Australian scientists at the University of Sydney have discovered that one breed of African honeybees is capable of producing nearly identical clones of working females. This allows the insects to avoid the harmful effects of virgin reproduction. The discovery is reported in an article published in the journal Proceedings of the Royal Society B: Biological Sciences.
The ability to clone oneself carries obvious advantages, as there is no need to look for a sexual partner, and there is no genetic dilution in the offspring, meaning that the original genome is preserved from generation to generation. Some insect populations have developed telitococcal parthenogenesis, where females are able to reproduce without fertilizing new females. The phenomenon occurs in some haplodiploid insects, in which males develop from unfertilized eggs and are haploid, i.e. have one set of chromosomes, while diploid females appear with a double set of chromosomes – from fertilized eggs.
In haplodiploidy, usually only the uterus is able to carry the eggs, from which the females emerge. The worker bees, which are also females, in rare cases (e.g. when the uterus dies) can only lay unfertilized eggs, from which males always emerge. But in the honey bee Apis mellifera capensis, thanks to a single mutation, the worker females can produce diploid offspring, i.e. new worker females, without the need to fertilize.
Heterozygosity loss (when different copies of the same chromosome contain different variants of the same gene) sometimes results from genetic recombination leading to a new combination of genes. Heterozygosity for certain genes is important for sex determination in bees. In Apis mellifera capensis, workers reproduce only telitocally, while queens always mate and reproduce sexually. However, this means that the working females had to reduce the recombination rate in order not to produce homozygous offspring.
Scientists conducted an experiment in which the uterus was taped to its reproductive organs to prevent it from mating with males, so it switched to a parthenogenetic method of reproduction. Results of full-genome insect DNA sequencing and microsatellite genotyping showed that approximately one hundred times more recombinations occurred in the offspring of the uterus than in the offspring of worker bees. In addition, the new worker bees appeared to be almost identical clones of their parents. In other words, some mechanism for blocking recombination was present only in the worker females, but not in the uterus.
The researchers also found that one of the worker bee lines in the hive successfully cloned itself for about 30 years, a clear indication that female worker bees in Kappa bees do not suffer from congenital defects or infertility.