Banner: A small group of orcas swimming (taken 2012)
Imagine this: you start dating a new guy or gal from out of town and it's going amazingly. They're sweet, smart, and you seem to share a lot in common. But you soon start to notice something a little strange… they only eat fish. Exclusively. Salmon for breakfast, tuna for lunch and trout for dinner. Their fish breath starts to become unbearable and all the discarded fish skins in the trash make you gag. You would have to break it off, right? Don't worry, these brainy dolphins agree with you, too!
Many animals have weird mating rituals and preferences, but some orca whales almost exclusively mate with individuals who have similar diets. These preferences are part of an orca food culture that is passed down from older orcas to younger orcas within a population. Depending on which population they're born into, a young orca will be introduced to hunting strategies, vocal calls, and social structures that are specific to their orca community. Many of these learned habits have to do with what prey they hunt. Groups of orcas with these distinct cultures are called ecotypes.
Ecotypes of orca whales are still the same species, so technically they can mate with individuals from different ecotypes, but here's the weird thing — they almost never do! Although separate ecotypes of orcas live in the same region and come across each other regularly, they purposely do not interbreed with an orca from another group. They can recognize these cultural differences in each other, essentially turning their big, black noses up at anyone who doesn't eat like them!
In the North Pacific, there are two main orca whale ecotypes that exemplify these cultural differences: resident orcas and transient orcas. Resident orcas specialize in hunting fish, and tend to have smaller home ranges. These fish specialists eat salmon, mackerel, halibut and cod, although subgroups of resident orcas prefer one fish over another. Transient orcas, also called Bigg's orcas, eat mammals. They live in smaller groups than resident orcas, and travel over a large range from Southern California to the Arctic circle. Subgroups within the transient ecotype have favorite types of prey; some prefer seals, while other groups prefer minke whales or grey whales. Subgroups of the same ecotype will still interbreed, as long as their partner still eats the same type of food. These groups inhabit the same regions, but we know the ecotypes don't interbreed with each other because they differ genetically.
Although the ecotypes of orca in the North Pacific differ genetically, ecotypes in the Northern Atlantic ocean are not as clearly defined. Andrew Foote, an evolutionary biologist at the University of Copenhagen found that although different Atlantic orca populations seem to form ecotypes based on cultural preferences like their Pacific cousins, there are no major genetic differences between Northern Atlantic orcas. Foote and his colleagues also noticed something interesting when collecting samples from a family of orcas killed by aboriginal hunters. Foote commented to Science magazine that, “Each whale had a seal pup in its stomach, yet their teeth were worn like those of the herring-hunting whales.†This finding suggests diet preferences are not as strict in Atlantic populations, leading these less picky groups to interbreed more freely than their Pacific cousins.
In summary, North Pacific orcas are more picky about what their partners eat than North Atlantic orcas. This explains why ecotypes in the Pacific have major genetic differences while ecotypes in the Atlantic do not. If genetic differences between pacific ecotypes continue to grow, it's possible that they may even evolve into two different species of orca!
Currently, there is only one species of Orca whale, but there is incredible variation within the Orcinus orca group. Orcas are separated into ecotypes based on their diet preferences, and can be picky when it comes to who they mate with. I can't help but wonder what exactly Orca dating would look like… do transient orcas call resident orcas “fish breath?†Are North Atlantic ecotypes the casual daters of the orca world? Are there any Romeo & Juliet type scenarios in the North Pacific? Luckily, Orcas can teach us one thing: you can definitely break up with your fishy-smelling, pescatariean partner.
About the author
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Ellen Krall is an undergraduate at UGA studying Plant Biology. When she's not in classes or at the lab, she enjoys long walks in the State Botanical Garden, being kind of good at several instruments (violin, ukulele, banjo), and naming her Beta fish after famous scientists. More from Ellen Krall. |
