Can Two Different Shark Species Hybridize?

Question: I just read an article about a beluga whale hybridizing with a narwhal. Can sharks hybridize too?

-Andrew D., Massachusetts

Answer: Yes, some shark species can hybridize, which means two distinct species of sharks can breed and produce offspring that’s a genetic mix of both species! The first example of this was published in 2011. A team of Australian researchers documented 57 individual sharks that were actually hybrids between common blacktip sharks and Australian blacktip sharks. This discovery got a ton of media coverage at the time, and most of it was wildly inaccurate (see my 2012 rant about this on my blog).

But wait—there’s more! In April 2019, another team of researchers published evidence of hybridization between scalloped hammerhead sharks and the newly discovered co-occurring Carolina hammerhead sharks. These scientists found 10 sharks that were hybrids between scalloped and Carolina hammerhead sharks, and 15 “backcrosses” (sharks that had one hybrid Carolina-scalloped as a parent and one pure Carolina hammerhead as a parent). This means that the hybrids are actually reproductively viable individuals in their own right, unlike, say, a mule.

Later this year, even more evidence of shark hybrids was published. (Technically this is in the July issue of Molecular Phylogenetics and Evolution, so it’s hot off the presses, even though it’s been online for months, because academia is weird like that.). In this case, scientists found evidence that dusky sharks and Galapagos sharks were interbreeding to create hybrids—and those hybrids were able to backcross!

So yes, several different shark species can hybridize, and this is probably more common than we know but just hasn’t been detected very much yet.

But wait, you may be thinking. I learned in high school biology that hybrids are all like mules and can never reproduce themselves! All I can tell you is that the technical definition of what exactly makes a species has given a lot of smart people headaches, and that the natural world is much more complicated and fascinating than introductory textbooks portray.

Ask a Marine Biologist is a biweekly column where Dr. David Shiffman answers your questions about the underwater world. Topics are chosen from reader-submitted queries as well as data from common internet searches. If you have a question you’d like answered in a future Ask a Marine Biologist column, or if you have a question about the answer given in this column, email Shiffman at WhySharksMatter@gmail.com with subject line “Ask a marine biologist.”

Dr. David Shiffman is a marine conservation biologist specializing in the ecology and conservation of sharks. An award-winning public science educator, David has spoken to thousands of people around the world about marine biology and conservation, and has bylines with the Washington Post, Scientific American, New Scientist, Gizmodo and more. Follow him on Twitter, Facebook and Instagram, where he’s always happy to answer any questions about sharks.