Oral grooming is highly effective in removing ectoparasites in ungulates and other species. The programmed grooming model postulates that preventive oral grooming bouts are periodically activated by an internal timing mechanism (clock), with grooming rates modulated according to fitness costs and benefits. The 'body size principle' of the programmed grooming model, developed from interspecific comparisons, predicts that animals or species of smaller size, because they cannot tolerate as great a density of engorging ticks per unit of body surface area, will groom at a higher rate than those of larger size. Accordingly, within a species, young animals should groom at a higher rate than adults. The 'tick challenge principle' states that the rate of programmed grooming will be regulated as a function of tick bites such that animals will groom more frequently when tick exposure in the habitat is greater. These predictions were tested by comparing self-grooming rates of impala, Aepyceros melampus, lambs and their mothers at three study sites ranging from tick-dense to tick-sparse or tick-free. As predicted, newborn lambs from 1-5 weeks postpartum self-oral groomed at about three times the rate of their mothers, and young lambs 6-12-weeks-old self-oral groomed at least twice as frequently as maternal conspecifics; self-oral grooming rate of older (7-8-month-old) lambs was no different from that of adults. Presumably, the timing mechanism slowly changes its rate as impala mature, reflecting increased costs of self-oral grooming (attrition of the dental elements used in oral grooming and distraction from vigilance over predators) relative to declining body surface:mass ratio. Both lambs and their mothers consistently self-groomed at a higher rate at the tick-dense study site compared with the tick-sparse or tick-free sites. The results are in line with the concept that an intrinsic grooming clock is responsible for regulating body-size and tick-challenge specific grooming rates that enable impala to survive and thrive in a tick-infested environment.
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics
- Animal Science and Zoology