Comparative Organization of Grooming Sequences in Adult and Young Sciurid Rodents

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Abstract
The present study is an attempt to link principles of organization of grooming sequences to environmental, ontogenetic and phylogenetic factors through a comparative study of five species of North American squirrels (Glaucomys sabrinus, Spermophilus columbianus, Spermophilus lateralis, Spermophilus richardsonii and Tamiasciurus hudsonicus) that occupy a variety of ecological niches and have different degrees of taxonomic relatedness and morphological similarity. Three measures of grooming organization are analysed: bout length distributions, transition structure and anatomical distribution. Grooming bout length distributions in both adult and young sciurids fit with the geometric model. Mean bout length varies between species and is possibly influenced by social and ecological factors such as disturbance by conspecifies and predator surveillance. Transition structure follows a cephalocaudal progression that appears to be characteristic of rodent grooming and could be phylogenetically very old. 'I'he degree of organization of the sequences, as measured by transition structure, seems to be related to average bout length. Postural facilitation can also be invoked to explain some of the transitions. No general rule emerges from the comparative analysis of transition structure. Ecology phylogeny and morphology influence anatomical distribution of grooming activity. The three Spermophilus spp. are similar in pattern. Tail size in T. hudsonicus and the possible use of echolocation in G. sabrinus favour more frequent care of the tail and head regions respectively in these species. The present study is an attempt to link principles of organization of grooming sequences to environmental, ontogenetic and phylogenetic factors through a comparative study of five species of North American squirrels (Glaucomys sabrinus, Spermophilus columbianus, Spermophilus lateralis, Spermophilus richardsonii and Tamiasciurus hudsonicus) that occupy a variety of ecological niches and have different degrees of taxonomic relatedness and morphological similarity. Three measures of grooming organization are analysed: bout length distributions, transition structure and anatomical distribution. Grooming bout length distributions in both adult and young sciurids fit with the geometric model. Mean bout length varies between species and is possibly influenced by social and ecological factors such as disturbance by conspecifies and predator surveillance. Transition structure follows a cephalocaudal progression that appears to be characteristic of rodent grooming and could be phylogenetically very old. 'I'he degree of organization of the sequences, as measured by transition structure, seems to be related to average bout length. Postural facilitation can also be invoked to explain some of the transitions. No general rule emerges from the comparative analysis of transition structure. Ecology phylogeny and morphology influence anatomical distribution of grooming activity. The three Spermophilus spp. are similar in pattern. Tail size in T. hudsonicus and the possible use of echolocation in G. sabrinus favour more frequent care of the tail and head regions respectively in these species.