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Scaling of axial muscle architecture in juvenile Alligator mississippiensis reveals an enhanced performance capacity of accessory breathing mechanisms
- Source :
- Journal of Anatomy
- Publication Year :
- 2021
- Publisher :
- Wiley, 2021.
-
Abstract
- Quantitative functional anatomy of amniote thoracic and abdominal regions is crucial to understanding constraints on and adaptations for facilitating simultaneous breathing and locomotion. Crocodilians have diverse locomotor modes and variable breathing mechanics facilitated by basal and derived (accessory) muscles. However, the inherent flexibility of these systems is not well studied, and the functional specialisation of the crocodilian trunk is yet to be investigated. Increases in body size and trunk stiffness would be expected to cause a disproportionate increase in muscle force demands and therefore constrain the basal costal aspiration mechanism, necessitating changes in respiratory mechanics. Here, we describe the anatomy of the trunk muscles, their properties that determine muscle performance (mass, length and physiological cross‐sectional area [PCSA]) and investigate their scaling in juvenile Alligator mississippiensis spanning an order of magnitude in body mass (359 g–5.5 kg). Comparatively, the expiratory muscles (transversus abdominis, rectus abdominis, iliocostalis), which compress the trunk, have greater relative PCSA being specialised for greater force‐generating capacity, while the inspiratory muscles (diaphragmaticus, truncocaudalis ischiotruncus, ischiopubis), which create negative internal pressure, have greater relative fascicle lengths, being adapted for greater working range and contraction velocity. Fascicle lengths of the accessory diaphragmaticus scaled with positive allometry in the alligators examined, enhancing contractile capacity, in line with this muscle's ability to modulate both tidal volume and breathing frequency in response to energetic demand during terrestrial locomotion. The iliocostalis, an accessory expiratory muscle, also demonstrated positive allometry in fascicle lengths and mass. All accessory muscles of the infrapubic abdominal wall demonstrated positive allometry in PCSA, which would enhance their force‐generating capacity. Conversely, the basal tetrapod expiratory pump (transversus abdominis) scaled isometrically, which may indicate a decreased reliance on this muscle with ontogeny. Collectively, these findings would support existing anecdotal evidence that crocodilians shift their breathing mechanics as they increase in size. Furthermore, the functional specialisation of the diaphragmaticus and compliance of the body wall in the lumbar region against which it works may contribute to low‐cost breathing in crocodilians.<br />The figure shows the head and upper torso of an American alligator.
- Subjects :
- Histology
Flexibility (anatomy)
breathing
Biology
ventilatory mechanics
Abdomen
allometry
medicine
Animals
Muscle, Skeletal
crocodilian
Molecular Biology
Ecology, Evolution, Behavior and Systematics
Alligators and Crocodiles
archosaur
axial anatomy
Respiration
Cell Biology
Anatomy
Fascicle
Original Papers
Trunk
locomotion
Muscles of respiration
flexibility
medicine.anatomical_structure
muscle architecture
Iliocostalis
Breathing
Original Article
Allometry
Muscle architecture
Developmental Biology
Subjects
Details
- ISSN :
- 14697580 and 00218782
- Volume :
- 239
- Database :
- OpenAIRE
- Journal :
- Journal of Anatomy
- Accession number :
- edsair.doi.dedup.....b2ce9f28c93452b3e3c38ca1cf397ce7