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Scientific VIEW

It's the Lady's Choice in the Animal World

November 14, 1986|BETTYANN KEVLES

"Ladybug, ladybug fly away home. Your house is on fire, your children will burn."

And so, we feel assured, the ladybug (in reality a beetle) stops whatever she has been up to and takes off. In popular mythology all ladybugs are females, and they are capable of making choices (such as attempting to rescue their offspring). But the idea that a real female animal can, and does, choose to act in a certain way has only recently been accepted by most evolutionary biologists.

When more than a century ago Charles Darwin suggested the idea of female choice as a part of the process he called "Sexual Selection," he met ridicule. The idea was roundly rejected by many of the same people who, in all other discussions of evolution through Natural Selection, had jumped on the Darwin bandwagon.

Men who willingly accepted the suggestion that the animals they were familiar with at the zoo in Regent's Park were not necessarily the same as those in the Garden of Eden, or even that biblical creation was a metaphor and human beings descended not from Adam but from some apelike ancestor, were so rooted in male chauvinism that the thought that a female animal might choose her own mate was unacceptable.

Darwin did not know how females made their choices, but he hazarded the suggestion that, at least in the more intelligent species, females at puberty developed aesthetic sensibilities while males became more rational. Thus he explained why peahens selected peacocks with the most gloriously colored tails.

Evolutionary biologists today recognize that females of many species select their mates. Field observation at a local high school reveals that adolescent human females follow the exploits of their football-playing classmates. They appraise the young men, favor a few and leave the others to drift unnoticed to the locker room.

Elsewhere in the animal kingdom, female Guinea hens bicker with each other over access to the shortest, fattest males. And female ladybugs select a mate according to the degree of color in his carapace.

Studies of a host of species indicate that female animals select their mates according to specific criteria. Females choose males that are likely to provide the best protection from predators, the best nutrients and the best genes for their offspring.

Whether these choices are random, or some kind of learned behavior, or are an inherited trait, is not well understood. But new research from the Department of Genetics at Cambridge University casts light on this complicated issue, at least as it concerns ladybugs.

Experiments with ladybugs-- adalia bipunctata-- (ladybirds in Britain) show that in a natural population of red, two-spotted ladybugs, colored males have a 20% advantage in mating over their plain brothers. But after the researchers artificially selected beetles for 14 generations, choosing those females that preferred colored mates, the preferential matings for colored males rose to 50%. Thus, by working with a controlled population, the researchers were able to conclude that a female's preference for a colored male can easily be explained by a single dominant gene.

The British researchers suggest that their study accounts for the steady proportion of colored and uncolored males in the entire ladybug population as well as for the proportion of females with a gene for preferring their colored counterparts. They conclude rather grandly that their research is proof that the sociobiological interpretation of animal behavior is correct, that a single gene may determine behavior as complicated as the choice a female animal makes in selecting her mate.

Those of us who have watched the behavior of pompon girls and football players, or peacocks and peahens have never doubted that female choice is a real factor in animal pairings. Yet one might argue that there is a great difference between a species that can be manipulated through 14 generations in a matter of weeks and has the relatively simple genetic structure of a beetle, and that of species that live many years in social groups. Moreover, even with ladybugs, those with a gene for choice only comprise a fifth of the population.

The Cambridge team has provided solid evidence that female choice is a real factor in animal behavior. But just how much genetic predispositions count in the decision-makings of ladybugs, much less of more complex creatures, is still open to dispute.

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