An Antarctic fur seal trying to mate with a king penguin. Photo by Tristan Scott |
By Ingfei Chen, The New York Times, November 26, 2012
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 as it repeatedly tried to escape.
Baffled at first, Mr. Scott, a wildlife researcher, realized 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,” Mr. Scott
recalled.
Disturbing as it may sound, such wayward mating behavior 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 Mr. 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 behavior.”
And Axel Hochkirch, an evolutionary biologist at the University of
Trier in Germany, called the behavior “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, Dr. Hochkirch said. The behavior is a form of
so-called 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 behavior 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?
Dr. 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.
Dr. de Bruyn pointed out that sexual aggression was common within many
marine mammal species; for instance, male fur seals often bite females on the
neck during mating. Sexual conflict occurs to varying degrees across the animal
kingdom, and in extreme cases, males’ coercive behavior may spill over to
forcing themselves on other species, said Janet Mann, a Georgetown University
field biologist.
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 program 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.
Observers documented 19 cases of attacks on harbor seals by Morgan and
at least two other male otters, mostly in the Elkhorn Slough area 30 miles
south of Santa Cruz. The aggressors were “harassing, dragging, guarding and
copulating with harbor seals” for up to a week after the pups were killed,
according to an analysis published in 2010.
That study, conducted at the California Department of Fish and Game in
Santa Cruz, was led by Dr. Harris, the sea-otter vet, who was then a research
assistant; Melissa Miller, a veterinary pathologist; and Stori Oates, a biologist
at Moss Landing Marine Laboratories. Their autopsies of seal corpses found bite
marks and lacerations on the nose and face, along with tearing consistent with
sexual trauma.
Diagnostic
tests found nothing awry in Morgan, who thereafter lived at the Fish and Game
wildlife facility; he participated in research conducted by the University of
California’s Long Marine Laboratory until he died of old age last March, at 17.
(Biologists remember him fondly: Mike Murray, a veterinarian at the Monterey
aquarium, said that during 11 years in captivity, Morgan taught scientists a
tremendous amount about “what makes sea otters tick.”)
Dr. Harris, Dr.
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 Dr. 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, Dr. Mann said.
And on the West Coast, from 2007 to 2010, the California Marine Mammal
Stranding Network recovered and autopsied 50 dead harbor porpoises
that were apparently beaten up by dolphins, said Frances Gulland of the Marine
Mammal Center in Sausalito, Calif. In one of three porpoise-bullying
episodes in Monterey Bay that they filmed, Mr. Cotter and his colleagues saw a
school of male dolphins batter a male porpoise to death.
The “porpicides,” as Mr. 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.
But because the observed assaults were perpetrated by young males “not
very high up on the social ladder,” Mr. Cotter said, high testosterone levels
during the breeding season may have fueled the violence.
He and other experts caution against judging animal aggressors by
human standards. “In nature, there’s really no right or wrong,” he said.
But conversely, said Dr. 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.”
Some biologists, afraid that animal sexual violence will be
misconstrued, are leery of discussing it. Wildlife scientists are usually
working to protect species, Dr. Mann said, and “they don’t want to jeopardize
that by sensationalized stories about their animals.”
Indeed, a few scientists declined interview requests, partly from
concerns that animals that engage in misdirected mating would wrongly be
perceived as sexual freaks. A case in point was Morgan the otter, who was cared
for by protective researchers. His death last March went unannounced — unlike
the passing of a female Monterey aquarium otter
who was eulogized in local newspapers that same month.
Terrie
Williams, a biology professor at Long Marine Lab, declined to answer questions
about Morgan. In an e-mail, she wrote: “My program’s involvement with Morgan
was strictly as an excellent and willing participant in our diving physiology studies.
I’d like to remember him as that.”
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