Locomotion pattern and trunk musculoskeletal architecture among Urodela

Abstract

We comparatively examined the trunk musculature and prezygapophyseal angle of mid-trunk vertebra in eight urodele species with different locomotive modes (aquatic Siren intermedia, Amphiuma tridactylum, Necturus maculosus and Andrias japonicus; semi-aquatic Cynops pyrrhogaster, Cynops ensicauda; and terrestrial Hynobius nigrescens, Hynobius lichenatus and Ambystoma tigrinum). We found that the more terrestrial species were characterized by larger dorsal and abdominal muscle weight ratios compared with those of the more aquatic species, whereas muscle ratios of the lateral hypaxial musculature were larger in the more aquatic species. The lateral hypaxial muscles were thicker in the more aquatic species, whereas the M. rectus abdominis was more differentiated in the more terrestrial species. Our results suggest that larger lateral hypaxial muscles function for lateral bending during underwater locomotion in aquatic species. Larger dorsalis and abdominal muscles facilitate resistance against sagittal extension of the trunk, stabilization and support of the ventral contour line against gravity in terrestrial species. The more aquatic species possessed a more horizontal prezygapophyseal angle for more flexible lateral locomotion. In contrast, the more terrestrial species have an increasingly vertical prezygapophyseal angle to provide stronger column support against gravity. Thus, we conclude trunk structure in urodeles differs clearly according to their locomotive modes.

Positional strategy of trunk muscles among aquatic, semi-aquatic and terrestrial species in Urodela

“…Trunk muscles were treated as 3 groups of muscles, namely the dorsal muscles, lateral hypaxial muscles and abdominal muscles, from the functions and positions according to Naylor [12] and Omura et al . [13, 14]. Dorsal muscles, lateral hypaxial muscles and abdominal muscles were examined from the cross-sectional images (Fig.…”

“…Omura et al . [13, 14] quantified the weight ratios at the middle of the trunk. They divided the trunk muscles into three components, namely dorsal muscles, lateral hypaxial muscles and abdominal muscle.…”

“…They showed that more terrestrial species possess larger dorsal muscles and a larger abdominal muscle which is separated from lateral hypaxial muscles by fascia, whereas aquatic species possess larger and thicker lateral hypaxial muscles and a smaller abdominal muscle which is not clearly separated from lateral hypaxial muscles by fascia. It was suggested that the more terrestrial species use their enlarged dorsal and abdominal muscles to stabilize the body and to sustain the animal’s own weight against gravity, whereas the aquatic species use larger lateral hypaxial muscles as powerful locomotor apparatus for lateral bending during swimming [13, 14]. …”

Anatomía funcional de los músculos de la pared antero lateral del abdomen

“…Comenzando con los peces teleósteos y pulmonados se observa en ellos, como ya mencionamos, dos masas hipoaxiales con orientaciones opuestas (OE y OI) y una banda longitudinal (Recto) (O' Reilly et al, 2000;Liem, 2001;Kardong, 2014). Incluso análisis de sección transversal de dicha musculatura han permitido establecer que la misma es relativamente más ancha que la musculatura abdominal de tetrápodos (Omura, 2015). Estos músculos actúan de manera sinérgica, junto con el paquete muscular epiaxial durante la locomoción acuática con un menor desarrollo de los miembros, a través de las sucesivas ondulaciones laterales (Kardong, 2014).…”

“…A partir de esta etapa la locomoción está más integrada entre eje y miembro (Schilling, 2011). El rol principal de los músculos hipoaxiales laterales en la locomoción fue alterado al depender de los miembros, mucho más robustos en especies terrestres (Omura, 2015).…”