Honeybee jobs: like father, like daughter.
Job specializaton among worker honeybees--long believed to be a function of environmental cues -- is strongly influenced by inherited predispositions for specific occupations, new research indicates.
Two studies, performed independently and published in the May 25 NATURE, demonstrate for the first time a genetic component to behavioral differences among related honeybees. The research hints at a resolution to one of the most vexing problems in evolutionary biology: How can worker bees -- which are sterile females and thus have no means of directly passing their genetic makeup to offspring--survive, specialize and evolve in the dog-eat-dog world of natural selection?
"This research answers some very fundamental questions about organization in social insects," says Roger Morse, chairman of the department of entomology at Cornell University in Ithaca, N.Y.
Both studies examined occupational trends in worker honeybees whose pedigrees were traced by different marker systems. Peter C. Frumhoff and Jayne Baker, working at the University of California at Davis, glued tiny, numbered and color-coded tags to the backs of more than 7,000 bees born to a queen artificially inseminated by two different males. Queen bees typically mate with and store sperm from as many as 17 males -- a behavior known as polyandry -- before settling down to a year or two of continuous egg-laying. By inseminating the queen with sperm from only two, genetically distinct males with different colored bodies, the researchers could keep track of which offspring shared the same father and the sorts of specialized jobs each offspring performed. Focusing particular attention on the occupational specialty of grooming, in which a few bees repeatedly groom nestmates over time, they found "striking partilineal differences in the propensity of workers to groom nestmates."
In an elegant departure from the body-color method for tracking honeybee genealogy, Gene E. Robinson and Pobert E. Page Jr. of Ohio State University in Columbus inseminated queens with sperm from males identical in appearance but who differed slightly in the chemical makeup of one enzyme, called an allozyme. Thus "blinded" to unintended bias based on body color, the researchers kept track of individual offspring that became "guard bees" and "undertaker bees," two occupational specialties found in honeybee hives. Later, they killed bees in each profession and analyzed their enzyme profiles to determine paternity. Statistical analysis showed that in both cases, genetic relatedness accounted for more than 80 percent of the likelihood of a bee "choosing" a particular job.
Specialized diets during the firsy days of life and varying social milieus in different parts of the hive are among the environmental factors usually cited as determining a bee's future occupation. But the new research, says Robinson, "highlights the fact that the genetic structure of an insect society has a very important role in the social structure. That was a link that was never made before." Such a link between genetic variation and colony behavior is critical to Darwinian theory, he says, because "then you have the raw material upon which natural selection can act" to change worker behavioar and colony organization through the course of evolution.
The researchers caution that queen-bee polyandry did not necessarily evolve just to satisfy the hive's need for genetic variation and job specialization. However, says Frumhoff, "No one expected that differences among lineages, if they existed, would be as strong as they are. And the greater the difference, the more likely you'd want to think that it has some functional significance."
Scientists now may have to explain how social cooperation among honeybees has been maintained in the face of such high degrees of genetic variation within hives, since variation usually leads to conflicts of interest. One controversial theory is that honeybees continue to practice cooperative behavior patterns not because they are altruistic, as some scientists have argued, but because they are oppressed by the "fittest" bee of all -- a ruthless queen.
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|Date:||May 28, 1988|
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