Ontogenetic allometry in the locomotor skeleton of specialized half‐bounding mammals

Abstract

Specialization for a locomotor behaviour may affect limb bone morphology throughout ontogeny. Ontogenetic development of the limb skeletons of two mammalian species, which are behaviourally specialized for the half-bounding gait (Chinchilla lanigera and Oryctolagus cuniculus), were compared to two similarly-sized species which are not specialized for half-bounding (Rattus norvegicus and Monodelphis domestica). Limb bone lengths and anteroposterior diameters (mediolateral diameters for the radius and metacarpal) were measured from radiographs taken throughout the ontogeny of each species. Body mass was also measured repeatedly during growth. Bone measurements were regressed against body mass, as well as forelimb bone length vs serially homologous hindlimb bone length, bone length vs total limb length and bone length vs width. Similar comparisons were made among adults of each species using ratios. Although there were many signi®cant differences among species, overall there were few consistent differences in adult scaling ratios or ontogenetic allometry slopes between specialized and generalized groups. Adult specialized half-bounders had signi®cantly narrower tibiae and metatarsals than the gaitgeneralized runners. Specialized half-bounders usually had similar slopes for hindlimb length vs width ontogenetic comparisons, but the non-specialized species did not group together. However, there were two patterns that occurred among all four species: (1) hindlimb bone lengths nearly always grew faster than the serially homologous forelimb bone lengths in all species; (2) proximal elements usually increased in length proportionally faster than distal elements. In conclusion, small mammals may share strong developmental constraints that govern their relative growth rates. It is also likely that there are different selective pressures on juveniles and adults, but that these selective pressures may not be different between specialized and unspecialized runners during ontogeny.

Sexual selection and genital allometry in the Hottentot golden mole (Amblysomus hottentotus)

“…Adaptive advantages of the observed allometry in length of the highly modified front foot in the females as opposed to males is difficult to ascertain, however, and the possibility of pleiotropy cannot be ruled out although positive allometry has been observed in the femur and tibia lengths of certain vertebrates (Lammers andGerman 2002, Farlow andPianka 2000). Consistent with results obtained by Pomiankowski and Møller (1995) coefficients of variation were notably higher in sexual than in non-sexual traits (see also Rowe and Houle, 1996).…”

Locomotor versatility in the white-handed gibbon (Hylobates lar): A spatiotemporal analysis of the bipedal, tripedal, and quadrupedal gaits

“…The quadrupedal gait of gibbons is also remarkable because the footfall patterns are more comparable to the bounding of some old world monkeys (e.g., colobines and langurs; McGraw, 1996;Byron and Covert, 2004;Workman and Covert, 2005) and the half-bounding of medium-sized mammals (e.g., rabbits, chinchillas, and bandicoots; Fischer et al, 2002;Lammers and German, 2002;Bennett and Garden, 2004) than to the typical diagonal sequence gait of most primates (Hildebrand, 1967;Vilensky, 1989;Larson, 1998;Lemelin et al, 2003).…”

Forelimb proportions and kinematics: how are small primates different from other small mammals?

“…Steudel, 1982 Table 2. Morphometry: species (number of specimens), body mass and limb segment lengths *The asterisk denotes that body weight is compiled from one of the following sources: Grzimek, 1987;Rowe, 1996;Garbutt, 1999;Nowak, 1999. between different sized adults of a species is determined by ontogenetic development (Wayne, 1986;Lammers and German, 2002;Schilling and Petrovitch, 2005), interspecific allometry reflects size-related mechanical adaptations. Accordingly, the limb proportions of different sized conspecifics do not scale isometrically and can be very different.…”