Until today, little was known of the mating practices of deep sea squids. Most of them live more than 400 meters beneath the ocean's surface, making it very difficult for humans to observe their behavior in the crushing darkness. But now, with the help of robot submersibles, researchers have discovered that the deep sea squid Octopoteuthis deletron is a promiscuous bisexual creature. Males of the species implant their sperm into males just as often as they do females. And there's photographic evidence.
O. deletron is a squid who lives in the depths of the Eastern Pacific. Their arms are covered in hooks, and they are capable of signaling to each other using phosphorescence and color-changing cells called chromatophores. They're relatively short-lived, going through only one mating season in their lives. And that may be one major reason why they mate like crazy with each other.
Monterey Bay Aquarium Research Institute marine biologist Hendrik J. T. Hoving and his colleagues followed O. deletron around in the Monterey Submarine Canyon for 19 years, capturing the lives and habits of 108 squid during that time. So how did they figure out that O. deletron was a promiscuous bisexual? When males inseminate females, they do it in typical squid fashion: They shoot out a giant sack of sperm called a spermatangia, which burrows into the skin of their chosen mate and squirts sperm into them. Here's how Hoving and colleagues put it:
Males of the genus Octopoteuthis transfer spermatophores, complex structures containing millions of sperm, using a long terminal organ often referred to as a penis.
If you're wondering what a spermatangia is like, PZ Meyers has a good description:
Squid are often captured festooned with spermatophores and spermatangia, and in many cases, the spermatangia may be imbedded deeply into the musculature of the animal - so it's not simply as if the spermatophores are lovingly placed in an appropriate orifice, they are piercing the female (or the male, again, they don't care that much), tearing deep into the interior. The question is, how do they get in there? The answer is that spermatophores also release digestive enzymes and actively burrow into the target tissue.
As Meyers points out here, you can actually see the spermatangia on the surface of the squid's skin (they are the little white specks on the squid's head in this picture). Hoving and his colleagues simply checked to see which squid were festooned with these sperm sacks. As the researchers put it, "Males were as likely to be found mated as females were." Indeed, some of the males they saw had up to 25 spermatangia lodged in their skin.
You may be wondering a couple of things. First, is it possible that these males had accidentally shot themselves with spermatangia? It's not such a silly question, because pressure on the squid penis can cause them to automatically shoot their wads. However, the researchers considered this issue, and found that the spermatangia on the males were in locations that they could not have reached with their penises. So, the sperm had to have come from other males.
Along those same lines, is it possible that these were just "misfires," or males accidentally shooting males when they'd intended to shoot females? Apparently not. Hoving and colleagues point out that the squid have ample means of identifying each other, using their luminescent, color-changing skin — females and males could signal their sexes to each other, but they don't. So the males are basically ejaculating on every O. deletron they meet, without any concern for the sex of their partners.
Finally, you may be concerned about whether it's a good idea to impose our human notions of bisexuality, or even sexuality, on a creature who mates by shooting sperm sacks at other members of its species from a distance. Unfortunately, until we can communicate better with squid and find out what terms they are comfortable with, we're stuck with our human terminology for sexual congress with both sexes.
Whatever we call this squid mating strategy, it's clearly a decent plan for O. deletron to "shoot in the dark," as the researchers put it. They conclude that promiscuous bisexuality has evolved among these squid because it's simply the best reproductive method:
In spite of the potential for recognizing mates and the relative availability of members of both sexes (a 1 : 1 sex ratio), we observed statistically indistinguishable proportions of mated males and females. We conclude, therefore, that male O. deletron mate non-selectively with any [member of its species] . . . Apparently, the costs involved in losing sperm to another male are smaller than the costs of developing sex discrimination and courtship, or of not mating at all. This behaviour further exempliﬁes the ‘live fast and die young' life strategy of many cephalopods.
That's right — live fast, die young, and leave a sperm-covered corpse.
You can read the full scientific article via Biology Letters
All images courtesy of the Monterey Bay Aquarium Research Institute's remotely-operated vehicle.