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False majesty

Genes explain the mystery of the queen bees that cannot reproduce

MARILDA CORTOPASSI LAURINOThe social life of bees, as is well known, depends on the formation of two casts of the female sex, the queens and the workers. This distinction generally occurs due to the type of food offered to the larvae. A typical case is that of the Apis mellifera, from the bee class with stingers, the major provider of honey, wax and propolis. Some elected few are gifted during all of the larval phase with royal jelly, a super food composed of vitamins, essential organic acids and protein compounds. In this manner they become queens. They can live for up to five years and can lay as many as 2,000 eggs per day. The others receive royal jelly only during the first three days of their existence. They become workers, living a lot shorter time – something around 45 days – and they spend their short existence dominated by the shared tasks of the hive. Bees without stings, native to Brazil, have similar social characteristics, but present differences in the manner in which the young are fed. The workers prepare the cells of the young in a peculiar fashion. The future queens are benefited with 2.5 to 4 times more food than the future workers.

The major exception to the rule is the stingless bees of the genre Melipona, found throughout the neo-tropical biomass. For them, all of the cells of the young have the same size, as well as the quantity of food being similar. For almost a century Brazilian science has been trying to uncover this peculiarity. In 1903, the Brazilian Helmut von Ihering observed that there was an excess of queens in the young bees of the melipona genre – at the level of one queen for every three workers. At the end of the 1940’s, the geneticist Warwick E. Kerr theorized a model of Mendel genetics suggesting that the reason observed in the casts could have a genetic base. But this could never be duly proven, because the offer the food also seemed to play a role in the development of these bees. When there would be a lack of food in the hive, the number of queens among the young would diminish. And, according to that observed during the decade of the 1970’s by the researcher Lucio Antonio de Oliveira Campos, from the Federal University of Viçosa, it was possible to produce an even greater number of queens when the larvae were treated with the synthetic hormone juvenile. This hormone, typical of insects, is produced by glands associated to the brain. Even at that, though they looked like queens, the majority of them did not manage to reproduce – which only increased the puzzle.

Now, this century old mystery is beginning to be unraveled with the help of molecular biology. The researcher Carla Cristina Judice Maria became involved with the Melipona quadrifasciata for her doctorate thesis at the Genetics Department of the State University of Campinas (Unicamp), supervised by professor Gonçalo Amarante Guimarães Pereira, the coordinator of Unicamp’s Genomics and Expression Laboratory. Her interest, in principle, revolved around comparing the programming of the genomes of the Melipona queens and workers and of comparing their standards of genetic expression with the casts of Apis mellifera.  In total, 1,278 EST’s were noted, the fragments of active genes that are given the name Expressed Sequence Tags. These pieces serve to note genes that carry the recipe used for the cells to manufacture their proteins. On validating the results, the researcher resolved not only to quantify the levels of genetic expression for queens and workers reared naturally, but to also include another control group. She decided to investigate the queens produced by the application of the synthetic juvenile hormone.

The gene expressions of the three groups provided evidence of the possible origin of the problem of the queens induced by the hormone in having difficulties in forming colonies. Although they were apparently noble, these artificial queens presented active genes with a configuration close to that of the workers. “The workers treated with the juvenile hormone managed to mimic the endocrine system of the queens, but its genetic programming remained similar to that of the normal workers”, says professor Gonçalo Amarante.

True or artificial, the queens of the genre Melipona quadrifasciata do not have exactly an easy life. Since there are naturally too many queens, the fate of a large part of them is tragic. The majority are killed by the workers a few days after their emergence from the cells of the young. There are only a few virgin queens that take off on their nuptial flight and mate, generally with one single male. And even these queens depend on a rare circumstance to survive, the creation of a new colony separate from the mother colony. Only a few manage to reign in a new colony. This wastage can perhaps explain why the hives of the Melipona quadrifasciata are much more modest in size than the other stingless bees.

While Gonçalo Amarante, from Unicamp, accompanies the search for expressive genes, the Klaus Hartfelder, a professor at the Medical School of the University of Sao Paulo in Ribeirao Preto, gave support to Carla’s doctorate thesis in the field of entomology, the branch of zoology that studies insects. The discovery by Carla that development conforms to the active genes in determined phases, can now be associated to ongoing studies at USP in Ribeirao Preto that are looking to establish genetic markers for finally proving Warwick Kerr’s theory. The Brazilian researchers’ interest in this field transcends the challenge of unraveling the puzzle of the casts in Melipona quadrifasciata. The curiosity consists in discovering the molecular basis of development and of animal behavior in general. Carla’s thesis traced out the expression of a group of genes, those that the bees share with other species. One of the genes was the dunce gene, with greater expression in the workers and in the artificial queens than in the true queens. The same gene is found in drosophila flies, and, in them, is linked to cooperative behavior and mating. “Probably common behavior in various species has a common molecular base”, says Gonçalo Amarante.

The finding has gained importance because recently it was observed that the Melipona quadrifasciata is not an isolated case in the genetic determination of the formation of queens and workers. Over the last five years at least four international scientific papers have provided evidence that this also occurs in certain types of ants. The imminent disclose of the complete genome of the Apis mellifera, the honey bee, should bring more elements that will allow for a comparison of different species. “The Melipona is a good model for comparing with the Apis”, says Klaus Hartfelder. “This type of research is important for making conclusions concerning evolutionary steps that generate social systems as complex as those of bees”, he states.