The mystery of Charlotte, the pregnant stingray

SHOW NOTES

After finding out what David has been up to since his last appearance on World of Sharks, we recap the Charlotte story so far [10.10]. The aquarium where Charlotte lives is located in North Carolina, U.S., in a small, rural community far from the ocean. Despite there being no male stingrays in the tank, Charlotte became pregnant, a story that the aquarium shared to social media and local news outlets along with speculation as to what might have happened. Within weeks, the story had spread like wildfire across TikTok, Twitter and the wider media. It was even the focus of a skit on Saturday Night Live! David says that a “lot of goofy nonsense was shared” which contributed to the popularity of the story. The outlandish nature of some of these theories meant that it gained interest, fast – along with the fact that Charlotte herself could be classed as ‘cute’.

In the beginning, one of the most popular theories – one shared by the aquarium itself – was that Charlotte could have mated with another species [13.10]. Charlotte might not have shared her home with one of her own species, but there were a number of small sharks in the tank with her, some male. Charlotte was also sporting some bite marks that matched the size of the shark’s mouth. This led to speculation that the father was, in fact, a shark. But while a shark-ray hybrid might have been cool, it is just not biologically possible. Sharks and rays are both cartilaginous fishes and share a common ancestor, but they have been separated by hundreds of millions of years of evolution. It’s the equivalent of our relation to king cobras! In short, their reproductive systems are too different to work together. In addition, their genetic information is so dissimilar that even if Charlotte had managed to mate with a shark (which again, is highly unlikely), she still wouldn’t have produced viable offspring.

The next, slightly more plausible, theory is that of sperm storage [17.30]. This is found throughout the animal kingdom. Females may mate with a male, but environmental or biological conditions might not be suitable to produce and raise offspring. In other words, the female may be under biological or ecological stress – for example, she may be malnourished, injured, or there may be external stressors. Becoming pregnant would put her body under further stress – perhaps endangering her offspring or even herself.  In these circumstances, what some females can do is store sperm until matters have improved. The record for the longest period of time between mating and giving birth is four years! And, in a similar case to Charlotte where a female shark had become pregnant, seemingly without mating, it transpired that she had stored sperm from a mate. However, it seems that there is no history of Charlotte having ever encountered another round stingray – so while this theory is entirely plausible, it still seems to not quite be the right fit.

Which brings us onto our last, and perhaps coolest, theory: parthenogenesis [20.19]. This is a zoological phenomenon that occurs when females get pregnant without mating. Instead of the babies being a mixture of mom and dad’s genes, their entire genetic makeup comes from the mom. And it has been documented in a number of different animals, including many species of shark and a few species of ray. It has most often been observed in captivity, where individuals are healthy and thriving, but have had little chance to come across a mate. But it has also been seen in the wild – and this is not a good sign. It usually means that the number of individuals in a population has fallen so low that the female believes there is a very low chance of her ever finding a mate (for example, it has been seen in critically endangered sawfish). It is a last resort. In nature, the purpose of sexual reproduction is not only to ensure the survival of the species, but also to increase the genetic diversity which is integral to the overall health of the population. Reproducing asexually limits the genetic diversity, and doing this in perpetuity would result in inbreeding – which could cause a whole number of problems. So, while it might seem like a female ‘striking out on her own’, in the wild it’s not so positive. But, it is still a very interesting phenomenon, and it adds to the growing list of the amazing capabilities of sharks and rays.

So, parthenogenesis is the most likely theory behind Charlotte’s pregnancy. But could all of this media coverage and public interest be a good thing for sharks and rays [32.30]? It’s hard to say. While getting elasmobranchs into the minds of more people is beneficial, it can also be damaging if it spreads misinformation. David thinks that this kind of viral story is more likely to do the latter. A consistent problem, he says, is that while sharks are one of the most well-known groups of animals, the most important facts about them are not well-known. Equally, it is very difficult to ascertain if people then went on to try and find out more about sharks and rays after seeing the story, or even more so, whether they engaged in pro-conservation behaviours. But, there are lots of shark scientists and science communicators who are getting the facts out there, and working hard to combat misinformation when it arises (many of whom are on this podcast!).

ABOUT OUR GUEST

Dr David Shiffman

Dr David Shiffman is a marine conservation biologist who studies sharks and how to protect them. An award-winning writer, educator, and public speaker, his writings have appeared in National Geographic, the Washington Post, Scientific American, and a monthly column in SCUBA Diving Magazine. His new book, Why Sharks Matter: A Deep Dive with the World’s Most Misunderstood Predator, is available now from Johns Hopkins University Press. You can follow him on Twitter, Facebook, and Instagram @WhySharksMatter, where he’s always happy to answer any questions anyone has about sharks.

You can check out his book, Why Sharks Matter, here.

You can also find David on social media by following @whysharksmatter across all platforms.

If you are interested in applying to the International Marine Conservation Congress (IMCC), you can find more information here.