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911.
Frédéric Angelier Henri Weimerskirch Stéphanie Dano Olivier Chastel 《Behavioral ecology and sociobiology》2007,61(4):611-621
The ultimate factors influencing age-specific reproductive performance in birds have been widely discussed, and several hypotheses
have been suggested to explain why young/inexperienced breeders have lower reproductive success than older individuals. In
comparison, proximate factors and, particularly, hormonal mechanisms influencing age-related reproductive performance have
received lesser attention. In this paper, we examined how baseline levels of corticosterone and prolactin, two hormones involved
in reproduction, changed with age and experience in a long-lived bird, the Black-browed albatross (Thallasarche melanophris) during the brooding stage. Corticosterone levels were not linked to age, whereas prolactin levels increased until individuals
reached 15 years of age. First-time breeders had higher corticosterone levels and lower prolactin levels than experienced
ones. Corticosterone levels were not correlated with breeding experience among experienced birds, whereas prolactin levels
slightly increased with advancing experience. Among experienced breeders, there was no effect of individual quality on corticosterone
and prolactin levels. Baseline corticosterone and prolactin levels were respectively, positively and negatively correlated
to time spent fasting/brooding on the nest. Moreover, the probability of successfully fledging a chick was negatively related
to corticosterone levels, but not to prolactin levels. Elevated corticosterone levels in first time breeders may serve as
evidence for depleted body reserves resulting from lower foraging/brooding capabilities and therefore support the constraint
hypothesis. Low prolactin levels in young/inexperienced birds may be interpreted either as evidence for their lower breeding
capacities (constraint hypothesis) or for their limited breeding investment (restraint hypothesis). Finally, we report, for
the first time, the hormonal changes associated with the onset of senescence. The very old and most experienced birds, which
had the lowest probability of successfully fledging a young, displayed elevated corticosterone levels and low prolactin levels,
possibly indicating a degradation of breeding skills and/or a disruption of the endocrine system in senescent birds. 相似文献
912.
Hydrodynamic forces are an important determinant of subtidal community structure, particularly when they limit the distribution
and foraging ability of mobile consumers. We examined the effect of wave action on the rate of movement and destructive grazing
of a kelp bed by the green sea urchin (Strongylocentrotus droebachiensis) under field conditions. We measured density and rate of advance at fixed intervals along ∼100 m of a grazing front over
1 year, and quantified individual movement rates in the barrens 5–10 m behind the urchin front using a time-lapse videography.
Seasonal variation in the mean rate of advance of the front (range: 0–4 m month−1) was explained by changes in urchin density at the front (120–360 individuals m−2), which in turn varied inversely with significant wave height (0.5–2 m). Water temperature (0.8–17.6°C) had no effect on
the rate of advance or on urchin density (aggregation) at the front, except when temperature exceeded 17°C. Movement of individual
urchins also was affected by wave action: we observed a significant decrease in speed and displacement of urchins with increasing
significant wave height. Wave action had no effect on the proportion of urchins moving or the degree of linearity of their
movements. We propose that the decrease in urchin density at the front associated with increased wave action, results from
de-aggregation, which reduces the risk of dislodgement, combined with a reduction in urchin movement in barrens, which supplies
new urchins to the front. 相似文献
913.
Frédéric Mineur Mark P. Johnson Christine A. Maggs Herre Stegenga 《Marine Biology》2007,151(4):1299-1307
Hull fouling is thought to have been the vector of introduction for many algal species. We studied ships arriving at a Mediterranean
harbour to clarify the present role of commercial cargo shipping in algal introductions. A total of 31 macroalgal taxa were
identified from 22 sampled hulls. The majority of records (58%) were of species with a known cosmopolitan geographical distribution.
Due to a prevalence of cosmopolitan species and a high turnover of fouling communities, species composition of assemblages
did not appear to be influenced by the area of origin, length of ship or age of coating. In the light of the present results,
hull fouling on standard trading commercial vessels does not seem to pose a significant risk for new macroalgal species introductions.
However, a high proportion of non-cosmopolitan species found on a ship with non-toxic coating may modify this assessment,
especially in the light of the increasing use of such coatings and the potential future changes in shipping routes. 相似文献
914.
The effect of salinity on embryonic development ofSepia officinalis (cuttlefish) in the Delta Area (South Western part of The Netherlands) was investigated in 1988/1989, and compared with data concerning the distribution ofS. officinalis in the three main parts of this area: Oosterschelde, Westerschelde and Grevelingen. Embryos hatched in water collected at Yerseke (Oosterschelde), Vlissingen (Western part of the Westerschelde) and Bommenede (Grevelingen), i.e., at salinity values above 28.1, but not in water sampled at Hoedekenskerke and Hansweert (Middle and Eastern part of the Westerschelde; salinities below 22.0). Under laboratory conditions, using diluted Oosterschelde water, the highest hatching percentages ofS. officinalis were found at salinities above 29.8. Some embryos hatched at a salinity value of 26.5 but no hatching occurred at salinities below 23.9. In embryos exposed to salinity changes during late embryonic development, the developmental rate decreased at salinity values of 28.7 or less. Below 22.4 embryos with morphological malformations were found. It can be concluded that salinity is an important factor limiting the distribution ofS. officinalis in most parts of the Delta Area, with the exception of the Western part of the Westerschelde and the Grevelingen.Contribution no. 489 of the Library of the Delta Institute for Hydrobiological Research 相似文献
915.
Karine Vallee-Rehel Valérie Langlois Philippe Guerin 《Journal of Polymers and the Environment》1998,6(4):175-186
Specific polymeric material applications as bioactive molecules delivery systems involve a strictly controlled degradation of polymer matrixes. One possibility to obtain a zero-order kinetic for small molecules release consists in a simple hydrolysis of ester groups contained in the macromolecular structure. The chemical degradation can lead to the continuous surface erosion of the formulated resins without loss of their mechanical properties and to a permanent activity of the delivery systems. Hydrolysis is a very well-known reaction in the case of organic molecules containing ester groups. The mechanism seems to be more complicated when ester groups are located in macromolecular structures. With the aim of antifouling applications, acrylic acid polymers bearing lateral ester groups of different chemical structures (hydrophilic, hydrophobic, hydrolyzable) have been prepared, characterized, and immersed in water, at pH 8, and their hydrolysis has been studied. Experimental data display two parameters, at least, which must be taken into account: the reactivity of the ester groups toward hydrolysis and the hydrophilic/hydrophobic balance of the polymer. The susceptibility of the acrylic polymers to hydrolysis has been compared to the erosion characteristics of the corresponding films. The results confirm that hydrolysis is necessary to obtain a regular degradation of the films without loss of mechanical properties. A relationship has been observed between the characteristics of hydrolysis and erosion for each studied polymer. 相似文献
916.
917.
918.
919.
V. Cacheux G. Tachdjian L. Druart J. F. Oury S. Sérero P. Blot C. Nessmann 《黑龙江环境通报》1994,14(2):79-86
The major aneuploidies diagnosed prenatally involve the autosomes 13, 18, and 21, and sex chromosomes. Fluorescence in situ hybridization (FISH) allows rapid analysis of chromosome copy number in interphase cells. This prospective study evaluated the use of four commercially available centromeric DNA probes (DXZ1, DYZ1, D18Z1, and D13Z1/D21Z1) for direct analysis of uncultured amniocytes. One hundred and sixteen amniotic fluid samples were analysed by FISH and standard cytogenetics. This evaluation demonstrated that FISH with, X, Y, and 18 alpha satellite DNA probes could accurately and rapidly detect aneuploidies involving these chromosomes and could be used in any prenatal clinical laboratory. In contrast, the 13/21 alpha satellite DNA probe hybridizing both chromosomes 13 and 21 was unreliable for prenatal diagnosis in uncultured amniocytes. 相似文献
920.
Laurent P Dooms C Braekman JC Daloze D Habib-Jiwan JL Rozenberg R Termonia A Pasteels JM 《Die Naturwissenschaften》2003,90(11):524-527
Several species of Doryphorina leaf beetles from Central- and South America produce oleanane triterpene glycosides in their defensive glands. The presence of pentacyclic triterpenes in insects is intriguing since they lack the key enzymes necessary to synthesize these compounds. Since -amyrin is a common constituent of leaf waxes, we hypothesized that these leaf beetles use this compound as a precursor to their oleanane glycosides. To test this hypothesis we first confirmed the presence of -amyrin in Ipomoea batatas, the food plant of Platyphora kollari. Next, adults of P. kollari were fed for 10 days with I. batatas leaf disks painted with a solution of [2,2,3-2H3]-amyrin ([2,2,3-2H3]-1). The secretion from their defensive glands was collected and analyzed by HPLC-ESIMS. The results demonstrated that the secretion of beetles fed with an amount of [2,2,3-2H3]-amyrin corresponding to the quantity of unlabeled (natural) -amyrin present in the leaf disks contained on average 5.1% of [2,2,3-2H3]-3-O--d-glucopyranosyl-(1-->4)--d-glucuronopyranosyl-hederagenin ([2,2,3-2H3]-2), whereas the secretions of beetles fed with 10 times this amount of [2,2,3-2H3]-amyrin contained on average 23.9% of [2,2,3-2H3]-2. In both series of experiments, the percentage of labeled versus unlabeled triterpene glycoside in the secretion was positively correlated with the amount of deuterated -amyrin ingested. These results demonstrate for the first time that some leaf beetles are able to metabolize a widespread triterpenic constituent of leaf wax into more complex glycosides that are stored in their defensive glands. 相似文献