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Surprise! This shark looks like a male on the outside, but it’s made babies

Bigeye houndsharks found off India’s coast had female reproductive systems

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10:00am, July 10, 2018
Male bigeye houndshark

BOY BITS  Male bigeye houndsharks have reproductive organs called claspers on their underbellies (inset), which have always been an easy way to distinguish them from females.

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It’s easy to tell a male from a female shark. Flip it over. If it has a pair of claspers — finger-like extensions jutting from the end of the pelvic fins — it is male; no claspers means female. Like a penis, claspers deliver sperm inside the female.

That was marine biologist Alissa Barnes’ understanding until she dissected seven bigeye houndsharks (Iago omanesis) with claspers and found a complete female reproductive system in each. None of the seven sharks had any internal male sex organs. Six were pregnant. Barnes, of the Dakshin Foundation, shared her findings June 25 at the 5th International Marine Conservation Congress in Kuching, Sarawak, Malaysia.

Barnes stumbled upon these hermaphrodite sharks at a port in Odhisa in eastern India in 2017. She was surveying local fishers to see if changes in their practices might explain a decline in hauls of sharks and rays. When she checked what the fishing vessels brought in, Barnes noticed two oddities. Male bigeye houndsharks greatly outnumbered females. And though males of this deepwater species are smaller than females, she saw immature males as large as female adults. Sensing something amiss, she took some sharks back to her lab for dissection.

“I was amazed,” says Barnes, who admits she squealed during the dissections. Even before opening the fish, she had pressed on the bellies of the "male" sharks and felt the pups inside.

“Hermaphroditism is very uncommon in sharks,” says shark biologist Colin Simpdendorfer of James Cook University in Townsville, Australia. He calls Barnes’ seven hermaphrodite sharks “one of the most unusual cases we have heard of” and says it’s an obvious developmental anomaly. Scientists can still use claspers to identify male sharks, Simpdendorfer assures.

Barnes’ finding isn’t the first among sharks. A 2005 study in the Journal of Fish Biology reported 68 hermaphrodites among 80 longhead catsharks (Apristurus longicephalus) from the Pacific and Indian Oceans. And surveys in the 1990s of bigeye houndsharks found more than 20 hermaphrodites among more than 60 sharks down the coast from where Barnes found hers.

With these other finds, Barnes is convinced “there is something going on” with the sharks. She suspects it might be pollutants in the water or hormonal changes — human-caused or otherwise — and is keen find out.

Citations

A. Barnes, M. Manoharakrishnan and N. Namboothri. Detecting drastic declines in a poor elasmobranch fisheries region. 5th International Marine Conservation Congress, Kuching, Sarawak, Malaysia, June 27, 2018.

A. Barnes, R.W. Jabado and N. Namboothri. Elasmobranchs through the looking glass. 5th International Marine Conservation Congress, Kuching, Sarawak, Malaysia, June 25, 2018. 

S. P. Iglesias, D.Y. Sellos and K. Nakaya. “Discovery of a normal hermaphroditic chondrichthyan species: Apristrus longicephalus.” Journal of Fish Biology. Vol. 66, February 2005, p. 417. doi: 10.1111/j.0022-1112.2005.00607.x.

Further Reading

S. Milius. Hermaphrodite wildflower has its own battle of the sexes. Science News. Vol. 192, August 5, 3017, p. 10. 

S. Milius. Battle of the hermaphrodites. Science News. Vol. 170, September 16, 2006, p. 186. 

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