Particle retention in suspension-feeding fish after removal of filtration structures

The suspension-feeding cichlids Oreochromis aureus (blue tilapia) and Oreochromis esculentus (ngege tilapia) are able to selectively retain small food particles. The gill rakers and microbranchiospines of these species have been assumed to function as filters. However, surgical removal of these oral structures, which also removed associated mucus, did not significantly affect the total number of 11–200 μm particles ingested by the fish. This result supports the hypothesis that the branchial arch surfaces themselves play an important role in crossflow filtration. Both species selectively retained microspheres greater than 50 μm with gill rakers and microbranchiospines intact as well as removed, demonstrating that neither these structures nor mucus are necessary for size selectivity to occur during biological crossflow filtration. After removal of the gill rakers and microbranchiospines, O. esculentus retained significantly more microspheres 51–70 μm in diameter and fewer 91–130 μm microspheres compared to retention with intact structures, but the particle size selectivity of O. aureus was not affected significantly. These results support conclusions from previous computational fluid dynamics simulations indicating that particle size can have marked effects on particle trajectory and retention inside the fish oropharyngeal cavity during crossflow filtration. The substantial inter-individual variability in particle retention by suspension-feeding fish is an unexplored area of research with the potential to increase our understanding of the factors influencing particle retention during biological filtration.     

Extreme climatic events constrain space use and survival of a ground‐nesting bird

Two fundamental issues in ecology are understanding what influences the distribution and abundance of organisms through space and time. While it is well established that broad‐scale patterns of abiotic and biotic conditions affect organisms’ distributions and population fluctuations, discrete events may be important drivers of space use, survival, and persistence. These discrete extreme climatic events can constrain populations and space use at fine scales beyond that which is typically measured in ecological studies. Recently, a growing body of literature has identified thermal stress as a potential mechanism in determining space use and survival. We sought to determine how ambient temperature at fine temporal scales affected survival and space use for a ground‐nesting quail species (Colinus virginianus; northern bobwhite). We modeled space use across an ambient temperature gradient (ranging from ?20 to 38 °C) through a maxent algorithm. We also used Andersen–Gill proportional hazard models to assess the influence of ambient temperature‐related variables on survival through time. Estimated available useable space ranged from 18.6% to 57.1% of the landscape depending on ambient temperature. The lowest and highest ambient temperature categories (35 °C, respectively) were associated with the least amount of estimated useable space (18.6% and 24.6%, respectively). Range overlap analysis indicated dissimilarity in areas where Colinus virginianus were restricted during times of thermal extremes (range overlap = 0.38). This suggests that habitat under a given condition is not necessarily a habitat under alternative conditions. Further, we found survival was most influenced by weekly minimum ambient temperatures. Our results demonstrate that ecological constraints can occur along a thermal gradient and that understanding the effects of these discrete events and how they change over time may be more important to conservation of organisms than are average and broad‐scale conditions as typically measured in ecological studies.     

重金属离子对凡纳滨对虾肝胰脏、鳃丝和血液SOD活力的影响

研究了3种重金属离子(Cu²⁺、Zn²⁺、Cd²⁺)在96 h内对凡纳滨对虾(Litopenaeus vannamei)对肝胰脏、鳃丝和血液超氧化物歧化酶(SOD)活力的影响.结果表明,凡纳滨对虾SOD活力在3种重金属离子作用下随取样时间变化显著(P＜0.0),Cu²⁺在实验浓度范围内(0.1～1 mg·L^-1),肝胰脏、鳃丝和血液的SOD活力随时间延长呈一峰值变化,Zn²⁺在10 mg·L^-1时对肝胰脏表现为显著抑制作用,Cd²⁺在0. mg·L^-1时对肝胰脏和鳃丝起显著抑制作用,0.2 mg·L^-1对鳃丝SOD活力无显著变化(P＞0.0),其他浓度Zn²⁺(＜10 mg·L^-1)、Cd²⁺(＜0.2 mg·L^-1)对各组织器官SOD活力的影响随时间延长均呈现先升高后下降的趋势.3种重金属离子对凡纳滨对虾肝胰脏、鳃丝、血液SOD活力的影响呈现明显的剂量-时间效应关系.其SOD活力大小顺序为肝胰脏＞鳃丝＞血液,3种重金属离子对凡纳滨对虾伤害大小顺序为Cd²⁺＞Cu²⁺＞Zn²⁺.     

Surface ultrastructure of gill arches and gill rakers in relation to feeding of an Indian major carp, Cirrhinus mrigala

The surface ultrastructure of the gill arches and the gill rakers of an herbivorous fish, Cirrhinus mrigala was investigated by scanning electron microscopy. These structures show significant adaptive modifications associated with the food and feeding ecology of the fish. Closely lying short gill rakers and narrow inter-raker channels on the gill arches are associated to filter and retain food particles. Prominent epithelial protuberances on the gill rakers and the gill arches enable the taste buds, located at their summit, to project well above the surface of the epithelium. This could increase the efficiency of the taste buds in selective sorting of palatable food. Surface specializations of the postlingual organ are recognized adaptive modifications for selecting, trapping or holding food particles. Prominent molariform teeth born on the lower pharyngeal jaw, and the chewing pad opposite it, are associated to work together as an efficient pharyngeal mill. Mucous goblet cells are considered to elaborate mucus secretions to trap, glue and lubricate food particles for their smooth transport for swallowing.     

Prolonged apoptosis in mitochondria-rich cells of tilapia (<Emphasis Type="Italic">Oreochromis mossambicus</Emphasis>) exposed to elevated salinity

The time-course of programmed cell death (apoptosis) during reorganization of gill epithelium in salinity-stressed tilapia was analyzed using a recently developed method based on laser scanning cytometry (LSC) of dissociated gill cells. Apoptosis in mitochondria-rich cells (MRC) was distinguished from that in other cell types using Na⁺/K⁺ ATPase (NKA) as a cell-specific marker. Caspase 3/7 activity in MRC, assessed using LSC and microplate assays, increased significantly starting at 6 h of salinity stress and remained elevated for at least 5 days. This time-course of apoptosis in MRC during acute salinity stress was reflected in elevated apoptotic DNA fragmentation. In parallel to induction of apoptosis, MRC showed a pronounced shift to G2 phase of the cell cycle, which is indicative of G2/M cell cycle arrest, and an increase in NKA abundance per MRC. Unlike in MRC, apoptosis was not significantly increased in other gill cell types, although there was a small transient increase in DNA fragmentation at 6 h. G2 arrest was also observed. Overall, we interpret our data as evidence for a significant role of apoptosis in the extensive reorganization of MRC populations that takes place during salinity acclimation, perhaps similar to its well-established role during organismal development.     

TEP on the tide in killifish (<Emphasis Type="Italic">Fundulus heteroclitus</Emphasis>): effects of progressively changing salinity and prior acclimation to intermediate or cycling salinity

Transepithelial potentials (TEP) were measured in killifish, acclimated to freshwater (FW), seawater (SW), 33% SW or cycling salinities relevant to tidal cycles in an estuary, and subsequently subjected to salinity changes in progressive or random order. Random compared to progressive salinity changes in an upward or downward direction in FW- and SW-acclimated fish, respectively, did not greatly influence responses to salinity change. Fish acclimated to SW or 33% SW as well as those acclimated to cycling salinities behaved similarly (TEP more positive than +15 mV in 100% SW, decreasing to ~0 mV at 20–40% SW, and more negative than −30 mV in FW). In contrast, FW-acclimated fish displayed a less pronounced TEP response to salinity (0 mV in FW through 20% SW, increasing thereafter to values more positive than +10 mV at 100% SW). We conclude that when evaluated under estuarine tidal conditions, the killifish gill exhibits adaptive electrical characteristics, opposing Na⁺ loss at low salinity and favouring Na⁺ extrusion at high salinity, changes explained at least in part by the Cl⁻ to Na⁺ permeability ratio. Thus animals living in the estuaries can move to lower and higher salinities for short periods with little physiological disturbance, but this ability is lost after acclimation to FW.     

二倍体和三倍体太平洋牡蛎鳃扫描电镜的比较

利用扫描电子显微镜技术对二倍体和三倍体太平洋牡蛎(Crassostrea gigas)鳃的表面结构进行了观察和比较。结果显示：三倍体牡蛎鳃丝的宽度、鳃丝间的距离较二倍体大;鳃丝的微细结构比二倍体更致密;鳃丝间通过丝问连接形成的孔洞大于二倍体。这些不同表明二倍体和三倍体呼吸及摄食可能存在差异。     

Global fold and backbone dynamics of the hepatitis C virus E2 glycoprotein transmembrane domain determined by NMR

E1 and E2 are two hepatitis C viral envelope glycoproteins that assemble into a heterodimer that is essential for membrane fusion and penetration into the target cell. Both extracellular and transmembrane (TM) glycoprotein domains contribute to this interaction, but study of TM–TM interactions has been limited because synthesis and structural characterization of these highly hydrophobic segments present significant challenges. In this NMR study, by successful expression and purification of the E2 transmembrane domain as a fusion construct we have determined the global fold and characterized backbone motions for this peptide incorporated in phospholipid micelles. Backbone resonance frequencies, relaxation rates and solvent exposure measurements concur in showing this domain to adopt a helical conformation, with two helical segments spanning residues 717–726 and 732–746 connected by an unstructured linker containing the charged residues D728 and R730 involved in E1 binding. Although this linker exhibits increased local motions on the ps timescale, the dominating contribution to its relaxation is the global tumbling motion with an estimated correlation time of 12.3 ns. The positioning of the helix–linker–helix architecture within the mixed micelle was established by paramagnetic NMR spectroscopy and phospholipid-peptide cross relaxation measurements. These indicate that while the helices traverse the hydrophobic interior of the micelle, the linker lies closer to the micelle perimeter to accommodate its charged residues. These results lay the groundwork for structure determination of the E1/E2 complex and a molecular understanding of glycoprotein heterodimerization.     

Identification of an abdominal ganglion neuron antagonizing L7-driven gill contraction in Aplysia

Gill motor neuron L7-induced longitudinal shortening of the gill in Aplysia kurodai and A. juliana was suppressed when extracellular stimuli were applied to a restricted dorsal central region of the abdominal ganglion. We found a neuron there which antagonized the L7-driven contraction. Since the contraction was suppressed when the identified neuron was activated simultaneously with L7, we refer to the newly found neuron as “Anti-L7”. Anti-L7 did not change the L7 impulse generation in the abdominal ganglion. No direct synaptic connection from L7 to Anti-L7 was detected. A fluorescent dye injected into the soma of Anti-L7 revealed that the neuron sent axonal branches to the branchial nerve. These results may show that Anti-L7 antagonizes L7 at the periphery inside the gill, rather than in the abdominal ganglion. EJPs induced by L7 were unaffected by Anti-L7. Activation of Anti-L7 alone did not induce any change in tone or membrane potential of the gill musculature. The suppressive effect of Anti-L7 lasts many seconds after the cessation of a train of Anti-L7 impulses. The results may suggest that the suppression is mediated through an inhibitory neuromodulatory mechanism without inhibition of L7 itself. Accepted: 1 April 1999     

中华绒螯蟹不同部位氨基酸的测定与分析

用日立Ｈ８３５－５０氨基酸分析仪测定了健康中华绒螯蟹不同部位的氨基酸含量,结果表明其氨基酸含量以步足最高,肝（蟹黄）最低。含量高低顺序为步足＞肌肉＞鳃＞肝