One of the ways to map the genetic background of the honeybee is via the haplotype. A haplotype tells something about the history of a population. Such a haplotype includes multiple genes that are inherited in a linked manner. The best-known example of a haplotype is the mitochondrial genome (all genes in a mitochondrion), which is only inherited via the mother’s side. The research discussed here on the occurrence of various haplotypes in Eastern Europe shows how much the Buckfast bee is on the rise there. This certainly also applies to the situation in the Netherlands.
Subspecies and haplotypes
The Western honeybee, Apis mellifera, has over 30 subspecies. According to current insights, these are divided into six regional haplotypes:
- the African (A) lineage with African subspecies such as Apis mellifera scutellata and A. m. adansonii;
- the Northern European M-lineage with subspecies from Western and Northern Europe to Central Asia in the east, such as A. m. mellifera;
- the C-lineage east and south of the Alps with subspecies such as A. m. carnica and A. m. ligustica;
- the Eastern (O) lineage with subspecies from Turkey and the Middle East;
- the Y-lineage with subspecies from Ethiopia and the Arabian Peninsula, such as A. m. yemenitica;
- the Z-lineage in Saudi Arabia and East Africa, with the newly discovered subspecies A. m. pomonella.
In Europe, the preservation of the genetic diversity of the honeybee is under pressure due to the preference of beekeepers for subspecies from the C-line. When preserving this genetic diversity, we often look at the distribution of the C-line within the original distribution area of the M-line. But it could well be that as a result of climate change and the large-scale commercialisation of breeding queens, the advance of bees with African genes (the A-line) should also become a point of attention.
Buckfast bees are usually considered to belong to the C-line, but they also have genes of African origin, as a result of the crossing of various African subspecies, started by Brother Adam and still continued by others. Buckfast bees are very heterogeneous and the share of African origin can vary greatly, because there is no central supervision of the breeding programmes. Every beekeeper can produce hybrids and sell them under the name ‘Buckfast bees’.
By the way, in honeybees in southwestern and southern Europe, we have found mitochondrial DNA with African genes for many years as a result of natural gene exchange. In the study by Oleksa et al. (2021) discussed below, the diversity of mitochondrial DNA in Eastern European honeybees is investigated.
The study
In the period 2017-18, a total of 427 workers were captured on flowers with a dip net over a large area, stretching from Poland in the north to Hungary and Romania in the south, divided over two narrow parallel strips of about 900 km long. Of those captured workers, 1.64% appeared to have the A-haplotype and were therefore of African origin through inheritance of mitochondrial DNA via the maternal line. It is very unlikely that the presence of the A-haplotype is the result of natural migration of African subspecies. It is much more likely that this is due to the introduction by humans of Buckfast queens with an A-line origin. There is no reason to assume that the situation for Western Europe would be different from that for Eastern Europe.
The C-line was most frequent in the caught workers (over 88%), the M-line considerably less (over 10%). From north to south, the C-line was increasingly common and the M-line increasingly less common. The distribution of the A-haplotype in the sampled areas was irregular, which also indicates that its spread in Eastern and Central Europe did not occur naturally, but was induced by humans.
The fact that almost 2% of the workers have the A-haplotype over such a large area indicates a fairly large introgression. Introgression is a form of hybridisation. Introgression is the term used when certain genes or phenotypes enter a population’s genome ‘from outside’ through natural or intentional crossbreeding. The influence of drones of African origin is not considered in this study, but it seems to be (still) much larger than the influence of queens with an A-haplotype.
What are the consequences?
According to the researchers, the observed expansion of the A-haplotype deserves more attention, as it could also result in the expansion of undesirable traits, pests and diseases. Although introgression of ‘foreign’ genes can lead to increased genetic diversity in a population, it can also mean that differences between locally adapted populations fade away. The result could be that many local varieties (subspecies and ecotypes) lose genetic uniqueness as they are replaced by hybrids with introduced bees.
Crossbreeding between subspecies is increasingly seen as a threat to the genetic diversity of the honeybee. Therefore, it is important to look at the spread of foreign subspecies of A. mellifera. Honeybees occur in a wide variety of environments, from tropical to temperate. Local populations have adapted to the specific conditions of that environment over time. Therefore, these local bee populations are important to preserve. Research has shown that colonies of local origin survive longer in their own environment than imported colonies (Büchler et al., 2014). Nevertheless, in European beekeeping practice, two subspecies from the C-line are mainly used: carnica and ligustica. In large parts of Europe, this has led to the decline of the European dark bee, Apis mellifera mellifera.
In addition, there is now another phenomenon that has a great influence on the genetic composition of the honeybee, and that is the expansion of genes of African origin. We all know the expansion of the Africanised bee in North and South America: African bees of the subspecies A. m. scutellata were introduced there. These crossed with various European subspecies – also once introduced there… – and produced incredibly aggressive hybrids.
The authors of the study mention a number of objections to the A-line. The danger of absconding, where an entire colony takes to the wing at once (very common in African bees), does not seem to be an issue in the European context, because the characteristic ‘no swarming’ is strictly selected for by Buckfast breeders. The same applies to the development of killer bees. African subspecies may harbour parasites and pathogens that do not occur in most European countries, including the small hive beetle.
All in all, this research seems to indicate a significant increase in African genes in bee colonies in Eastern Europe, but it remains unclear what negative consequences this actually has.
Literature:
Oleksa, A., Kusza, S., Tofilski, A., 2021. Mitochondrial DNA suggests the introduction of honeybees of African ancestry to East-Central Europe. Insects 12(5): 410.
Büchler, R. et al., 2014. The influence of genetic origin and its interaction with environmental effects on the survival of Apis mellifera L. colonies in Europe. Journal of Apicultural Research 53, 205–214.