Hos många djurarter uppvisar individer olika typer av reaktioner på samma form av stress, något som brukar relateras till som antingen en aktiv eller en passiv typ av stressrespons (proactive stress coping/reactive stress coping styles). Hur olika individer reagerar tycks till stor del vara genetiskt bestämt, men påverkas även till viss del av uppväxtmiljön. Dessa olika strategier i bemötandet av hot kännetecknas av specifika fysiologiska och beteendemäs-siga reaktioner. En aktiv stressrespons innefattar t.ex. aggressivitet och en kraftigt förhöjd sympatisk aktivitet, men även en relativt liten förhöjning av plasmanivåerna av glucocorticoider (kortisol). Djur med en huvudsakligen passiv stressrespons uppvisar istället ingen eller liten aggressivitet och en-dast en svag förhöjning av den sympatiska aktiviteten, men en kraftig för-höjning av glucocorticoid nivåerna i blodet då de utsätts för ett hot. Tidigare studiers resultat tyder på att dessa olika strategier också finns hos laxfiskar. Det har nyligen påvisats att kompensationsodling av öring resulterar i för-ändringar av beteende och neuroendokrina stressresponser, effekter som visar på att kompensationsodling av öring kan resultera i en oavsiktlig selek-tion för individer med en aktiv stressrespons. Hos gnagare och fåglar har det även påvisats att överlevnadsvärdet hos de olika strategierna är beroende av födotillgång och miljö. Om kompensationsodling resulterar i en selektion för en specifik stressrespons kan detta få allvarliga konsekvenser för diversiteten hos öringpopulationerna, något som väcker en oro för att kompensationsod-ling kan leda till en förlust av genetisk variation och att den odlade stammen divergerar från den vilda fenotypiska normen, Denna oro är särskilt baserad på det faktum att kompensationsodlad laxfisk idag svarar för en betydande andel av de totala bestånden. Syftet med kompensationsodling bör vara att i möjligaste mån bevara diversiteten hos de naturliga populationerna och ett resulterande i en selektion för fisk med en viss specifik stressrespons kan ses som en direkt motverkan mot just detta syfte.
Detta arbete (1) verifierar att dessa två stressrespons strategier förekommer hos öring, (2) undersöker om olika öringpopulationer skiljer sig med avseen-de på anavseen-delen indiviavseen-der med aktiv och passiv stressrespons, (3) unavseen-dersöker om kompensationsodling påverkar fördelningen av individer med olika typer av stressrespons inom populationen, (4) samt undersöker om tidig könsmog-nad hos öringhannar är kopplad till någon av ovanstående
stresshanterings-strategier. Vidare, (5) undersöker den om det är någon skillnad i hur öring som utrycker respektive stresshanteringsstil förändrar sitt beteende när de är med om upprepade försök.
I tre av artiklarna har två olika grupper med klara, korrelerade skillnader i både fysiologiska och beteendemässiga variabler identifierats. Dessutom så har det i två av artiklarna påvisats skillnader mellan olika öringpopulationer i fråga om andelen individer som uppvisar respektive stresshanteringsstrategi. I dessa artiklar framgår det även att populationerna med odlingsbakgrund har högre andel fiskar med en aktiv (proactive) stresshanteringstil jämfört med populationerna från vilda miljöer. I artikel III så påvisas det att tidig köns-mognad inte verkar vara kopplat till stresshanteringstil, men att öringar som kläckts ur små romkorn däremot har större sannolikhet att könsmogna tidigt. Dessutom kan romkornsstorlek ha betydelse för vilken stresshanteringsstil man kommer att utveckla. Det viktigaste resultatet från den sista artikeln är att sympatisk reaktivitet var positivt korrelerat till hur kraftigt fisken föränd-rar sitt beteende vid upprepad exponering av samma test. Detta indikeföränd-rar att sympatisk aktivitet är kopplat till inlärningsförmåga eller, alternativt, benä-genhet att förändra sitt beteende.
Sammantaget så styrker resultaten i den här avhandlingen hypotesen om att olika stresshanteringsstrategier existerar hos fisk. Dessutom visar den på skillnader i frekvens av stresshanteringsstilar mellan olika populationer av öring, vilket indikerar att stresshanteringsstilar är kopplat till den adaptiva repertoaren av fenotypiskplasticitet.
ACKNOWLEDGEMENTS
The methodology in this thesis was approved by Uppsala Animal Research Ethical Committee. I was financed by the Swedish Research Council for Environment, Agriculture Sciences and Spatial Planning (FORMAS). The work with this thesis was further supported by scholarships from The Royal Swedish Academy of Sciences, FACIAS and numerous grants offered by the Uppsala University.
There are a bunch of people that I need to thank for their help and support during my work with this thesis. Svante, you are probably the best supervi-sor one could ever wish for. Thank you for always doing your best to help, discuss and inspire. Most of all, thank you for so freely sharing your unparal-leled wisdom of fish neuroendocrinology. On the other hand Erik, you are probably the best co-supervisor one could ever wish for. I can´t even imag-ine what would have happened with these data sets if you hadn´t helped me interpret and analyze them. Also, after every meeting with you I somehow always found new energy, which helped me survive some of the agony the work with this thesis sometimes brought. I would also like to thank all other friends and colleagues at IFU and EBC for your company and offered sup-port when in need of such. Especially the last remains of the “fishboys”, Tobias and PO, whom I have shared many happy moments with. Further, I would like to thank Prof. Kenneth Söderhäll for providing an excellent working environment. I also owe Prof. Olle Tottmar many thanks for being the perfect co-worker in the lab. teaching students, but perhaps most of all for his anecdotal stories about the institution.
Moreover, I would like to thank all the staff at the hatchery in Älvkarleby, especially Anna-Carin Löf, for their hospitality and assistance. Prof. Carin Magnhagen, thank you for inviting me to Umeå and especially for introduc-ing me to your peculiar perch. Dustin, thank you for the help in Älvkarleby, even though I know you enjoyed it more than is considered normal. Further, without your help the errata list would have been longer than the thesis itself. Bema I owe you serious amounts of beer, or in other words thank you for the invaluable effort with the illustrations.
I would also like to thank my homeboys Frox, Rick, G, Sim and all other close friends for not harassing me to much over the fact that I talk about fish personalities when I am drunk. To all my relatives in Värmland thank you
for always making me look forward to visiting you. Monica and Ove thank you for being super kind to me and taking such good care of my children. My Mother deserves many thanks for delivering me into this mysterious world. Father, without you I would probably never have chosen this path to begin with.
Last, but not least, Hanna - my fiancée, Julia - my daughter, and Melker - my son; all the work with this thesis would have been so easy, but so utterly irrelevant, without you. Thank you for your unconditional love, support and understanding.
“I can’t put my finger on it but there is definitely something fishy about this thesis” / Daniel, 2008
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