Transgender Creatures Are Hetero

Feminized Bugs Still Straight

Contributed by Jodie Miller


NEW YORK (Reuters) -- New research into the sexual orientation of the lowly fruit fly has geneticists admitting that the origins of sexuality may be far more complex than previously believed.

"The complex nature of sexual identity in an animal as relatively simple as the fruit fly indicates that simplistic explanations of the genetic bases of sexuality are unlikely to be true," conclude a team of researchers from the Universite Paris-Sud, in Orsay, France; University of Cambridge in Cambridge, England; and New York University in New York City. Their findings appear in the current issue of the journal Science.

The researchers manipulated the genes of maturing fruit flies, focusing on two aspects of their sexuality: orientation (determining the gender of a desired mate), and attractiveness (the gender the fly attracts).

The perceived 'attractiveness' of one fly to others is in part determined by its emission of pheromones, or odors secreted from its abdomen. These pheromones are deemed appealing by one gender, while the other treats them with indifference.

The researchers introduced a specific 'transformer' gene into the brains of developing male flies. This 'feminized' their pheromonal systems, so that they emitted the odors normally associated with females.

Feminized But Straight

These altered pheromonal systems "elicited a more vigorous courtship response in... (other) males," the study authors discovered. However, at the same time the altered (male) flies "retained a strong and typical male heterosexual behavior, suggesting no relation between the feminization of their (pheromones) and their sexual orientation."

In other words, even though 'female' genes were introduced into male flies, sexual orientation remained unchanged. Only sexual expression -- via odor emissions -- was altered. The results were 'womanizing' male flies who, unfortunately for themselves, attracted only other males of the species.

The study authors conclude that "our analysis shows that in (the fruit fly), two aspects of individual sexual identity -- the perception of others and the presentation of self to others -- are under separate genetic and anatomical control." If either of these factors are genetically altered in heterosexual flies, they say "homosexual courtship may take place."

But just how closely can we parallel fruit fly and human sexuality? The lead author of the study, Dr. Jean-Francois Ferveur of the Universite Paris-Sud, believes "the fruit fly is the very best model (in my opinion and that of many researchers in the world) to study genes and function. With the fruit fly Drosophila, you can... build your own experimental fly carrying the gene you want to study... all genes found in the fly are homologous, to various degrees, to the ones mapped in Man."

However, he says that while the genetics may be similar, human and fly sexual behaviors differ widely. "I do not want to draw a parallel between behaviors of both species Drosophila melanogaster and Homo sapiens because I think that behavioral studies in both fields are highly interpretive," said Ferveur.

Of course, pheromones themselves play a more obvious role in the courtship rituals of the fruit fly. But Ferveur believes they remain a primitive element in human mating rituals as well. "In humans, the role of odors has been underinvestigated, probably because in recent centuries, society has tried to mask our odors (our pheromones) in the form of perfumes, antiperspirants, and all other natural and synthetic substances," he explains. "But, it is true that we all have our own smell... a precise chemical signature.... Human and other vertebrate animals diversely use these 'traces' to smell progeny, mark territory, find a mate, get sexually... aroused, and other social behaviors."

In any case, Ferveur and his colleagues believe human sexual response may be a complex mix of genetics, hormones, neurology, and culture -- not easily amenable to the tinkerings of science.

He casts a baleful eye on those who might advocate gene manipulation as a means of altering sexual orientation in an embryo. "In humans, (the) genome has started to be also manipulated, and I hope, as (an) ethical view, that it is only for severe disease-therapy," Ferveur said. "I am against manipulation of the human embryo for selection, except in cases of genetic anomaly."

SOURCE: Science (1997,276:1555-1557)


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