Earwax Tells A Whale Of A Story

The earwax of some whales builds up in layers continuously over their lifetimes. This phenomenon has been used to age the animals, much like tree rings. Sascha Usenko and Stephen J. Trumble of Baylor University have taken this tracking method a step further by tracing the concentrations of pollutants and hormones trapped in a blue whale’s earwax plug over time (Proc. Natl. Acad. Sci. USA 2013, DOI: 10.1073/pnas.1311418110). For Trumble, one of the most interesting findings is that testosterone spiked at around nine years of age, indicating the onset of sexual maturity, and the stress hormone cortisol spiked shortly thereafter. “Being a male, you can sort of say, ‘That makes sense,’ ” he says. “You’re roughing it up with the big guys out there and trying to mate; you can understand a spike in the stress hormone.” Going forward, the team will study earwax plugs in museum collections as well as from sources such as the ship collision that felled this blue whale. The team anticipates that the technique will fundamentally transform assessment of human impact on whales and their ecosystems.