| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 2419085 | Animal Behaviour | 2006 | 9 Pages |
The programmed grooming model proposes that animals groom in response to an internal timing mechanism that has evolved to control ectoparasites. This model predicts that polygynous males will groom less frequently than smaller females (sexually dimorphic grooming) because (1) parasitism is more costly for smaller individuals (body size principle), and (2) during the breeding season, sexual selection has favoured males that reduce grooming to enhance vigilance for mates and rivals (vigilance principle). The proximate mechanism for vigilance-mediated suppression of grooming may be either time budget conflicts (males are too busy breeding to groom) or physiological suppression (the action of elevated testosterone). In this study, we examined the influence of body size, breeding activity and androgens on sexually dimorphic grooming in American bison, Bison bison. Bison were observed before (pre-rut) and during the breeding season (rut) at National Bison Range (NBR) and Fort Niobrara (FTN) national wildlife refuges; androgens were measured in FTN males. Females oral-groomed two to five times more than males during pre-rut, and 5–40 times more than tending males (guarding oestrous females) during the rut; tending males oral-groomed less than pre-rut males at both sites. Rutting activity of tending males was much greater than that of nontending or nonrutting males, but all males groomed at the same low rate. Androgen levels increased between pre-rut and rut for all males, but androgen levels of tending males were higher than those of nontending males. In a subsample of males for whom both androgen and grooming data were available, androgen levels were negatively correlated with oral-grooming rate, as predicted by the physiological suppression model. We conclude that effects of body size and sexually selected vigilance work independently and additively to produce sexually dimorphic grooming in bison. The vigilance-associated suppression of grooming rate in breeding males appears to be due to the action of elevated testosterone rather than conflicting time budgets.
