For obvious reasons, there's not a lot of observational data concerning the behavior of deep-sea-dwelling squid. But a new study has found indirect evidence that one species of squid—the 5-inch long Octopoteuthis deletron—mates both bisexually, and promiscuously.
How do you get indirect evidence of sex? If you've ever watched CSI, you can guess. It's all about looking for sperm.
Or, in this case, spermatophores. Squid mate differently from humans. Instead of depositing sperm-filled semen directly into a female, heterosexual squid mating involves a sperm-filled biological container, of sorts. The male attaches this spermatophore to the female, and over time the sperm get absorbed into her skin. (Which is, frankly, weird. Even for spermatophore-based sex.) So, when researchers wanted to see how much sex the squid were having, they just started looking at video of squid and counting the attached spermatophores. From the BBC:
"Going through hours of video, we found that both males and females carry sperm packages. As the locations of sperm packages were similar in both sexes, we concluded that males mate with males and females."
The finding surprised the team, said Dr Hoving.
The researchers found equal numbers of female and male squid that had had sperm packages deposited on them, indicating that same-sex mating was as frequent as encounters between squid of the opposite sex.
The number of sperm packages that had been deposited also suggested that these animals were promiscuous, the researchers said.
How you interpret those findings gets a lot more speculative, though. Hoving and his team are chalking it up to the fact that the normally solitary squid don't encounter many potential mates, and, thus, mate with every other squid they see. Just in case. But there are probably other directions you could take the same data. We just don't know enough about these squid to say for sure.
Image: Ventral view of O. deletron, holotype, 109 mm ML, showing photophore pattern. Drawing from Young (1972). Used through CC via Tree of Life Project.