Abstract
We compared horn growth of rams from 2 study populations of Dall's sheep (Ovis dalli dalli) living under different nutritional regimes. The wild herd in Kluane National Park is characterized by a high density and nutritional limitations; the captive herd held in a large enclosure at the Yukon Game Farm near White-horse, receives high quality supplementary feed. The captive herd had its origin in the wild herd; genetic implications therefore can be ruled out as a contributing factor in explaining the differences observed. Captive rams developed larger and more massive horns. Their horns reached a length of 1,000 mm in their eighth year, those of wild rams rarely exceeded 950 mm even after 12 years. More pronounced were the differences in horn circumference, averaging about 18% over all age classes. When length and circumference measurements were combined to calculate volume, 7-year-old captive rams had horns with volumes averaging 2,750 cm 3 ; their wild counterparts only horns with 1,500 cm 3 . We demonstrate the great phenotypic plasticity residing in these sheep, which was revealed through increase in resource availability.
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