Our tale of a whale: how we investigated the evolution of sonar in whales

 

Nick and I looked back on the unexpected pathway of our research on the evolution of sonar in whales.  Here we summarize highlights, and to the right, we actually traced our journey through the science flowchart. 

It all started when my grad student and I were asked to write a book chapter about whale ecology.

•   Our literature search led us to ask questions about the evolution of sonar in whales. We found one hypothesis already out there: sonar was originally an adaptation for hunting in turbid freshwater.


•   We rejected that hypothesis based on the isotopic signatures of fossil whale bones: whales seem to have been ocean dwelling at the time that echolocation evolved.


•   We went back to the drawing board and were chatting one day when we suddenly realized that cephalopod diel migration (moving between surface and deeper waters during the day) might have something to do with it: perhaps sonar evolved as whales began to hunt cephalopods near the ocean's surface at night.


•   We tested this first by looking for a correlation between the evolution of sonar and whales moving from coastal areas to the open ocean, and second by reconstructing a cephalopod phylogeny to double check that cephalopods had already evolved diel migration at that time.


•   Then we spotted something in the literature that caused us to consider hard-shelled cephalopods as easily echolocated targets for whales. This led us to an additional line of supporting evidence: nautilus diversity crashed just as whale sonar evolved!


•   We published and soon got an email from another scientist in Denmark. His group was looking at a similar concept and is now investigating the utility of sonar in detecting nautiloids!