Some whales have up to 14 spleens
Almost every species of vertebrate has a spleen, an organ for filtering blood. But why settle for just one when you could have 14? That seems to be the strategy of some cetaceans, the group that comprises whales and dolphins. When scientists first noticed extra spleens in some of these animals, they thought they might be related to injuries from ship strikes, because similarly traumatic events can lead humans to develop multiple copies of the organ. But a team of scientists in Brazil now reports that the accessory organs are apparently normal in cetaceans and may help the animals keep their blood oxygen levels up while making deep dives. They reached this conclusion after dissecting 63 cetaceans from 14 species, all found stranded on the northern coast of Brazil between 2009 and 2013. Thirty-eight of the stranded animals had extra spleens, with an additional one to 14 per cetacean, the team reports in this month’s issue of Zoomorphology. The accessory organs showed up in 13 species, including humpback whales (Megaptera novaeangliae), minke whales (Balaenoptera acutorostrata), short-finned pilot whales (Globicephala macrorhynchus), melon-headed whales (Peponocephala electra), and Guiana dolphins (Sotalia guianensis). Only a single specimen of a pygmy sperm whale (Kogia breviceps) had just one spleen. The extra organs weren’t associated with any sign of trauma or animals of a particular sex or age and were found in various places, with some firmly attached to the main spleen and others to the stomach. The scientists did find more spleens in larger cetaceans and species known for making particularly deep dives, such as humpback (pictured above) and short-finned pilot whales. The additional spleens, which would contract during a dive to release fresh blood with oxygenated red blood cells, are likely an adaptation for this behavior, the researchers say. The extra spleens found in other animals, including rabbits, Chinese hamsters, chickens, and capuchin monkeys, meanwhile, may be due to developmental problems.