Welcome to our brand new series “Evolution Events”! We are so excited to delve into some fascinating topics including fossils, DNA, evolution and animal behaviour. For our first episode, we are so excited to discuss a fascinating event that is killer whale, or orca, ecotype evolution. Much of this information has been summarized from the paper listed at the end of this article.
Did you know that there are various ecotypes of orca (Orcinus orca) all around the globe? Orcas are found in almost every ocean. In the North Pacific, three genetically distinct ecotypes of orca make their home; offshore, resident (Northern, Southern) and Bigg’s (transient) orcas. Each ecotype feeds on different prey and speaks a different language, or dialect. It is believed that Bigg’s and resident orcas diverged from a common ancestor at least 68,000-35,000 years ago, but some argue earlier.
The presence of different populations is not unique to the North Pacific, and other ecotypes exist around the world with varying genetics, prey, behaviour and communication. These populations may also have different physical characteristics (e.g. dorsal fins, saddle patches, size), travel in different sized groups and have unique hunting methods. In these images; a photo of an adult male Bigg’s orca (leftmost) and an adult male Southern Resident orca. What are some differences you can see?
Note that the left image has been flipped horizontally for comparison.
What might have led to these unique populations? Scientists think that a combination of factors may have been responsible for these changes that occurred over long periods of time. When animals diversify behaviourally (e.g. this can be due to environmental pressures or genetic variation), it can open up new pockets or “niches” in the ecosystem where animals can be successful, often with less competition.
Also according to this study, the structure of orca families and lives permits transfer of knowledge and social learning through matriarchs, allowing information to be kept.
It is important to keep in mind, however, that these niches are not claimed overnight and present-day ecotypes can not simply move freely between a variety of hunting, social and language varieties. This is evolution acting over time to produce unique populations of animals. This is why it is incredibly important to preserve the prey sources of all ecotypes of orcas, such as Chinook salmon for the endangered Southern Resident Killer Whales.
Summary by: Alexa D. B.Sc., Marine Naturalist for Five Star Whale Watching.
Article: Foote, A., Vijay, N., Ávila-Arcos, M. et al. Genome-culture coevolution promotes rapid divergence of killer whale ecotypes. Nature Communications 7, 11693 (2016). https://doi.org/10.1038/ncomms11693.