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MHC variation predicts several life history parameters in a passerine bird – the great reed warbler

Roved, Jacob (2013) BION32 20131
Degree Projects in Biology
Abstract
Abstract

Host genes for resistance to pathogens and parasites have been a subject of long-term research efforts and continue to be a hot subject in biology. Many important theories have been hypothesized through the years, and they are now being complemented by new and more detailed ones leading to increased understanding of the complex dynamics between host life history strategies and the selection induced by pathogens and parasites. The genes of the major histocompatibility complex (MHC) have been assigned a major role in the ongoing battle between hosts and parasites, and with the emergence of next generation sequencing technologies, it has become possible to characterize population-wide variation in these genes on nucleotide level.... (More)
Abstract

Host genes for resistance to pathogens and parasites have been a subject of long-term research efforts and continue to be a hot subject in biology. Many important theories have been hypothesized through the years, and they are now being complemented by new and more detailed ones leading to increased understanding of the complex dynamics between host life history strategies and the selection induced by pathogens and parasites. The genes of the major histocompatibility complex (MHC) have been assigned a major role in the ongoing battle between hosts and parasites, and with the emergence of next generation sequencing technologies, it has become possible to characterize population-wide variation in these genes on nucleotide level. In this study, 454-sequencing technology was employed to investigate the impact of within-individual MHC variation on a number of fitness-related life history parameters in an intensively monitored wild population of the passerine great reed warbler (Acrocephalus arundinaceus). The results showed that the MHC variation predicts several of the fitness related life history parameters, but with highly dimorphic effects between the sexes. Where males benefitted from high allelic and functional diversities in almost all the investigated life-history parameters, females only experienced advantageous effects on a single parameter and even suffered detrimental effects on another. Individual alleles showed very little effects in the males while a number of significant effects were found in the females. These results indicate that females have a higher immune responsiveness than males, possibly because of a regulatory effect of estrogen on immune expression. I hypothesize that the fitness interests of the males have a higher impact on the MHC variation because of a differential selection induced by the polygynous mating system in this species. A proximate mechanism that could explain the adverse effects of MHC variation in females is the risk of cross-reactivity between MHC molecules and own peptide fragments, for example heat shock proteins produced during intense physical activity. This, in combination with an increased immune responsiveness, could result in an increased susceptibility to autoimmune reactions in females. (Less)
Abstract (Danish)
Populärvetenskaplig sammanfattning.

Immunforsvarets gener har forskellig påvirkning på hanner og hunner hos drosselrørsangere

I dette studie anvendtes ny genteknologi til at undersøge diversiteten i immunforsvarets gener hos en population af drosselrørsangere i Sverige. Diversiteten hos hvert individ sammenholdtes med informationer om hvordan fuglene klarede sig igennem livet, og nogle spændende og overraskende resultater kom frem. Dette har givet en ny og mere detaljeret indsigt i betydningen af den immunogenetiske diversitet hos vilde fugle.

Biologer har igennem mange år haft teorier om at immunforsvarets gener spiller en afgørende rolle for hvordan enkelte individer klarer sig i deres liv. Det er dog først indenfor de seneste... (More)
Populärvetenskaplig sammanfattning.

Immunforsvarets gener har forskellig påvirkning på hanner og hunner hos drosselrørsangere

I dette studie anvendtes ny genteknologi til at undersøge diversiteten i immunforsvarets gener hos en population af drosselrørsangere i Sverige. Diversiteten hos hvert individ sammenholdtes med informationer om hvordan fuglene klarede sig igennem livet, og nogle spændende og overraskende resultater kom frem. Dette har givet en ny og mere detaljeret indsigt i betydningen af den immunogenetiske diversitet hos vilde fugle.

Biologer har igennem mange år haft teorier om at immunforsvarets gener spiller en afgørende rolle for hvordan enkelte individer klarer sig i deres liv. Det er dog først indenfor de seneste år at der er udviklet en teknologi som gør det muligt at undersøge diversiteten i et bestemt gen hos et stort antal individer i detaljen. Med denne nye teknologi (Next Generation Sequencing) har man i dette studie undersøgt diversiteten i de såkaldte MHC-gener hos sangfugle af arten drosselrørsanger (Acrocephalus arundinaceus). MHC er en forkortelse for Major Histocompatibility Complex, og disse gener spiller en afgørende rolle for hvilke emner som kan opdages og bekæmpes af immunforsvaret hos det enkelte individ. Det er de samme gener som f.eks. hos mennesker er afgørende for om organer frastødes af kroppen ved transplantationer. Den overordnede effekt af MHC-generne menes at være positiv, men man har også koblet dem til autoimmune sygdomme, som skyldes reaktioner hvor immunforsvaret fejlagtigt angriber kroppens egne celler.

Ved at undersøge 150 drosselrørsangere, fandt man ud af at MHC-generne har en afgørende betydning for fuglenes liv, men at der er stor forskel imellem kønnene. Hos hanner har diversiteten en direkte betydning for hvor længe hvert individ lever, hvor gode territorier de opnår, hvor mange unger de får igennem livet og hvor levedygtige ungerne er. Jo større diversitet, desto bedre klarer de sig. Det ser også ud til at de hanner som har den største diversitet i MHC-generne synger med et større repertoire når de skal tiltrække sig hunner i parringssæsonen. Hos hunnerne, derimod, fandt man at generne kun havde en betydning for hvor tidligt hunnerne ankom til ynglepladsen om foråret, og at en øget diversitet endda havde en negativ effekt på ungernes levedygtighed.

Disse forskelle imellem kønnene mener man muligvis kan tilskrives kønshormonerne testosteron og østrogen, idet man ved tidligere undersøgelser på andre arter har observeret at hunner generelt har et kraftigere udtryk af immunforsvaret end hanner. Dette kraftigere udtryk kan forårsage en forstærket effekt af MHC-generne hos hunner sammenlignet med hanner, og dermed øge risikoen for autoimmune sygdomme, med negative effekter til følge. Hos drosselrørsangerne lever hunnerne ofte i haremmer hos særligt succesfulde hanner, og dette kan medføre at hannerne har en større påvirkning på diversiteten i MHC-generne i populationen end hunnerne, idet en succesfuld han giver sine gener videre til et større antal unger end en gennemsnitlig hun. Dermed kan der let opstå en situation, hvor diversiteten i MHC-generne er mere tilpasset hannernes behov end hunnernes, og dette menes at være en sandsynlig forklaring på den udtalte forskel i effekten af MHC-generne som er observeret i dette studie.


Handledare: Helena Westerdahl och Bengt Hansson
Examensarbete för masterexamen i zooekologi, 45 hp, 2013
Biologiska institutionen, Lunds Universitet (Less)
Please use this url to cite or link to this publication:
author
Roved, Jacob
supervisor
organization
course
BION32 20131
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
4091984
date added to LUP
2013-10-15 11:15:07
date last changed
2013-10-15 11:15:07
@misc{4091984,
  abstract     = {Abstract

Host genes for resistance to pathogens and parasites have been a subject of long-term research efforts and continue to be a hot subject in biology. Many important theories have been hypothesized through the years, and they are now being complemented by new and more detailed ones leading to increased understanding of the complex dynamics between host life history strategies and the selection induced by pathogens and parasites. The genes of the major histocompatibility complex (MHC) have been assigned a major role in the ongoing battle between hosts and parasites, and with the emergence of next generation sequencing technologies, it has become possible to characterize population-wide variation in these genes on nucleotide level. In this study, 454-sequencing technology was employed to investigate the impact of within-individual MHC variation on a number of fitness-related life history parameters in an intensively monitored wild population of the passerine great reed warbler (Acrocephalus arundinaceus). The results showed that the MHC variation predicts several of the fitness related life history parameters, but with highly dimorphic effects between the sexes. Where males benefitted from high allelic and functional diversities in almost all the investigated life-history parameters, females only experienced advantageous effects on a single parameter and even suffered detrimental effects on another. Individual alleles showed very little effects in the males while a number of significant effects were found in the females. These results indicate that females have a higher immune responsiveness than males, possibly because of a regulatory effect of estrogen on immune expression. I hypothesize that the fitness interests of the males have a higher impact on the MHC variation because of a differential selection induced by the polygynous mating system in this species. A proximate mechanism that could explain the adverse effects of MHC variation in females is the risk of cross-reactivity between MHC molecules and own peptide fragments, for example heat shock proteins produced during intense physical activity. This, in combination with an increased immune responsiveness, could result in an increased susceptibility to autoimmune reactions in females.},
  author       = {Roved, Jacob},
  language     = {eng},
  note         = {Student Paper},
  title        = {MHC variation predicts several life history parameters in a passerine bird – the great reed warbler},
  year         = {2013},
}