Many species exhibit sexual dimorphism, where the physical characteristic of the males and females are different from one another. Elasmobranchs are no different. Males have a pair of claspers, finger-like projects that extend out from the pelvic fins. The claspers are the equivalent of a penis, delivering sperm packages inside the female during mating (Parker, 2008; Skomal, 2016). Females lack claspers.
NOAA (Photographer). (n.d.). Sharpnose Shark Male v Female Gentials [Digital Image]. Retrieved from https://www.floridagofishing.com/species/species-sharks.htmlSo imagine marine biologist Alissa Barnes’ surprise when she began a dissection on what she believed to be seven male bigeye houndsharks (Iago omanensis) and found that not none of them had internal male organs to accompany their external male genitalia! Instead, each of them possessed a complete female reproductive system and six of them were pregnant (Law, 2018). Barnes shared her findings at this year’s 5th International Marine Conservation Congress in Malaysia (Barnes, Jabado, & Naboothri, 2018).
You might be wondering how on earth Barnes managed to not only find one case of hermaphroditism in this species, but seemed to hit the mother load with 6 out of 7 sharks. So what exactly is going on here? Well in 2017 Barnes came across these sharks in a port in Odhisa in Eastern India. She had been surveying local fisheries, observing changes in practices to try to explain the declines in shark and ray landings (Law, 2018). During these surveys, Barnes notices something unusual. Male bigeye hounsharks were greatly outnumbering females, and while male deepwater sharks are typically smaller than females, she noticed immature males were as large as the adult females. So it was off to the lab for dissection!
This is not the first finding of hermaphroditism in sharks, although it is incredibly rare. In the 1990’s, 20 hermaphroditic bigeye houndsharks were documented in the same region that Barnes discovered hers in a group of 60 (Devadoss, & Batcha, 1997). In 2005, Iglésias, Sellos, & Nakaya documented 68 hermaphroditic longhead catsharks (Apristurus longicephalus) among 80 specimens. For now, it is still a safe assumption that that external presence of claspers indicates a male shark. However, with more hermaphroditic sharks being observed, it is logical to wonder if these sharks have always been a part of the population and we are just starting to learn about their existence? Or could this change in biology be a response to changes in their environment? Pollutants or hormonal changes linked to other substrates in the water? Could we be doing this to them?
Thanks for checking out this odd and wonderful moment in elasmo-news! If you missed our Featured Species Friday, go take a peak at the tiger shark! There’s so much more to them than their incredible appetite!
Remember you can make a difference for marine ecosystems by contacting your Congress man or woman and telling them that you care about the quality of our waters! Sharks, rays, and other marine organisms cannot speak or be represented in Congress. They need your voice. Get involved and stand up for sharks. Until next time finatics.
Featured Image Source
Rotman, J. (Photographer). (2002). Bigeye houndshark [Digital Image]. Retrieved from http://www.pbs.org/
Barnes, A., Jabado, R. W., & Naboothri, N. (2018, June 25). Elasmobranchs through the looking glass. Speech presented at 5th International Marine Conservation Congress, Kabu.
Devadoss, P., & Batcha, H. (1997). Sex change in hound shark, along Madras coast. Marine Fisheries Information Service, Technical and Extension Series, 146, 9-10.
Iglésias, S. P., Sellos, D. Y., & Nakaya, K. (2005). Discovery of a normal hermaphroditic chondrichthyan species: Apristurus longicephalus. Journal of Fish Biology, 66(2), 417-428.
Law, Y. (2018, July 12). Surprise! This shark looks like a male on the outside, but it’s made babies. Retrieved from https://www.sciencenews.org/article/surprise-shark-looks-male-outside-its-made-babies