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For sheep horns, bigger is not better

Trade-offs between studliness and survival keep less endowed sheep in the mix

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3:58pm, August 21, 2013

HORNY GENES  This big-horned Soay ram will fight other males of his species for females on the St. Kilda archipelago during the spring rut. His ample horns, however, may not necessarily give him the best competitive edge, genetically.

Sometimes it pays to be mediocre. A new study shows that sheep with a 50/50 blend of genes for small and big horns pass along more of their genes over a lifetime than their purely big-horned brethren, who mate more often.

The finding offers rare insight into an enduring evolutionary paradox—why some traits persist despite creating a reproductive disadvantage.

The results, published online August 21 in Nature, reveal that while big-horned sheep mated most successfully each season, small-horned sheep survived longer. Rams who inherited one of each type of gene from their parents got the best of both worlds: they lived longer than bigger-horned sheep and mated more successfully than those with the smallest horns.

As a result, middle-of-the-road sheep passed on more of their genes over time. “They’re the fittest of them all,” says Jon Slate of the University of Sheffield in England, who led the study.

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