Breeding Value Estimations for Honey Bees
What is a breeding value
The breeding value states, for a specific characteristic, how valuable an animal is for breeding purposes. There are distinctive differences between colonies with respect to honey production, behavior, or varroa tolerance, etc. However, these differences, which depend on the heritability of the characteristic, are largely called forth by environmental conditions. The breeding value of a colony only refers to the differences which can be traced back to the quality of the genes. Only heritable differences are important for the selection of breeding colonies, as only these genes, for better or worse, will be passed on to offspring. For breeding value estimation, environmental influences in the various apiaries and the level of inbreeding are first taken into account. This is why the test results of all related colonies are used to estimate the genetic value of an individual colony. Every colony is an informant for related colonies, and thus profits from the inclusion of related colonies' test results into the calculations of its own breeding value.
Since 1997, breeding values have been given as percentages. The average of the measured value during performance and behavior tests over the last five years are used as a (sliding) reference base for each characteristic. By giving the breeding values as a percentage, it is much easier to recognize the colonies' genetic superiority or inferiority. The comparison between colonies has also been improved by taking the different scattering rates of breeding characteristics into account. (Behavior characteristics are much less scattered.) Due to this adjustment, it is possible to directly compare, for example, a breeding value of 105% for honey production to a breeding value of 80% for swarm drive.
What does a Breeding Value mean?
The breeding value percentage concretely states how far that colony is genetically above or below the average of all tested colonies. A value of 100% means that the colony is exactly equal to the average of all tested colonies. An 80% value expresses that the colony lies 20% below average and for this particular characteristic does not have a good genetic makeup for breeding purposes. A genetic superiority in the selected parents, demonstrated by high breeding values, will also be found in the offspring. A colony with breeding values of 120% in honey production is mated (via its drones) to a virgin queen, whose mother had a 100% value for honey production. What type of offspring can you expect? On average, they will produce 10% more honey than the reference base because the mean value for the parents is (120% + 100%)/2 = 110%. If this sounds too complicated, just keep this simple rule in mind when interpreting breeding values:
One selects the colonies that have the highest percentage value for the desired characteristics.
Breeding values are as easy to interpret as familiar deviations from the average, but the selection of colonies will be much more reliable. During selection, it is important to remember not just to take one breeding value into account, but rather all characteristics. When examining all breeding value estimation results, it quickly becomes clear that colonies with unusually high values in all breeding categories only occur rarely. So, the breeder must decide where to compromise. Inbreeding coefficients (in %) for the queen and workers are given in addition to the breeding values.
No Breeding without Quantifying
The breeder can positively influence the quality of the breeding value estimations by following these steps:
Reliability of Breeding Values
The breeding value is only one appraisement of an animal's genetic value. Appraisements can be estimated very reliably or less exactly. The quality of the breeding value estimations is largely dependent on the number of related colonies tested. If a colony has many full sisters, was placed in a frequently used mating station (with many fatherly half-sisters), and the full pedigree is available (detailed information about ancestors), an exact breeding value can be estimated. If only minimal information is available from related colonies, then the reliability of the breeding value estimations leaves much to be desired.
The reliability coefficients of the breeding value estimations are a gauge for the reliability of the results. The reliability of the breeding value estimations can vary from 0 (no reliability) to 1 (very high reliability). Both extremes are rare. The reliability is dependent upon the number of information carriers, family relations, and the heritability of each characteristic. As the size of the sister group increases, the information gain grows under-proportionally, so there is little point in testing more than 8 colonies.
The reliability of breeding value estimations influences the calculation of breeding values in so far as that when calculating from many data sets, the breeding values are more reliable and thus more trustworthy.
Incest refers to the mating of related individuals. With related animals, at least one ancestor is identical. This creates the possibility that the related offspring will inherit the identical gene from the maternal and paternal side. The closer the parents are related, the higher the inbreeding. The inbreeding coefficient indicates the extent of inbreeding. This coefficient expresses the probability of having identical genes (inherited from the father or mother) for a specific gene loci. The value ranges from 0% (no inbreeding) to 100% (100% identical genes). In comparison with other animal species, the amount of inbreeding is very difficult to calculate for honey bees. This is because the queen mates with multiple drones and the drones are haploid. The calculation method for bees is described by BIENEFELD et al. 1989, Apidologie (20:439-450).
As inbreeding has negative effects on performance and disease resistance for all animals, closely related matings should be avoided in breeding. With honey bees, close matings result in more diploid drones due to particularities of gender inheritance. These sterile, diploid drones are cannibalized by worker bees shortly after hatching, which causes the typical checkered brood. From this, one can conclude that the inbreeding of worker bees more strongly influences the colony than the inbreeding of the queen.
With inbreeding coefficient higher than 15%, breeders should consider bringing in new blood.