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Biology

Ear wax holds untold treasures for whale researchers

Article: Trumble, S.J.; Robinson, E.M.; Berman-Kowalewski, M.; Potter, C.W.; Usenko, S. Blue whale earplug reveals lifetime contaminant exposure and hormone profiles. PNAS. September 16, 2013. doi: 10.1073/pnas.1311418110

Blue whale and human diver off the coast of Costa Rica (Published by National Geographic March 2009)

Blue whale and human diver off the coast of Costa Rica (Published by National Geographic March 2009)

I am sure many of you, like me, tend to pause before taking a Q-tip to your ear.  How could we simply discard ear wax, a product intended to protect our ear canals by effectively blocking out dust and bugs while removing dead cells and dirt?  But, in the end, a build-up of earwax could impede one’s hearing.  This is because land mammals use air-filled ear canals to guide sound waves to their eardrums.

The Blue whale’s lack of access to Q-tips, and its inability to use one should it stumble across a CVS, means ear wax, or cerumen, builds up through the years.  However, like toothed whales, baleen whales may use a lobe of fat connected to their jawbones to transmit sounds to their ears rather than air.  So, this wax may not greatly impede their hearing, and in fact, forms an earplug in whales’ ear canals which provides a unique and powerful tool for scientists to monitor chemical exposure and production over a whale’s lifetime.

Typically, pollutants are measured in whales through blubber (fat), blood, feces, and water spout samples.  However, these samples are limited in scope since they only provide a snapshot of net toxics accumulation at the time of collection.  A recent article in the Proceedings of the National Academy of Sciences explored the possibility of using a deceased Blue whale’s waxy earplug to determine its exposure to persistent organic pollutants (POPs) (i.e. pesticides, flame retardants, PCBs, fossil fuel emissions) every 6 months over its entire lifespan.

Illustration of a blue whale earplug. (A) Schematic diagram showing the location of the earplug within the ear canal: (a) whale skull, (b) tympanic bulla, (c) pars flaccida/tympanic membrane (“glove finger”), (d) cerumen (earplug), (e) external auditory meatus, (f) auditory canal, (g) muscle tissue, (h) blubber tissue, and (i) epidermis. (B) Extracted blue whale earplug; total length 25.4 cm. (C) Earplug longitudinal cross-section. (D) View (20x) or earplug cross-section showing discrete laminae. (Trumble et al. 2013)

Illustration of a blue whale earplug. (A) Schematic diagram showing the location of the earplug within the ear canal: (a) whale skull, (b) tympanic bulla, (c) pars flaccida/tympanic membrane (“glove finger”), (d) cerumen (earplug), (e) external auditory meatus, (f) auditory canal, (g) muscle tissue, (h) blubber tissue, and (i) epidermis. (B) Extracted blue whale earplug; total length 25.4 cm. (C) Earplug longitudinal cross-section. (D) View (20x) of earplug cross-section showing discrete laminae. (Trumble et al. 2013)

Ingested contaminants, along with hormones, are preserved in the whale’s earplug.  Unlike muscle and blubber, ear wax does not allow rapid biodegradation of compounds.  This wax builds up in laminar layers throughout the whale’s lifetime, producing a timeline of the whale’s existence, much like tree rings.  Researchers have successfully used earplugs in the past to determine the age of whales, but new research conducted by Baylor University’s Dr. Steven Trumble and colleagues effectively analyzed successive layers to reconstruct lifetime chemical profiles.

Combined with age estimates for each layer, wax rings can reveal when during the animal’s life that it generated certain hormones.  The whale analyzed was a 12 and a half year old male.  Testosterone spikes in individual wax layers were used to determine the age of sexual maturity (10 years of age).  Likewise, times of stress, such as weaning (around 12 months of age), migration, food availability, environmental conditions (including human-generated noise), and mating competition with other males can be tracked by cortisol levels in the wax layers.

Additionally, these wax layers can tell us when the whale was exposed to particular contaminants.  Measurements from this whale indicate that 20% of its POPs burden accumulated during the first 12 months of its life.  This was the same time period it was receiving milk from its mother, leading researchers to conclude that maternal transfer is a significant portion of a whale’s total lifetime toxics burden.  After that spike, pollutant concentrations in the whale increased steadily with age.  Mercury levels were also measured, however, Dr. Trumble’s group found that peak concentrations did not correlate with maternal transfer, and instead, may be related to regions of higher mercury concentrations along its route of migration.

This work is exciting because, until now, lifetime chemical profiles for the majority of species on the planet have been unattainable.  Even though earplugs can only be extracted after death, they are an invaluable record of a whale’s life and the impact of human activity over several years.  Anthropogenic, or human created, pollutants are having an impact on organisms and environments far from their origins.  The majority of organic pollutants are generated in the temperate zone of the Northern Hemisphere (30-60oN).  However, we see accumulations of these compounds in human and wildlife populations in remote areas, especially polar regions.  Such disproportionate concentrations are due to the long-range atmospheric transport of POPs.  Top predators suffer high levels of toxics in their bodies through bioaccumulation, the build-up of pollutants through the consumption of contaminated food.  Earplug analysis provides new ways to track contaminant exposure in the oceans through time.

Discussion

One Response to “Ear wax holds untold treasures for whale researchers”

  1. Neat research! How does ear wax reveal levels of human-generated noise? What about natural noises such as volcanic eruptions? Are the noises recorded in the wax just “large” ones such as the Navy is creating with weapons, or are “smaller” noises like ship propulsion also recorded?

    Posted by Judith | October 9, 2013, 8:09 pm

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