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  • 501.
    Yahya, Saleh A.S.
    Stockholm University, Faculty of Science, Department of Zoology.
    Habitat structure, degradation and management effects on coral reef fish communities2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Coral reefs are among the most diverse and productive ecosystems on earth, and are critical to the survival of tropical marine ecosystems and sustenance of local human populations. However, coral reefs are quite vulnerable to disturbances, both natural and anthropogenic. This thesis looks at how coral reef communities have responded to climactic disturbances, particularly the 1997-98 El Niño Southern Oscillation (ENSO) and subsequent coral bleaching and mortality that affected much of the Indian Ocean, including the coastal waters of Tanzania, where the study was conducted. In particular, it investigates the effects of coral bleaching, habitat degradation and reef spatial arrangement on reef fish assemblages.

    Habitat structural complexity and spatial arrangement of reefs had an effect on reef fish communities. Fish communities showed patterns in distribution among habitats and between patch and continuous reefs. Fishes preferred live to bleached/dead or eroded coral, but trophic groups reacted differently to patch and continuous reefs. There were slight changes in fish abundance and significant changes in fish diversity on experimental, bleached branching Acropora coral plots over a period of one year. While fish abundance on one site increased shortly after a bleaching event, 6 years later fish abundance had decreased significantly. Conversely, coral reef communities in northern Tanzania had changed little over an 8-year period, with minor changes associated with the 1997-98 ENSO and the presence or absence of fisheries management. The coral reefs in the region were found to show high variability in community structure and responses of associated fish and invertebrate communities.

    The findings of this thesis indicate the importance of habitat structure and spatial arrangement of reefs, the detrimental effects of coral bleaching, and the possibility that some reefs and some (generalist) reef fish taxa may exhibit resilience to climate change.

  • 502.
    Yahya, Saleh A.S.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Zoology.
    Öhman, Marcus
    Stockholm University, Faculty of Science, Department of Zoology.
    Jiddawi, Narriman
    Mgaya, Yunus
    Fish assemblages in relation to quality, structure and configuration of staghorn coral reefs at Mafia and Zanzibar islands, TanzaniaManuscript (Other academic)
  • 503.
    Yahya, Saleh A.S.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Muhando, Christopher
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Zoology.
    Fish and sea urchin community patterns and habitat effects on Tanzanian coral reefsManuscript (preprint) (Other academic)
  • 504.
    Yamamoto, Daniel L.
    Stockholm University, Faculty of Science, Wenner-Gren Institute for Experimental Biology.
    Adrenergic signaling in insulin-sensitive tissues2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Glucose metabolism in insulin-sensitive tissues such as skeletal muscle and adipose tissue is tightly regulated by external stimuli. Metabolic changes in these tissues have direct effects on whole body metabolism. Such metabolic changes can be induced or influenced by adrenergic stimulation.

    In L6 skeletal muscle cells, we have seen that the β2-adrenergic receptor increases glycogen synthesis to the same extent as insulin. The β2-adrenergically mediated effect is independent of cyclic AMP but dependent on PI3K.

    In brown adipocytes, our data suggest that signaling from the β-adrenergic receptors consists of an acute cyclic AMP effect that is rapidly desensitized and then a prolonged signal involving PI3K.

    In skeletal muscle cells in culture, we have shown that DPI (a NADPH oxidase inhibitor) increases glucose uptake through a signaling pathway independent of NADPH oxidase and insulin signaling. DPI instead inhibits complex 1 in the mitochondrial respiratory chain, which lowers ATP levels. This activates AMPK, an activator of glucose uptake.

    Furthermore, we have developed a model system for ordered fusion of skeletal muscle cells in culture. In this system, differentiating skeletal muscle cells can be studied separately. This system is optimal for microscopy techniques and easily adaptable for micromanipulations. We have seen that the myogenic factor MyoD can have different expression of the protein in different nuclei within the same myotube. This system could be used with advantage for intracellular signaling and metabolic studies.

  • 505.
    Zadravec, Damir
    et al.
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Brolinson, Annelie
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Fisher, Rachel
    Carneheim, Claes
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Csikasz, Robert
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Bertrand-Michel, Justine
    Borén, Jan
    Guillou, Hervé
    Rudling, Mats
    Jacobsson, Anders
    Stockholm University, Faculty of Science, The Wenner-Gren Institute .
    Ablation of the very long chain fatty acid elongase ELOVL3 in mice leads to constrained lipid storage and resistance to diet-induced obesity2010In: The FASEB Journal, ISSN 0892-6638, E-ISSN 1530-6860, Vol. 24, no 11, p. 4366-4377Article in journal (Refereed)
    Abstract [en]

    Although saturated and monounsaturated very-long-chain fatty acids (VLCFA) have long been associated with undesirable effects on health, including obesity, heart failure and atherosclerosis, the physiological role of endogenous synthesis is largely unknown. The fatty acid elongase ELOVL3 is involved in the synthesis of C20-C24 saturated and monounsaturated VLCFA mainly in liver, brown and white adipose tissue and in triglyceride rich glands such as the sebaceous and meibomian glands. Here we show that ablation of ELOVL3 leads to reduced adiponectin levels, constrained expansion of adipose tissue and resistance against diet-induced obesity, a situation that is more exaggerated in female mice. Both female and male knockout mice show reduced hepatic lipogenic gene expression and triglyceride content, a situation, which is associated with, reduced expression of PPARg and its target genes. As a consequence, the VLDL-triglyceride level in serum is significantly reduced. Remarkably, despite increased energy expenditure, markedly reduced serum levels of leptin and increased expression of orexigenic peptides in the hypothalamus, the Elovl3-/- mice do not compensate by increased food intake. Thus, these results reveal that C20-C22 saturated and monounsaturated VLCFA produced by ELOVL3 are indispensable for appropriate synthesis of liver triglycerides, fatty acid uptake and storage in adipose tissue.

  • 506. Zavorka, L.
    et al.
    Brijs, J.
    Wengstrom, N.
    Wallerius, M. L.
    Näslund, Joacim
    Stockholm University, Faculty of Science, Department of Zoology.
    Koeck, B.
    Aldven, D.
    Lassus, R.
    Hojesjo, J.
    Johnsson, J. I.
    Cucherousset, J.
    Laboratory captivity can affect scores of metabolic rates and activity in wild brown trout2019In: Journal of Zoology, ISSN 0952-8369, E-ISSN 1469-7998, Vol. 307, no 4, p. 249-255Article in journal (Refereed)
    Abstract [en]

    Phenotypic scoring of wild animals under standardized laboratory conditions is important as it allows field ecologists and evolutionary biologists to understand the development and maintenance of interindividual differences in plastic traits (e.g. behaviour and physiology). However, captivity is associated with a shift from a natural familiar environment to an unfamiliar and artificial environment, which may affect estimates of plastic phenotypic traits. In this study, we tested how previous experience with laboratory environments and time spent in captivity affects behavioural (i.e. activity) and metabolic (i.e. standard and maximum metabolic rates) scoring of our model species, wild brown trout Salmo trutta. We found that individuals with previous experience of laboratory captivity (10.5 months earlier) showed higher activity in an open field test than individuals with no prior experience of laboratory captivity. Previous experience with captivity had no significant effect on metabolic rates. However, metabolic rates seemed to increase with increasing time spent in captivity prior to the collection of measurements. Although there are benefits of keeping wild animals in captivity prior to scoring, our results suggest that while allowing for sufficient acclimatization researchers should aim at minimizing time in captivity of wild animals to increase accuracy and ecological relevance of the scoring of plastic phenotypic traits.

  • 507.
    Zhang, Shi-Jin
    Stockholm University.
    Regulation of Intracellular Calcium in Brown Adipocytes1999Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Intracellular Ca2+ is considered a primary regulator of cell function. In the present study, the control and the effects of intracellular Ca2+ in brown adipocytes have been investigated. Cytosolic Ca2+ levels ([Ca2+]i) are the resultant of the activity of Ca2+ transport systems. Results concerning Ca2+transport systems in the plasma membrane, endoplasmic reticulum and mitochondria are presented.

    [Ca2+]i, monitored with Fura-2/AM, is increased when brown adipocytes are stimulated with norepinephrine (NE). The NE effect is mediated via a1-adrenoceptors and involves both release from intracellular Ca2+ stores and influx of extracellular Ca2+. The NE-induced [Ca2+]i response could be desensitized by pretreatment with NE. The desensitization is also mediated by a1-receptors and intracellularly by increased [Ca2+]i and calmodulin but not by protein kinase C. The kinetics of the desensitization are similar to those of inhibition of protein synthesis or transcription and the desensitization is associated with a comparable decrease in the number of a1-receptors.

    Mitochondrial Ca2+ levels ([Ca2+]m) were monitored within brown adipocytes with mitochondrially targeted aequorin. [Ca2+]m was not a simple reflection of [Ca2+]i; rather, evidence is presented for the existence of a b-adrenergic, cAMP-mediated signal that augments the [Ca2+]m/[Ca2+]i ratio. This signal causes the mitochondria to sequester Ca2+ even in the absence of increased cytosolic levels. Inhibition of mitochondrial Ca2+ uptake augments the cytosolic responses. Mitochondria may thus play an important role even in cytosolic Ca2+homeostasis in brown adipocytes.

    Chronic treatment of brown adipocytes with NE resulted in marked alterations of cytosolic Ca2+ handling, but the mitochondria retained their ability to sequester Ca2+during adrenergic stimulation, i.e. under conditions when UCP1 should be active.

    The effects of an increase in [Ca2+]i involve activation of a cAMP phosphodiesterase, and the presence of this component explains the unusual kinetic characteristics of norepinephrine-induced cAMP accumulation. [Ca2+]i is also involved in the regulation of gene expression: increased [Ca2+]i interacts synergistically with cAMP in the control of c-fos expression which may be of significance for regulation of cell proliferation and differentiation.

    It was concluded that Ca2+ is a primary regulator of physiological functions in brown adipocytes. The Ca2+ transport systems in brown adipocytes are involved in the regulation of intracellular and intraorganellar Ca2+. Changes of the free cytosolic Ca2+ concentration by hormone stimulation induces the activation of many physiological processes.

  • 508.
    Zidar, J.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Lovlie, H.
    Stockholm University, Faculty of Science, Department of Zoology.
    Scent of the enemy: behavioural responses to predator faecal odour in the fowl2012In: Animal Behaviour, ISSN 0003-3472, E-ISSN 1095-8282, Vol. 84, no 3, p. 547-554Article in journal (Refereed)
    Abstract [en]

    Chemical communication is used by diverse organisms in a variety of contexts and can have strong fitness consequences for the individuals involved. However, despite the extensive use of birds as models for many research areas in biology, avian olfaction has been poorly investigated. Studies on bird species that lack well-developed olfactory organs and those investigating responses to predator odours are particularly scarce. We investigated behavioural responses of the domestic fowl, Gallus gallus domesticus, a ground-living species with intermediate olfactory bulb size, to several predator and nonpredator faecal odours. We found that the birds spent less time foraging and were more vigilant when exposed to predator faecal odour compared with nonpredator faecal odour. Individuals showed a similar response when exposed to increased amounts of faeces. Taken together, our results demonstrate that domestic fowl can distinguish between herbivore and predator faecal odour, and respond to predator olfactory cues alone, without prior experience. Our results have implications for the understanding of predator-prey interactions and responses to olfactory cues in general, and for chemical communication in avian species more specifically. (C) 2012 The Association for the Study of Animal Behaviour.

  • 509.
    Åhman, Mikael
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Karlsson, Bengt
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Flight endurance in relation to adult age in the green-veined white butterfly Pieris napi2009In: Ecological Entomology, ISSN 0307-6946, E-ISSN 1365-2311, Vol. 34, p. 783-787Article in journal (Refereed)
    Abstract [en]

    Abstract. 1. The flight apparatus in butterflies as well as in other insects is costly to manufacture. Since most animals live in a world where resources are limited, trade-offs are expected and available resources must thus be allocated between flight and other functions such as reproduction.

    2. To mitigate this trade-off, previous studies have shown that butterflies can break down flight muscles in the thorax as they age in order to use muscle nutrients for reproduction.

    3. Although breakdown of flight muscles is expected to reduce flight ability, relative flight muscle ratio (thorax mass/body mass) in many butterfly species does not decrease with age.  Our aim in this study was to test the relationship between flight endurance and adult age in the green-veined white butterfly Pieris napi (L.). The tests were performed in the laboratory under five different temperatures.

    4. The results showed that age has a significant influence on butterfly flight endurance; older butterflies showed reduced flight endurance. Male butterflies fly for a longer time than females and flight endurance increase with temperature in both sexes.

  • 510.
    Åsling, Bengt
    Stockholm University, Faculty of Science.
    Molecular characterization of genes in the antibacterial response of two insect species; Hyalophora cecropia and Drosophila melanogaster1996Doctoral thesis, comprehensive summary (Other academic)
  • 511.
    Önfelt Tingvall, Tove
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Regulation of innate immunity genes in Drosophila embryos and larvae2003Doctoral thesis, comprehensive summary (Other academic)
891011 501 - 511 of 511
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