A phylogenetic test of the relationship between saltation and habitat openness in gerbils (Gerbillinae, Rodentia)

Abstract

Saltation is movement by means of hopping on two legs, or jumping on four. This locomotory mode is common in various taxa, including desert rodents, that inhabit open, arid environments and is associated with the elongation of hind feet and tails. Many adaptive hypotheses have been proposed to explain why saltation is common in open habitats, including considering it as a strategy for antipredation and/or energy conservation. Yet, the association between saltation ability (i.e., leap distance) and habitat openness has not been demonstrated statistically within any taxonomic group. Here, I use phylogenetic generalized least squares analyses (PGLS) to statistically test the association between indices of saltation, with those of habitat openness, in gerbils. I find that habitat openness is significantly (positively) correlated with relative hind foot length (RHFL), but not with relative tail length (RTL), indicating that gerbil species living in more open environments, have proportionately greater RHFL (and by inference greater leap distance). This supports the hypothesis that increased saltatorial ability is adaptive to more open habitats. The association between RHFL, RTL, in addition to relative ear length (REL) with indices of habitat temperature, was also tested. Temperature was found to be significantly (positively) correlated with RTL, in accordance with Allen’s rule (indicating that gerbils from warmer habitats have proportionately greater RTL), but not with RHFL or REL. These results indicate that, in gerbils, different appendages may be responding to different environmental adaptive pressures (i.e., saltatorial ability vs. thermoregulation).