Killer whales are one of the most cosmopolitan creatures on Earth, swimming in every ocean around the world. They patrol the frigid waters near the poles and appear regularly in tropical regions from West Africa to Hawaii.
Although killer whale habitats and habits vary widely, all killer whales are considered to be part of a single global species. killer whale. (Despite their common name, killer whales are actually a member of the marine mammal family known as marine dolphins.)
Now, building on decades of research, scientists have found that two orca populations commonly observed off the Pacific coasts of the United States and Canada are actually very different from each other and from other killer whales. This suggests that they should be considered separate species.
In a paper published Tuesday in the journal Royal Society Open Science, scientists proposed giving new species designation to two groups of animals. One is known as the resident orca, and the other is often referred to as the big orca. Both types live in the eastern North Pacific, but their diets differ. Resident killer whales eat fish, with a particular preference for salmon, while big killer whales hunt marine mammals such as seals and sea lions.
The proposal includes many other documented behavioral, physical and genetic differences between the two killer whale populations, which have evolved apart from each other for hundreds of thousands of years, the scientists noted. did.
“These two types are genetically two of the most distantly related types in the entire world,” said Philip Morin, a geneticist at the National Oceanic and Atmospheric Administration's (NOAA) Southwest Fisheries Science Center and author of the study. he said. “They don't just behave differently. They're actually on the evolutionary trajectory that we think of as separate species.”
There is no single definition of what qualifies as a species, and the boundaries between animal populations are often blurred. But this taxonomic distinction could have conservation implications, allowing experts to make more informed decisions about how to manage different killer whale populations, scientists say. say:
“Orcas do face a variety of threats,” said John K. Ford, an orca expert and scientist emeritus at the Canadian Institute of Fisheries and Oceanography, who is not an author of the new paper.
In recent decades, for example, seal and sea lion populations have rebounded, fueling a population boom for Bigg's killer whales, he said. Meanwhile, resident killer whales are threatened by declining wild salmon stocks.
Dr Ford said the authors of the new paper made a “very strong case” by summarizing a growing body of evidence that resident killer whales and big killer whales are clearly different creatures. “These multiple lines of evidence all point in the same direction,” he says.
Dr Morin said the next step would be to submit a proposal to a committee of taxonomists from the Marine Mammal Society, which maintains the “most authoritative list of species.”
In recent years, scientific advances have allowed scientists to perform more sophisticated analyzes of killer whale genomes. Data suggests that Big Killer Whales diverged from other killer whales between 200,000 years ago and 300,000 years ago. As residents, they diverged from other killer whales about 100,000 years ago. Genetic and behavioral analyzes suggest that there has been little interbreeding between big killer whales and resident killer whales in recent years.
“It's very convincing evidence to suggest that they represent different species,” said Kim Parsons, a geneticist at NOAA's Northwest Fisheries Science Center and author of the study. .
Overall, the genomes were sufficiently different that scientists were able to predict with high accuracy whether a killer whale was a big killer whale or a killer whale based solely on its DNA.
The shape of the skull is similarly predictable. Biggs killer whales have larger, wider skulls than their inhabitants, and deeper, more curved jaws. This is a characteristic that may help them catch larger prey. Big killer whales are also slightly larger overall than their inhabitants, have wider and more pointed dorsal fins, and have different black and white markings.
There are also behavioral differences. Native killer whales live in large, stable pods and are known for being talkative and easily communicating while chasing fish. Big killer whales, on the other hand, live in small groups and hunt quietly. When they vocalize, their whistles sound different from those of the inhabitants.
The authors proposed a new scientific name for resident orcas. Orcinus arter. If the Marine Mammal Society accepts the proposal, scientists said they would consult with indigenous tribes in the Pacific Northwest to choose a new common name that reflects the cultural importance of killer whales.
Scientists have proposed that Big orca adopt a new scientific name, while keeping its common name in honor of influential killer whale researcher Michael Big. Orcinus lectipinus.
Further analysis may reveal other killer whale populations that are recognized as separate species, the scientists said.
“There's a lot of diversity in the ocean that we don't know about,” Morin says. “Even if it's an animal the size of a school bus.”