http://www.nytimes.com/2001/07/10/science/10MATE.html?pagewanted=all

July 10, 2001

Mating Dances Go On and On

By NATALIE ANGIER

Fairy tales never reveal exactly what happens once the prince and princess
have shaken the rice from their hair, but here's a sample of how other
coupled creatures interpret the phrase, "And they lived happily ever after":

Any time a pair of great-crested grebes reunites after a separation, the
white-cheeked, pointy-beaked water birds celebrate with an aquatic version
of the tango. As one bird dives and swims toward the other, its partner
arches its back and fluffs itself up, cat-style, until the diver bursts
through the water right next to it in the "ghost display," wings extended,
body erect. The two part, plunge back under and re- emerge with weeds
clutched like roses in their beaks. Pressing their breasts together, they
rise up and begin trampling their feet on the water, heads turning back and
forth.

For the siamang gibbons of Indonesia, marital harmony requires just that.
Pairs of the shaggy black primates sing duets for 15 minutes every other
day, barking, booming and screaming in such precise sequences that it often
takes newlyweds many months to learn to make beautiful music together.

How do porcupines do it? Very carefully — and very often. Improbable as it
seems, a porcupine pair copulates every day, 365 days a year, whether it's
breeding season or not.

Researchers have long attended to the details of animal courtship, of how
animals find mates, battle for mates, inspect, reject and select mates.
Scientists have sought to understand exactly what a peahen prefers in a
peacock or why two perfectly healthy young cichlid fish of the opposite sex
snub each other, or why men love a woman with glossy hair, high cheekbones
and Barbie doll proportions.

The field of sexual selection theory has exploded in recent years, with
scientists seeing in the nuances of mate choice an explanation for much of
nature's diversity, cruelty and beauty.

But a report in a recent issue of the journal Animal Behaviour argues that
researchers have been remiss when it comes to exploring and explaining the
many ritualized behaviors that animals engage in once they have chosen
their mates.

In a review entitled "Display in Monogamous Pairs," Carl-Adam Wachtmeister
of the University of Stockholm describes some of the spectacular and often
vigorous performances that a broad array of birds, mammals, fish and
insects engage in long after they have secured a partner. The displays may
be visual, sonic or sensual, or some artful exploitation of all body
systems at once.

Birds are especially prone to these exhibitions because the vast majority
breed in socially monogamous pairs. In at least 200 bird species, males and
females sing tightly scripted duets throughout their relationship.

Many others dance, dive in synchrony or mount each other in a Kama Sutra
suite of positions even when the male's testes have shut down for the
season and conception is impossible.

And while pair-bonding is much less common among mammals, where it does
occur, it is likely to be accompanied by a spectrum of marital rituals.
Mated tree shrews, for example, regularly lick each other's faces and necks
in a very specific fashion, with the recipient of the lick keeping its head
at a 45-degree angle and its eyes half-closed. Not until the recipient's
chin and nape have been exactingly groomed does it allow the licker to plop
down on top of it so the two can take a nap.

Far from being less flamboyant or stereotyped than courtship displays, said
Dr. Wachtmeister, post-pair-formation behaviors often are comparatively
more elaborate and time-consuming, and therefore should be placed within a
theoretical framework that can account for their evolution and maintenance.

As Dr. Wachtmeister sees it, traditional explanations of displays among
coupled animals have been either too hazy and generic — "strengthening the
pair bond" — or they have not been supported by evidence.

For example, he said, many biologists have proposed that the displays are
meant to keep the partner impressed and committed, thereby preventing the
mate from leaving the relationship. In essence, he said, such theories view
postmarital displays as a continuation of prenuptial displays, as a way of
flaunting one's quality and evident superiority over other potential partners.

But if fear of divorce were enough to inspire mated animals to spend so
much time and effort displaying to each other, said Dr. Wachtmeister, then
one would expect to see evidence that divorce or desertion were likely
possibilities among displaying monogamous species. That evidence, he said,
does not exist.

"In a lot of species that display extensively, the divorce rate is quite
low," he said in a telephone interview. "Often there seem to be very few
benefits to divorcing or changing partners, while the displays themselves
are very demanding. It doesn't make sense to go to all that effort if the
real risk of divorce is small."

As an alternative, Dr. Wachtmeister proposes that many of the displays are
a form of manipulation, a way of subtly persuading one's partner to take on
a greater share of family burdens and chores. By this theory, there is
always a question of who is going to tend to the nest, defend against
predators, forage for the next meal.

Displays, he said, might be one way in which the partners exhort each other
to pay attention, snap out of torpor and help out around the house. And the
more the animals rely on display to elicit help or effort from a partner,
said Dr. Wachtmeister, the more extreme and conspicuous those displays are
likely to become over time.

Other scientists said they appreciated Dr. Wachtmeister's effort to
highlight nature's panoply of postpairing displays, but not all of them
agreed with his interpretation of their purpose.

On the concurring side is Dr. Richard Dawkins, an evolutionary biologist at
Oxford University who with John Krebs wrote an influential paper in 1978
about various animal signals and whether they were intended to convey
information or to manipulate the recipient.

"I am naturally sympathetic to manipulation theories," Dr. Dawkins said.
People often confuse manipulation with deception, he said, but the two are
distinctly different phenomena.

Deception is information transmission, he said — misleading information.
Manipulative signals, by contrast, do not necessarily convey information
but are instead an attempt to change another's behavior.

"I am glad that Wachtmeister has restored the original emphasis on
manipulation," Dr. Dawkins said.

But Dr. Geoffrey Miller, an evolutionary psychologist at the London School
of Economics and author of "The Mating Mind," said flatly, "Wachtmeister's
explanation doesn't work."

"His empirical observations are reasonable, and he's asking very
interesting and important questions," Dr. Miller continued. "But the
problem with manipulation is that it doesn't tend to be evolutionarily
stable. It's too easy for the intended recipient to evolve resistance to
the manipulative display, to essentially ignore it."

Dr. Wachtmeister is by no means the first biologist to wonder about
postnuptial displays. In the early 20th century, the renowned biologist Sir
Julian Huxley noted many of these performances, including those of the
tango-loving grebes. Sir Julian argued that Darwin's theory of sexual
selection could not easily be applied to these behaviors because they
occurred after mates had been chosen, even after young had been born.

Since then, biologists have recorded an array of pair displays, tagging
them by descriptive terms that may or may not reflect what they are really
about. A number of birds engage in so-called nest relief ceremonies. For
example, in the avocet, a shorebird with a characteristically upturned
beak, when one flies in to take over incubation duties, the seated bird
rises up in greeting. The two exchange a series of "cwit-cwit- cwit" sounds
(quitting time!) and begin throwing straw at each other. Finally, the
relieving partner settles onto the eggs and the freed mate flies off.

Many paired creatures are masterful greeters. Nothing is more elegant than
the sight of a seahorse reunion, as the female and male fish jointly
entwine their tails around a blade of seagrass, knock snouts and quiver in
apparent pleasure, or perhaps relief that neither has been eaten.

Other species will perform "triumph ceremonies" that seem partly
territorial in nature. When a pair of wedded geese have evicted an intruder
from their nest, for instance, the geese first extend their necks forward
and wave them up and down, then hold their necks horizontal to the ground
and emit a formalized series of cackles that sound like snores.

Charming and even romantic as some of these behaviors may seem, evolution
is not driven by gratuitous sentiment, so Dr. Wachtmeister and his
colleagues have performed computer simulations of how displays may evolve.

Their work points to a role for manipulation among pair-bonding creatures.
"In these species, there is conflict over the amount of parental effort
each partner should contribute," Dr. Wachtmeister writes. "Evolution may
favor individuals that can persuade their partner to make a greater
investment," thereby saving their own resources for future reproduction
should their current mate die, or perhaps to invest in a sneaky extra-pair
relationship of the moment.

The displays become something of an arms race, with each partner ratcheting
up the noise of the signal to catch the mate's attention. Dr. Wachtmeister
admits that the theory is in its fledgling stage and not yet proven with a
body of field data. However, he said, some evidence supports it.

For example, Dr. Nancy Burley of the University of California at Irvine has
demonstrated that, when she artificially manipulates certain traits on the
pair-bonding zebra finch, enhancing the size of their crest or changing the
color of their leg bands, the mate often responds by increasing or
decreasing its willingness to work hard on parental duties.

Dr. Patricia Adair Gowaty of the University of Georgia has found that
female bluebirds that signal their neediness, even incompetence, to their
mates end up getting comparatively more help from the husband than do those
females that seem fit and competent — though as yet there is no evidence
that the helpless act increases a female's reproductive success.

Dr. Miller dismisses the likelihood that manipulation plays a sustained
role in animal displays. Instead, he favors the explanation that Dr.
Wachtmeister discounts — that the displays are an extension of courtship
behaviors, intended to trumpet what a wonderful match the mate has made.

In essence, partners in a relationship are forever evaluating its worth and
wondering if something better doesn't lie in other straw-stitched quarters.

Even the rarity of divorce among displaying animals is no argument against
this theory, Dr. Miller said. He points out that recent DNA studies have
shown infidelity to be rampant among socially monogamous birds and mammals.

Thus, the displays could evolve as an effort on each partner's part to
minimize the mate's tendency to roam.

"It's more a stable strategy if your partner is giving an honest signal,
saying, `I'm healthy, I'm fit, I'm a good partner,' " Dr. Miller said.
"Then it's very much in your interest to listen to them and respond
positively," rather than to become immune to attempts at manipulation.

One way to check this proposition, Dr. Miller said, would be to compare the
rates of infidelity among high- and low-displaying species. "I would
predict that the greater the incidence of sexual infidelity, the greater
the rate of pair displays," he said.

He also said that many displays might exist, not so much to demonstrate
each individual's quality but as a way of showing each other how well they
work as a team, a gentle reminder of a coordinated program that has taken
time to nurture and that might be difficult to recapitulate elsewhere.
"Look at how long it takes gibbons to perfect their dueting skills," he said.

Dr. Miller said the Wachtmeister paper had inspired him to think of the
role of marital displays among humans. "This paper, this line of research,
might lead to some interesting marriage counseling suggestions," he said.
"Instead of talking out their problems together, maybe couples should learn
joint skills together, like ballroom dancing or doubles tennis. Hanging
wallpaper together is my parents' favorite." Thanks — but I'd rather go
toss some straw.

Copyright 2001 The New York Times Company