One day during field observations last year at Marion Island, a remote nature preserve in the southern Indian Ocean, something bizarre caught Tristan Scott’s eye: On a rocky beach, a sleek young male Antarctic fur seal was trying to mate with a king penguin.
The fur seals normally hunt penguins and eat them. But this seal was wrestling with the bird, chasing it as it repeatedly tried to escape. Baffled at first, Scott, a wildlife researcher, realised that the seal “was trying to court the penguin as if it were a female seal.”
When that failed, he “tore the bird to shreds and ate it,” Scott recalled.Disturbing as it may sound, such wayward mating behaviour is not unheard-of. An earlier episode of seal-on-penguin sexual violence, also at Marion Island, was reported in 2008 by Nico de Bruyn and colleagues at the University of Pretoria, in South Africa, where Scott is a graduate student.
The phenomenon is called misdirected mating, and it extends to other marine mammals. Wildlife experts say sea lions and sea otters have occasionally been seen forcing themselves on other types of seals and killing them. Indeed, some researchers say misdirected mating is not abnormal.
“These things happen in wildlife,” said Heather Harris, a veterinarian who has studied sea otters in Monterey Bay. “We think that it is within the spectrum of possible normal behaviour.”
And Axel Hochkirch, an evolutionary biologist at the University of Trier in Germany, called the behaviour “simply a bad mistake,” and added, “nature is not perfect.”
Nor is such mating limited to marine mammals. Insects, spiders, worms, frogs, birds and fish do it, too, Hochkirch said. The behaviour is a form of reproductive interference, in which an animal’s mate-recognition radar is imperfect; the encounters do not necessarily end fatally.
Some couplings between closely related species result in familiar hybrids, like the mule. But when mixed matings result in no viable offspring, scientists say, the behaviour is difficult to understand from the standpoint of evolution.
Why, for example, would a fur seal try to mate not just with a different species but with an entirely different class of animal? De Bruyn speculated that the episodes started out as normal penguin hunting but that “wires somehow got crossed” and set off a sexual response. Both incidents happened near the end of the seal breeding season – a time when males experience ‘huge testosterone boosts’ but when mating opportunities are monopolized by a few dominant males, leaving lower-ranking males with no outlet for their sexual excitement. As a result, the researchers say, the two frustrated male fur seals may have turned on the penguins.
Infamous reputation
Another example comes from Monterey Bay, where the local news media give expansive coverage to stranded California sea otter pups rehabilitated by the Monterey Bay Aquarium. One graduate of that programme had an infamous reputation: Morgan, who was rescued as a pup in 1995, released and then recaptured in 2001 after being spotted forcibly copulating with Pacific harbor seal pups, five of which did not survive.
Harris, Miller and their colleagues suspect the attacks were fostered by a recent demographic shift that resulted in more male otters than females. The species is polygynous – mating is dominated by a few males, as with the Antarctic fur seals – and Elkhorn Slough had become a bachelor pad for many nonterritorial male otters that were shut out of the mating game.
The researchers think that as a result, Morgan and the other misbehaving otters redirected their normal sexual responses toward the harbor seal pups, born at a large rookery in the same area.
That hypothesis is plausible, said Hochkirch, the German biologist. Something about how the seals looked or moved may have attracted the otters. For a wild male animal, “if you don’t find a good mate, you might try to copulate with something which is as close to a mate as possible,” he said. Sperm is cheap, so wasting it on the wrong species would probably not hurt the male’s reproductive success.
Here, too, the seal abuse is reflective of the sexual violence that is typical among sea otters. “Everyone thinks they’re cute and cuddly,” said Mark P Cotter, a biologist with Okeanis, a nonprofit marine research organization in Moss Landing. But when otters mate, he went on, the male bites the female on the face so she can’t get away. Female sea otters often die from mating trauma.
Another sexually aggressive species is the bottlenose dolphin. In the Bahamas, bottlenose dolphins are routinely seen sexually coercing smaller spotted dolphins, Mann said.
And on the West Coast, from 2007 to 2010, the California Marine Mammal Stranding Network recovered and autopsied 50 dead harbour porpoises that were apparently beaten up by dolphins, said Frances Gulland of the Marine Mammal Center in Sausalito. In one of three porpoise-bullying episodes in Monterey Bay that they filmed, Cotter and his colleagues saw a school of male dolphins batter a male porpoise to death.
The “porpicides,” as Cotter and colleagues called them in a paper last year, are mystifying: They confer no clear advantage to the dolphins, which seldom compete with porpoises for the same prey off California. “In nature, there’s really no right or wrong,” he said.
But conversely, said Mann of Georgetown, the mere fact that sexual conflicts are “natural” in wildlife does not imply that they are “moral or justifiable or anything else that has to do with human culture.”