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Screening MHC alleles of Great Reed Warblers (Acrocephalus arundinaceus) from hatching to breeding using 454-sequencing technique

Taşkent, Recep Özgür (2012) BION34 20121
Degree Projects in Biology
Abstract
Abstract
The Major histocompatibility complex (MHC) plays a central role in the vertebrate immune system. The protein products of MHC genes present foreign peptides to T-cells, which then initiates the appropriate immune responses. MHC genes show extreme level of polymorphism and this was suggested to be maintained by selective pressures exerted by various parasites. Although associations between MHC and different fitness components have been revealed previously in many species, the effects of MHC exclusively on juvenile mortality, where the infection-related mortality is highest, and thus on recruitment have rarely been investigated. In this study, we screened MHC class I alleles of great reed warblers (Acrocephalus arundinaceus) from... (More)
Abstract
The Major histocompatibility complex (MHC) plays a central role in the vertebrate immune system. The protein products of MHC genes present foreign peptides to T-cells, which then initiates the appropriate immune responses. MHC genes show extreme level of polymorphism and this was suggested to be maintained by selective pressures exerted by various parasites. Although associations between MHC and different fitness components have been revealed previously in many species, the effects of MHC exclusively on juvenile mortality, where the infection-related mortality is highest, and thus on recruitment have rarely been investigated. In this study, we screened MHC class I alleles of great reed warblers (Acrocephalus arundinaceus) from hatching to breeding in order to reveal potential effects of MHC on recruitment success of fledglings. The study is based on a breeding population of great reed warblers located at Lake Kvismaren in Southern Central Sweden, and for the cohort that we gathered the samples from (the 1998 cohort) we had a good estimate of recruitment rate via an extensive censusing through the species’ whole Swedish breeding range. Hence, any non-recruited individual was assumed to be dead. We expected to find that MHC genes have effects on recruitment success of juveniles. More specifically, we expected that: either (i) certain MHC alleles, as they may provide resistance to certain pathogens and/or (ii) overall MHC diversity (the total number of MHC alleles) in an individual, as it may provide a general resistance against a variety of pathogens, affect recruitment success of the young. Additionally, we used a UniFrac analysis to investigate whether the cumulative MHC profiles of individuals cluster themselves according to recruitment success (being recruited or not-recruited). We used a next generation sequencing technique (454-pyrosequencing) to MHC genotype individuals in this study. Although the pyrosequencing reaction is relatively more error-prone than the classical Sanger sequencing, with proper filtering we reached a 92.7 % repeatability ratio, indicating a reliable genotyping. We found two potentially susceptibility alleles as these alleles were associated with lower recruitment success. Moreover, we failed to find evidence for heterozygote advantage; individuals with more MHC alleles did not have higher recruitment success. However, MHC diversity-recruitment relationship revealed an odd result, as individuals with only one MHC allele –which was fixed in the population and thus present in all individuals- had significantly higher survival than the individuals with more MHC alleles regardless of the number of additional alleles. Potential explanations were suggested for this odd result. The most plausible explanation is that we failed to amplify some MHC class I alleles due to restricted feature of the primer set that we used. Hence, further studies are needed to reach more conclusive results on the effect of particular MHC alleles and MHC diversity on recruitment success of juvenile great reed warblers.

Popular science summary:

Immunity Genes partly explain if birds will survive their first winter in tropical Africa

Immune system of vertebrates resembles gate guards of a castle, considering the castle is the body. Well, despite not being wrong, it is not the full-story. There are private detectives too, wandering inside the castle, looking for thieves. Here, private detectives are specialized immune cells and thieves are pathogens. We found that a group of these private detectives, called as major histocompatibility complex (MHC), partly explain the survival success of juvenile birds, great reed warblers (Acrocephalus arundinaceus) in their first winter in Africa.
Belonging to the department of private detectives, the Major Histocompatibility Complex (MHC) is the main desk responsible for the discrimination of self from non-self. Once recognized the non-self particles inside the body, it binds to them and calls for appropriate immune responses. In other words, it is the trigger of the immunity gun, hence crucial for a successful shoot, i.e. immunity. Given this, it is expected that the genes encoding MHC proteins will be associated with altered disease susceptibility, and thus altered survival success. In line with expectations, this has been shown to be the case in many vertebrate species.
Like other vertebrates, birds have MHC too; and as diseases are an important source of mortality, especially in young, i.e. juvenile, birds, MHC might have an important effect on birds’ survival success. Together with the fact that juvenile birds are never exposed to severe tropical pathogens until they reach wintering grounds in Africa, this makes MHC a leading actor in the film “guess if juvenile birds will succeed migrating back to breeding grounds in Europe”. Following the logic, we suspected that the MHC profile of a juvenile great reed warbler (Acrocephalus arundinaceus) might explain its survival success in its first winter in tropical Africa.
MHC profile of a bird refers to both individual MHC gene variants, i.e. alleles, and the total number of MHC gene variants. Considering that the binding principle of MHC proteins to particles of pathogens is like building up puzzle pieces, MHC-pathogen relationship is a restricted one: individual MHC proteins either bind to a particular pathogen-particle or not. Therefore, while having more variants may seem advantageous, and indeed so in many occasions, missing the important one may easily lead to death.
We found two MHC variants having potentially negative effects on survival success of great reed warbler chicks as these variants were associated with lower migrating-back rates -of chicks bearing those alleles- than the population average, and that overall MHC-diversity in an individual did not have any effects on chick-survival. This stresses the importance of individual MHC variants rather than the overall MHC diversity when survival success of great reed warbler chicks is concerned.



Advisor: Helena Westerdahl
Master´s Degree Project 45 credits in Molecular Ecology, 2013
Department of Biology, Lund University (Less)
Please use this url to cite or link to this publication:
author
Taşkent, Recep Özgür
supervisor
organization
course
BION34 20121
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
3567371
date added to LUP
2013-03-15 11:30:28
date last changed
2013-04-29 14:15:01
@misc{3567371,
  abstract     = {Abstract
The Major histocompatibility complex (MHC) plays a central role in the vertebrate immune system. The protein products of MHC genes present foreign peptides to T-cells, which then initiates the appropriate immune responses. MHC genes show extreme level of polymorphism and this was suggested to be maintained by selective pressures exerted by various parasites. Although associations between MHC and different fitness components have been revealed previously in many species, the effects of MHC exclusively on juvenile mortality, where the infection-related mortality is highest, and thus on recruitment have rarely been investigated. In this study, we screened MHC class I alleles of great reed warblers (Acrocephalus arundinaceus) from hatching to breeding in order to reveal potential effects of MHC on recruitment success of fledglings. The study is based on a breeding population of great reed warblers located at Lake Kvismaren in Southern Central Sweden, and for the cohort that we gathered the samples from (the 1998 cohort) we had a good estimate of recruitment rate via an extensive censusing through the species’ whole Swedish breeding range. Hence, any non-recruited individual was assumed to be dead. We expected to find that MHC genes have effects on recruitment success of juveniles. More specifically, we expected that: either (i) certain MHC alleles, as they may provide resistance to certain pathogens and/or (ii) overall MHC diversity (the total number of MHC alleles) in an individual, as it may provide a general resistance against a variety of pathogens, affect recruitment success of the young. Additionally, we used a UniFrac analysis to investigate whether the cumulative MHC profiles of individuals cluster themselves according to recruitment success (being recruited or not-recruited). We used a next generation sequencing technique (454-pyrosequencing) to MHC genotype individuals in this study. Although the pyrosequencing reaction is relatively more error-prone than the classical Sanger sequencing, with proper filtering we reached a 92.7 % repeatability ratio, indicating a reliable genotyping. We found two potentially susceptibility alleles as these alleles were associated with lower recruitment success. Moreover, we failed to find evidence for heterozygote advantage; individuals with more MHC alleles did not have higher recruitment success. However, MHC diversity-recruitment relationship revealed an odd result, as individuals with only one MHC allele –which was fixed in the population and thus present in all individuals- had significantly higher survival than the individuals with more MHC alleles regardless of the number of additional alleles. Potential explanations were suggested for this odd result. The most plausible explanation is that we failed to amplify some MHC class I alleles due to restricted feature of the primer set that we used. Hence, further studies are needed to reach more conclusive results on the effect of particular MHC alleles and MHC diversity on recruitment success of juvenile great reed warblers.

Popular science summary:

Immunity Genes partly explain if birds will survive their first winter in tropical Africa

Immune system of vertebrates resembles gate guards of a castle, considering the castle is the body. Well, despite not being wrong, it is not the full-story. There are private detectives too, wandering inside the castle, looking for thieves. Here, private detectives are specialized immune cells and thieves are pathogens. We found that a group of these private detectives, called as major histocompatibility complex (MHC), partly explain the survival success of juvenile birds, great reed warblers (Acrocephalus arundinaceus) in their first winter in Africa. 
Belonging to the department of private detectives, the Major Histocompatibility Complex (MHC) is the main desk responsible for the discrimination of self from non-self. Once recognized the non-self particles inside the body, it binds to them and calls for appropriate immune responses. In other words, it is the trigger of the immunity gun, hence crucial for a successful shoot, i.e. immunity. Given this, it is expected that the genes encoding MHC proteins will be associated with altered disease susceptibility, and thus altered survival success. In line with expectations, this has been shown to be the case in many vertebrate species. 
Like other vertebrates, birds have MHC too; and as diseases are an important source of mortality, especially in young, i.e. juvenile, birds, MHC might have an important effect on birds’ survival success. Together with the fact that juvenile birds are never exposed to severe tropical pathogens until they reach wintering grounds in Africa, this makes MHC a leading actor in the film “guess if juvenile birds will succeed migrating back to breeding grounds in Europe”. Following the logic, we suspected that the MHC profile of a juvenile great reed warbler (Acrocephalus arundinaceus) might explain its survival success in its first winter in tropical Africa. 
MHC profile of a bird refers to both individual MHC gene variants, i.e. alleles, and the total number of MHC gene variants. Considering that the binding principle of MHC proteins to particles of pathogens is like building up puzzle pieces, MHC-pathogen relationship is a restricted one: individual MHC proteins either bind to a particular pathogen-particle or not. Therefore, while having more variants may seem advantageous, and indeed so in many occasions, missing the important one may easily lead to death. 
We found two MHC variants having potentially negative effects on survival success of great reed warbler chicks as these variants were associated with lower migrating-back rates -of chicks bearing those alleles- than the population average, and that overall MHC-diversity in an individual did not have any effects on chick-survival. This stresses the importance of individual MHC variants rather than the overall MHC diversity when survival success of great reed warbler chicks is concerned. 
 

 
Advisor: Helena Westerdahl
Master´s Degree Project 45 credits in Molecular Ecology, 2013
Department of Biology, Lund University},
  author       = {Taşkent, Recep Özgür},
  language     = {eng},
  note         = {Student Paper},
  title        = {Screening MHC alleles of Great Reed Warblers (Acrocephalus arundinaceus) from hatching to breeding using 454-sequencing technique},
  year         = {2012},
}