Hindlimb Structure Research Articles

Hindlimb muscle function in turtles: is novel skeletal design correlated with novel muscle function?

Variations in musculoskeletal lever systems have formed an important foundation for predictions about the diversity of muscle function and organismal performance. Changes in the structure of lever systems may be coupled with changes in muscle use and give rise to novel muscle functions. The two extant turtle lineages, cryptodires and pleurodires, exhibit differences in hindlimb structure. Cryptodires possess the ancestral musculoskeletal morphology, with most hip muscles originating on the pelvic girdle, which is not fused to the shell. In contrast, pleurodires exhibit a derived morphology, in which fusion of the pelvic girdle to the shell has resulted in shifts in the origin of most hip muscles onto the interior of the shell. To test how variation in muscle arrangement might influence muscle function during different locomotor behaviors, we combined measurements of muscle leverage in five major hindlimb muscles with data on muscle use and hindlimb kinematics during swimming and walking in representative semiaquatic cryptodire (Trachemys scripta) and pleurodire (Emydura subglobosa) species. We found substantial differences in muscle leverage between the two species. Additionally, we found that there were extensive differences in muscle use in both species, especially while walking, with some pleurodire muscles exhibiting novel functions associated with their derived musculoskeletal lever system. However, the two species shared similar overall kinematic profiles within each environment. Our results suggest that changes in limb lever systems may relate to changes in limb muscle motor patterns and kinematics, but that other factors must also contribute to differences in muscle activity and limb kinematics between these taxa.

Aspects of the Hindlimb Morphology of Some Australian Birds of Prey: A Comparative and Quantitative Study

AbstractWe quantified the extent of adaptive radiation in the evolution of the hindlimb in the bird-of-prey community on Tasmania. Assessments of the ecological capabilities of raptor species are often based on a visual inspection of their hindlimb structure, with little recourse to direct biomechanical or functional evidence. We examined the links between hindlimb structure and patterns of diet, foraging, and habitat use in raptors by analytically investigating tarsus, toe, and talon measurements. We identified groupings on the basis of dietary preference, hunting-killing technique, and phylogeny. We found that the bird-catching specialists, which possessed relatively long digits with short talons, were consistently separable. The large-mammal and fish specialists were equipped with relatively short and robust tarsi, and short digits with long and robust talons. The hindlimbs of medium-mammal specialists were characterized by long digits and a large digit 1 talon. However, the generalist group did not possess any specializations, because their structural elements were comparable to those of other dietary groups. An association was found between the ratio of toe to talon length and the selective pressures of prey capture and ease of killing. Morphological variation in this feature was consistent with phylogeny, because the Accipitridae were characterized by a larger ratio of toe to talon length on digits 1 and 2 than the Falconidae, and the diurnal raptors possessed an interdigital pattern of larger variation in ratio of toe to talon length than the nocturnal raptors. No link was found between dietary habit and tarsus length or robustness, because these features were apparently attributed to variations in hunting style. Our analysis highlights the interrelationship between the morphology of hindlimb structure and the functional pressures associated with predatory lifestyles.Aspects de la morphologie des membres postérieurs de quelques oiseaux de proie australiens : Une étude comparative et quantitative

Sequence Variation in theTbx4Gene in Marine Mammals

The amino-acid sequences of the T-domain region of the Tbx4 gene, which is required for hindlimb development, are 100% identical in humans and mice. Cetaceans have lost most of their hindlimb structure, although hindlimb buds are present in very early cetacean embryos. To examine whether the Tbx4 gene has the same function in cetaceans as in other mammals, we analyzed Tbx4 sequences from cetaceans, dugong, artiodactyls and marine carnivores. A total of 39 primers were designed using human and dog Tbx4 nucleotide sequences. Exons 3, 4, 5, 6, 7, and 8 of the Tbx4 genes from cetaceans, artiodactyls, and marine carnivores were sequenced. Non-synonymous substitution sites were detected in the T-domain regions from some cetacean species, but were not detected in those from artiodactyls, the dugong, or the carnivores. The C-terminal regions contained a number of non-synonymous substitutions. Although some indels were present, they were in groups of three nucleotides and therefore did not cause frame shifts. The dN/dS values for the T-domain and C-terminal regions of the cetacean and artiodactylous Tbx4 genes were much lower than 1, indicating that the Tbx4 gene maintains it function in cetaceans, although full expression leading to hindlimb development is suppressed.

ASPECTS OF THE HINDLIMB MORPHOLOGY OF SOME AUSTRALIAN BIRDS OF PREY: A COMPARATIVE AND QUANTITATIVE STUDY

We quantified the extent of adaptive radiation in the evolution of the hindlimb in the bird-of-prey community on Tasmania. Assessments of the ecological capabilities of raptor species are often based on a visual inspection of their hindlimb structure, with little recourse to direct biomechanical or functional evidence. We examined the links between hindlimb structure and patterns of diet, foraging, and habitat use in raptors by analytically investigating tarsus, toe, and talon measurements. We identified groupings on the basis of dietary preference, hunting-killing technique, and phylogeny. We found that the bird-catching specialists, which possessed relatively long digits with short talons, were consistently separable. The large-mammal and fish specialists were equipped with relatively short and robust tarsi, and short digits with long and robust talons. The hindlimbs of medium-mammal specialists were characterized by long digits and a large digit 1 talon. However, the generalist group did not possess any specializations, because their structural elements were comparable to those of other dietary groups. An association was found between the ratio of toe to talon length and the selective pressures of prey capture and ease of killing. Morphological variation in this feature was consistent with phylogeny, because the Accipitridae were characterized by a larger ratio of toe to talon length on digits 1 and 2 than the Falconidae, and the diurnal raptors possessed an interdigital pattern of larger variation in ratio of toe to talon length than the nocturnal raptors. No link was found between dietary habit and tarsus length or robustness, because these features were apparently attributed to variations in hunting style. Our analysis highlights the interrelationship between the morphology of hindlimb structure and the functional pressures associated with predatory lifestyles. Aspects de la morphologie des membres postérieurs de quelques oiseaux de proie australiens : Une étude comparative et quantitative

Biomechanical capabilities influence postural control strategies in the cat hindlimb

During postural responses to perturbations, horizontal plane forces generated by the cat hindlimb are stereotypically directed either towards or away from the animal's center of mass, independent of perturbation direction. We used a static, three-dimensional musculoskeletal model of the hindlimb to investigate possible biomechanical determinants of this “force constraint strategy.” We hypothesized that directions in which the hindlimb can produce large forces are preferentially used in postural control. We computed feasible force sets (FFSs) based on hindlimb configurations of three cats during postural equilibrium tasks and compared them to horizontal plane postural force directions. The grand mean FFS was bimodal, with maxima near the posterior–anterior axis (−86±8° and 71±4°), and minima near the medial–lateral axis (177±8° and 8±8°). Experimental postural force directions clustered near both maxima; there were no medial postural forces near the absolute minimum. However, the medians of the anterior and posterior postural force direction histograms in the right hindlimb were rotated counter-clockwise from the FFS maxima ( p<0.05; Wilcoxon signed-rank test). Because the posterior–anterior alignment of the FFS is consistent with a hindlimb structure optimized for locomotion, we conclude that the biomechanical capabilities of the hindlimb strongly influence, but do not uniquely determine the force directions observed in the force constraint strategy. Forces used in postural control may reflect a balance between a neural preference for using forces in the directions of large feasible forces and other criteria, such as the stabilization of the center of mass, and muscular coordination strategies.

La bipédie des Oiseaux, facteur déterminant de leur réussite adaptative

The birds are flying animals but they are also basically bipeds. The theropod dinosaurs, precursors of the birds, were already cursorial bipeds. Because the body structure was modelled by aerodynamical constraints during the evolution, all birds, even those that do not fly anymore, share a typical avian body shape. The osteological differences between birds are more adjustments than deep disruptions. Nevertheless, the birds are very diversified in their way of life and habitat. Yet, the hind limbs of the birds are surprisingly efficient in many manners, such as taking off, landing, swimming and walking. The limb structures adaptability to the various tasks require different mechanical fitness or device such as shock absorber during landing, or thrusters during tacking off. Moreover, almost all birds can walk, even if they have another locomotor specialization, as swimming or flying. Depending on the specialization, the gait features of the walk and the kinematics pattern are slightly modified. The functional adaptability of their hind limb structure may be a key to the evolutive success of the birds.

Notes on Hind Limb Structure in the Salamander, Paramesotriton deloustali, and Its Mode of Life

Notes on Hind Limb Structure in the Salamander, Paramesotriton deloustali, and Its Mode of Life

Patterns of Morphological Evolution in Bird Genera of New World and Old World Peatlands

Morphological convergence is defined in evolutionary ecology as evolution toward similar dimensions of traits in unrelated animals that live in the same or similar environments. Because the genus is a taxonomic unit in which differences among species represent directional changes in morphology from a common ancestor, I look for evidence of morphological convergence by comparing radiations in sets of congeneric species of birds that occur in peatland habitats of northern Minnesota and eastern Finland. Through discriminant function analysis, I determined that habitats selected by species in peatland shrub areas of Minnesota were similar to habitats selected by species in peatland shrub areas Finland. This pattern held for the species in peatland forests, also, but not for those found in open peatlands. Open peatlands in Finland had more water pools and less vegetation than those in Minnesota. The morphological analysis used 15 characters: size and 14 shape variables (skeletal measurements adjusted for size) pertaining to three functional complexes (bill, flight apparatus, and hind limb). Special emphasis was placed on four genera in Minnesota, Zonotrichia, Spizella, Geothlypis, Dendroica, and one genus in Finland, Emberiza, because these genera have species that occur both in shrub and coniferous forest peatland habitats. In all five genera, species in shrub vegetation are consistently smaller, have relatively longer pelves and legs, and have wider and shallower sterna than their respective congeners forests. Furthermore, with the exception of Emberiza and Spizella, the bill, sternum, and humerus are relatively longer in the shrub—dwelling peatland species than in their respective congeners in coniferous forest. The most abundant species in the shrub vegetation in Minnesota (Cistothorus platensis) and in Finland (Acrocephalus schoenobaenus) are among the most extreme in this respect; they are relatively small, with relatively wide and shallow sterna, relatively long pelves and legs. Also, warblers breeding in shrub peatlands have relatively deeper and wider bills, but sparrows have relatively shallower and narrower bills than their respective congeners in coniferous forests. These morphological relationships indicated significant (P = .03, sign test) directional patterns of differentiation among distantly related genera (warbleres and sparrows) for morphology associated with movement through the habitat (e.g., hind limb structure, size, and sternal shape). Morphological differences associated with feeding, however, showed trends at the family level that probably reflect differences in diet and behavior between sparrows and warblers. The consistency of these patterns among the genera studied emphasizes (1) the sensitivity of species adaptations in morphology to habitat structure, and (2) the likelihood of a common underlying mechanisms for these results.