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Having lice is one of life’s lower moments. It causes much wailing, rending of garments, purchasing of funny little combs, and a crushing feeling of ickiness. But lice are common in the animal kingdom, afflicting everything from a teensy mouse to one of Earth’s most majestic creatures, the humpback whale. And according to a new paper, those lice may offer a peek into the whale’s world-spanning social networks.
Seven breeding populations of humpback whale summer in Antarctic waters. In winter, they migrate north into different parts of the Pacific, Atlantic, and Indian Oceans. How, and even if, these populations interact, especially during their annual migrations, has been a scientific mystery. But the study’s lead author Tammy Iwasa-Arai, a postdoctoral researcher at the Federal University of Rio de Janeiro, Brazil, has unearthed some clues. She focused on lice, common whale parasites, betting that they would offer more insight into the whales’ social contacts than satellite tags or other tracking methods.
“With a satellite, you are studying one single whale,” Iwasa-Arai says. Lice, however, allow researchers to study interactions between whale populations. And that means better data for policy and conservation.
Scientists have looked at many whales and dolphins’ social lives through a lousy lens before, but this is the first study of humpback lice. The louse in question is Cyamus boopis. The pale, quarter-sized crustacean eats skin and primarily clusters near the whales’ blowholes, scars, genitals, and also around the large barnacles that grow in their skin.
The louse makes a great whale migration-tracking tool for a few reasons. First, since it is host-specific and only parasitizes humpbacks, researchers know that an infected humpback could only have gotten the lice from another humpback. And, second, unlike other parasites with a free-swimming larval stage, C. boopis spends its entire life cycle attached to a whale. This means that in order for the lice to spread, a whale actually has to come in contact with another whale, such as when they fight or mate, explains Iwasa-Arai.
To get her data, Iwasa-Arai collected lice found on stranded humpbacks in Australia, Brazil, Argentina, and Namibia, covering four of the seven major populations. She sequenced the same small DNA snippet in each louse and then compared them. From previous studies of whale lice and their hosts she knew that the more the populations of whales—and thus their piggybacking lice—were in contact, the more similarities in the lice DNA sequences. The seven populations have strong ties to their own migration routes and breeding and feeding grounds; if the whales seem to have shared lice, it means they’ve likely interacted.
Since this is a preliminary study the sample size was small, but the lice genetics still hinted at unexpected patterns. For example, humpbacks from the western part of the South Atlantic did not share similar lice with their close neighbors in the eastern South Atlantic. Instead, their lice suggested that they had more contact with humpbacks from the more distant western South Pacific. Why whales would fraternize with another population from across the world more than with their close neighbors is an unanswered but intriguing question.
“I really think it’s a very interesting paper,” says Natalia Fraija Fernández, a postdoctoral researcher at the University of Valencia in Spain. Fernández studies whale parasites and has researched lice in pilot, gray, and southern right whales, and has examined dolphin population dynamics in the Atlantic Ocean and Mediterranean Sea by studying their parasites. She values studies like this because they illustrate how useful parasites can be to population studies. “The more data you know about a species and everything related to that species,” Fernández says, “[the more] you will have enough to provide accurate data to decision-makers.” Robust data on the whales’ interactions will eventually inform policy on which feeding, breeding, or meeting grounds need protection.
That nascent body of knowledge took a hit in 2018 when fire destroyed many of Iwasa-Arai’s lice samples at Brazil’s National Museum. But she is continuing her search for new specimens as she pursues her PhD. “We are trying to reconstruct the collection,” she says.
So, while most folks are desperately trying to get rid of lice, others are scouring the world for them. Science can bring about these absurdities: lice may be a source of annoyance, but they can also be an excellent source of data. Though, that’s probably cold comfort to parents trying to track down who shared their kindergartener’s hat.