The evolution of parasite-defence grooming in ungulates

Abstract

Grooming repertoires are exhibited by all terrestrial mammals, and removal of ectoparasites is an important ances- tral and current function. Parasite-defence grooming is regulated both by a central control mechanism (programmed grooming model) and by cutaneous stimulation from bites (stimulus-driven model). To study the evolution of para- site-defence grooming in ungulates, we compared species-typical grooming behaviour with host morphology and hab- itat to test predictions of the programmed grooming model while taking into account phylogenetic relatedness. We observed grooming in 60 ungulate species at ectoparasite-free zoological parks in which the confound of differential tick exposure was controlled for and stimulus-driven grooming was ruled out. Concentrated-changes tests indicated that sexually dimorphic grooming (in which breeding males groom less than females) has coevolved with sexual body size dimorphism, suggesting that intrasexual selection has favoured reduced grooming that enhances vigilance of males for oestrous females and rival males. Concentrated-changes tests also revealed that the evolution of complex oral grooming (involving alternate use of both teeth and tongue) and adult allogrooming (whereby conspecifics oral groom body regions not accessible by self grooming) was concentrated in lineages inhabiting closed woodland or for- est habitat associated with increased tick exposure, with such advanced grooming being most concentrated in Cervidae. Regression analyses of independent contrasts indicated that both host body size and habitat play a role in the evolution of species-typical oral grooming rates, as previously reported. These results indicate that the observed grooming represents centrally driven grooming patterns favoured by natural selection in each lineage. This is the first phylogenetically controlled comparative study to report the evolution of parasite-defence grooming behaviours in response to selection pressures predicted by the programmed grooming hypothesis. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81, 17-37. ADDITIONAL KEYWORDS: body size - habitat - parasites - programmed grooming - sexual size dimorphism - ticks - vigilance.