Science - November 8, 2007

Rainfall visible in buffalo genes

The number of offspring of genetically different African buffalo correlates with the amount of rainfall, ecologists have discovered. The ‘barren’ male Y chromosome appears to play a prominent role in this natural selection mechanism.

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The Y chromosome in mammals is not only physically much smaller than the other chromosomes. According to geneticists, apart from sex determination and a general role in sperm production, there is little that is genetically exciting about it. ‘What’s striking about the discovery in the African buffalo is the determining role that this chromosome plays,’ explains Dr Pim van Hooft of the Resource Ecology group. ‘We’ve found a direct relation in a mammal between genes and a changing environmental factor, in this case rainfall. That rain has such a strong genetic effect is not something you’d expect.’

Van Hooft – together with colleagues from South Africa and the United States – discovered the effect after performing a genetic analysis of two separate populations of African buffalo in South African national parks. The results were published on 31 October in the online journal PLoS ONE.

The research involved analysing blood samples from 216 animals from herds in the Kruger Park and 170 animals from herds in the Hluhluwe-iMfolozi Park. ‘The samples were taken while the tranquilised buffalo were being tested for tuberculosis. Because experts had estimated the age of the animals, we were able to work back to the year of birth and compare the genetic data with how much rain had fallen in the year before their birth,’ says Van Hooft.

For the DNA analyses, the scientists used three genetic markers originally developed for cattle. If there is high rainfall for a number of consecutive years, it appears that up to eight times as many offspring are born with a certain Y chromosome variant, while after a number of dry years the bulls tend to have the other variant.

Van Hooft hopes that future studies will be able to link differences in reproductive success between lean and fat years to physiological strategies: whether for example a bull’s investment in good physical condition is achieved at the cost of high sperm production and vice versa. ‘We have enough data to be able to say more about this,’ says Van Hooft.

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