As far as soft-bodied, tentacled creatures go, vampire squid live unusually long. And now, researchers studying these sinister-sounding squid have discovered something else that sets them apart: their sex lives. While most other cephalopods enjoy just one high-energy burst of reproduction, vampire squid have multiple reproductive cycles, according to findings published in Current Biology this week.
Vampire squid (Vampyroteuthis infernalis) were named after the undead bloodsuckers of lore because of their dark and sanguine coloration, the webbing of skin between their arms look cape-like, and their eyes can appear red or blue depending on the lighting. And while they aren’t immortal, their lifespan is longer than many other cephalopods because they live at a slower pace: Inhabiting the open ocean at depths of 500 to 3,000 meters (1,600 to 9,800 feet) means they don’t swim so much as float, and they survive on little oxygen while consuming a low-calorie diet of zooplankton and miscellaneous detritus. And now it looks like they’re the exception to yet another cephalopod rule.
All living cephalopods, from octopuses to cuttlefish (except the chambered nautilus) undergo just one single—sometimes spectacular—reproductive cycle, typically later in life. And after that, they die. Although some may grow between spawning events or spawn multiple batches, the eggs are created in one go and there’s no “gonadal resting phase.” Spawned adult female fish in this phase, for example, have no developing eggs in their ovaries.
While perusing decades-old vampire squid museum collections, Henk-Jan Hoving of the GEOMAR Helmholtz Centre for Ocean Research Kiel noticed that many females had spawned but had no ripe or developing eggs. Were they in a reproductive resting phase? So Hoving and colleagues examined 43 female vampire squids collected in net tows off southern California. Sure enough, these deep-sea dwellers seem to alternate between reproductive and resting phases.
Female vampire squid spawn their eggs, then return to a resting reproductive state that’s then followed by the development of a new batch of eggs. Ovulation is discontinuous, and this cycle might be repeated more than twenty times.
One 102-milimeter-long, 448-gram (1 lb) female in a resting phase had released at least 3,800 eggs—yet still had 6,500 eggs for future spawning. If an average batch size is 100 eggs, this female had already spawned about 38 times and has enough in her reserve for another 65 spawning episodes. Furthermore, based on her, the researchers think that the adult stage lasts for at least 3 to 8 years—so the total lifespan must exceed that.
“Their slow mode of life seems insufficient to support one big reproductive event," Hoving says in a news release. "Perhaps it is therefore that vampire squid return to a gonadal resting phase after spawning, and presumably start accumulating energy for a new reproductive cycle." However, given their low metabolic rates and low-calorie diet, it might take a long time to accumulate enough resources for the next spawning event. Although, if times get tough, they might reabsorb their developing eggs to save energy.
Images: Citron / CC-BY-SA-3.0 via Wikimedia (top), "Aus den Tiefen des Weltmeeres" by Carl Chun, 1903 via NOAA Photo Library (middle)