It is a well-known phenomenon that within mammalian species, females tend to outlive males. The male sex hormone testosterone not only puts males at behavioural risk of injury in terms of aggression and competitiveness (as well as involving high energy expenditure), but also increases levels of harmful LDL cholesterol in the blood, leading to a greater risk of heart disease and stroke. As such, a broad variety of immune-related genes may be more important in males than it is in females. Researchers studying the Alpine chamois (Rupicapra rupicapra) have recently investigated this hypothesis. Observing wild chamois living in the eastern Alps, scientists discovered that in areas affected by scabies, reproductive-age males had a higher death rate than both females and younger males. They noted that mature males depleted their fat stores at the end of the winter around 6 weeks earlier than females and younger males, presumably due to the large amount of energy expended in rutting. Lower fat reserves leave less energy for maintaining a strong immune system. Researchers wanted to know whether variation in genes that influenced immune response could improve male probability of survival.The scientists chose to examine a gene called MHC class II DRB from what is known as the major histocompatibility complex (MHC). This is a set of around 128 active genes along with 96 non-functional pseudogenes that have an important role in the immune system. The MHC shows huge variation between individuals - 100 times greater than the genome average, giving a 10% difference between any two unrelated individuals. These variations seem to correspond with differences in susceptibility to a whole host of diseases such as malaria, tuberculosis and HIV/AIDS.In areas affected by scabies, the proportion of males that were heterozygous (had two different copies of the gene) increased with age, implying that homozygous individuals (those with two identical copies of the gene) had higher mortality rates. Male individuals heterozygous at the locus were indeed found to survive significantly longer than homozygous individuals - but this did not apply in females. The research supports the theory that when the immune system is compromised, heterozygosity in immune genes increases male chances of survival.Ref:  Schaschl H., Suchentrunk F., Morris D. L. et al., 2012. Sex-specific selection for MHC variability in Alpine chamois. BMC Evolutionary Biology 12:20 [link]Twyman R., 2003. The major histocompatibility complex. Wellcome Trust: The Human Genome [link]

It is a well-known phenomenon that within mammalian species, females tend to outlive males. The male sex hormone testosterone not only puts males at behavioural risk of injury in terms of aggression and competitiveness (as well as involving high energy expenditure), but also increases levels of harmful LDL cholesterol in the blood, leading to a greater risk of heart disease and stroke. As such, a broad variety of immune-related genes may be more important in males than it is in females. Researchers studying the Alpine chamois (Rupicapra rupicapra) have recently investigated this hypothesis. Observing wild chamois living in the eastern Alps, scientists discovered that in areas affected by scabies, reproductive-age males had a higher death rate than both females and younger males. They noted that mature males depleted their fat stores at the end of the winter around 6 weeks earlier than females and younger males, presumably due to the large amount of energy expended in rutting. Lower fat reserves leave less energy for maintaining a strong immune system. Researchers wanted to know whether variation in genes that influenced immune response could improve male probability of survival.

The scientists chose to examine a gene called MHC class II DRB from what is known as the major histocompatibility complex (MHC). This is a set of around 128 active genes along with 96 non-functional pseudogenes that have an important role in the immune system. The MHC shows huge variation between individuals - 100 times greater than the genome average, giving a 10% difference between any two unrelated individuals. These variations seem to correspond with differences in susceptibility to a whole host of diseases such as malaria, tuberculosis and HIV/AIDS.

In areas affected by scabies, the proportion of males that were heterozygous (had two different copies of the gene) increased with age, implying that homozygous individuals (those with two identical copies of the gene) had higher mortality rates. Male individuals heterozygous at the locus were indeed found to survive significantly longer than homozygous individuals - but this did not apply in females. The research supports the theory that when the immune system is compromised, heterozygosity in immune genes increases male chances of survival.

Ref:  Schaschl H., Suchentrunk F., Morris D. L. et al., 2012. Sex-specific selection for MHC variability in Alpine chamois. BMC Evolutionary Biology 12:20 [link]
Twyman R., 2003. The major histocompatibility complex. Wellcome Trust: The Human Genome [link]

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