Scientists Zhen Li and Jill D. Pasteris set out to investigate these changes in Atlantic bottlenose dolphins of varying ages: newborns less than three months old, juveniles of about two and a half years, and adults around twenty years old.Their toolkit included Raman spectroscopy and electron microprobe analysis for detailed, point-by-point examination, as well as carbon analysis instruments from UIC Inc. for broader measurements.
What they found was a bone unlike any other. The central areas of adult bullae contained a staggering 96% mineral content, with about 10% of that being carbonate. This is substantially more mineral than found in typical bones, and even more than the edges of the same bulla.
As the dolphins aged, their bullae underwent a transformation.
The researchers observed that the bones became more uniform in structure and composition. The porous edges filled in, and organic material decreased. Perhaps most intriguingly, they found that carbonate content increased with age, reaching that 10% level in adults.
This increase in carbonate came with an unexpected twist. Typically, in synthetic apatite (the mineral form found in bone), more carbonate means less crystallinity – a measure of structural order. But in the dolphin bullae, crystallinity held steady even as carbonate increased. The researchers propose this might be due to a simultaneous swap of sodium for calcium ions, maintaining the crystal structure.
The study revealed that the bulla’s transformation wasn’t uniform across time or space.
Changes in physical properties didn’t always align with chemical shifts, and the most significant alterations occurred later in life, rather than in the transition from newborn to juvenile.
While the extreme mineral content of the bulla sets it apart from “normal” bone, the researchers argue it still serves as a valuable model. Its unique properties allowed for detailed analysis impossible in collagen-rich bone, offering insights into how bone mineral might change with age in longer-lived mammals, including humans.
As we grapple with bone-degrading conditions like osteoporosis, understanding these mineral changes could prove crucial. The dolphin’s bulla, this oddity of the animal kingdom, may yet shed light on the aging process in our own bones.
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DOI: http://dx.doi.org/10.1016/j.bbagen.2014.03.012
