Whale lifetime recorded in earwax
Earwax from a blue whale has enabled scientists to reconstruct the lifetime hormone levels, development, maturation and exposure to environmental toxins of a blue whale.
The young animal, estimated to have been about 12 years old when it died, was the victim of a collision with a ship off the coast of Santa Barbara in California.
Scientists recovered the body and were able to study it in detail, including conducting an analysis of a structure called the earplug.
Over time, just like humans, whales produce a build-up of wax or cerumen in their ear canals. This accumulates in layers, like tree rings, enabling the animal to be aged.
Now Baylor University scientist Stephen Trumble and his colleagues, writing in PNAS, have successfully extracted from each of the "tree rings" of the 25cm long earplug from their whale traces of hormones, including testosterone and the stress-signal cortisol, as well as environmental contaminants, like DDT and its breakdown products, and mercury.
These substances are deposited in the layers of wax from the bloodstream, enabling the scientists to assemble a profile for each of these chemicals over the lifetime of the whale.
This is the first such a time course has been generated for blue whales and reveals periods when the animal was stressed, abrupt mercury peaks presumably coinciding with the whale feeding on contaminated plankton in certain geographies and a slow rise in testosterone to age ten and then a surge as the whale matured.
These findings add clarity to previous observations and speculations about blue whale physiology, which, because these animals are so rare, is notoriously hard to study.
The team also point out that there are many earplug specimens similar to the one they analysed here in museums. Analysed in the same way, these could provide a valuable glimpse into the realms of the world's largest animal, and perhaps point towards better ways to conserve a species on the brink of extinction.