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Immunity: What's Fertility Got To Do With It?

Lamb from the Island of Hirta, St. Kilda, Scotland: Photo by Arpat Ozgul/University of EdinburghLamb from the Island of Hirta, St. Kilda, Scotland: Photo by Arpat Ozgul/University of Edinburgh Do you catch every cold or flu that comes along?  Or do you somehow manage to avert the most contagious of them?  Either way, it's possible that this study of immunity among Scottish sheep may turn out to provide the reason.

Ecological researchers from Princeton University and the University of Edinburgh studied wild Soay sheep on the Island of Hirta, St. Kilda, off the coast of Scotland, to compare their levels of antibodies with their levels of fertility. What they found was a reverse correlation between the two: sheep with stronger imune responses were healthier and likely live longer, but gave birth to fewer children each year.  Those with weaker immunities were less healthy,  lived shorter lives but had more children each year.  Additionally, these same traits were genetically passed on to the offspring in families.

St. Kilda is just 100 miles off the coast of Scotland: image via WikiSt. Kilda is just 100 miles off the coast of Scotland: image via WikiStudying animals in the wild allowed the Princeton and Edinburgh scientists to explore how these variations naturally occurs, as opposed to studying animals, like lab or circus animals, whose genetics may have at some time been altered by humans to select certain factors.  Though lab studies and manipulations have been extremely useful to medicine, some have also used them to create hunting dogs or faster horses or the 'perfect race.'

The Princeton - Edinburgh study gives us the opportunity to know what it was that nature intended.  And in the case of the sheep, nature intends to choose immunity for some and not for others; fertility for some and not for others. 

 Andrea Graham, professor at Princeton and Edinburgh, led the study, published October 29, 2010 in Science. "This genetic basis means that natural selection has the chance to shape the trait," Graham said. If differing responses to infection still result in equal long-term reproductive success, she said, this means "selection seems actually to be maintaining this genetic variation in immunity."

 

Sheep on the Island of Hirta, St. Hilda, Scotland: Photo by Arpat Ozgul/University of EdinburghSheep on the Island of Hirta, St. Hilda, Scotland: Photo by Arpat Ozgul/University of Edinburgh

 

Perhaps this might also help to explain some differences in the rate of evolution among species.


Princeton University via RDMag