Alpha males don’t have all the advantages, animal study shows

Physical dominance can give some wild animals the edge over their sexual rivals – but their weaker competitors have some breeding advantages too, a new study suggests.

Researchers from the University of Sheffield's Department of Animal and Plant Sciences studied wild sheep living on St Kilda and investigated the size of males’ horns – a characteristic that can help them win mates, much like deer antlers or peacock tail feathers.

Scientists discovered a gene that controls horn size, and found that rams can grow large, medium or small horns, depending on the genes they inherit from their parents.

The research shows that although large-horned rams win more females in the annual rut, rams with small or medium-sized horns are more likely to live longer.

In addition, sheep with medium-sized horns carry the small-horned gene, and can pass it on to successive generations by mating as successfully as their big-horned cousins, and living relatively long lives.

Scientists from the Universities of Sheffield and Edinburgh, who carried out the study, say their work explains how small horns have survived for thousands of years and have not been lost, despite the relative mating success of big-horned males.

Researchers used more than 20 years’ worth of data gathered from the wild flock on St Kilda.

Dr Susan Johnston, of the University’s School of Biological Sciences, who carried out the study, said: “Until now, we did not fully understand why small horns had not died out. Although it may appear that larger horns are better, we found that the increased survival of medium-horned rams allowed them to catch up with their big-horned rivals in terms of how many offspring they have. As they are carriers of the small horn gene and have many offspring, this means that small horned rams will continue to turn up in the population.”

The study, published in Nature, was funded by the Natural Environment Research Council, European Research Council, and Biotechnology and Biological Sciences Research Council.

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