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Updates on the Ray-Hybrid Phenomenon

April 17, 2024

In the Aquarium and Shark Lab of Team ECCO in North Carolina, there is a mystery in the water: Charlotte the California round stingray has become pregnant with three or four pups despite the lack of male rays!

Before we get into this mystery, let’s learn a little more about Charlotte. She is a round stingray with brown and yellow muddled spots. This type of stingray can be anywhere from 20 to 55 centimeters in length. Most round stingrays are found near California or in the eastern Pacific Ocean. They like to eat all types of invertebrates, like shrimps and crabs. Round stingrays are usually pregnant for 3-4 months before giving birth to up to six pups. Now that we know more about Charlotte, let’s get back into uncovering this scientific phenomenon.

 

The news of Charlotte’s pregnancy caught the attention of many online and it continued to snowball when the head of the aquarium suggested that the stingray could have been impregnated by one of their sharks. 

 

While this was a very popular theory amongst those on social media, there are actually a few more scientifically reasonable ways for a ray to become pregnant without males.

 

The director of Team ECCO, Brenda Ramer, explained that while some rays can store sperm, there is no chance Charlotte could be pregnant this way, because no male stingrays have ever been in her tank. But wait, there were male sharks in her tank. There were two white spot bamboo sharks that had shared the tank with Charlotte last year. For some male sharks, they mate with females by biting them, so when the team found that Charlotte had some bite marks, the whole scenario just got more confusing. 

 

If you’re still wondering if a shark can actually breed with a stingray, think about it ilke this: according to Dr. Noah Bressman, “sharks and rays are as distantly related as humans and snakes, so a snake knocking up a human is just as likely as a shark knocking up a ray” (Bluesky). In short, their DNA is simply incompatible. 

 

So knowing that cross-species hybrids are plausible but extremely rare, we turn to a more likely explanation. While sexual reproduction is the norm for rays, some can occasionally pull off something different. They have this asexual reproduction method called parthenogenesis, which means “virgin birth.” This uncommon method lets them develop embryos without needing sperm. It’s not unheard of, though – this phenomenon “has been observed in more than 80 vertebrate species, many of which are fish and reptiles (Forbes).  

 

As of right now, there are not any updates from Team Ecco regarding Charlotte’s pregnancy. They’ve posted an image of her ultrasound on their Instagram and some other cute videos as well. Hopefully Charlotte has a smooth delivery!

 

Sources:

Hobson, M. (22 February 2024). This stingray is about to have a ‘virgin birth’. Scientists explain how. Discover Wildlife. https://www.discoverwildlife.com/news/stingray-virgin-birth-parthenogenesis

Large, H. (13 February 2024). Shark-Ray Hybrid? Aquarium Suggests Shark May Have Impregnated Its Lone Stingray. IFL Science. https://www.iflscience.com/shark-ray-hybrid-aquarium-suggests-shark-may-have-impregnated-their-lone-stingray-72919

Murray, C. (14 February 2024). No, Sharks Cannot Impregnate Stingrays – As North Carolina Aquarium Investigates Mysterious Pregnancy. Forbes. https://www.forbes.com/sites/conormurray/2024/02/14/no-sharks-cannot-impregnate-stingrays-as-north-carolina-aquarium-investigates-mysterious-pregnancy/?sh=6b7774aa28ed

Whitehead, B., Berger, J. (17 February 2024). ‘Miraculous birth’ expected from stingray with no mate, possible impregnated by shark. ABC 13 News. https://wlos.com/news/local/stingray-miracle-birth-expected-team-ecco-shark-lab-hendersonville-aquarium-parthenogenesis-possibly-impregnanted-shark-no-male-mate-clone-female-charlotte-jurassic-park#

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  Timothy Durham was convicted of rape when a test showed his DNA genotype matched the DNA recovered from the crime scene. Eye witnesses testified that Durham was in a different state at the time of the incident, but he wasn’t exonerated from his 3000 year sentence until follow up DNA analysis showed that the preliminary forensic analysis used in the trial was misinterpreted (Thomas et al.). DNA testing serves an invaluable part in our criminal justice system, but it comes with complications and bias that can lead to wrongful convictions and misinformed juries.  

Background:

Forensic genetics aims to identify the origin of a biological sample. It can be traced back to Karl Landsteiner who discovered human ABO blood groups. With blood groups, suspects could be eliminated based on their blood type. For example, if a suspect had type A blood and there was type B blood left at the scene by the perpetrator, the investigators could rule out the suspect. Unfortunately, the reverse didn’t work. If the suspect and perpetrator both had the same blood type, it can’t be concluded that the suspect was guilty. Blood identifiers evolved into 8 distinct categories which improved the ability to eliminate suspects, but could only conclude that (if the system matched) it might be the perpetrator or this person might be related to the perpetrator (Jobling and Gill). The field evolved in the 1980s with the discovery of Minisatellites, lines of repetitive DNA that don’t encode proteins. Minisatellite patterns in DNA create what we know today as the DNA fingerprint, and it has a much higher accuracy rate than previous methods (Augustyn et al.). Around the same time, a breakthrough for victims of sexual assault was discovered. In the case of assault, bodily fluids of both the victim and the assaulter can get mixed. A process called differential lysis was created which could selectively increase the concentration of sperm in a fluid sample thereby allowing for accurate DNA testing (Jobling and Gill). Forensics evolved to use single-locus probe testing after several years because of its ease of interpretation. It looked at specific minisatellites that had high variability between subjects. This was the first DNA-based method to be used in a criminal investigation. Two murder homicides from several years apart were connected using DNA evidence. The evidence was then used to exonerate an innocent man, and the guilty party was found when he tried to evade mandatory DNA testing for all men in the small town. His guilt was then reinforced when the DNA profiles matched, and he gave a confession (Jobling and Gill). Finding DNA at a crime scene doesn’t guarantee that you’ll find a murderer. There are issues with non-pure samples and limited samples that make DNA work difficult, and accreditation of facilities and new techniques and take time (Jobling and Gill).  

Subjectivity of DNA Interpretation:

In a 2009 publication, the National Academy of Science discusses the possibility for subjective influence in lab based forensics. The interpretation bias happens in complex cases where, for example, there could be a mixture of DNA. A study published in 2011 looked specifically at this issue. A gang rape happened in Georgia, and the mixture in DNA from the case was used to prosecute one suspect after another suspect took a plea bargain to testify against him. With DNA mixtures, there are three possible conclusions: suspect excluded, suspect cannot be excluded, and inconclusive. If the suspect is excluded, it means that there’s little to no possibility that his DNA is part of the sample. If the suspect cannot be excluded, it means that there’s a possibility that his DNA is part of the sample. In the trial, the DNA examiners who knew the context of the case concluded that the suspect being prosecuted could not be excluded. The 2011 study gave the DNA evidence from this case and the DNA profiles of the suspects to 17 forensic examiners. These examiners had no context of the case, and they all worked independently. Of the 17, only 1 came to the same conclusion (suspect cannot be excluded) as the examiners who knew the context of the case. Twelve of the 17 concluded that the suspect who was prosecuted and convicted had no relation to the DNA found in the sample. Not only does this show that subjectivity occurs due to the context of the case, but the 17 examiners came up with different findings based on their past experiences meaning that not all DNA analysis is objective. Some organizations like the Scientific Working Group on DNA Analysis Methods say that quantitative statistical evidence should be presented with every categorical conclusion, but the US doesn’t require this (Dror and Hampikian).

False Positives:

There are two categories that cause wrongful identification in a DNA report: coincidental matches and false positives. Coincidental matches are DNA matches between two unrelated people. The probability of these matches is about 1 to 500,000 for white individuals and about 1 to 350,000 for black individuals. This small probability of coincidental matches makes people feel confident in DNA evidence. False positives, on the other hand, are matches between DNA and test DNA that result from issues in the forensics lab. There have been multiple cases of forensics labs accidentally switching victim and suspected rapist DNA which lead to convictions that were later overturned when the lab realized the error. There are also cases of misreading or misunderstanding a sample. In a case from 1993, a man was convicted of rape because someone interpreted a mixed sample of victim and perpetrator DNA as an individual sample. The conviction was again overturned. To prevent false convictions, retesting DNA is allowed, but it’s not an efficient solution. Many people are pushing for statistical information on the probability of false positives, so that the jurors can make accurate judgements based on DNA evidence (Thomas et al.).  

Conclusion:

DNA analysis is a useful tool for the criminal justice system, but subjectivity can be an issue in forensic testing. To combat wrongful convictions, there are organizations like The Innocence Project who use DNA testing to free the innocent, but reformed forensic testing standards should be put in place to prevent subjectivity and to ensure juries are correctly informed during trials. https://www.innocenceproject.org/    

Citation:

Augustyn , Adam, et al. “DNA Finerprinting.” Encyclopedia Britannica , 26 Apr. 2018, www.britannica.com/science/DNA-fingerprinting#ref153186. Dror, Itiel E., and Greg Hampikian. “Subjectivity and Bias in Forensic DNA Mixture Interpretation.” Science & Justice, vol. 51, no. 4, 2011, pp. 204–208., doi:10.1016/j.scijus.2011.08.004. Jobling, Mark A., and Peter Gill. “Encoded Evidence: DNA in Forensic Analysis.” Nature Reviews: Genetics, vol. 5, no. 10, Oct. 2004, pp. 739–751., doi:10.1038/nrg1455. Thompson, William C, et al. “How the Probability of a False Positive Affects the Value of DNA Evidence.” Journal of Forensic Sciences, vol. 48, no. 1, Jan. 2003, pp. 1–8., doi:10.1520/jfs2001171.