Benthic structure plays an important role as shelter and feeding habitat for demersal fauna. While many studies have investigated the relationship between structural complexity of aquatic vegetation and the number of species or abundance of motile organisms, little is known of the attractiveness of submerged mangrove roots. We tested the importance of various root attributes in attracting fish species in a field experiment using different artificial mangrove units (AMUs) with PVC pipes mimicking roots to exclude interaction with other environmental and biotic factors. We manipulated length, vertical orientation, and three-dimensional structural complexity of root mimics in the AMUs to explore their effects on the fish community variables: fish abundance, number of species and community composition. Pipe length and three-dimensional structure did not have an effect on fish community variables. Vertical pipe orientation had a significant effect and AMUs with standing pipes showed higher total fish abundances and number of species than AMUs with hanging pipes. Also community composition differed greatly between AMUs with standing versus hanging pipes. At species level, demersal fish species mainly occupied AMUs with standing pipes and occurred only at very low abundances when hanging pipes dominated in the AMUs; in contrast, the semi-pelagic swimmer Sphyraena barracuda showed a trend of higher abundance in AMUs with mainly hanging pipes. When analyzed across all AMUs, fish abundances of demersal as well as semi-pelagic species decreased significantly with increasing interspatial pipe distance among AMUs, suggesting that distance to refuge may be the underlying mechanism for the observed patterns. The above findings are important in the context of the worldwide degradation of mangroves, because human alteration to mangrove vegetation affects its structure and thus composition and size of fish communities. 相似文献
Yellow band and dark spot syndromes have been frequently observed to affect coral species throughout the Caribbean within the last 10 years. These syndromes significantly impair at least three important reef-building species. Yellow band (also known as yellow blotch) appears as rings or blotches on Montastrea annularis throughout the Caribbean. The coral tissue necrosis occurs at a rate of approximately 0.6 cm/month. Transect measurements at various locations indicated that as many as 90% of M. annularis were affected by yellow band during 1997–98. Tissue samples reveal a 41–96.9% decrease in zooxanthellae/sample compared to healthy specimens, depending on distance from healthy tissue. Mitotic indices (MI) of zooxanthellae (symbiotic algae appearing as doublets) for M. annularis are 2.5%. MI in yellow band samples directly bordering healthy tissue are less than 0.9%, and zooxanthellae directly within the band bordering exposed skeleton had a mitotic index of 0.0%. This indicates impairment of zooxanthellae cell division in yellow band specimens. Zooxanthellae are not expelled and appear vacuolated and devoid of organelles. Dark spot, characterized by tissue necrosis as well as a depression of the colony surface, affects Stephanocoenia michelinii and Siderastrea siderea throughout the Caribbean. Transects showed that as many as 56% of S. michelinii and S. siderea showed signs of dark spot during 1997–98. Affected tissues of S. siderea died at a rate of 4.0 cm/month. In dark spot samples from S. siderea, the total number of zooxanthellae was 56% of that in healthy tissue; dark spot-affected specimens of S. michelinii showed a 14% decrease in the number of zooxanthellae compared to healthy tissue samples. Mitotic indices of zooxanthellae from healthy specimens of S. sidereawere 1.20% compared to 0.40% in dark spot samples. Mitotic indices of healthy S. michelinii were 1.54% compared to 0.23% in dark spot samples, also indicating a decrease in algal cell division. Zooxanthellae from dark spot tissue are swollen and darker in pigment. Due to the changes that are evident in the symbiotic algae, we suggest that both syndromes act primarily on the zooxanthellae symbiont, and secondarily on the cnidarian host. 相似文献
Poleward range extensions of coral reef species can reshuffle temperate communities by generating competitive interactions that did not exist previously. However, novel environmental conditions and locally adapted native temperate species may slow tropical invasions by reducing the ability of invaders to access local resources (e.g. food and shelter). We test this hypothesis on wild marine fish in a climate warming hotspot using a field experiment encompassing artificial prey release. We evaluated seven behaviours associated with foraging and aggressive interactions in a common range-extending coral reef fish (Abudefduf vaigiensis) and a co-shoaling temperate fish (Microcanthus strigatus) along a latitudinal temperature gradient (730 km) in SE Australia. We found that the coral reef fish had reduced foraging performance (i.e. slower prey perception, slower prey inspection, decreased prey intake, increased distance to prey) in their novel temperate range than in their subtropical range. Furthermore, higher abundance of temperate fishes was associated with increased retreat behaviour by coral reef fish (i.e. withdrawal from foraging on released prey), independent of latitude. Where their ranges overlapped, temperate fish showed higher foraging and aggression than coral reef fish. Our findings suggest that lower foraging performance of tropical fish at their leading range edge is driven by the combined effect of environmental factors (e.g. lower seawater temperature and/or unfamiliarity with novel conditions in their extended temperate ranges) and biological factors (e.g. increased abundance and larger body sizes of local temperate fishes). Whilst a future increase in ocean warming is expected to alleviate current foraging limitations in coral reef fishes at leading range edges, under current warming native temperate fishes at their trailing edges appear able to slow the range extension of coral reef fishes into temperate ecosystems by limiting their access to resources.
Objective: To further address the function of the Y5 receptor in energy homeostasis, we investigated the effects of a novel spironolactone Y5 antagonist in diet-induced obese (DIO) mice. Methods and Procedures: Male C57BL/6 or Npy5r−/− mice were adapted to high-fat (HF) diet for 6–10 months and were submitted to three experimental treatments. First, the Y5 antagonist at a dose of 10 or 30 mg/kg was administered for 1 month to DIO C57BL/6 or Npy5r−/− mice. Second, the Y5 antagonist at 30 mg/kg was administered for 1.5 months to DIO C57BL/6 mice, and insulin sensitivity was evaluated using an insulin tolerance test. After a recovery period, nuclear magnetic resonance measurement was performed to evaluate body composition. Third, DIO mice were treated with the Y5 antagonist alone, or in combination with 10% food restriction, or with another anorectic agent, sibutramine at 10 mg/kg, for 1.5 months. Plasma glucose, insulin, and leptin levels, and adipose tissue weights were quantified. Results: The spironolactone Y5 antagonist significantly reduced body weight in C57BL DIO mice, but not in Npy5r−/− DIO mice. The Y5 antagonist produced a fat-selective loss of body weight, and ameliorated obesity-associated insulin resistance in DIO mice. In addition, the Y5 antagonist combined with either food restriction or sibutramine tended to produce greater body weight loss, as compared with single treatment. Discussion: These findings demonstrate that the Y5 receptor is an important mediator of energy homeostasis in rodents. 相似文献
Alcohol consumption of college students has a fluctuating nature, which might impact the measurement of intervention effects. By using 25 follow-up time-points, this study tested whether intervention effects are robust or might vary over time.
Methods
Data were used from a two-arm parallel group randomized controlled trial applying ecological momentary assessment (EMA) with 30 data time-points in total. Students between 18 and 24 years old who reported heavy drinking in the past six months and who were ready to change their alcohol consumption were randomly assigned to the experimental (n = 456: web-based brief alcohol intervention) and control condition (n = 451: no intervention). Outcome measures were weekly alcohol consumption, frequency of binge drinking, and heavy drinking status.
Results
According to the intention-to-treat principle, regression analyses revealed that intervention effects on alcohol consumption varied when exploring multiple follow-up time-points. Intervention effects were found for a) weekly alcohol consumption at 1, 2, 3, 4, and 7 weeks follow-up, b) frequency of binge drinking at 1, 2, 7, and 12 weeks follow-up, and c) heavy drinking status at 1, 2, 7, and 16 weeks follow-up.
Conclusions
This research showed that the commonly used one and six month follow-up time-points are relatively arbitrary and not using EMA might bring forth erroneous conclusions on the effectiveness of interventions. Therefore, future trials in alcohol prevention research and beyond are encouraged to apply EMA when assessing outcome measures and intervention effectiveness.
Risk assessment for the deliberate release of microorganisms into the environment is traditionally carried out on a case-by-case basis. In a similar approach to that used when assessing human pathogenicity, we propose an alternative approach by introducing risk classes to facilitate or complement this type of risk assessment. These consider several sets of scenarios that address the different values that need to be protected. Examples of this approach include risk-class definitions for soil fertility and biodiversity. 相似文献
Two cDNAs, GluClα and GluClβ, encoding glutamate-gated chloride channel subunits that represent targets of the avermectin
class of antiparasitic compounds, have recently been cloned from Caenorhabditis elegans (Cully et al., Nature, 371, 707–711, 1994). Expression studies in Xenopus oocytes showed that GluClα and GluClβ have pharmacological profiles distinct from the glutamate-gated cation channels as
well as the γ-aminobutyric acid (GABA)- and glycine-gated chloride channels. Establishing the evolutionary relationship of
related proteins can clarify properties and lead to predictions about their structure and function. We have cloned and determined
the nucleotide sequence of the GluClα and GluClβ genes. In an attempt to understand the evolutionary relationship of these
channels with the members of the ligand-gated ion channel superfamily, we have performed gene structure comparisons and phylogenetic
analyses of their nucleotide and predicted amino acid sequences. Gene structure comparisons reveal the presence of several
intron positions that are not found in the ligand-gated ion channel superfamily, outlining their distinct evolutionary position.
Phylogenetic analyses indicate that GluClα and GluClβ form a monophyletic subbranch in the ligand-gated ion channel superfamily
and are related to vertebrate glycine channels/receptors. Glutamate-gated chloride channels, with electrophysiological properties
similar to GluClα and GluClβ, have been described in insects and crustaceans, suggesting that the glutamate-gated chloride
channel family may be conserved in other invertebrate species. The gene structure and phylogenetic analyses in combination
with the distinct pharmacological properties demonstrate that GluClα and GluClβ belong to a discrete ligand-gated ion channel
family that may represent genes orthologous to the vertebrate glycine channels.
Received: 30 September 1996 / Accepted: 15 November 1996 相似文献
Soda lakes contain high concentrations of sodium carbonates resulting in a stable elevated pH, which provide a unique habitat to a rich diversity of haloalkaliphilic bacteria and archaea. Both cultivation-dependent and -independent methods have aided the identification of key processes and genes in the microbially mediated carbon, nitrogen, and sulfur biogeochemical cycles in soda lakes. In order to survive in this extreme environment, haloalkaliphiles have developed various bioenergetic and structural adaptations to maintain pH homeostasis and intracellular osmotic pressure. The cultivation of a handful of strains has led to the isolation of a number of extremozymes, which allow the cell to perform enzymatic reactions at these extreme conditions. These enzymes potentially contribute to biotechnological applications. In addition, microbial species active in the sulfur cycle can be used for sulfur remediation purposes. Future research should combine both innovative culture methods and state-of-the-art ‘meta-omic’ techniques to gain a comprehensive understanding of the microbes that flourish in these extreme environments and the processes they mediate. Coupling the biogeochemical C, N, and S cycles and identifying where each process takes place on a spatial and temporal scale could unravel the interspecies relationships and thereby reveal more about the ecosystem dynamics of these enigmatic extreme environments. 相似文献