Greinar - Hólar

Varanleg URI fyrir þennan undirflokkhttps://hdl.handle.net/20.500.11815/75

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Niðurstöður 1 - 15 af 15

Gene expression in the phenotypically plastic Arctic charr (Salvelinus alpinus): A focus on growth and ossification at early stages of development
(Wiley, 2018-11-26) Beck, Samantha V.; Räsänen, Katja; Ahi, Ehsan P.; Kristjánsson, Bjarni K.; Skúlason, Skúli; Jónsson, Zophonías Oddur; Leblanc, Camille; Líf- og umhverfisvísindastofnun (HÍ); Institute of Life and Environmental Sciences (UI); Fiskeldis- og fiskalíffræðideild (HH); Department of Aquaculture and Fish Biology (HUC); Verkfræði- og náttúruvísindasvið (HÍ); School of Engineering and Natural Sciences (UI)
Gene expression during development shapes the phenotypes of individuals. Although embryonic gene expression can have lasting effects on developmental trajectories, few studies consider the role of maternal effects, such as egg size, on gene expression. Using qPCR, we characterize relative expression of 14 growth and/or skeletal promoting genes across embryonic development in Arctic charr (Salvelinus alpinus). We test to what extent their relative expression is correlated with egg size and size at early life‐stages within the study population. We predict smaller individuals to have higher expression of growth and skeletal promoting genes, due to less maternal resources (i.e., yolk) and prioritization of energy toward ossification. We found expression levels to vary across developmental stages and only three genes (Mmp9, Star, and Sgk1) correlated with individual size at a given developmental stage. Contrary to our hypothesis, expression of Mmp9 and Star showed a non‐linear relationship with size (at post fertilization and hatching, respectively), whilst Sgk1 was higher in larger embryos at hatching. Interestingly, these genes are also associated with craniofacial divergence of Arctic charr morphs. Our results indicate that early life‐stage variation in gene expression, concomitant to maternal effects, can influence developmental plasticity and potentially the evolution of resource polymorphism in fishes.
Bacterial diversity in Icelandic cold spring sources and in relation to the groundwater amphipod Crangonyx islandicus
(Public Library of Science (PLoS), 2019-10-02) Gudmundsdottir, Ragnhildur; Kreiling, Agnes-Katharina; Kristjánsson, Bjarni Kristófer; Marteinsson, Viggó; Palsson, Snaebjorn; Líf- og umhverfisvísindadeild (HÍ); Faculty of Life and Environmental Sciences (UI); Fiskeldis- og fiskalíffræðideild (HH); Department of Aquaculture and Fish Biology (HUC); Matvæla- og næringarfræðideild (HÍ); Faculty of Food Science and Nutrition (UI); Verkfræði- og náttúruvísindasvið (HÍ); School of Engineering and Natural Sciences (UI); Heilbrigðisvísindasvið (HÍ); School of Health Sciences (UI)
Crangonyx islandicus is a groundwater amphipod endemic to Iceland, considered to have survived the Ice Ages in subglacial refugia. Currently the species is found in spring sources in lava fields along the tectonic plate boundary of the country. The discovery of a groundwater species in this inaccessible habitat indicates a hidden ecosystem possibly based on chemoautotrophic microorganisms as primary producers. To explore this spring ecosystem, we assessed its microbial diversity and analysed whether and how the diversity varied between the amphipods and the spring water, and if was dependent on environmental factors and geological settings. Isolated DNA from spring water and from amphipods was analysed using metabarcoding methods, targeting the 16S rRNA gene. Two genera of bacteria, Halomonas and Shewanella were dominating in the amphipod samples in terms of relative abundance, but not in the groundwater samples where Flavobacterium, Pseudomonas and Alkanindiges among others were dominating. The richness of the bacteria taxa in the microbial community of the groundwater spring sources was shaped by pH level and the beta diversity was shaped by geographic locations.
The mitochondrial genome of common whelk Buccinum undatum (Neogastropoda: Buccinidae)
(Informa UK Limited, 2019-01-08) Jónsson, Zophonías Oddur; Palsson, Snaebjorn; Westfall, Kristen M.; Magnúsdóttir, Hildur; Goodall, Jake; Örnólfsdóttir, Erla Björk; Líf- og umhverfisvísindadeild (HÍ); Faculty of Life and Environmental Sciences (UI); Fiskeldis- og fiskalíffræðideild (HH); Department of Aquaculture and Fish Biology (HUC); Verkfræði- og náttúruvísindasvið (HÍ); School of Engineering and Natural Sciences (UI)
The complete mitogenome of Buccinum undatum obtained from transcriptome analysis is presented here. The mitogenome is 15,265 bp in length and comprises 13 protein-coding genes, 2 ribosomal subunit genes, and 22 transfer RNAs. The complete genome was used to perform a phylogenetic analysis together with other Buccinoidea representatives with mitogenome data from GenBank.
Distribution of Recent non-marine ostracods in Icelandic lakes, springs, and cave pools
(Oxford University Press (OUP), 2019-04-25) Alkalaj, Jovana; Hrafnsdottir, Thora; Ingimarsson, Finnur; Smith, Robin J; Kreiling, Agnes-Katharina; Mischke, Steffen; Jarðvísindastofnun (HÍ); Institute of Earth Sciences (UI); Verkfræði- og náttúruvísindasvið (HÍ); School of Engineering and Natural Sciences (UI)
Ostracods in Icelandic freshwaters have seldom been researched, with the most comprehensive record from the 1930s. There is a need to update our knowledge of the distribution of ostracods in Iceland as they are an important link in these ecosystems as well as good candidates for biomonitoring. We analysed 25,005 ostracods from 44 lakes, 14 springs, and 10 cave pools. A total of 16 taxa were found, of which seven are new to Iceland. Candona candida (Müller, 1776) is the most widespread species, whereas Cytherissa lacustris (Sars, 1863) and Cypria ophtalmica (Jurine, 1820) are the most abundant, showing great numbers in lakes. Potamocypris fulva (Brady, 1868) is the dominant species in springs. While the fauna of lakes and springs are relatively distinct from each other, cave pools host species that are common in both lakes and springs. Icelandic non-marine ostracods include mostly generalist species, as well as species adapted to cold climates and resemble those of other north European countries while sharing very few species with the North American Arctic. Iceland is experiencing impacts from climate change and a booming tourism. It is possible to use selected freshwater ostracods as biomonitoring tools by constructing a detailed database of these species.
A way forward with eco evo devo: an extended theory of resource polymorphism with postglacial fishes as model systems
(Wiley, 2019-06-19) Skúlason, Skúli; Parsons, Kevin J.; Svanbäck, Richard; Räsänen, Katja; Ferguson, Moira M.; Adams, Colin E.; Amundsen, Per‐Arne; Bartels, Pia; Bean, Colin W.; Boughman, Janette W.; Englund, Göran; Guðbrandsson, Jóhannes; Hooker, Oliver E.; Hudson, Alan G.; Kahilainen, Kimmo K.; Knudsen, Rune; Kristjánsson, Bjarni K.; Leblanc, Camille; Jónsson, Zophonías Oddur; Öhlund, Gunnar; Smith, Carl; Snorrason, Sigurður S.; Fiskeldis- og fiskalíffræðideild (HH); Department of Aquaculture and Fish Biology (HUC); Líf- og umhverfisvísindadeild (HÍ); Faculty of Life and Environmental Sciences (UI); Verkfræði- og náttúruvísindasvið (HÍ); School of Engineering and Natural Sciences (UI)
A major goal of evolutionary science is to understand how biological diversity is generated and altered. Despite considerable advances, we still have limited insight into how phenotypic variation arises and is sorted by natural selection. Here we argue that an integrated view, which merges ecology, evolution and developmental biology (eco evo devo) on an equal footing, is needed to understand the multifaceted role of the environment in simultaneously determining the development of the phenotype and the nature of the selective environment, and how organisms in turn affect the environment through eco evo and eco devo feedbacks. To illustrate the usefulness of an integrated eco evo devo perspective, we connect it with the theory of resource polymorphism (i.e. the phenotypic and genetic diversification that occurs in response to variation in available resources). In so doing, we highlight fishes from recently glaciated freshwater systems as exceptionally well-suited model systems for testing predictions of an eco evo devo framework in studies of diversification. Studies on these fishes show that intraspecific diversity can evolve rapidly, and that this process is jointly facilitated by (i) the availability of diverse environments promoting divergent natural selection; (ii) dynamic developmental processes sensitive to environmental and genetic signals; and (iii) eco evo and eco devo feedbacks influencing the selective and developmental environments of the phenotype. We highlight empirical examples and present a conceptual model for the generation of resource polymorphism – emphasizing eco evo devo, and identify current gaps in knowledge.
Chironomidae fauna of springs in Iceland – assessing the ecological relevance behind Tuxen’s spring classification
(PAGEPress Publications, 2018-05-31) Kreiling, Agnes-Katharina; Olafsson, Jon S.; Palsson, Snaebjorn; Kristjansson, Bjarni K.; Fiskeldis- og fiskalíffræðideild (HH); Department of Aquaculture and Fish Biology (HUC); Líf- og umhverfisvísindadeild (HÍ); Faculty of Life and Environmental Sciences (UI); Verkfræði- og náttúruvísindasvið (HÍ); School of Engineering and Natural Sciences (UI)
In 1937, S.L. Tuxen studied the animal community of hot springs in Iceland, and classified springs according to their relative temperature into cold, tepid, and hot. Eighty years after Tuxen’s study, we revisited some of the hot springs in Skagafjörður, Northern Iceland. Our aim was to compare the invertebrate community of 1937 and today, and to assess the stability of hot spring habitats over the years. To test Tuxen’s spring classification on an ecological basis, we furthermore collected chironomid larvae from 24 springs of a broad range of temperature, with samples taken both at the surface area of the spring and at the groundwater level. The chironomid species composition of hot springs differed from that of cold and tepid springs. Whereas Cricotopus sylvestris, Arctopelopia sp., and Procladius sp. characterised the chironomid community in Icelandic hot springs, cold and tepid springs were dominated by Eukiefferiella minor, Orthocladius frigidus and Diamesa spp. Community composition analyses and the exclusive occurrence of taxa in one of the temperature classes validated the ecological relevance of Tuxen’s spring classification for the chironomid species community. Both environmental parameters and invertebrate community of Icelandic hot springs seem to be the same as 80 years ago. Although springs have the potential to provide stable habitats, they are currently under high anthropogenic pressure, and should be increasingly considered in nature conservation.
Diel activity and foraging mode of juvenile Arctic charr in fluctuating water flow
(Wiley, 2018-02-28) Larranaga, Nicolas; Valdimarsson, S.K.; Linnansaari, T.; Steingrímsson, Stefán Óli; Fiskeldis- og fiskalíffræðideild (HH); Department of Aquaculture and Fish Biology (HUC); Líf- og umhverfisvísindastofnun (HÍ); Institute of Life and Environmental Sciences (UI); Verkfræði- og náttúruvísindasvið (HÍ); School of Engineering and Natural Sciences (UI)
Streams fluctuate in water flow because of natural (e.g., rain) and human‐induced events (e.g., hydropeaking). Magnitude, frequency, and predictability of these events can have drastic consequences for fish populations. We studied how rapid modifications of water flow affect diel activity and foraging mode of juvenile Arctic charr Salvelinus alpinus in stream enclosures exposed to either stable (intermediate) or fluctuating (low vs. high) water flow. Under stable conditions, Arctic charr showed limited activity (9.4%). In fluctuating water flow, charr increased activity during low flow periods, especially during the first hours after the flow decreased, but ceased activity almost completely at high flow. Charr were mostly nocturnal, and more nocturnal at low than intermediate water flow. Fish were more mobile and swam faster during prey search and attacked prey at longer distances at low water flow. Activity and foraging mode differed between the first and second day after reduced water flow, suggesting that Arctic charr require time to adjust their foraging behaviour. This study demonstrates the importance of behavioural flexibility for population ecology in fluctuating environments such as regulated rivers.
Shell morphology and color of the subtidal whelk Buccinum undatum exhibit fine-scaled spatial patterns
(Wiley, 2018-04-10) Magnúsdóttir, Hildur; Palsson, Snaebjorn; Westfall, Kristen M.; Jónsson, Zophonías Oddur; Örnólfsdóttir, Erla Björk; Líf- og umhverfisvísindadeild (HÍ); Faculty of Life and Environmental Sciences (UI); Fiskeldis- og fiskalíffræðideild (HH); Department of Aquaculture and Fish Biology (HUC); Verkfræði- og náttúruvísindasvið (HÍ); School of Engineering and Natural Sciences (UI)
Geographical patterns in morphology can be the result of divergence among populations due to neutral or selective changes and/or phenotypic plasticity in response to different environments. Marine gastropods are ideal subjects on which to explore these patterns, by virtue of the remarkable intraspecific variation in life‐history traits and morphology often observed across relatively small spatial scales. The ubiquitous N‐Atlantic common whelk (Buccinum undatum) is well known for spatial variation in life‐history traits and morphology. Previous studies on genetic population structure have revealed that it exhibits significant differentiation across geographic distances. Within Breiðafjörður Bay, a large and shallow bay in W‐Iceland, genetic differentiation was demonstrated between whelks from sites separated by just 20 km. Here, we extended our previous studies on the common whelk in Breiðafjörður Bay by quantifying phenotypic variation in shell morphology and color throughout the Bay. We sought to test whether trait differentiation is dependent on geographic distance and/or environmental variability. Whelk in Breiðafjörður Bay displayed fine‐scale patterns of spatial variation in shape, thickness, and color diversity. Differentiation increased with increasing distance between populations, indicating that population connectivity is limited. Both shape and color varied along a gradient from the inner part of the bay in the east to the outer part in the west. Whelk shells in the innermost part of Breiðafjörður Bay were thick with an elongate shell, round aperture, and low color diversity, whereas in the outer part of the bay the shells were thinner, rounder, with a more elongate aperture and richer color diversity. Significant site‐specific difference in shell traits of the common whelk in correlation with environmental variables indicates the presence of local ecotypes and limited demographic connectivity.
Differential gene expression during early development in recently evolved and sympatric Arctic charr morphs
(PeerJ, 2018-02-07) Guðbrandsson, Jóhannes; Franzdottir, Sigridur Rut; Kristjansson, Bjarni K.; Pashay Ahi, Ehsan; Maier, Valerie H.; Kapralova, Kalina; Snorrason, Sigurður S.; Jónsson, Zophonías Oddur; Palsson, Arnar; Líf- og umhverfisvísindadeild (HÍ); Faculty of Life and Environmental Sciences (UI); Líf- og umhverfisvísindastofnun (HÍ); Institute of Life and Environmental Sciences (UI); Lífvísindasetur (HÍ); Biomedical Center (UI); Fiskeldis- og fiskalíffræðideild (HH); Department of Aquaculture and Fish Biology (HUC); Verkfræði- og náttúruvísindasvið (HÍ); School of Engineering and Natural Sciences (UI)
Phenotypic differences between closely related taxa or populations can arise through genetic variation or be environmentally induced, leading to altered transcription of genes during development. Comparative developmental studies of closely related species or variable populations within species can help to elucidate the molecular mechanisms related to evolutionary divergence and speciation. Studies of Arctic charr (Salvelinus alpinus) and related salmonids have revealed considerable phenotypic variation among populations and in Arctic charr many cases of extensive variation within lakes (resource polymorphism) have been recorded. One example is the four Arctic charr morphs in the ∼10,000 year old Lake Thingvallavatn, which differ in numerous morphological and life history traits. We set out to investigate the molecular and developmental roots of this polymorphism by studying gene expression in embryos of three of the morphs reared in a common garden set-up. We performed RNA-sequencing, de-novo transcriptome assembly and compared gene expression among morphs during an important timeframe in early development, i.e., preceding the formation of key trophic structures. Expectedly, developmental time was the predominant explanatory variable. As the data were affected by some form of RNA-degradation even though all samples passed quality control testing, an estimate of 3′-bias was the second most common explanatory variable. Importantly, morph, both as an independent variable and as interaction with developmental time, affected the expression of numerous transcripts. Transcripts with morph effect, separated the three morphs at the expression level, with the two benthic morphs being more similar. However, Gene Ontology analyses did not reveal clear functional enrichment of transcripts between groups. Verification via qPCR confirmed differential expression of several genes between the morphs, including regulatory genes such as AT-Rich Interaction Domain 4A (arid4a) and translin (tsn). The data are consistent with a scenario where genetic divergence has contributed to differential expression of multiple genes and systems during early development of these sympatric Arctic charr morphs.
Variation in the magnitude of morphological and dietary differences between individuals among populations of small benthic Arctic charr in relation to ecological factors
(Wiley-Blackwell, 2018-01-03) Kristjansson, Bjarni K.; Leblanc, Camille; Fiskeldis- og fiskalíffræðideild (HH); Department of Aquaculture and Fish Biology (HUC)
The early stages of intraspecific diversity are important for the evolution of diversification and speciation. Early stages of diversification can be seen in individual specialization, where individuals consume only a portion of the diet of the population as a whole, and how such specialization is related to phenotypic diversity within populations. Here, we study the strength of the relationship between morphological and dietary distances among individuals in eighteen populations of Icelandic small benthic charr. We furthermore studied if the strength of the relationship could be related to variation in local ecological factors these populations inhabit. In all the populations studied, there was a clear relationship between morphological and dietary distances, indicating that fish that had similar morphology were at the same time-consuming similar food items. Our findings show a systematic variation in the relationship between morphology and diet at early stages of diversification in a highly specialized small benthic charr morph. The results show the importance of fine scale comparisons within populations and furthermore the value that systematic comparisons among populations under parallel evolution can contribute toward our increased understanding of evolutionary and ecological processes.
Plio-Pleistocene phylogeography of the Southeast Asian Blue Panchax killifish, Aplocheilus panchax
(Public Library of Science (PLoS), 2017-07-25) Beck, Samantha V.; Carvalho, Gary R.; Barlow, Axel; Rüber, Lukas; Hui Tan, Heok; Nugroho, Estu; Wowor, Daisy; Mohd Nor, Siti Azizah; Herder, Fabian; Muchlisin, Zainal A.; de Bruyn, Mark; Fiskeldis- og fiskalíffræðideild (HH); Department of Aquaculture and Fish Biology (HUC); Líf- og umhverfisvísindastofnun (HÍ); Institute of Life and Environmental Sciences (UI); Verkfræði- og náttúruvísindasvið (HÍ); School of Engineering and Natural Sciences (UI)
The complex climatic and geological history of Southeast Asia has shaped this region’s high biodiversity. In particular, sea level fluctuations associated with repeated glacial cycles during the Pleistocene both facilitated, and limited, connectivity between populations. In this study, we used data from two mitochondrial and three anonymous nuclear markers to determine whether a fresh/brackish water killifish, Aplocheilus panchax, Hamilton, 1822, could be used to further understand how climatic oscillations and associated sea level fluctuations have shaped the distribution of biota within this region, and whether such patterns show evidence of isolation within palaeodrainage basins. Our analyses revealed three major mitochondrial clades within A. panchax. The basal divergence of A. panchax mitochondrial lineages was approximately 3.5 Ma, whilst the subsequent divergence timings of these clades occurred early Pleistocene (~2.6 Ma), proceeding through the Pleistocene. Continuous phylogeographic analysis showed a clear west-east dispersal followed by rapid radiation across Southeast Asia. Individuals from Krabi, just north of the Isthmus of Kra, were more closely related to the Indian lineages, providing further evidence for a freshwater faunal disjunction at the Isthmus of Kra biogeographic barrier. Our results suggest that Sulawesi, across the Wallace Line, was colonised relatively recently (~30 ka). Nuclear DNA is less geographically structured, although Mantel tests indicated that nuclear genetic distances were correlated with geographic proximity. Overall, these results imply that recent gene flow, as opposed to historical isolation, has been the key factor determining patterns of nuclear genetic variation in A. panchax, however, some evidence of historical isolation is retained within the mitochondrial genome. Our study further validates the existence of a major biogeographic boundary at the Kra Isthmus, and also demonstrates the use of widely distributed fresh/brackishwater species in phylogeographic studies, and their ability to disperse across major marine barriers in relatively recent time periods.
Lífsstíll verður ferðavara; þróun fyrirtækja í hestamennsku á Íslandi
(Viðskiptafræðideild og hagfræðideild Háskóla Íslands, viðskiptafræðideild Háskólans í Reykjavík og Seðlabanki Íslands., 2016) Sigurðardóttir, Ingibjörg; Ferðamáladeild (HH); Department of Tourism Studies (HUC)
Í þessari grein er skoðað hvað einkenni þróun fyrirtækja í hestamennsku (e. horse industry) á Íslandi og hverjar séu helstu ástæður þess að hestamennska sem áhugamál eða lífsstíll er þróuð yfir í fyrirtæki. Auk þess er rýnt í það hver sé þáttur ferðaþjónustu í þróun hestamennsku sem atvinnugreinar á Íslandi. Skoðað er hvernig hestamennska og ferðamennska mætast í fjölþættri og ört vaxandi atvinnustarfsemi, ekki síst í dreifbýli. Talsverðar rannsóknir eru til um einkenni og þróun lífsstílsfyrirtækja m.a. í ferðaþjónustu en lítið er um rannsóknir meðal slíkra fyrirtækja í hestamennsku. Rannsóknin var eigindleg og framkvæmd í gegnum hálfopin viðtöl við 16 rekstraraðila í hestamennsku. Vísbendingar komu fram um að fyrirtæki í hestamennsku gangi fremur milli kynslóða en ferðaþjónustufyrirtæki almennt, sem kemur nokkuð á óvart og vekur athygli á mögulegri sérstöðu hestamennsku og hestatengdrar ferðaþjónustu samanborið við önnur form ferðaþjónustu. Tengsl hestamennsku og ferðaþjónustu eru fjölþætt og spanna allt frá því að fyrirtæki í hestamennsku hafi tekjur sínar eingöngu af ferðaþjónustu yfir í að fyrirtækin hafi engin bein tengsl við ferðaþjónustu. Leitt er líkum að því að í þeim fyrirtækjum þar sem ferðaþjónusta hefur ekki bein áhrif innan fyrirtækjanna sjálfra hafi ferðalög tengd þeim töluverð óbein efnahagsleg áhrif innan ferðaþjónustunnar.
The developmental transcriptome of contrasting Arctic charr (Salvelinus alpinus) morphs
(F1000 Research, Ltd., 2016-12-02) Guðbrandsson, Jóhannes; Pashay Ahi, Ehsan; Franzdottir, Sigridur Rut; Kapralova, Kalina; Kristjansson, Bjarni K.; Steinhäuser, Sophie S.; Maier, Valerie H.; Johannesson, Isak M.; Snorrason, Sigurður S.; Jonsson, Zophonias O.; Palsson, Arnar; ; Líf- og umhverfisvísindadeild (HÍ); Faculty of Life and Environmental Sciences (UI); Fiskeldis- og fiskalíffræðideild (HH); Department of Aquaculture and Fish Biology (HUC); Verkfræði- og náttúruvísindasvið (HÍ); School of Engineering and Natural Sciences (UI)
Species and populations with parallel evolution of specific traits can help illuminate how predictable adaptations and divergence are at the molecular and developmental level. Following the last glacial period, dwarfism and specialized bottom feeding morphology evolved rapidly in several landlocked Arctic charr Salvelinus alpinus populations in Iceland. To study the genetic divergence between small benthic morphs and limnetic morphs, we conducted RNA-sequencing charr embryos at four stages in early development. We studied two stocks with contrasting morphologies: the small benthic (SB) charr from Lake Thingvallavatn and Holar aquaculture (AC) charr. The data reveal significant differences in expression of several biological pathways during charr development. There was also an expression difference between SB- and AC-charr in genes involved in energy metabolism and blood coagulation genes. We confirmed differing expression of five genes in whole embryos with qPCR, including lysozyme and natterin-like which was previously identified as a fish-toxin of a lectin family that may be a putative immunopeptide. We also verified differential expression of 7 genes in the developing head that associated consistently with benthic v.s.limnetic morphology (studied in 4 morphs). Comparison of single nucleotide polymorphism (SNP) frequencies reveals extensive genetic differentiation between the SB and AC-charr (~1300 with more than 50% frequency difference). Curiously, three derived alleles in the otherwise conserved 12s and 16s mitochondrial ribosomal RNA genes are found in benthic charr. The data implicate multiple genes and molecular pathways in divergence of small benthic charr and/or the response of aquaculture charr to domestication. Functional, genetic and population genetic studies on more freshwater and anadromous populations are needed to confirm the specific loci and mutations relating to specific ecological traits in Arctic charr.
Svæðisbundin áhrif íslenskra háskóla
(Háskóli Íslands, 2016-12-16) Bjarnason, Thoroddur; Edvardsson, Ingi Runar; Arnarson, Ingólfur; Skúlason, Skúli; Baldursdóttir, Kolbrún Ósk; Félagsvísinda- og lagadeild (HA); Faculty of Social Sciences and Law (UA); Viðskiptafræðideild (HÍ); Faculty of Business Administration (UI); Viðskiptafræðideild (HB); Faculty of Business (UB); Fiskeldis- og fiskalíffræðideild (HH); Department of Aquaculture and Fish Biology (HUC); Hug- og félagsvísindasvið (HA); School of Humanities and Social Sciences (UA); Félagsvísindasvið (HÍ); School of Social Sciences (UI)
Mikill munur er á menntunarstigi þjóðarinnar eftir landshlutum. Árið 2011 höfðu þannig 38% íbúa höfuðborgarsvæðisins á aldrinum 25–64 ára lokið háskólaprófi en 21–23% í flestum öðrum landshlutum. Þessi munur skýrist að hluta af takmörkuðu framboði starfa sem krefjast háskólamenntunar en að hluta af skorti á háskólafólki til starfa. Í þessari rannsókn eru upptökusvæði og áhrif háskóla á búsetuþróun metin á grundvelli gagna um allar brautskráningar frá Háskóla Íslands, Háskólanum á Bifröst, Háskólanum á Hólum og Háskólanum á Akureyri á tímabilinu 1991–2015. Niðurstöður sýna að meirihluti háskólanema sem stunda nám í heimabyggð býr þar áfram eftir brautskráningu en yfirleitt snýr mikill minnihluti háskólanema heim frá háskólanámi utan heimabyggðar. Háskólanemar í fjarnámi eru hins vegar álíka líklegir til að búa áfram í heimabyggð og þeir sem stunda staðarnám við háskóla þar sem þeir eru búsettir. Fjallað er um niðurstöðurnar í samhengi við niðurstöður erlendra rannsókna og byggðaþróun á Íslandi.
Experimental design and statistical analyses of fish growth studies
(ELSEVIER SCIENCE BV, 2015-11-01) Thorarensen, Helgi; Kubiriza, Godfrey; Imsland, Albert Kjartansson; Fiskeldis- og fiskalíffræðideild (HH); Department of Aquaculture and Fish Biology (HUC)
Every year, numerous studies are published that compare the effects of different factors on the growth of aquaculture fish. However, comparatively little attention has been given to the experimental designs of these studies - in how many rearing units should each treatment be replicated, how many fish should be in each tank (n) and how should the data be analysed. The reliability of the results increases with increased replication and n. In reality, however, the experimental design must strike a balance between limited resources and the reliability of the statistical analysis. A survey of recent publications in Aquaculture suggests, that most (83%) aquaculture growth studies apply each treatment in triplicates with an average of 26 fish in each tank (range: 4 to 100). The minimum difference that can reliably be detected with statistical analyses is determined by the number of replications of each treatment, n, the variance of the data and the number of treatments applied. In the present study, we accumulated information on the variance of data in aquaculture growth studies on different species to estimate the minimum detectable difference and to assist researchers in designing experiments effectively. These results suggest that the variance is similar for different aquaculture species and, therefore, the same designs (level of replication and n) are suitable for studies on different species of fish. The minimum difference (MDD) in mean body-mass of different treatment groups that can be detected in a typical aquaculture study (triplicates, 25 fish in each tank and average variance) with 80% statistical power (less than 20% chance of Type II error) is around 26% of the grand mean. Increasing the n from 25 to 100 will reduce the MDD to 19% of the grand mean, while a further increase in n will have comparatively lesser effect. Increasing replication to quadruplicates or sextuplicates (with n as 100), will further reduce the MDD to 16% and 12% of the grand mean respectively. MDD under 10% of the grand mean is only possible when fish for the experiment are selected within a narrow size range to reduce variance. Simulations were performed, where samples (experiments) were repeatedly drawn from artificial populations with identical distribution and with the same experimental design as is commonly used in growth studies. Two of the populations had dose-dependent responses to treatment while one population showed no response to treatment. The resulting data was analysed with a mixed model ANOVA and by fitting either polynomials or asymptotic models to the data. Contrary to earlier suggestions, the critical treatment (minimum treatment to generate maximum response) estimated with the ANOVA approached more closely the population responses than did the critical treatments estimated with the non-linear models

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