly from seedbanks, the site should have greater resiliency against invasion, while disturbed sites where native plants do not rapidly establish may be rapidly colonized by P. australis. We surveyed the soil seedbank of three vegetation cover types in five Chesapeake Bay subestuaries: areas where P. australis had been removed, where P. australis was left intact, and with native, reference vegetation. We determined the total germination, the proportion of the seedbank that was attributable to invasive species, the richness, the functional diversity, and the overall composition of the seedbanks in each of the cover types (i.e., plots). After 2 years of herbicide treatment in the P. australis removal plots, vegetation cover type impacted the total germination or the proportion of invasive species in the seedbank. In contrast, we also found that seedbank functional composition in tidal brackish wetlands was not influenced by vegetation cover type in most cases. Instead, plots within a subestuary had similar seedbank functional composition across the years and were composed of diverse functional groups. Based on these findings, we conclude that plant community recovery following P. australis removal is not seed-limited, and any lack of native vegetation recruitment is likely the result of yet-to-be-determined abiotic factors. These diverse seedbanks could lead to resilient wetland communities that could resist invasions. However, due to the prevalence of undesirable species in the seedbank, passive revegetation following invasive plant removal may speed up their re-establishment. The need for active revegetation will need to be assessed on a case-by-case basis to ensure restoration goals are achieved.     

Determination of the single-scattering albedo of a dense rayleigh-scattering atmosphere with true absorption

A procedure is developed to determine the single-scattering albedo from polarization measurements of the angle-dependent intensity at two locations within, or on the boundaries of, a homogeneous finite atmosphere which scatters radiation according to Rayleigh's law with true absorption. The density of the atmosphere need not be known.