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 BhattacharjeeNew York Times - 6/25/2002Topic: Biodiversity
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