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排序方式: 共有345条查询结果,搜索用时 15 毫秒
131.
132.
Casey L. Yanos Eeke P. Haanstra Fiona Colgan Carey Sorsha A. Passmore Johan S. Eklf Ulf Bergstrm Joakim P. Hansen Michael C. Fontaine Martine E. Maan Britas Klemens Eriksson 《Ecology and evolution》2021,11(18):12485
Intraspecific niche differentiation can contribute to population persistence in changing environments. Following declines in large predatory fish, eutrophication, and climate change, there has been a major increase in the abundance of threespine stickleback (Gasterosteus aculeatus) in the Baltic Sea. Two morphotype groups with different levels of body armor—completely plated and incompletely plated—are common in coastal Baltic Sea habitats. The morphotypes are similar in shape, size, and other morphological characteristics and live as one apparently intermixed population. Variation in resource use between the groups could indicate a degree of niche segregation that could aid population persistence in the face of further environmental change. To assess whether morphotypes exhibit niche segregation associated with resource and/or habitat exploitation and predator avoidance, we conducted a field survey of stickleback morphotypes, and biotic and abiotic ecosystem structure, in two habitat types within shallow coastal bays in the Baltic Sea: deeper central waters and shallow near‐shore waters. In the deeper waters, the proportion of completely plated stickleback was greater in habitats with greater biomass of two piscivorous fish: perch (Perca fluviatilis) and pike (Esox lucius). In the shallow waters, the proportion of completely plated stickleback was greater in habitats with greater coverage of habitat‐forming vegetation. Our results suggest niche segregation between morphotypes, which may contribute to the continued success of stickleback in coastal Baltic Sea habitats. 相似文献
133.
C. Joakim Ek Mark D. Habgood Jennifer K. Callaway Ross Dennis Katarzyna M. Dziegielewska Pia A. Johansson Ann Potter Benjamin Wheaton Norman R. Saunders 《PloS one》2010,5(8)
Cellular mechanisms of secondary damage progression following spinal cord injury remain unclear. We have studied the extent of tissue damage from 15 min to 10 weeks after injury using morphological and biochemical estimates of lesion volume and surviving grey and white matter. This has been achieved by semi-quantitative immunocytochemical methods for a range of cellular markers, quantitative counts of white matter axonal profiles in semi-thin sections and semi-quantitative Western blot analysis, together with behavioural tests (BBB scores, ledged beam, random rung horizontal ladder and DigiGait™ analysis). We have developed a new computer-controlled electronic impactor based on a linear motor that allows specification of the precise nature, extent and timing of the impact. Initial (15 min) lesion volumes showed very low variance (1.92±0.23 mm3, mean±SD, n = 5). Although substantial tissue clearance continued for weeks after injury, loss of grey matter was rapid and complete by 24 hours, whereas loss of white matter extended up to one week. No change was found between one and 10 weeks after injury for almost all morphological and biochemical estimates of lesion size or behavioural methods. These results suggest that previously reported apparent ongoing injury progression is likely to be due, to a large extent, to clearance of tissue damaged by the primary impact rather than continuing cell death. The low variance of the impactor and the comprehensive assessment methods described in this paper provide an improved basis on which the effects of potential treatment regimes for spinal cord injury can be assessed. 相似文献
134.
135.
Tomas Näsström Mikael Karlsson Lars Lannfelt Joakim Bergström 《Biochemical and biophysical research communications》2009,378(4):872-437
Recently, the aldehyde 4-oxo-2-nonenal (ONE) was identified as a product of lipid peroxidation and found to be an effective protein modifier. In this in vitro study we investigated structural implications of the interaction between ONE and α-synuclein, a protein which forms intraneuronal inclusions in neurodegenerative disorders such as Parkinson’s disease and dementia with Lewy bodies. Our results demonstrate that ONE induced an almost complete conversion of monomeric α-synuclein into 40-80 nm wide and 6-8 nm high soluble β-sheet-rich oligomers with a molecular weight of ∼2000 kDa. Furthermore, the ONE-induced α-synuclein oligomers displayed a high stability and were not sensitive to treatment with sodium dodecyl sulfate, indicating that ONE stabilized the oligomers by cross-linking individual α-synuclein molecules. Despite prolonged incubation the oligomers did not continue to aggregate into a fibrillar state, thus suggesting that these α-synuclein species were not on a fibrillogenic pathway. 相似文献
136.
Magdalena Nutu Birgitta Weijdegård Peter Thomas Ann Thurin-Kjellberg Håkan Billig DG Joakim Larsson 《Reproductive biology and endocrinology : RB&E》2009,7(1):89
Background
The controlled beating of cilia of the fallopian tube plays an important role in facilitating the meeting of gametes and subsequently transporting the fertilized egg to its implantation site. Rapid effects of progesterone on ciliary beat frequency have been reported in the fallopian tubes of cows, but the identity of the receptors mediating this non-genomic action of progesterone is not known. We recently identified a member of the non-genomic membrane progesterone receptor family, mPR gamma, as a candidate for mediating these actions of progesterone. Here, we investigated the possible presence of a related receptor, mPR beta, in the fallopian tubes of mice and women as well as the possible hormonal regulation of mPR beta and gamma. 相似文献137.
The effects of nutrients on aquatic ecosystems are widespread and trying to understand the reaction of different response indicators is a complex issue. In this study, we used a data set of 21 stream site-samples situated in southern Sweden to assess the strength of single and multimetric indices and multivariate approaches for detecting the effects of nutrient enrichment on stream ecosystems using benthic macroinvertebrate communities. Our results showed both multimetric and multivariate approaches to be reliable tools for detecting the effects of nutrient enrichment on stream macroinvertebrate communities, superior to single metric approaches. In particular, the multimetric DJ index and the multivariate CA scores were sensitive (high coefficients of determination) to the stressor gradient and had high precision (low error). The Saprobic index was the ‘best’ of the six single metric approaches tested here. However, due to differences in the way taxa lists are managed in multimetric and multivariate approaches, we recommend that, if possible, both methods should be used in assessing the effects of nutrient enrichment of stream ecosystems. 相似文献
138.
E. Petter Axelsson Joakim Hjältén Carri J. LeRoy Riitta Julkunen-Tiitto Anders Wennström Gilles Pilate 《Ecosystems》2010,13(7):1049-1059
In addition to potential benefits, biotechnology in silviculture may also be associated with environmental considerations,
including effects on organisms associated with the living tree and on ecosystems and processes dependent on tree residue.
We examined whether genetic modification of lignin characteristics (CAD and COMT) in Populus sp. affected leaf litter quality, the decomposition of leaf litter, and the assemblages of aquatic insects colonizing the
litter in three natural streams. The decomposition of leaf litter from one of the genetically modified (GM) lines (CAD) was
affected in ways that were comparable over streams and harvest dates. After 84 days in streams, CAD-litter had lost approximately
6.1% less mass than the non-GM litter. Genetic modification also affected the concentration of phenolics and carbon in the
litter but this only partially explained the decomposition differences, suggesting that other factors were also involved.
Insect community analyses comparing GM and non-GM litter showed no significant differences, and the two GM litters showed
differences only in the 84-day litterbags. The total abundance and species richness of insects were also similar on GM and
non-GM litter. The results presented here suggest that genetic modifications in trees can influence litter quality and thus
have a potential to generate effects that can cross ecosystem boundaries and influence ecosystem processes not directly associated
with the tree. Overall, the realized ecological effects of the GM tree varieties used here were nevertheless shown to be relatively
small. 相似文献
139.
Massimiliano Cardinale Jacob Hagberg Henrik Svedäng Valerio Bartolino Todd Gedamke Joakim Hjelm Patrik Börjesson Fredrik Norén 《Population Ecology》2010,52(2):251-262
Over the past century, advances in technology and historical events such as climate change have resulted in significant changes
in the exploitation pattern, population sizes and the potential yield of fish stocks. These variations provide contrast in
the data that improves our knowledge on population dynamics and our ability to develop management strategies for long-term
sustainable exploitation. In this study, we use a standardized scientific trawl survey to obtain a historical time series
(1901–2007) of relative abundance, recruitment and size structure for plaice in the Kattegat–Skagerrak. Our work extends the
available time series by more than 80 years so that the evaluation of trends is more informative than is possible from the
current assessment. We show that the current adult biomass is approximately 40% of the maximum observed at the beginning of
the century and during the 1960s. The average maximum individual length has been reduced by 10 cm over the studied time period.
An analysis of trends in mean length indicates that fishing mortality was variable during the first half of the century and
has increased steadily over the past 20 years. Recruitment has been the highest on record during recent years, suggesting
that the alleged link between coastal environmental degradation and juvenile survival is of low importance. The overall findings
of our work will provide managers with a historical perspective on the population dynamics of the stock, which will support
the long-term management of plaice in the Kattegat–Skagerrak. 相似文献
140.
The phylogenetic position of onychophorans is still being debated; however, most phylogenies suggest that onychophorans are a sister group to the arthropods. Here we have analysed neurogenesis in the brain of the onychophoran Euperipatoides kanangrensis. We show that the development of the onychophoran brain is considerably different from arthropods. Neural precursors seem to be generated at random positions rather than in distinct spatio-temporal domains as has been shown in insects and chelicerates. The different mode of neural precursor formation is reflected in the homogenous expression of the proneural and neurogenic genes. Furthermore, the morphogenetic events that generate the three-dimensional structure of the onychophoran brain are significantly different from arthropods. Despite the different mode of neural precursor formation in insects and chelicerates (neuroblasts versus neural precursor groups), brain neurogenesis shares more similarities in these arthropods as compared to the onychophoran. Our data show that the developmental processes that generate the brain have considerably diverged in onychophorans and arthropods. 相似文献