A team of researchers from Brazil has sequenced the nuclear and mitochondrial genomes of Frieseomelitta varia, a stingless bee that has, as a peculiarity, a completely sterile worker caste.
Frieseomelitta varia, a species of bee in the tribe Meliponini (stingless bees), was chosen for this genome project because of its peculiar reproductive biology.
Different from most other stingless bee species, Frieseomelitta varia workers are completely sterile and, thus represent an extreme end in the queen-worker and worker-worker conflict of interest over male production in a bee colony.
“We chose a species to test our ability to sequence a whole genome in a pilot project,” said Professor Klaus Hartmann Hartfelder, a researcher in the Ribeirão Preto Medical School at the University of São Paulo.
“ Frieseomelitta varia is an emblematic species because its workers are completely sterile. This trait distinguishes it from the vast majority of species in the tribe Meliponini.”
Professor Hartfelder and colleagues found that the total size of the Frieseomelitta varia genome is similar to the sequenced genomes of other bees.
They also identified a large number of repetitive genome components and long non-coding RNAs, which could provide the molecular basis for gene regulatory plasticity, including worker reproduction.
“In humans, for example, these RNAs are associated with processes that regulate development of the central nervous system, among others,” they noted.
“In Frieseomelitta varia, these sequences may be linked to the lack of ovaries that makes the workers sterile. The queen is highly fertile, of course.”
“As in the vast majority of social insects, the eggs are all the same. Any egg can develop into a worker or queen,” Professor Hartfelder added.
“During the larval stage, however, some molecular signaling pathways diverge so that the bees differentiate into two types of individuals, one fertile queen and many infertile workers.”
“In the European honeybee (Apis mellifera), this is engineered by giving the queen different food in the larval stage, but in stingless bees, it seems to be more a matter of the amount of food.”
The researchers also found a high degree of conservation (synteny) in a block of genes previously described in the European honeybee and related to pollen hoarding by colonies.
“The finding surprised us, given that European honeybees and stingless bees diverged into different lineages more than 70 million years ago. That’s a long time for a species to conserve a trait as it evolves,” Professor Hartfelder said.
“We want to see if the same is true of other bees and if it happened by chance or afforded an evolutionary advantage.”
In contrast to the examples of conservation in the nuclear genome, the mitochondrial genome of Frieseomelitta varia revealed major changes in gene order in comparison to the European honeybee and also to the other two stingless bee mitochondrial genomes sequenced so far.
“For Frieseomelitta varia we found evidence for major reshuffling events in gene order that should be of interest for the analysis of other stingless bee mitogenomes, as this group may represent a hotspot in mitogenome structural evolution,” the scientists said.
A paper on the findings was published in the journal BMC Genomics.