Dietary protein constraint on age at maturity: an experimental test with wild deer mice

1. Five populations of Peromyscus maniculatus borealis (Mearns) were live-t rapped in the Kananaskis Valley, Alberta, throughout the breeding seasons o f 1996 and 1997, to test the hypothesis that growth and maturation of young -of-the-year (YY) females are limited by dietary protein. 2. In 1996, two populations received a high protein (30%) food supplement, one received a high energy, but low protein (14%) food supplement and two o thers were unsupplemented. In 1997, three populations received the protein (30%) supplement and two served as controls. 3. In 1996, control populations had high nestling growth rates and many (43 %) YY females bred. In 1997, nestling growth rates were lower in control po pulations and no YY females bred. 4. Supplementation of high protein food resulted in consistently high nestl ing growth rates in both 1996 and 1997, and a significantly higher proporti on of YY females bred than controls in both years. 5. Supplementation of high energy, but low protein food had no effect on YY growth or maturation. 6. Neither protein nor energy supplementation had any effects on the number of litters conceived per season, litter success, litter size or sex ratio of litters born to overwintered females. 7. We conclude that growth and maturation of YY female Peromyscus maniculat us in this area are limited by the availability of dietary protein.