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Mortality selection during the 2003 European heat wave in three-spined sticklebacks: effects of parasites and MHC genotype.

Wegner KM, Kalbe M, Milinski M, Reusch TB - BMC Evol. Biol. (2008)

Bottom Line: The within family MHC effects were, however, small compared to between family effects, suggesting that other genetic components or non-genetic effects were also important.The correlation between parasite load and mortality that we found at both individual and family level might have appeared only in the extraordinary heatwave of 2003.Due to global warming the frequency of extreme climatic events is predicted to increase, which might intensify costs of parasitism and enhance selection on immune genes.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Integrative Biology (IBZ), Experimental Ecology, ETH Zürich, Universitätstrasse 16, CH - 8092 Zürich, Switzerland. mathias.wegner@env.ethz.ch

ABSTRACT

Background: Ecological interaction strength may increase under environmental stress including temperature. How such stress enhances and interacts with parasite selection is almost unknown. We studied the importance of resistance genes of the major histocompatibility complex (MHC) class II in 14 families of three-spined sticklebacks Gasterosteus aculeatus exposed to their natural macroparasites in field enclosures in the extreme summer of 2003.

Results: After a mass die-off during the 2003-European heat wave killing 78% of 277 experimental fish, we found strong differences in survival among and within families. In families with higher average parasite load fewer individuals survived. Multivariate analysis revealed that the composition of the infecting parasite fauna was family specific. Within families, individuals with an intermediate number of MHC class IIB sequence variants survived best and had the lowest parasite load among survivors, suggesting a direct functional link between MHC diversity and fitness. The within family MHC effects were, however, small compared to between family effects, suggesting that other genetic components or non-genetic effects were also important.

Conclusion: The correlation between parasite load and mortality that we found at both individual and family level might have appeared only in the extraordinary heatwave of 2003. Due to global warming the frequency of extreme climatic events is predicted to increase, which might intensify costs of parasitism and enhance selection on immune genes.

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Relationship between number of MHC class IIB sequence variants and residual survival probability of each MHC genotype. Note that all fish entered this analysis, i.e. both dead ones reconstructed for their MHC genotype and those that survived. Residual survival probability was calculated as the difference between survival probability if a certain genotype and the overall survival probability of the family. The quadratic polynomial (survival = -0.560 + 0.190 * Nsequence variants - 0.016 * Nsequence variants2, R2 = 0.364, F2,30 = 8.601, P = 0.001) shows that within segregating families fish with a number of 6.086 MHC class IIB sequence variants have highest chance of survival.
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Figure 5: Relationship between number of MHC class IIB sequence variants and residual survival probability of each MHC genotype. Note that all fish entered this analysis, i.e. both dead ones reconstructed for their MHC genotype and those that survived. Residual survival probability was calculated as the difference between survival probability if a certain genotype and the overall survival probability of the family. The quadratic polynomial (survival = -0.560 + 0.190 * Nsequence variants - 0.016 * Nsequence variants2, R2 = 0.364, F2,30 = 8.601, P = 0.001) shows that within segregating families fish with a number of 6.086 MHC class IIB sequence variants have highest chance of survival.

Mentions: The survival probability of each MHC genotype centered by the family mean followed a quadratic polynomial relationship (Fig. 5, survival = -0.560 + 0.190 * Nsequence variants - 0.016 * Nsequence variants2, R2 = 0.364, F2,30 = 8.601, P = 0.001). Separating the parameters of the polynomial reveals that only the quadratic term was significantly different from 0 (t = -3.98, P < 0.001) while the intercept and the linear term were not (tintercept = -0.45, P = 0.658; tlinear = 1.00, P = 0.327). Maximum survival described by this function can be found at 6.086 sequence variants. Since the analysis included all segregating families except family 6 (no survivors), this result may have been biased by inclusion of families that only consisted of a single surviving fish. When these families were excluded from the analysis the result changed only little (R2 = 0.487, F2,15 = 7.116, P = 0.007). The same applied to the predicted number of MHC class II variants associated with maximum survival (i.e. 6.18 sequence variants).


Mortality selection during the 2003 European heat wave in three-spined sticklebacks: effects of parasites and MHC genotype.

Wegner KM, Kalbe M, Milinski M, Reusch TB - BMC Evol. Biol. (2008)

Relationship between number of MHC class IIB sequence variants and residual survival probability of each MHC genotype. Note that all fish entered this analysis, i.e. both dead ones reconstructed for their MHC genotype and those that survived. Residual survival probability was calculated as the difference between survival probability if a certain genotype and the overall survival probability of the family. The quadratic polynomial (survival = -0.560 + 0.190 * Nsequence variants - 0.016 * Nsequence variants2, R2 = 0.364, F2,30 = 8.601, P = 0.001) shows that within segregating families fish with a number of 6.086 MHC class IIB sequence variants have highest chance of survival.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2386451&req=5

Figure 5: Relationship between number of MHC class IIB sequence variants and residual survival probability of each MHC genotype. Note that all fish entered this analysis, i.e. both dead ones reconstructed for their MHC genotype and those that survived. Residual survival probability was calculated as the difference between survival probability if a certain genotype and the overall survival probability of the family. The quadratic polynomial (survival = -0.560 + 0.190 * Nsequence variants - 0.016 * Nsequence variants2, R2 = 0.364, F2,30 = 8.601, P = 0.001) shows that within segregating families fish with a number of 6.086 MHC class IIB sequence variants have highest chance of survival.
Mentions: The survival probability of each MHC genotype centered by the family mean followed a quadratic polynomial relationship (Fig. 5, survival = -0.560 + 0.190 * Nsequence variants - 0.016 * Nsequence variants2, R2 = 0.364, F2,30 = 8.601, P = 0.001). Separating the parameters of the polynomial reveals that only the quadratic term was significantly different from 0 (t = -3.98, P < 0.001) while the intercept and the linear term were not (tintercept = -0.45, P = 0.658; tlinear = 1.00, P = 0.327). Maximum survival described by this function can be found at 6.086 sequence variants. Since the analysis included all segregating families except family 6 (no survivors), this result may have been biased by inclusion of families that only consisted of a single surviving fish. When these families were excluded from the analysis the result changed only little (R2 = 0.487, F2,15 = 7.116, P = 0.007). The same applied to the predicted number of MHC class II variants associated with maximum survival (i.e. 6.18 sequence variants).

Bottom Line: The within family MHC effects were, however, small compared to between family effects, suggesting that other genetic components or non-genetic effects were also important.The correlation between parasite load and mortality that we found at both individual and family level might have appeared only in the extraordinary heatwave of 2003.Due to global warming the frequency of extreme climatic events is predicted to increase, which might intensify costs of parasitism and enhance selection on immune genes.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Integrative Biology (IBZ), Experimental Ecology, ETH Zürich, Universitätstrasse 16, CH - 8092 Zürich, Switzerland. mathias.wegner@env.ethz.ch

ABSTRACT

Background: Ecological interaction strength may increase under environmental stress including temperature. How such stress enhances and interacts with parasite selection is almost unknown. We studied the importance of resistance genes of the major histocompatibility complex (MHC) class II in 14 families of three-spined sticklebacks Gasterosteus aculeatus exposed to their natural macroparasites in field enclosures in the extreme summer of 2003.

Results: After a mass die-off during the 2003-European heat wave killing 78% of 277 experimental fish, we found strong differences in survival among and within families. In families with higher average parasite load fewer individuals survived. Multivariate analysis revealed that the composition of the infecting parasite fauna was family specific. Within families, individuals with an intermediate number of MHC class IIB sequence variants survived best and had the lowest parasite load among survivors, suggesting a direct functional link between MHC diversity and fitness. The within family MHC effects were, however, small compared to between family effects, suggesting that other genetic components or non-genetic effects were also important.

Conclusion: The correlation between parasite load and mortality that we found at both individual and family level might have appeared only in the extraordinary heatwave of 2003. Due to global warming the frequency of extreme climatic events is predicted to increase, which might intensify costs of parasitism and enhance selection on immune genes.

Show MeSH
Related in: MedlinePlus