Honeybees

The European Honeybee, a key pollinator, has suffered from population decline at least since 2006, when the first cases of Colony Collapse Disorder were reported in the United States. Similar events have been reported to a minor degree in Europe and Asia. The reasons for these are not totally understood, with the current understanding pointing towards a combination of factor. One of the potential risk factors is that a decline of genetic diversity may contribute to a narrower range of hygienic behaviours, or decrease the immune response to pathogens.

In order to test this hypothesis we compared 40 post-2006 honeybees to 40 specimens from Europe collected from 1870 to 2006. A subset of the honeybee genome was captured and sequenced.

We analyzed two datasets of genomic sequences corresponding to modern and historical honeybee samples. calculated error rates, depth of coverage, population admixture, population diversity and differentiation. I also performed two haplotype networks using mitochondrial regions, namely the cytochrome b and the cytochrome oxidase I (COI)and II region (COII). The error rates in modern samples resulted to be low and higher in historical samples. The damage in the historical samples, probably due to post-mortem de-amination was calculated and corrected. The depth of coverage in the modern samples was between 12 and 27. In the case of the historical samples, we verified that the capture procedure had worked fine. The admixture analyses and the phylogenetic tree were consistent with the 5 lineages of honeybees described, and revealed high levels of admixture in ancient European samples. The haplotype networks also confirmed the lineages. The haplotype network of COI-COII suggested an African origin of the evolutionary branches M, C, O and Y of Apis mellifera. As for the genetic diversity, interestingly, the values of theta Watterson and pairwise are higher in ancient honeybee samples than in modern ones. The levels of population differentiation showed a big differentiation in the Y lineage with respect to the other populations and a smaller differentiation in other comparisons. The results suggested that a loss of genetic diversity has occurred during the last century, which might make honeybees more vulnerable against the many stressors that they face.

Collaborators:

  • Paula Campos
  • Rute Fonseca
  • Alba Rey de la Iglesia
  • Lucia Robles
  • Annette Bruun Jensen
  • Tom Gilbert