In The Animal Kingdom, A New Look At Female Beauty


In the grand story of evolution that scientists have been
reconstructing since Charles Darwin's voyage on H.

M.S. Beagle, the
chapter on mate selection reads something like this: males compete
among themselves to attract females, showing off their antlers,
bright plumage or other ornaments that signal good health. Females
watch the display from the sidelines, aloof and picky, like wealthy
patrons at an art exhibition.


When a male meets a female's approval, she agrees to court him
and finally grants him permission to impregnate her.
That account of mate choice, in which males do all the
dancing-to-impress and females sit on the judging panel, is being
increasingly viewed by scientists as too simplistic a broad-brush
picture that tells only part of the story.
Zoologists and evolutionary experts are coming up with evidence
that suggests greater evenness in gender equations across the
animal kingdom, meaning that females as well as males at least in
some species strive to attract the opposite sex.
A major part of this evidence is coming from studies of female
beauty in various bird and animal species, an area that has
received relatively little attention.

Since Darwin's time,
scientists have focused largely on male ornaments like the
peacock's flashy tail, whose main purpose is to impress a mate. The
view has been that males are the ones that are pressed into
developing ornamental features over many generations by an
evolutionary process known as sexual selection. The black bib of
the male house sparrow, for instance, is a result of female
preference for males having that feature.
Researchers are now finding that evolving such natural tuxedos
is not the sole privilege of males, suggesting that being choosy in
mates is not reserved for females.

They are also questioning the
belief that ornaments in females often duller versions of male
ornaments serve no function and are essentially genetic
gifts of male evolution that get
passed along in diluted fashion.
In many species, the researchers say, females are just as
strikingly adorned as males, and some of these ornaments are so
different in character as to suggest that some female ornamentation
may have evolved independently of males.
One scientist encouraging this change of opinion is Dr. Trond
Amundsen, a zoologist at the Norwegian University of Science and
Technology.

In recent years, he has emerged as something of a
champion of female beauty in the animal world. He lists numerous
species in which females have dazzling ornaments, like parrots,
hummingbirds, angelfish and butterflyfish.
In The Proceedings of the National Academy of Sciences last
November, Dr. Amundsen and Dr.

Elisabet Forsgren of Goteborg
University in Sweden reported that the male two-spotted goby, a
small fish found in rocky shores, prefers to mate with brightly
colored females.
At the time of breeding, male gobies display a pattern of blue
spots on their fins and sides while females develop a bright
yellow-orange patch on their bellies. In one experiment, the
researchers observed the behavior of male gobies toward females
that were naturally more or less colorful. In a second experiment,
they took pairs of females with matching roundness of bellies a
feature that could have influenced mating preference and painted
the two fish in each pair to make one look brighter than the
other.


In the experiments, the scientists found that the males engaged
in more courtship displays with the more colorful females.
(Typically, the male swims up to a female, displaying his fins and
lets his body break into a succession of shivers. An interested
female may bend over backward to seduce a male by showing off her
colorful belly.)
Other species also show ornamentation in females, but in most
cases they have reversed sex roles: female pipefish, for example,
compete aggressively for males instead of the other way around.


(Who plays what role in a species is determined mainly by its
male-to-female ratio.)
"Studies have shown that reversed sex roles can lead to reversed
ornamentation," Dr. Amundsen said. "This is unsurprising because
female ornaments in sex-role-reversed species are analogous to male
ornaments in conventional role species.

"
The flashy belly of the female goby, on the other hand, is
surprising because the males and females perform conventional sex
roles. Its presence suggests that females may evolve ornaments of
their own even when the pressure of finding a mate lies mostly on
the male.
The absence of a similar ornament in the male goby, the
researchers say, gets at the heart of the debate over how female
beauty originated. It strongly suggests, they add, that the
ornament cannot be attributed to genetic correlation or the
similarity between genes inherited by the two sexes, an argument
that scientists have traditionally used to explain female
ornamentation.


Although the scientists have not done genetic tests to confirm
the lack of correlation, Dr. Amundsen says it is extremely unlikely
that the blue spots and orange belly would be produced by the same
genes.
"It's simplistic to say that if genetic correlations occur,
sexual selection does not, and if one sex is choosy, then the other
sex isn't," Dr. Amundsen said.

"None of these need be entirely
true, and that's what we are now starting to acknowledge."
Other signs that genetic correlation may not be the whole story
come from studies of changes in male and female coloration in some
bird species over evolutionary time.
Dr. Geoff Hill of Auburn University, for example, found that the
plumes of the female house finch, a bird with reddish feathers on
its head and breast, grew brighter from one generation to the next
with no corresponding increase in male brightness.

"It wasn't
consistent with the idea of genetic correlation driving female
brightness," Dr. Hill said.
Combined with experimental evidence showing that male finches
prefer brighter female finches, the observation was a compelling
pointer to sexual selection acting on the female, he said.
Dr.

Russell Lande, a biologist at the University of California
at San Diego who in the 80's helped develop the genetic correlation
theory, says his original explanation for female ornamentation
still holds for "the most common situation in the animal kingdom
described by Darwin that is, for polygamous species in which males
have an exaggerated secondary sexual trait and females have a
rudimentary expression."
"In species where both sexes have similar ornamentation and both
parents care for the young," Dr. Lande said, "it is likely that
both sexes are involved in choosing mates to a nearly equal extent,
leading to parallel evolution of ornaments."
Such species have been the focus of studies in recent years,
confirming that males can be choosy when they benefit from
obtaining the highest-quality female, as is the case in species
where males provide a substantial amount of parental care to the
offspring.

In experimental studies on the crested auklet, a sea
bird that has a forward-curving tuft on its head, researchers have
found that both males and females show a preference for life-size
bird models with more prominent crests. Scientists studying the
Inca tern, a medium-size seabird, have shown that both males and
females display a long white mustache of feathers to advertise good
health.
What muddies the conclusions from some of these studies, said
Dr. Anders P.

Moller, a researcher at the Laboratory of Functioning
and Evolution of Ecological Systems in Paris, is the possibility
that the preference for an ornament may itself be inherited from
the opposite sex. "What's at the bottom of the story," Dr. Moller
said, "is whether the preference evolved first in females and was
later expressed in males."
In his own studies on barn swallows, Dr.

Moller found that
females preferred males with elongated tails but males did not show
a similar preference for long-tailed females. Although both male
and female swallows with longer tails produced more offspring, long
tails provided no benefit to females. In fact, artificially
lengthened tails hampered the females' ability to fly and reduced
their chances of survival.
Dr.

Moller's studies indicate that the association of an
ornament (long tail) with a sign of
fitness (more offspring) does not
automatically imply that the ornament has been sexually selected in
the female. It could still be a result of genetic correlation with
the male. "We need more studies showing the link between female
ornaments and female quality," Dr. Moller said.


Dr. Amundsen welcomes the suggestion, pointing out that female
beauty has been in the shadows for too long. "From a closer look at
female ornamentation," he said, "we are already beginning to
understand that mating competition may be more complex than
previously thought."
By Yudhijit Bhattacharjee
New York Times - 6/25/2002
Topic: Biodiversity

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