Age-related male reproductive effort in two mountain ungulates of contrasting sexual size dimorphism

In polygynous ungulates, the reproductive effort of adult males peaks during a short period in which feeding activities are sacrificed for mating activities. Hence, both fat reserves and body mass are predicted to decline markedly during this period. The decline is also predicted to be greater in fat reserves than in body mass because fat is catabolized before muscle, and to increase with the intensity of sexual selection. In contrast, no specific patterns are expected in females for which late gestation and lactation rather than mating are the energetically most demanding periods. We tested these hypotheses in two mountain ungulates of contrasting sexual size dimorphism (SSD): Himalayan tahr (Hemitragus jemlahicus (H. Smith, 1826)) (SSD = 123%) and alpine chamois (Rupicapra rupicapra (L., 1758)) (SSD = 26%). As expected, kidney fat declined more rapidly than body mass in adult males of both species. Kidney fat declined faster in adult male tahr compared with adult male chamois. There was no consistent pattern of changes in body mass or kidney fat in female tahr or female chamois. Our results suggest that adult males of species with strong SSD allocate more energy to mating than males of less dimorphic species.