Alternatively, it may be that waterborne residues from human contraceptive pills or other "gender-bending" pollutants known to be affecting fish and amphibians are also harming the squid, Hoving said.
(Related news: "Sex-Changing Chemicals Found in Potomac River" [January 22, 2007].)
Previous studies have suggested "contaminating chemicals are slowly getting into the deep-sea food web," Hoving noted.
Another surprise was the first recorded case of a squid that fertilizes its eggs internally.
In a still largely mysterious process, female squid are generally thought to release their eggs into the water to be fertilized by sperm left on their bodies by males.
But females of the mini-squid Heteroteuthis dispar were found to have an internal sperm storage sac that connects to the oviducts, the tubes through which eggs pass.
"Spawning and fertilization is usually external in squid, but this species suggests it can happen internally," Hoving said. "The sperm is able to migrate toward the eggs before they leave the body."
Squid expert Vladimir Laptikhovsky, a government fisheries scientist for the Falkland Islands, described the find as "an outstanding discovery."
Laptikhovsky, who collaborated with Hoving on related studies, said that "internal fertilization occurs in octopods, but in squids it is the first time [this has been recorded]. Nobody could expect such an evolutionary novelty."
Mike Vecchione of the Smithsonian's National Museum of Natural History in Washington, D.C., called the internal fertilization find "remarkable."
The discovery of male squid with female characteristics is also "completely new," he said.
Strange reproductive strategies are often seen among deep-sea creatures, Vecchione noted.
"For instance, there are angler fishes where the males are basically parasitic on the female. The male sniffs out the female and then bites her, and then turns into a parasitic bag of sperm," he said.
"The deep sea is an alien environment that's huge and very diffuse," he added, "so finding a mate and sticking with her until fertilization occurs is a challenge."
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