Testing the biomechanical optimality of the wall thickness of limb bones in the red fox (Vulpes vulpes).
The optimum for the ratio K of the internal to external diameter of a marrow-filled tubular bone with minimum mass designed to withstand a given type of strength (yield/fatigue, stiffness, fracture or impact) depends on Q = rhom/rhob only, where rhom and rhob are the densities of marrow and bone. With computer-assisted evaluation of radiographs of 62 femurs in the red fox (Vulpes vulpes) we measured the values of K. The mean and standard deviation of K are 0.68 and 0.036, and K changes in the rather wide range from 0.59 to 0.74. Accepting the assumption of earlier authors that Q = 0.50 or 0.44, our data would support the hypothesis that the fox femurs are optimized to withstand yield, fatigue or stiffness strengths. However, since the Q-values are unknown, the possibility cannot be excluded that any studied fox bone with an appropriately selected Q-value is optimized for any strength type. Assuming Q = 0.50 or 0.44, the relative mass increments mu of the investigated fox bones are smaller than 5% under all four mechanical conditions. The evolutionary relevance of such tiny mu-values is questionable.
Bernáth
Balázs
B
Department of Biological Physics, Eötvös University, Pázmány Péter sétány 1, H-1117 Budapest, Hungary.
Suhai
Bence
B
Gerics
Balázs
B
Csorba
Gábor
G
Gasparik
Mihály
M
Horváth
Gábor
G
D000818:Animals; D001696:Biomechanical Phenomena; D015519:Bone Density; D001853:Bone Marrow; D005269:Femur / Q000000981:diagnostic imaging / Q000502:physiology*; D005589:Foxes / Q000502:physiology*; D006814:Hungary; D007091:Image Processing, Computer-Assisted; D066298:In Vitro Techniques; D011859:Radiography