The genome sequence of the western honeybee
may help explain the molecular and genetic basis of this insect's unusual sociality, according to the authors of the published sequence
in this week's Nature
. The Honeybee Genome Sequencing Consortium
has completed the first draft of the sequence, as well as a spate of analyses covering the development, reproduction, gene regulation, neurobiology and behavior, and population genetics of the insect.
The paper accomplishes for the honeybee "in a single package" what took more than a decade to produce for the fruit fly, said Sergey Nuzhdin
of the University of California, Davis, who was not involved in the project. Besides assembling the genome sequence, the researchers "have managed to interpret genome information in a truly functional sense," Nuzhdin told The Scientist
The research teams cloned and sequenced more than 230 million bases of the Apis mellifera genome, leaving about 26 million bases, which lie in unclonable regions of the genome. They found that the honeybee genome is more A-T rich than other sequenced insects and contains an unusually small number of transposons.
The honeybee genome also appears to have evolved more slowly than those of the fruit fly Drosophila melanogaster
and the malaria mosquito Anopheles gambiae
, making the honeybee much more closely related than the other two insects to humans.
Honeybees "do things that are just really complicated that distinguish them from Drosophila
and from mosquitoes," said principal investigator Richard Gibbs
of Baylor College of Medicine in Houston. The scientists found that several types of honeybee genes are more similar to vertebrate genes than to other insect genes, including many involved in circadian rhythms,RNA interference
, DNA methylation, and learning and memory.
The authors also found many changes in gene number between honeybees and Drosophila
, which they say may underlie the honeybee's distinctive social behavior. For example, honeybees have a larger family of genes for producing major royal jelly proteins
, which are needed for brood feeding and for caste development between queens and workers. Honeybees also have greatly expanded families of odorant receptors, which they need to communicate via pheromones and to recognize flower types and family members.
On the other hand, honeybees have a much smaller array of taste receptors than do fruit flies and mosquitoes, possibly because adults feed their larvae and rarely encounter toxins in their mutualistic relationships with flowers, the authors speculate. Honeybees also have novel genes involved in using nectar and pollen.
Finding these types of genetic differences between honeybees and other insects is "really interesting, because it right away links genome evolution to the ecology of the animal," said Yehuda Ben-Shahar
of the University of Iowa in Iowa City, who was not involved in the project.
Some of the sequence analyses couldn't be easily explained, however. Honeybees have fewer innate immunity
genes, which is a surprise, Gibbs said, since they live in colonies and therefore pass infectious pathogens among themselves. Also, honeybees possess genes similar to known Drosophila
sex determination genes, even though honeybees have an entirely different mechanism
of determining sex. According to the authors, exploring these paradoxes will "establish the honeybee as a new model for several fundamental processes of life."
It's probably too early to say with certainty which gene families underlie social behaviors in the honeybee, Ben-Shahar told The Scientist
. Sequencing other eusocial
insects like termites or wasps may provide some insight into genes or regulatory regions important for insect sociality, but expecting to find similar genes underlying sociality in primates or dogs, for example, "might be a stretch," Ben-Shahar said.
Finishing the sequence allows geneticists to study honeybee polymorphisms and "opens the door to really doing genetics in the organism," Gibbs told The Scientist
. "To me, that's the most exciting thing."
article appears simultaneously with related papers in Genome Research
. Genome Research
has devoted its entire issue to the biology of the honeybee, while articles in Science use the genome data to study the honeybee's vertebrate-like DNA methylation; to reveal the honeybee's evolutionary origins in Africa; and to identify neuropeptides that could aid in the study of the honeybee's sociality.
Melissa Lee Phillips
Links within this article:
M.A. Watanabe, "Honeybee Sequencing: One Honey of an Idea," The Scientist
, June 24, 2002.
The Honeybee Genome Sequencing Consortium, "Insights into social insects from the genome of the honeybee Apis mellifera," Nature
443:931-949, October 26, 2006.
Honeybee Genome Sequencing Consortium
T.M. Powledge, "How many genomes are enough?" The Scientist
, November 17, 2003.
G. Dutton, J.M. Perkel, "Shhh: Silencing Genes with RNA Interference," The Scientist
, April 7, 2003.
S. Albert et al., "The family of major royal jelly proteins and its evolution," Journal of Molecular Evolution, August 1999.
C. Holding, "Evolution of innate immunity," The Scientist
, July 8, 2004.
C. Holding, "Sex and the Honeybee," The Scientist
, August 27, 2003.
E.O. Wilson et al., "Eusociality: origin and consequences," PNAS
, September 20, 2005.