Meeting Abstract
A female bird must mobilize an enormous amount of calcium over a short time to create an eggshell. To prepare for this challenge, she creates a unique mineralized tissue, medullary bone, on the inner surface of her bone cavities before laying an egg. Although many bird species create medullary bone, we know little about how it alters whole-bone morphology and mechanics. Furthermore, we know almost nothing about the extent to which medullary bone protects the skeleton during eggshell formation. To clarify the influence of medullary bone formation and egg-laying on whole-bone morphology and mechanics, we perform two experiments. First, to outline the influence of medullary bone formation, we created an artificial model of medullary bone by implanting adult male zebra finches (Taeniopygia guttata) with a silastic tube filled with β-estradiol, and compared them with males given an empty implant. Second, to describe the influence of egg-laying, we obtained female T. guttata in the process of creating an eggshell and compared them with females that were not yet laying. We collected micro-computed tomography data from the humerus to analyze bone morphology and performed finite element analyses (FEA) to determine effects on whole-bone mechanics. Initial results show that medullary bone formation increases bone volume fraction in the midshaft, resulting in a slight increase in whole-bone resistance to torsion and bending. Trabecular (spongy) bone volume fraction also increases via increases in number and thickness of trabecular struts. These results suggest that medullary bone may be protective, but we are working on FEA and results from the egg-laying females to form a full picture. A better understanding of how the avian skeleton handles forming an eggshell will teach us about the evolution of egg-laying behavior.
